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Thread: Let's Build a Flat Burr Coffee Grinder

  1. #1
    Member Stavros's Avatar
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    Let's Build a Flat Burr Coffee Grinder

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi Guy

    Twelve or so years ago, my first ‘coffee machine’ was a Braun Espresso Master, which came with a Braun spice grinder. Wow, I was set, and had ‘real’ coffee. The nasty little Braun is long gone, but the grinder lives on as a great spice grinder.


    When the Braun died, I started reading up and visiting forums, over-researching things in my usual aspergers-like fashion. Based on reviews and opinions on this forum, I got a second-hand Rancilio Audrey, which came with a Sunbeam EM0480 grinder. Now I was cooking with gas. While Audrey was a weapon compared to the Braun, the EM0480 was a nightmare – plastic gears, wobbly burrs, wear and tear, needing shims to keep it grinding fine, it wore out in no time – you know the story.

    So, back to the forum, and I picked up a second-hand Rocky grinder of Fleabay, and fitted new burrs. After the EM0480, the Rocky impressed me – steel, brass, aluminum, smooth, and heft, mucho heft. (The mother-in-law will attest to this, she picked it up from Taree, and brought him down to Canberra in her carry-on luggage.) And better yet, Rocky, like Audrey, was pull-apart-able. No silly plastic clips, but real threads and fasteners. They were designed to be repaired - to live forever. Now Rocky isn’t perfect, the adjusting thread is a bit loose, the speed is a bit fast, and the adjusting detent is a little coarse. As per advice on the forum, Teflon tape fixed two of the problems, and Rocky is well loved.

    Now, I’m not fanatical about my coffee, but I am a bit of a tinkerer. And as a retired machinist with too much time on his hands, and a workshop full of machinery, I sometimes start projects for projects sake. So it wasn’t surprising that I kept thinking someone could build a better grinder. All you need to do was attach a couple of big flat burrs to a variable speed geared motor. How hard could it be? More like how crazy would you be to do it!

    tenor.jpg

    This thread will cover the build of the grinder. More to come, , , ,

    Cheers, Steve.
    Last edited by Stavros; 4 Weeks Ago at 02:20 PM. Reason: Formatting
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  2. #2
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    Hi Guys,

    Firstly - the design. Basically, I started with a set of Mazzer Major 83mm flat burrs burrs, two SKF 80mm x 50mm x 16mm deep-groove ball bearings, a 375 watt three-phase electric motor with a 9:1 planetary gearbox, a single-to-three phase variable frequency drive, and 12kg of 150mm and 100mm 6061 aluminum bar.

    IMG_2120.JPG

    IMG_2118.JPG

    I spent quite a few night on the CAD package designing the grinder. Wherever possible, I applied good engineering practices, (typically used for machine spindles and shafts on lathes, pumps,etc), to maintain axial alignment and parallel faces. Initially Iwas planning to mount the rotating burr carrier directly onto the output shaftof the gearbox, as it is fairly rigid, and is supported in a reasonable sized bearing. This would have greatly simplified the design, and made it quite compact.

    IMG_2119.JPG

    However, call me stupid, but I decided touse a completely separate one-piece shaft and carrier, supported between two ball bearings, and connect it to the gearbox with a flexible coupling. This allowed me to use an adjustable nut to preload the bearings to remove any axial and radial play. It would also allow me to fit a different motor/gearbox one day if required.

    Sketch.JPG



    Now just to clarify, I’m not trying to built a commercial grade grinder, or a mega-grinder. It only has a 375 watt motor, with a 9:1 ratio gearbox, so it will grind at a moderate 300 rpm. With frequency control, I can ramp the speed up to a max of 600 rpm. That's pretty much in the ballpark with other domestic grinders. I’m just trying to keep the burrs consistently aligned and spaced apart.

    Cheers, Steve
    Last edited by Stavros; 4 Weeks Ago at 03:57 PM. Reason: Spelling again.
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  3. #3
    Member Stavros's Avatar
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    Hi Guys,

    To maintain alignment between the various components, there are mating spigots and recesses in adjacent parts, with just a few thou' clearance. The burrs are also mounted on machined steps and spigots on the spindle and carrier to keep everything in alignment. So, basically, (ignoring accumulated tolerances / clearances), everything should line up, no matter how many time I pull it apart to clean it.

    IMG_2122.JPG

    IMG_2124.JPG

    Burr gap adjustment is basic - by a 95mm
    diameter thread between the body cap and fixed burr carrier. The pitch of the thread is 16tpi, (or about 1.5mm), so 1/4 of a revolution will cause a gap of approximately 15 thou' of an inch. I think this will be fine enough to get the required adjustment. The first time I machined the thread it was not good enough, and I had to start again. Thankfully, the second thread is very smooth with minimum clearance, so there is no wobble or axial play. I must admit that I was a bit slack when it came to a means of locking the adjustment. I should have used a split cap with a clamping arangement, but I'm using a grub screw in the cap which will press on the carrier thread. I will however, use a rubber slug under the screw to prevent damage to the thread.

    IMG_2127.jpg

    The main spindle and rotating burr carrier are machined as a single piece. This should remove any potential problem with play or alignment, like when separate carriers are mounted on motor shafts etc.

    IMG_2128.JPG

    A pair of deep-groove ball bearings support the spindle. They are more than adequate to handle any loads generated by the grinding process, and will last forever. Again, these are readily available and cheap. If I wanted to make it sexier, I could have used a pair of precision angular-contact bearings, (like used in some high-quality machine spindles), but again, way too much $$$. A single lip seal is located under the carrier to prevent coffee grounds getting into the bearing area


    Note that I chose a standard industrial three-phase / frequency drive to run the grinder. Mainly because they are common, and I'm familiar with them. They are easy to set up, and are simple to control - variable speed is by a 10k potentiometer, and run/stop by a low voltage input / switch. The newer 'sensorless vector' drives are very nice - they have nearly 100% torque at any speed. They are also cheap on FleaBay. I did consider a Parker brand servo drive and motor, which I've previously used for CNC applications, but I couldn't justify the extra $$$. The downside of this is a big ugly motor and gearbox - this is never going to look like a neat little kitchen coffee grinder. Maybe I should have just bought a Mazzer Major, , ,

    Cheers, Steve


    Last edited by Stavros; 4 Weeks Ago at 06:36 PM. Reason: Gaa - formatting
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  4. #4
    Mal Dimal's Avatar
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    Quote Originally Posted by Stavros View Post
    Now just to clarify, I’m not trying to built a commercial grade grinder, or a mega-grinder. It only has a 375 watt motor, with a 9:1 ratio gearbox, so it will grind at a moderate 300 rpm. With frequency control, I can ramp the speed up to a max of 600 rpm.
    Super impressed with your work Steve...

    The one thing though, that catches my attention, is that the gearbox ratio and the speed numbers you have quoted seem to indicate that the motor you are using is a 2-Pole motor with a nominal ~2,900 rpm rated speed. Given if this is the case, I would have to caution against running this motor at anything above 100% rated speed as this will place enormous stresses upon the integrity of the Rotor. Wanting to achieve an output speed of 600 rpm at the gearbox would require the motor to be able to run at ~5,400 rpm, significantly above its design capability I would think, and safe operation....

    Mal.
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  5. #5
    Member Stavros's Avatar
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    Good point Mal, I may have to contact the motor manufacturer and see what they recommend for the maximum speed. I should also do they same for the gearbox, it may not appreciate too high an input speed.

    Edit: Just looked up the technical specifications for the Varvel gearbox, and the maximum input speed is 6000 rpm. Lets see what the motor is good for.

    Edit: I contacted the Royce Cross Group, who distribute the Chinese made TEFC motors. One of their technical guys was familiar with frequency drives. He seemed more concerned with the frequency/voltage/current issues than the mechanical limitations. Once I told him it was on a little coffee grinder, he laughed and said no more than 100Hz on a two pole motor.
    I also went off to the WEG site, who have a lot more technical documents available, and a table (see below) listed the maximum speed at 7200rpm. I would imagine that WEG motors have a better electrical and mechanical build quality than a $120 Chinese import, so for the time being, I will limit the overspeed to 70%.

    IMG_2137.PNG

    Cheers, Steve.
    Last edited by Stavros; 4 Weeks Ago at 03:23 PM. Reason: Add information.
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  6. #6
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    Hi Guys,

    The machining of the parts is by bread-and-butter means – turning in a lathe and milling in a mill. I am relatively fortunate here, as over the years I’ve accumulated a number of quality English, German, Swedish and Japanese machines. Even though some are up to 50 years old, they are in good condition, and will hold tight tolerances and give good finishes. (No Chinese machines here – if there was a machinery snobs site, I would be a founding member.)

    When starting with bar stock, there is a lot of meat to remove. I think 60% of the aluminium ended up as swarf and chips.

    IMG_2067.JPG

    Everything was machined with more care than usual, with critical bores and faces mostly completed in single settings. I machined the discharge path in the body today. It is at a tangent to the outside diameter of the grind chamber, and exits the main body at the centre. I will probably end up fitting a chute from a Rancilio Rocky, so made the final width of the port to suit.

    IMG_2115.JPG

    Well, so far, so good. Everything is coming together OK. I made a couple of temporary nylon bushes slightly smaller than the bearings, which allowed a quick and easy assembled of the parts to double check the design. I didn’t want to use the ball bearings as they are an interference fit in the body, and I want to install them once only, after everything is complete.

    IMG_2083.jpg

    I still need to make the thrower fingers on the spindle, these will be made from a fancy plastic called PEEK, which has a combination of mechanical strength, resistance to chemicals, wear, and temperatures up to 260°C. These will locate in slots in the spindle flange, and will be secured with M4 cap screws. The material is ordered, and should arrive next week. I made the height of the grinding chamber 20mm - about the same height as the burr set plus a little bit. Hopefully this will limit the amount of old grounds which will accumulate in the chamber.

    IMG_2132.JPG

    I had a chat to a few anodising companies yesterday. As there are none in Canberra, I'll have to use one in Sydney or Melbourne. (If anyone can recommend a company I would appreciate it.)I was advised that before I send it, to make sure that I've got all of the machine marks and scratches out of it, as anodising is a pretty unforgiving finish, which will show up all the imperfections. I was also warned about acid from fingerprints, which can leave invisible pitting which makes the final anodising blotchy. Woops, I probably messed that up.

    I did run into a problem with the Mazzer burrs. After they were bolted to the spindle, I did a trial assembly, and found that they were not quite parallel. It turns out that there are some ugly little burrs at the back of the three mounting holes, enough to stop them seating flat on the spindle. I'll need to stone these off tomorrow and check it again.

    And finally, this is the last thing a coffee bean will ever see - Arrrrrrrrrrrrrr, munch, munch, munch, munch. Bwahahaha!

    IMG_2135.JPG

    Well, time for a beer. Cheers, Steve.
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  7. #7
    WME
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    Awesome work mate, super interesting read and looking forward to seeing the end result.
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  8. #8
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    This is awesome, love this thread. Can't wait for the next updates

  9. #9
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    That’s amazing, great work!

  10. #10
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    That's some real fine machine work there. Will be following this closely!

    Vector drives are amazingly cost competitive. Loved them to bits in a past life. Will you be putting an anti static wire across the tangential port?


    Would love to see the enclosure you put around it!
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  11. #11
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    Go cold anodising in a grey or dark green. It would look very military in the latter. Cold anodising is very hard wearing.

  12. #12
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    Hi guys,

    What's a static wire? I'll have to google that. Mind you - the entire grind chamber, spindle etc are metal, and they are physically bolted to a motor/gearbox, which is earthed, so would this do the same thing?

    An enclosure? What an odd concept - who would want to hide the 'industrial chic' look of the grinder? Well, probably my wife, I suspect she will be horrified when Rocky is replaced with this eyesore, even though the coffee machine and grinder live in a sneaky laundry, mostly out of sight.

    To be honest, I haven't given it much thought as I have had target-fixation of the construction, not the end use! I could knock up a simple plywood box for the time being. It could house the motor and drive, with just the end of the gearbox sticking out with the grinder on top, and a run switch on the front. It may cut down some of the noise too. Some time this year I want to tidy up the laundry, and replace the free standing tub and shelf with a proper laminate kitchen bench and cupboards. I could put a 70mm hole in the bench, and stick the gearbox up through that, with only the grinder body visibly on the bench. Now that would look swank! Hmmm, that's odd - I just googled "coffee grinder hidden in bench", and it seems no one else is doing it, , , I wonder why? Perhaps they are sane.

    Cheers, Steve
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  13. #13
    Senior Member Lyrebird's Avatar
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    Quote Originally Posted by Stavros View Post
    Hi guys,

    What's a static wire? I'll have to google that. Mind you - the entire grind chamber, spindle etc are metal, and they are physically bolted to a motor/gearbox, which is earthed, so would this do the same thing?
    The only source of triboelectric potential is the PEEK, if there is earthed metal in the path after the PEEK it should dissipate.
    Last edited by Lyrebird; 3 Weeks Ago at 09:29 PM.
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  14. #14
    CoffeeSnobs Owner Andy's Avatar
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    Even an earthed grinder (most already are!) will do this:




    What's a static wire?
    It's become known as a static wire but it's really just something to lower the velocity of the coffee exiting the shute.

    Mazzer's patent can be seen here:
    https://patents.google.com/patent/US6948668

    " The grid reduces the velocity of the ground coffee, or powder, so that the powder does not accumulate upon, or adhere to, the walls of the funnel. "

    An even simpler solution was done by DesignedByCoffee a few years ago:
    https://coffeesnobs.com.au/grinders/...-grid-mod.html

    I suggest you wait and see what sort of mess your grinder makes before working out how to best fix it.

    Great work so far too!
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  15. #15
    Mal Dimal's Avatar
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    Quote Originally Posted by Stavros View Post
    Edit: I contacted the Royce Cross Group, who distribute the Chinese made TEFC motors. One of their technical guys was familiar with frequency drives. He seemed more concerned with the frequency/voltage/current issues than the mechanical limitations. Once I told him it was on a little coffee grinder, he laughed and said no more than 100Hz on a two pole motor.
    I also went off to the WEG site, who have a lot more technical documents available, and a table (see below) listed the maximum speed at 7200rpm. I would imagine that WEG motors have a better electrical and mechanical build quality than a $120 Chinese import, so for the time being, I will limit the overspeed to 70%.
    Good stuff Steve...

    Wasn't referring to Chinese imports by the way. Plenty of standard build induction motors are only tested to 120% of nameplate rated speed and is normally the absolute maximum allowed.

    Mal.

  16. #16
    Senior Member artman's Avatar
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    Wow, that is just so awesome!! Great work!

    Are you having any other "path" for the grinds beyond the burr assembly? I have always wondered why the horizontal paths are completely horizontal so a grinds hang there an usually sit until the next dose pushes them away and down the exit chute to be replaced by the new grinds that sit there. I have seen this on all "traditional" grinders I have had a look at. WHy isnt this part angled downwards to prevent the accumulation of girinds in the path?

    Cant wait to see the finished product. Hope you dont hide your handiwork and leave it looking mechanically beautiful.

    Cheers
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  17. #17
    Member Stavros's Avatar
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    Guys,

    Thanks for all the feedback and encouragement, I appreciate it.

    As Andy points out, I will have to wait and see how it runs. I'm hoping it will fling the ground coffee out the port like a madman, where it will hit the plastic Rocky chute I'm fitting, and drop neatly into the container below. Artman's comments are correct - I know my Rocky doesn't discharge the coffee out the chute in an orderly fashion. It seems to pack it in the chamber port, and then push more behind it until some falls down the plastic chute. When I clean the grinder, there is always coffee packed in the port. It probably retains a teaspoon of grounds in the path. I note the first coffee of the day is never as good as the second and third.

    I was looking at the Niche Zero grinder the other day. I love the cute look of it. They seem to have got their act together, as there is a near vertical drop right after the grind chamber.

    bs-niche-zero-lrg-840x440.jpg

    Cheers, Steve
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  18. #18
    Senior Member SniffCoffee's Avatar
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    What a great thread and project! Steve, please keep the updates and photos coming.

    Sniff

  19. #19
    Senior Member Jackster's Avatar
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    Awesome looking work here. I watch a bit of 'this old tony' on utube, so this is really awesome.
    I will add a observation.. I think the beans will bank up at the entrance to the burrs (I think your plastic things are in the grinds chamber?). Beans are crazy and bank up everywhere they can. But still, very easy to add a mixing paddle there somewhere...

    I like that you have put the step under the burr. Stops all the grinds packing up inside there.
    I also like the preload adjuster. Great to stop the float. I think this float is most of the reason grinders settings are different between hopper full, and single dosing..

    Watching this space!
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  20. #20
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    Quote Originally Posted by Stavros View Post
    Hi guys,

    What's a static wire? I'll have to google that. Mind you - the entire grind chamber, spindle etc are metal, and they are physically bolted to a motor/gearbox, which is earthed, so would this do the same thing?

    An enclosure? What an odd concept - who would want to hide the 'industrial chic' look of the grinder? Well, probably my wife, I suspect she will be horrified when Rocky is replaced with this eyesore, even though the coffee machine and grinder live in a sneaky laundry, mostly out of sight.

    To be honest, I haven't given it much thought as I have had target-fixation of the construction, not the end use! I could knock up a simple plywood box for the time being. It could house the motor and drive, with just the end of the gearbox sticking out with the grinder on top, and a run switch on the front. It may cut down some of the noise too. Some time this year I want to tidy up the laundry, and replace the free standing tub and shelf with a proper laminate kitchen bench and cupboards. I could put a 70mm hole in the bench, and stick the gearbox up through that, with only the grinder body visibly on the bench. Now that would look swank! Hmmm, that's odd - I just googled "coffee grinder hidden in bench", and it seems no one else is doing it, , , I wonder why? Perhaps they are sane.

    Cheers, Steve
    No enclosure is fine too, I like anything naked.
    (hope that joke didnt go too far......)

    edit* I had a think about it, probably not everything naked.......
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  21. #21
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    Hi, guys,

    I got the PEEK today and made the three fingers for the spindle. I popped the temporary delrin bushes in the body, and installed the spindle and burrs to check if the fingers would foul the cap and fixed burr carrier. A little bit more off the ends of the fingers, and it was OK. I couldn’t resist bolting it to the gearbox, and taking it for a spin. It probably wasn’t the brightest thing to do, as the bushes have quite a lot of clearance, and things would only be basically aligned, so I limited it to 300 rpm. The planetary gearbox was noisy, probably the straight-cut gears, but otherwise it seemed OK.

    So what the heck, why not run a few bean through it too. Holy crappola - it grinds coffee! It spewed grounds out over the workshop bench and floor. I’m definitely going to need a chute to direct it downwards, or have a portafilter the size of a bucket! The fines built up in about half of the port, and some clung to the outside of the body. Maybe if I mill an angle on the bottom of the port, it will assist the flow.


    IMG_2145.jpg


    I opened it up and checked inside - looks like a few places which will trap old grounds.

    IMG_2141.jpg



    Here's a link to a video of the test grind.

    Anyway, this is encouraging. Time to finish the parts and send it them off to the anodisers.

    Cheers, Steve

    PS. When you run it in reverse, it does not grind coffee.
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  22. #22
    Mal Dimal's Avatar
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    Quote Originally Posted by Stavros View Post
    PS. When you run it in reverse, it does not grind coffee.
    Funny that...

    You can also see why a fine wire grid at the entrance of the discharge chute will assist in discharging the accumulated charge of the grinds.

    Mal.

  23. #23
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    Hi guys,

    I had a fiddle around with the PEEK fingers again. I milled an outwards and upwards taper on them, to see if it would assist ejecting the grinds out the port.

    IMG_2162.JPG

    It sort of worked, it can certainly pitch the ground out, and there is slightly less buildup in the port.

    IMG_2160.JPG

    IMG_2153.JPG

    Cheers, Steve
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  24. #24
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    G'day Steve

    Very impressive work.

    I suggest you try mounting the whole thing at 90 degrees (i.e. vertical burrs) to see how that disperses before you do too much more work. There is a reason the EK43 (and its distant ancestors) have vertical burrs - low retention of grinds.

    TampIt
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    I so wish I could go do a machining course! Nice work!

  26. #26
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    Hi guys,

    Well, the guy who invented static electricity needs to be shot! It's driving me nuts.

    I stuck the Rocky chute to the side of the grinder with double-sided tape, and tried it out. OK, it works, but grinds still build up behind it in the port. It's not as bad as the Rocky, which basically packs the coffee in the port, but it's not ideal.

    IMG_2181.JPG

    I trawled through the forum and focused on threads where Mazza grinders have been converted to doserless, and took my cue from there. I bodgied up a HDPE bracket for an aluminium jam funnel, and stuck it to the side of the grinder with double-sided tape.

    IMG_2165.JPG

    A couple of tablespoon of beans. Smug was I. Damn! Didn't expect that. Most grinds were ejected out and down the funnel, but it still accumulated outside the port, and backed up in the port. It seems if there is plastic anywhere near the port, it's not good.

    IMG_2170.JPG


    I did try it without a chute, with the grinder nearly horizontal, choked up on a plastic kitchen container, and the port at the side. Failed again - what is wrong with static electricity? Can't it stay in the carpet where it belongs! Can I blame the plastic container for that? (Note: I stood it up again for the photo.)

    IMG_2175.JPG


    TampIt suggested vertical discharge. I also kept all plastic well away from it. It was hard to feed the beans into the burrs, (resist the urge to use your fingers to poke them in Steve, you remember what happened with the garden shredder). OK, heaps better, but I'm not completely sold on mounting the grinder horizontal.

    IMG_2176.JPG

    Note: No real beans were harmed during the testing of the grinder - only Lazzio Dark Roast.

    And for your viewing pleasure, attached link of the frequency drive running the grinder at about 1/2 a rpm.

    http://www.users.on.net/~m27373/Grinder/IMG_2179.MOV


    Cheers, Steve
    Last edited by Stavros; 3 Weeks Ago at 07:50 PM.
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    Wow you work HDPE as well, very impressive!

    As for vertical mounting, it's a pretty good idea, the EK43 speaks for itself, must be doing something right.

    As for the static, you can add a drop of water to the beans to reduce them (not sure if that's what you want while optimizing the exit chute design atm...)
    Maybe take queue from Mazzer and put a wire screen? (just google mazzer anti static screen)

    Let us know how you go
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  28. #28
    Member Stavros's Avatar
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    Hi guys,

    Thanks 392392. Yep, I have a small but solid CNC router which cuts polyethylene like butter. It's not too bad on timber either, so I knocked up a temporary base to hold the grinder at 30 degrees, with the discharge port on the right, bottom side. (As the grinder spits the grounds out at an angle of 45 degrees to the port face, this pretty much points the ground vertically down.)

    IMG_2188.JPG

    IMG_2189.JPG

    I ran a cup of beans through it, and let it run for about 20 seconds after it finished grinding. I'm fairly happy with the limited buildup of grounds in the chamber and port. I think with a simple vertical chute it will be quite useable. Although, if I leave it at this angle, I may have to modify the feed chute/funnel so it's easier to direct the beans into the burrs.

    IMG_2186.JPG

    Cheers, Steve
    Last edited by Stavros; 3 Weeks Ago at 07:45 AM. Reason: formatting
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  29. #29
    Mal Dimal's Avatar
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    G'day Steve...

    Now looking a little reminiscent of an old Mortar weapon.

    12 Inch Mortar.jpg

    Mal.
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  30. #30
    Member Stavros's Avatar
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    Yes Mal, I’m beginning to worry that it will never look like a modern kitchen appliance. I can feel the Australian ‘Excellence in Design and Innovation’ award slowly slipping away. The guy who built Dilbert’s power supply has more style than me.

    Dilbert.gif

    It’s funny, my brother was around yesterday, and saw the grinder for the first time. He laughed and called it a mortar too. He said to put four wheels on it, so it looked like a gun carriage.

    IMG_2192.JPG

    Good idea! I could tow it behind the car to Parliament house, and lob a few rounds into House of Representatives.

    Barnaby.jpg

    Cheers, Steve
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  31. #31
    338
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    Steve, seems to resemble the Monolith Flat Burr grinder by Kafatek. No bad thing and will probably work out less than the US$2450 retail

    MonolithFlat_Web.jpg

  32. #32
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    338, Kafatek will probably be offended by that comment. "We spent tens of thousands of dollars on design consultants, to ensure ours wouldn't look like a, , like a, , , like an artillery piece!!!"

    It looks like I have about 3kg too much aluminium, maybe it needs to go on a milling machine diet. And I bet their grinder chute didn't cause them as much angst as mine did.

    Cheers, Steve
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  33. #33
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    Hi Guys,

    Despite the good advice I have received from members of the forum regarding horizontal mounting of the grinder, I would still prefer to operate the grinder in a vertical position. (Yes, I know - target-fixation.) So I reduced the size of the horizontal part of the port, (which tended to catch grinds), and replaced it with a near vertical chute. (Artman is going to love this.) I did have second thoughts, as I had to bore a tapered cylindrical slot in the side of the body to accept the angled tubular chute, and once I started there would be no easy way back if it didn't work.

    IMG_2206.JPG

    The chute mounts in the cylindrical recess, and has a corresponding port to match the grinder. I may grab the die grinder tomorrow, and taper the tube wall thickness and blend it into the port.

    IMG_2213.JPG

    I tested it again, and it's not too bad. Most of the coffee get spat into the chute, and drops down. A bit still collects in the port, and a bit sticks to the far wall of the chute, but I think it's acceptable.

    IMG_2218.JPG

    Well, overall, I'm pleased I decided to try this. I still need to make a removable cap for the top of the chute, (to allow for a quick clean), make a new wooden base, (which doesn't look like a gun carriage), and tidy up a few things, but I think that's all I'm going to do.

    IMG_2219.JPG

    Cheers, Steve.
    Last edited by Stavros; 2 Weeks Ago at 08:58 PM. Reason: Formatting
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  34. #34
    Mal Dimal's Avatar
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    That does look like a significant improvement Steve, and terrific work again mate...

    Mal.

  35. #35
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    Hi guys,

    The parts went off to the anodisers today. Before I sent them, I took a light skim cut off all the external surfaces to remove any dings, scratches, and possible acid fingerprints which would affect the anodising finish. I asked that they be anodised black over the machined finish, without any additional bead-blasting or brushed finish. I included an additional piece of aluminium, with a flat smooth finish, which can be used for an engraving test once I get them back in a week or two.

    If all goes well, I will engrave a grind scale directly into the black finish of the top cap, which should show up as a bright aluminium figures. In the meantime, I have used a simple CADCAM program called CamBam, and the CNC router to make a 1mm thick brass tag with the same engraving on it as a back-up. I'll need to get some black paint into the engraving for contrast. From 'art to part' in an afternoon.

    Capture.JPG

    IMG_2228.JPG

    Cheers, Steve

    PS. I'm considering naming the grinder 'Black Betty'. She's always ready. She's all rock steady. Yeah Black Betty. Bam-ba-lam.
    Last edited by Stavros; 2 Weeks Ago at 05:55 PM.
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  36. #36
    Senior Member Lyrebird's Avatar
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    Quote Originally Posted by Stavros View Post
    I'll need to get some black paint into the engraving for contrast.

    Last One.jpg

    I spent a bit of time developing a method that works and lasts.

    I don't use paint, I use filled epoxy.

    I carefully clean the surfaces with acetone on 0000 steel wool. I then mix carbon black into a quality* two part epoxy and fill the engraving with the mixture.

    Draw a flat polythene or polypropylene scraper across the surface to remove the excess from the brass. Allow the epoxy to cure.

    Clean again with steel wool to achieve brushed surface if desired.

    Overcoat with "Like Armour" brass lacquer: you can use other acrylic coatings but this is the best I've found.

    The pic shows a unit I built where the faceplate was done with this method.


    * not the crap you buy at Bunnings. Talk to your local boatbuilder.
    Last edited by Lyrebird; 2 Weeks Ago at 07:45 PM. Reason: Realised pic showed brushed finish, changed text to suit.
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  37. #37
    Senior Member artman's Avatar
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    Wow, amazing job!! nothing like a good DIY and this on a completely insane level.

    Cheers

  38. #38
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    Definitely, worth a close look at the techniques Denis of Kafatek used in his designs.
    The Monolith flat motor and gearing makes no appreciable noise, (all you hear is the crunching of the beans).
    Although I'm sure you will find a simple way to keep static at acceptable levels (as most of the manufactures have had to do).
    A shot of fine water spray onto the beans just prior to grinding definitely improves static, clumping and the fluffiness of the grind (and it's a very easy extra step that more coffee snobs should try).
    The grind I get with a Monolith flat is so fluffy I can't get 18G into a 20G basket without a pre tamp before I remove the funnel from the top of the portafilter - or I spill coffee grounds.

    Perfectionist designers are a dying breed, it's good to see that a few from the old school are still around, well done.

    P.S.
    If you name your grinder Renaldo you will immediately get 1,000,000 orders from soccer players all over the world.

    (If you don't control the static enough, you will get just as many orders if you name it Messi).

    Should win the prize for the thread of the year.

    Cheers,

    Snowytec.
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  39. #39
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    Thanks for the comments Snowytec.

    I did a bit of googling and read up on the Kafatek Monolith. There is not a lot of detailed information out there, as people seem to buy them to grind coffee, not to pull completely to bits to see how they are built. It looks like it has a stepper motor with a gearbox. I ass-u-me the gearbox has helical gears?, and hence is pretty quiet. Man, there are some smick grinders out there - the Niche Zero and Kafatek to mention a few. And the proposed Lagom P64 also looks interesting - I can't wait till someone buys one and pulls it apart. (Slightly off topic, but I jagged a report of the Niche by someone called 'Davec' who had some interesting stuff to say about the difference between flat and conical burrs.)

    Still waiting on the anodisers, so took the opportunity to make a spindle bearing spacer to ensure a rigid and fixed bearing preload, instead of just screwing the spindle nut down and hoping for the best. I made two spacers to simulate the final assembly. One to separate the outer races the same distance as the step in the grinder body, (13.57mm), and the other to space the inner races apart just enough to remove any axial/radial play.

    IMG_2252.JPG

    It was a suck-it-and-see process, machining a smidgen off the inner spacer, assembling it on the spindle, and checking the bearing play.

    IMG_2251.JPG

    Then pulling it apart, taking off incremental amounts and checking again, repeat, repeat, repeat, until I couldn't measure any play, (Ended up at 13.45mm).

    IMG_2254.JPG

    Note that I couldn't do this once the grinder is assembled, as the bearings are an interference fit in the body, and once they go in, the inner spacer is trapped between them, and couldn't easily be remove it to skim a bit off etc.

    Cheers, Steve

    PS. I had to google Messi before I got the joke - very good 'dad' joke.
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  40. #40
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    I usually start nicking ideas anywhere I can about halfway through projects, "research", (when I've further developed my instinct for the real issues).
    It's understandable that designers want to protect their core intellectual property, so it's really hard to get "real" information.
    Quite a lot of good stuff on grinders at Home - Barista.com.
    Kafatek have a newish forum that you have to register for, it's a good place to ask Denis your most important questions,(one at a time).
    Before I settled on my choice of grinder I emailed him and told him he'd already got the order, that we drank one cappuccino every morning followed by 5-6 Espresso based long blacks thought the day, (Yeah - wired !) using home roasted prize winning beans and where members of Coffeesnobs.com.au
    Which model should I buy ?
    Denis replied that the best machine for our coffee habits focussing on maximum extraction of subtle taste shifts was the flat SSP burr design.
    Took me about a year to get my hands on one.

    (It's turned out to be a soulmate to a Cremina).

    (You're definitely heading the right way),

    Cheers,
    Snowytec.

  41. #41
    Member Stavros's Avatar
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    Snowytec,

    In the short amount of time I've been looking and thinking about coffee grinders, I've came to the opinion that the basics aren't rocket science. There's nothing cutting edge about a set of burrs and a motor, nothing commercial-in-confidence about how they bolt together or how the electricity is turned into torque and rotation, the technology hasn't made a massive leap forward lately. However, the devil is in the detail of the actual implementation.

    It seems that when you look at the big commercial units, (Mazzer etc), they are designed to do the job, run all day, shoving the coffee grounds out a chute with some sort of restriction, (flap, wires, grids etc), that turns the fine grounds into a more manageable, (read less static and fluff), semi-compacted 'cake'. Retention isn't a problem for the big coffee shops, as the turnover all day manages the problem. Now I've personally experienced the frustrating effects of static, I have a little bit more insight into the problems the big manufacturers have solved by doing this.

    In my limited experience, some of the common home ones 'cake' the grounds too, maybe by deliberate design, or maybe by following commercial designs. That doesn't seem to be a big issue at home, as most people cope with clumps, and produce a decent shot. Maybe most people just don't notice or care - they don't bother getting down in the weeds. Then there are the boutique manufacturers, catering for the coffee snobs and 'zero-retention' crowd, investing cash, sweat and tears in the design and details. You have to admire them for making the effort. I can see why these manufacturers don't broadcast all the design, material, and construction details, probably because they don't want to see a Chinese manufactured knock-off in the shops in six months.


    In the way I've built my grinder, I initially focussed on a few personal mechanical bugbears, without really thinking through the whole design. Research was minimal. As I naively mentioned in the first post, "All you need to do is attach a couple of big flat burrs to a variable speed geared motor. How hard could it be?" Turns out the basics are dead easy, but along the way, I've realised how much goes into making something which is both practical, and of an attractive appearance. Imagine being a business and trying to make it commercially feasible too? Again, well done to the boutique manufacturers.

    Regardless of this, it's been an interesting project - I've enjoyed it. I'm looking forward to the final assembly and use. I think it will only do 90% of what a good boutique one will do. But in the back of my mind there is the nagging thought that, maybe, next time, I'll could do it better.

    Cheers, Steve.

    PS. Man, those Creminas are frighteningly $$$$$$.


    Last edited by Stavros; 5 Days Ago at 03:58 PM. Reason: formatting

  42. #42
    Senior Member Lyrebird's Avatar
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    Quote Originally Posted by Stavros View Post
    There's nothing cutting edge about a set of burrs

    I see what you did there
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    Totally agree Stavros, putting your best effort into unearthing the detail, (but only after you've dicovered the questions) and before you commit to much to the final design is often hardest.
    Learning from pioneers, standing on their shoulders and then moving final designs forward was always easiest for me.
    Only chimed in because I also knew that your next steps would make all the difference.
    What I see in your pictures is probably how the Monoliths where born, your work is too good to screw up the detail.

    (Only difference between a $50 and $5,000 dollar grinder is in the detail).

    Yep Cremina prices reflect what professionals at the top of their game can charge, (a ridiculous amount).
    The quality of the steel used is unbelievable, (I should have broken at least three of their lever arms when conducting my early profiling experiments, but the original arm is still in perfect condition).

    The finish is the best i've ever seen, (they must spend $1,000 just polishing).

    You're next project could be a Cremina copy to go with your grinder.

    Cheers.



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