Hi Steve, pretty sure they do rotate clockwise, see here.
Really interested to see your grinder, hopefully you will post pics!
I'm a first-time poster, but long time lurker. A big thanks to the forum, it's been a wealth of information over the years. It was this forum that got me interested in a 'proper' espresso machine years ago - resulting in the purchase of a Rancilio Audrey and Rocky for home, then a second Audrey and Rocky for work, and finally a third Audrey, just in case one of the other two broke down.
Anyway, I'm making my own coffee grinder using Mazzer Major 83mm flat burrs, and I'm about to machine a tangential discharge port in the grinder body, and thought I should double check the direction of rotation of the burrs before I make a mistake!
If you are looking down on the rotating burr, (the one attached to the motor shaft), I assume that the rotation is clockwise?
Last edited by Andy; 4 Weeks Ago at 01:31 PM.
Thanks very much magnafunk,
I just found the packet the burrs came in, (mine are the T151A coated ones), and there on the bottom below the burr dimensions is "Rotation - Clockwise". Duh! I should have had a proper look.
Yep, once I get the required number of post, I'll put up a few pictures up. Basically, I started with the 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, and started machining. It's a big ugly industrial lump - I should paint it green, and call it "Shrek".
Last edited by Stavros; 4 Weeks Ago at 08:40 PM. Reason: Spelling
Interested to know how you are doing the burr gap adjustment and what you are doing to maintain coaxial alignment. I've been playing with ideas for my own grinder and these seem to be the hardest things to achieve. I'm thinking of using a 4" BSP nipple and socket.
My first choice of drive is a DC motor because variable speed is so easy, your 1/2 HP VSD approach is clever. I have a 2 kW 1 -> 3 phase VSD in the shed somewhere.
Burr gap is adjusted by a 95mm diameter thread between the body cap and fixed burr carrier. The pitch of the thread is 16tpi, (or about 1.5mm if you like those new-fangled dimensions), so 1/4 of a revolution will cause a gap of approximately 15 thou' of an inch. The thread is very smooth with minimum clearance, so there is no wobble or axial play.
I'm a machinist by trade, and during the design and manufacture, I applied good general engineering practices, (typically used for machine spindles on lathes, pumps, etc), to maintain axial alignment and parallel faces. Everything was machined with care, with critical bores and faces completed in single settings. There are mating spigots and recesses in adjacent parts, with just a few thou' clearance. So, basically, (ignoring accumulated tolerances/clearances), everything should line up. The spindle design also includes an adjustable nut to preload the bearings to remove any axial and radial play. (A common practice on metal lathe spindles.)
I chose a three-phase / frequency drive because I'm familiar with them, and the newer 'sensor-less vector' drives have nearly 100% torque at any speed. (They are also cheap and common on FleaBay.) I was temped to use a Parker brand servo drive and motor, because I've used them on CNC equipment, but I couldn't justify the $$$.
My mate, who is an IT guy, says it's overkill for a coffee grinder, but I say it's just the right amount of kill.
PS. With your 2kW VSD, you should be able to grind the whole coffee tree!
Thanks for that, you are evidently well in front of my noodling.
BTW they're hardly new fangled, the metric system was formally adopted in Australia in 1971, nearly 50 years ago.
If you count the decimalisation of the currency, it's over 50 years (hands up if you knew that "the 14th of February Nineteen Sixty Six" is sung to the tune of "click go the shears")
Last edited by Lyrebird; 4 Weeks Ago at 10:13 PM.
Ooooh would love to see photos of your progress on this...
Last edited by Stavros; 4 Weeks Ago at 12:01 PM. Reason: Try to attach image
A thing of beauty stavros !
So she's only light duty then
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. The path is the height of the grind chamber - 20mm, which is approximately the total height of the burr set. I had to a take a corresponding bit out of the locating spigot in the cap, to clear the path.
I will probably end up fitting a chute from a Rancilio Rocky, so made the width of the port to suit.
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.
I had a chat to a few anodising companies today. As there are none in Canberra, I'll have to use one in Sydney or Melbourne. 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 beautifully.
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 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.Cheers, Steve
Now SanderP - I haven't really did a Tim-The-Toolman on the grinder, it only has a 375 watt motor, with a 9:1 ratio gearbox, so it will grind at a moderate 300 rpm. That's pretty much the same as other 'domestic' grinders. I just made it a little solid, with a wee bit extra metal.
Last edited by Stavros; 4 Weeks Ago at 07:00 PM. Reason: Spelling, always spelling.
This is a fantastic build project. Could you start a new thread so that the subject becomes clearer to potential viewers, please. I am sure that there are plenty who would enjoy following this build. Good luck with the rest of the build - but it is clear that luck doesn't really come in to it.
Yes, I knew someone would say this sooner or later. Will do so.
We could always ask our friendly admins to edit the thread title to something of Stavros's choosing
OK. There is a new post in the Grinders area called 'let's build a flatt burr coffee grinder'.