Saturday, July 28, 2012

Update 2: DIY Hario conical burr grinder Kitchenaid stand mixer attachment

More updates to the previous 3D printed prototypes. The pieces are available on Thingiverse and Shapeways. These pieces were 3D printed by Shapeways in their White, Strong, Flexible material. Screwing the set screws directly into the plastic instead of tapping the holes kept the piece viable for several months before it wore out.

Managed to get a pretty decent locating fit for a 3/8" x 5/8" x 5/32" sealed, pre-lubricated ball bearing from VXB. They have a lot of options in this size. I ordered two to choose from, but only one fit into the printed flange piece easily with just my hand pressure even though they were rated for the same maximum OD and tolerance. So I think the current design is close to the edge of hand pressed fitting for the low tolerance of the current SLS 3D printing process.

If you look carefully at the bottom edge of the flange where it contacts the drill adapter, you can see there is a step-wise pattern; this is because I tried to give the surface that contacts the drill adapter a gentle slope to match the slope on the front surface of the drill adapter. It basically works, but the 3D printing leaves this step pattern instead of a smooth slope. Probably not worth the trouble.

Here's the whole thing assembled. Note that the square driver piece is taking on a healthy coffee color due to the plastic material being porous and absorbing bits of coffee grounds. I've had this piece a while now and it's showing no signs of failing, so I think the 3D printed parts are reasonably successful for medium use. It's also kind of nice to know that the plastic part will fail before you kill the KitchenAid motor if you happen to jam things up some how.

Here's a picture of the extra 5/8" OD bearing I bought that didn't quite fit nicely. I also bought a 9/16" OD needle bearing to try, but it seemed better to stick to something with less depth and the 5/8" OD ball bearing was a small enough OD to work.

Sunday, May 20, 2012

Update: DIY Hario conical burr grinder Kitchenaid stand mixer attachment

Update 3: More updates to the design, particularly housing for a ball bearing in the flange.

Update 2: It seemed like a Wiki was actually more appropriate, so I am retiring the Google Group in favor of a new Wikia page. Please join in!

Update: I created a Kitchenaid DIY Google Group to try to get together some of the handful of people who have been hacking on this. Also posted a listing of known projects.

Substantial updates to the earlier prototype. Here I've added an adapter flange that holds it in place against the Kitchenaid adapter hub. This was also supposed to house a sleeve bearing but I made the dimensions too tight so that will have to wait for next iteration. Also I found some nice, small, cheap, sealed ball bearings from VXB so will probably design for that instead. The coupling between the square hub and the 3/8" drill shaft is essentially the same as before, only shorter to leave room for the flange.

Here's a video of this version in action. Note that now I'm using it to drive the older Hario conical burr grinder model, rather than the Hario Slim. (We have both, one for home and one for my office. Kitchenaid only at home though ;).)

One advantage of the older Hario is that the coupling from the drill adapter to the grinder is simpler. The Hario Slim uses a pentagonal (AKA 5-point) drive in a small nonstandard size (~3/16"). I tried a 3D printed adapter for that but I don't think the Shapeways "Strong, Flexible" material is strong enough. I'm trying a lasercut acrylic piece next.

For the older Hario, the situation is much simpler. The drive has a nonstandard shape (cylindrical with flats on two opposite sides) for hand cranking, but it's also threaded as M6-1 so you can just screw something down on top of it. Actually, you can even just clamp the drill adapter directly down on this, as jeffkobi did in his original design. I wanted to try something simple and off-the-shelf to avoid clamping directly to the grinder, so I looked for M6-1 coupling nuts that would fit into the 3/8" drill adapter, but unfortunately they are all slightly too large. However, a 1/4-20 coupling nut fits snugly into the adapter (you may have to test a few to find one with clearance) and screws smoothly onto the grinder drive for the first few turns. I don't have any MechE, so can't really tell you the relative benefit of either clamping directly to the drive or screwing an unmatched thread onto it, but as long as I include some washers so that the 1/4-20 is only riding the M6 threads a little way I think this might be a little nicer. An M6@1/4-20 adapter nut or just an M6 with a smaller outer diameter would be ideal but I haven't found such a product.

The previous hub coupling has already worn out, so it's still not clear whether these 3D printed parts are viable. The first thing to go was the set screw holes; on the failed piece the screws get pushed back through their threads so the coupling no longer grips the 3/8" shaft. But I think the mistake there was to tap the holes and use nylon set screws before switching to steel set screws. On the new piece I just screwed steel set screws through the untapped hole so the fit is tighter and it seems to be holding up better so far. Probably a clamping adapter design would be better, although it would be a tight fit and I'm not sure how well 3D printed plastic would handle that kind of stress.

Sunday, April 15, 2012

Kitchenaid drill adapter

Update: this coupler has started to fail. See details on the update post, as well as a new model. Here are the links to Thingiverse and Shapeways, but be aware the current 3D printed plastic material ("White Strong Flexible") is not proven for long-term use.

Update: here's a video of it in action with the drill adapter clamped directly onto a Hario Slim Burr Grinder. Actually works pretty well as is, so I will put the piece on Thingiverse soon. Lots of refinements planned though.

A while back I had a brief flirtation with the idea of DIY Kitchenaid attachments, but never really got going on the project. Then recently, jeffkobi posted a nice Instructable on how to attach a Kyocera manual burr coffee grinder to your Kitchenaid and it rekindled my interest (not least because I own the same model burr grinder).
I really liked jeffkobi's idea of using an inexpensive Milescraft 90 degree drill adapter as the intermediary between the mixer and the grinder. So I've been trying to develop some simple 3D printable pieces to make it easier to couple the drill adapter to the Kitchenaid attachment hub. This is a work in progress and is going to take at least one more iteration to refine, but I'm pretty happy with how it looks so far, so here's some teasers.

Thursday, March 15, 2012

Matlab internals and in-place editing

Here's a couple of articles I wrote for the blog Undocumented Matlab: If you're interested in how Matlab works behind the scenes and/or how to use this information to write more efficient C/C++ mex code, check it out.