Daniel's Work Thread: Toward a Hackerspace Scanner

[Gerard]

couldn't you just pump the fine dusty air down the toilet? maybe with some water sprinkler

or use the dusty air in an oven (dust explosions could be a problem)

[daniel_reetz]

Hahahaa, I like your thinking, Gerard. Actually a mist system would be a great idea and I have a general interest in such things (it would also be useful for scrubbing the output of my laser cutter). But hopefully this garbage-can thing works well enough. I have two small modifications to make today and I'm going to call it good.

[daniel_reetz]

Phil the philter is installed. Overall, it definitely decreases flow on the system, but it's also keeping my dust bag empty and the remains of my filter clean after AN ENTIRE GARBAGE BAG full of dust went through it. So I'm happy.

I've been having troubles with maintaining Z position, and it seemed to be related to the Delrin nut that the Z axis drives on. I called up CNCRouterParts and indeed, they have a better mechanism now. Well, it came Friday so I spent the morning tearing down my Z axis and installing the new nut.

Z_fix_IMG_20120520_092426.jpg (25.43 KiB) Viewed 798 times

Z_fix_2IMG_20120520_092426.jpg (42.99 KiB) Viewed 798 times

[daniel_reetz]

knuckles_IMG_20120520_112840.jpg (60.8 KiB) Viewed 797 times

All work and no play makes Daniel a dull and grumpy boy, so I drew up some Birch Knuckles for fun.

[daniel_reetz]

Well, I'm trying to assemble one of the kits I've been cutting, and I found a few more mistakes. One, there were still some bearing pockets being cut "climb" instead of "conventional", so they are undersized. OK. Two, the cradle lift arms were drawn with a 1/2" extension instead of a .7" extension. I probably did that.

So.

1. Fix bearing pocket milling strategy.
2. Rethink/fix cradle lift arm depth.
3. Fix back brace pocket (slightly too short)
4. VXB Order
5. Fastenal check on bearings.

Going to investigate all the single-bearing approaches from earlier.

[daniel_reetz]

Also, I'm coming around to DPC's ideas about drill-pressing in the bearings so I can do dual bearings, right now I'm about 50/50 on that and jck57's idea about retaining washers.

Here's the "button button" thread by cfmorrill with the correct bit size.


Here's dpc's original drill press suggestion (I can see some nice ways to make this work and work repeatably now - and some post-processing is almost certainly going to be necessary -- I apologize for my earlier, somewhat unrealistic negativity toward the idea).

dpc also had a good insight about spacers, which can be purchased in bulk, for cheap...and I think all the machining would remain single-sided. Have to think a bit or just try this one.

Here's jck57's retainer idea, which is looking pretty shiny.

Ultimately I would like to take the approach dpc outlines here - basically do a whole sheet of these things and then flip it over for processing the other side. I'm a bit concerned about losing steps and ruining whole batches of parts, tho.

dpc, jck57, Rob, thank you for all the help and ideas - means a lot to me and has really improved things overall. Also on my mission tonight is to re-read this entire thread and absorb more of the insight from everyone that bounced of my thick skull.

Also I am 90% through drawing up jck57's cradle. just dying to test that thing.

[jck57]

Also, I'm coming around to DPC's ideas about drill-pressing in the bearings so I can do dual bearings, right now I'm about 50/50 on that and jck57's idea about retaining washers.

The pockets on the lift arms you sent me were the perfect size for pressing in with a vise. I am 100% confident these bearings will never work loose and can only be removed by deliberate mayhem. As is apparent from the pics I posted, I attached the lift arms so the bearing is on the cradle side. This meant I had to thread the nut through the smaller hole in the arm. I ground down a socket to fit but if the hole was made 3/4" diameter, any socket would fit. With this scheme all you need for fastening is a 5/16 x 1.5" long bolt and a couple of washers. If you can get consistent enough cuts on the bearing pockets to make press-fitting feasible, I would recommend pressing in the bearings before you ship the scanner, as Rob has suggested.

Also I am 90% through drawing up jck57's cradle. just dying to test that thing.

If you are making the sliding tables according to revised design with pressed-in axles, don't forget to cut the rabbets to 7/32" depth instead of 3/8" shown in my drawing.

[jck57]

Since we're all posting drawings, this is what I was referring to earlier.

If you're going to use a single bearing, it should be on the outside of the two arms to offer the most support of an radial load.

I missed this the first time. Dpc, can you explain why outside is better than inside? My thinking is that inside is better because the bolt can be shorter and thus less subject to leverage.

[dpc]

As the arm moves, the bolt is subject to shear forces. So if you then consider the bolt itself to be a lever, positioning the bearings near the center (fulcrum) would have more force on the bearing than the same bearing moved out to the end of the bolt (which would be subject to less force but more movement).

This is the reason why the bearings on a wheel are located on the outside of the wheel rather than closer to the middle. Also any bearing run-out (i.e. slop) is less apparent when the bearings are located as far as possible from the center of the wheel's axle.

[daniel_reetz]

From a machining perspective, it's best to have all machining operations on just one side of the part. A quirk of the current design is that the bearing on the lifter arm would be better on the "outside" as drawn by DPC.

I'm going to try pressing and/or pressing with epoxy or cyano glue. I guess I wouldn't mind pressing the arms if I did 50 or 100 at once and didn't have to think about it for a long time.