Shrapnel Phase One


OK, so now my hands hurt from tapping 30 or so 4mm holes in that shiny nickel-coated aluminum plate. Getting all of these holes lined up so I could mount the hardened and ground linear rail was no easy task. The holes could be no more than 1/64" off or the bolt would not go in so I took plenty of care getting the marks correct before drilling.


Greg sourced the rails and bearings from AMT. I believe these are of Taiwanese make, but their quality is quite impressive. You can also see here the excellent quality 5/8" cast aluminum tooling plate that is being used for the work surface. This may be a bit overkill for a machine of this size, but there will be no flex on this table.


The cast tooling plate is top quality and has an almost mirror finish that they somehow grind into the surface. My only complaint about these plates is that they aren't cut exactly square by about 1/32 of an inch.

Screw-up number 1: I somehow laid out the holes in the tooling plate incorrectly and one set of holes on the right side does not line up with the bearings underneath. The holes are only off by .2", so it will be very tough if not impossible to re-drill another set of holes and counterbores so close to what is already there. I may end up just using one bolt per bearing on the right side rail. I don't think it will effect the operation of the mill though. This hefty aluminum plate glides like it is on ice and it is tough to even discern how much the plate weighs due to the low friction of the ball bearing linear rails.


Got some time on the CNC mill to cut out the motor mounts and the lead screw supports. Here is a shot of the CNC mill in action.


And here is the finished bearing holder/lead-screw support. Just need to mount them up and see how things line up!


After deburring the part, it is ready to install. I opted for the round bearing retainer with bolts placed every 120 degrees for a clean look and simple but effective thrust bearing retention.


Here you can see the fit-up of the thrust bearing retainer along with the delrin AB nut that I fabricated. This was a trick process getting everything to line up correctly, but I used some creative ideas on the design to allow for a bit of adjustment so that everything goes together smoothly. By mounting the AB nut all the way forward on the table, it allows for a bit of flex in the lead screw in case things start to bind up when the table slides back to the motor end.


A shot of the table as it now sits. I need to get some different motor to lead screw couplers, but for now, the cheapo ones that I have on will work.


Here you can see how the motor mounts to the table along with the motor couplers that I used.


I desperately needed bench space so I opted to move the construction of the Shrapnel over to a table that I set up in the garage. This is actually quite nice because it is great to be able to sit down and work on this thing. In this pic, you can see how I used an Acme nut to hold the lead screw in position against the thrust bearing. On the other side of the bearing, I used a 1/8" roll pin pressed into the lead screw as a fixed stop up against the bearing. On the nut, I drilled and tapped a 6/32 hole for a set screw that locks the nut inplace once tightened. This setup works extremely well and requires very little machine work. Now I just wish I had some Acme threaded rod that was actually straight!


Arcsin all wired up to the X axis. This really was a fun moment for me as I have been working on the Arcsin for some time now. It was incredible to see it all start to come together.


I actually used toner transfer to put the silk screen on the aluminum housing. I did this just to make sure everything lined up OK before I get a production run of housings built. The toner transfer works surprisingly well for this and the only drawback is that it is kind of white because of the paper that remains embedded in the melted toner.


And finally, here is the video!