Dovetail could be a thing

So today’s goal was to make the first leg joint today. That was apparently a bit ambitious, but at least I managed to finish the dovetail vice and prep the first stock.

So this is the last chance I am giving milling for now. If this fails, then I will redesign to use other techniques.

Dovetails FTW!

So after last week, I essentially gave up on the 4th axis machining. But when I realized that the problem was the stick-out, together with the fact that the chuck was removable, I realized I could make a replacements part for the chuck that was short and stubby and had a dovetail mount. All good in theory…

So time to mill a dovetail chuck. Got a new 6mm carbide endmill that should supposedly run at 13000rpm and a whooping 1500 mm/min. So that was really scary.

So I learned two things today.

  1. Do not let a 6mm endmill slot more than 1mm deep. It get filled with chips in like 3 seconds. Yeah, I am lookign at you, Horizontal. What is it with gloign in and slotting right to the middle of the surface area. Couldn’t you choose a better movement pattern? Use a helix like all other sensible methods.
  2. Do not skimp on the alcohol. Cutting down the mister to just a moisturizing mist was clearly not the way to go.

So that lesson almost cost me the end mill 4 times, and unfortunately, it now has quite a few scrapes on it. So that was sad….

But the dovetail endmill seems to have done its thing:

Hopefully I will be able to make something useful out of this after all….

Forth axis and yet another dissapointment

So last week I tried to use the 4th axis. Here was the setup. Loots pretty snazzy…… ๐Ÿ˜€

Here is the result. Unfortunately, the vibrations caused my favourite 8mm endmill to snap. :ยด(

When you look at it, it is fairly obvious. The total stickout including the chuck is something like 15cm or even more. And since I only used the first two bolts, you really could not expect much…..

So one more end-mill, one more lesson. Instead, I mounted the Emco vice and aligned it and gave up on the 4th axis plans.


So first attempt att making a real part today, and on top of that I wanted to try the new superglue+masking tape method. Many have spread the word about this method, but NYC CNC do it best, as usual:

The problem is that none of the products they mention can be bought in Sweden, and even their links to Amazon are getting stale. So I tried TESA Premium Classic masking tape and Loctite Power Flex Gel. I gave the glue a few minutes to harden properly below.

Then I noticed that the mister wasn’t working. So I had to take it apart. It seems that the O-ring does not grip the inner tube properly, meaning pressure air leaks into the space where the alcohol should run. Forcing the tube to become a little wider by forcing a 2.5mm drill bit into it seemed to do the trick. Now it sprays a fine and stable mist.

So mister was fixed. Time to see if the glue method really worked…..

Worked like a charm! Part came out just the way I was hoping for.

Lessons learned:

  • CNC-ing is an expensive hobby. Jogged a 4mm end-mill straight off while touching off. Great start…… fortunately, I had a spare.
  • Assuming that the top of the spoil-piece will be perfectly square with the machine once you mount it is a bit naive, give the types of equipment I am working with here. Next time I will place the spoilpiece in the machine, polish off the top to ensure it is flat and square, then glue the stock while the spoil piece is in place in the machine.
  • Using tabs was a great idea. With the super-glue method, surface area is everything. By using a contour with tabs to finish off any pockets that go all the way through, any pocket large enough will get a piece in the middle that helps keep the part down.
  • Getting tape-glue into the end-mill is probably a really bad thing, so next time, I will add a second layer of masking tape to n open space on the spoil-piece and touch off my z against that. This should mean that the end-mill will not mill into any of the actual tape. Worst-case scenario, the end-mitt doesn’t go all the way down through the metal, but the remaining piece will be so thin it does not matter. I can cut it with a knife, even. I will still have to file down the tabs anyways.

Open heart surgery

So it was quite clear last time that something had gone wrong with the Y-axis. It really was moving back and forth a full 0.1mm with a distinct click to it. So I opened up the machine again and pulled out the Y axis ball screw (Getting rather good at that by now :P).

The nice thing is that I realized I could do this without affecting any of the calibration of the machine. Just slide the X-axis over a bit to expose the Y-axis ball screw fastener bolts. Once done, reattach the Y-axis, slide back the X-axis and atach the X-motor to the bed. And done!

The issue causing the backlash seems to be that the spring steel pin wasn’t being springy enough and the screw bolt was not attached to the bearing fastener. What to do?

Fortunately, I found some solid metal pins of the right dimensions. With 8 layers of aluminium foil forming a shim, and some bearing glue, and the beasing fastener was rock solid again. Reshim the bearing house with an equal 8 layers of foil and put all of the pieces back together again.

Now the Terco has a backlash of 0.01 in Y and 0.02 in X. Unfortunately, the entire chassis is a bit springy, so the total flex adds up to something like 0.05mm. But at least we can now confidently say that the Terco performs at less than 0.1mm error in all scenarios.

Finally, the inaugeration of milling with the 4th axis. It worked like a charm! At least until I ran the end mill right into the chuck and ruined the mill and made a big mark in the chuck. Lesson learned: When doing 4-axis milling, model your chunk into your CAD model so you can verify that you are not cutting into it.

Also, Delrin is not as solid as I had assumed (Obvious in retrospect) so the vibrations were completely unreasonable if this had been anything but a test cut part.