X2, Pt. 3

Another one of the big-ish upgrades I decided to do on my Sieg X2D was to upgrade the spindle drive system from gears to belt.  The stock gears are very noisy, and are prone to breaking if you crash hard.  They also limit the RPM of the spindle.  I could have made my own conversion, but the Little Machine Shop belt drive conversion is a drop on set and is reasonably priced. The spindle now runs very quietly, I have double the RPM capability, and if I crash I don't have to worry about tearing the head apart to replace gears.

The next upgrade isn't new, but I never really showed it.  The stock rubber way cover bellows work fine for most of these mills, but they wouldn't work for me.  My Y axis limit switch is placed such that the bellows might accidentally trip it.  So, I drew up and 3D printed my own way cover.  There is room for improvement so I might make a V2 some day, but for now it gets the job done.

Lastly, it occurred to me that I never showed my vice.  Good machinists vices are expensive, and I am cheap, so I came up with my own.  In my stash of "That looks like it might be handy some day," I had the compound rest from a giant old lathe(with no giant old lathe in sight).  It wasn't even too involved.  Basically, I split it in half where the tool post went, pinned and bolted the back section to the base, and made a set of steel jaws to bolt to it.    Now I've got a very solid, very precise, and repeatable vice for almost zero dollars.

"I've got balls" or "I'm screwed now" Take your pick.

The upgrades on my mini mill so far have been fairly small, and I promised "big" changes.  Well, here's the first big change: I decided up upgrade to ball screws.  When I did my original conversion, I made some low backlash Delrin nuts for the lead screws.  They worked great, but the screws themselves leave a bit to be desired.  It takes a lot of energy to turn a standard lead screw, and the original screws were very fine so it took a lot of turns so get anywhere.  Since stepper motors like mine make their max torque at low RPM, the high RPM needed to move my mill table quickly meant I was risking skipping steps.

For this application, ball screws are better in almost every respect.  They take much less energy to drive because the friction is so much lower.  Lead screws are generally about 20% efficient, while ball screws are around 90% efficient.  That means that much more of my motors' energy can go into moving the mill instead of being wasted just turning the screw.  Ball screws have a much more course pitch too, so it takes fewer turns to move the table, lowering the RPM the motor has to turn so it operates closer to it's maximum torque.  The only real down side is that you can backdrive ball screws, meaning if you shove the table hard enough, it will turn the screw.  Lead screws can't do that, and that's why you don't see ball screws on manual machines.

I'm using 1605 ball screws that I got on e-bay.  They are not the world's highest quality screws, but they were inexpensive and are much better than the original screws.

The Y screw was basically a direct replacement for the original.  The X screw took a bit more work.  There is very little room for the X ball nut on this mill.  The first thing I had to do was whack the top off the ball nut flange.  In what will probably be a shock to everyone, this cheap low end ball nut is through hardened and was very hard to machine.  Not realizing how hard it was when I started, I chewed up one of my carbide endmills in the process.  You can also see here the sleeve going through the middle that I 3D printed allowing me to take the screw out of the nut without all the balls falling out(it's tedious to get them all back in the right way, assuming you don't lose any).

I also had to clearance the bottom of the cross slide.  I could have ground down the nut, but I was more comfortable clearancing the cross slide.  Cast iron is much easier to remove than hardened steel.

Here's how the nut and screw sit in the cross slide:

I goofed and ordered my X screw just a little bit too short.  I should have gone one size longer.  Oops...  To make up for that without losing any table travel, I decided to make a longer end bushing instead of a bearing like I was planning.  I used the same aluminum bronze that I made my gibs from because this is exactly the application this material is made for.  Here's my new longer bushing on the right with the original on the left:

Here's how the bushing fits in the table:

Big upgrades for my little mill, Pt 1

If you've been following along, you know that I have a Sieg X2D mini mill that I've converted to CNC.  I've had it several years now, and I decided that it was time to give it an upgrade.

One thing I've never been satisfied with on this mill is the gibs.  The originals are cast iron and use a screw/locknut arrangement for adjustment.  They are finicky to adjust and don't slide as well as I'd like when adjusted to zero backlash.  So I decided to make some new ones.  I made a jig with all the correct angles and whittled out some new gibs from aluminum bronze.  It's a great material to use for gibs and bushings and other things that use sliding friction.

I also got some self-locking gib adjustment screws from Little Machine Shop.  Here you can see an original gib and screws next to the new ones.

I also decided to upgrade my motor couplers.  I had been using cheap aluminum couplers are they work ok, but under high load you could see them wind up and unwind like a spring.  Not much, but enough to bother me.  I've also snapped several of them on light crashes, they twist off pretty easily.  I decided to replace them with much more durable diaphragm style couplers.  New on the left, old on the right:

More to come soon...

Look Ma! A 3D printed rifle!(sort of)

At long last here's how my SCR-ish rifle turned out.  Quick recap:
AR based straight pull bolt action
Bear Creek side charging upper in 7.62x39
Bear Creek 16" stainless barrel with cheap ebay muzzle brake
Gas block installed backwards to block off the gas port in the barrel
3D printed lower in eSun PLA+, stock and free float handguard in Ziro Marble PLA
AR hammer and trigger modified to work with relocated and 3D printed trigger and transfer bar
Rise Armament anti-walk pin set for the printed trigger and transfer bar (I still need one more longer screw for the trigger because the printed lower is thicker than a standard AR through the trigger pin location)

Once I get a few hundred rounds through it and am more satisfied that the lower won't crack with use, I'll probably reprint it in black.  Here's how it looks all assembled:

It's hard to believe that these are basically the same rifle: