the only part that would not line up was the rear lug. Thought it would be easy enough to change. everything else was spot on with both lowers.
Good! I’m glad everything fit. I made those changes after I printed mine, so I’ve never fit a receiver in the jig like it’s supposed to. I started two prints on the final design but my extruder stepper kept skipping. I think I need to clear my Bowden tube and extruder (not looking forward to fixing that).
That does make sense about the rear takedown pin not fitting. I knew that the rear buffer lug is extended backwards, but I forgot so is the takedown pin (obviously they don’t use the same takedown pin locations).
I wish I would’ve seen this sooner and would have replied. I recently engraved about 20 ARs on my X Carve. Like you, I created a fixture and found that only a thousandth off is too much. Although it may not help you, others may find this useful.
After identifying my high corner by probing, I set a z0 and manually moved to my low corner with the CNC at z0. I then pried lightly up on the receiver until it contacted the bit with the same pressure as the high corner and with the other hand, squirted a drop of hot glue underneath. I then rechecked and added a drop here and there as needed. Because lifting up changed my high points zero a small amount I ended up having to go around 2 or 3 times.
I let the glue cool and easily popped out the receiver, leaving numerous little dots on the fixture that were squished flat on top. I then squirted a lot of glue on my fixture and shoved the receiver in until it squashed the hot glue down to the level of the cold glue ( done quickly, your leveling points won’t have time to melt) creating a solid fixture base that has a slight rubbery give to it. This helped the quality of my engraving as it seemed to keep a constant pressure on the bit. It worked so well I built up a dam around the fixture against the receiver with multiple buildups of glue. It allowed me to snap one receiver after another into the exact same position and the dam held it solid with no clamps.
I built four different fixtures. Left and right each of an AR15 and AR10. The process took about an hour per fixture. Hope this helps someone.
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Great…I’ve been on this forum for 10 minutes and found a project I need to do.
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It sounds like we arrived at the same solution from two different points. I ended up using my fixture and sheets of paper to true it up, you use hot glue. That’s a novel idea I hadn’t considered. Did you find any consistency in your receivers after the first one was leveled? I’ve wondered if forgings from the same batch are consistent, or if it’s just entirely random.
I’m running mostly 80%Arms lowers. All were identical and it ran really true. The only problem I found was that I was initially using wd40 as a lubricant. That began to loosen the glue from the fixture. I ended up cutting dry. I’m sure it was harder on the tool (but I had a 10 pack and only used 3) but the quality was fine.
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Nice! Hemet, CA, where my grandmother use to live. Small world!
I see that you have a billeted lower that would have been machined from a solid block. that would make it more likely to run true as the cnc than machined it should have kept all tolerance at a minimum. @Pyrex has a forged lower that is not machined and therefor has variations in the forge.
I just wanted to point this out as others might not be familiar with the difference between the two types of lowers.
That’s a great observation. I noticed it was a billet lower but I didn’t put two and two together. Yes, any billet lower would more than likely be 100% flat for the purposes of engraving.
yeah, as long as you go deep enough it isn’t an issue. The problem is when you want more detail, which requires shallower cuts and more accuracy.
Is the whole jig made of hot glue or did you start out with something 3d printed?
awesome work!
I actually made plaster molds of each side of my lower to get me within a .01 or so. When you’re only engraving 5 thou a small difference in mounting height is a big deal. The hot glue filled in the gaps and helped with leveling. I’d imagine making the entire thing with hot glue would be too spongy to engrave.
How can I get a jig like that to hold it?
see post 12 there is a link to thingiverse
download and 3D print or you can pay to have it printed and shipped. find a friend with a 3d printer and have it printed etc etc.
Ok, so the issue isn’t your machine or jig but rather the poor surface quality of the casting. So that seems where to attack. Just like on my Tormach when I am working on billet stock aluminum or steel the first thing I do it hit it with a face-mill to get it true and flat. Why can’t you mill the part (take a thou off or 2?). Or hit it on a CNC grinder? When I get my bar stock the faces are simply flat enough to hit with a face mill without crashing, it would suffer the same issue. I normally take off .002” to get it all nice, clean and flush.
I’m assuming this is not a functional surface which mates with anything? I don’t know enough about the part, but since you can engrave text in it I assume nothing needs that surface “just which would allow you to face it.
What feeds and speeds did you use to engrave this? Havent done any alluminum engraving yet so would be nice to have a starting point.
If i may ask what program did you use to develop your roll marks? I have been referred toThis writer but I get no where Cl I se