Has anyone used the modular arms jig to mill a polymer lower?

Modulus Arms?   Like this one?

I did a Polymer80 in one and it worked ok. The buffer support that you screw into the buffer tube wouldn't thread in.  I just used it without it and it seemed to be ok.  I got a really good deal on the polymer lower so I didn't care if I screwed it up.  It went really fast, obviously.  

I wonder what stopped the buffer screw from not working.

I tried a Polly on a drill press and it was ruined.  I have no problem doing a metal one with the jig, so thought I might try a Polly.

What's the point? Polymer80 receivers come with a jig.

The reason is the modular arms jig you can use router to do the milling.  With the polymer jig  I would only have the drill press option, since I do not have a mill.

I did a polymer80 lower with a dremel. What you can do with a router is to use a router table, or build a platform for your router to sit on. Otherwise use a trim router with a base small enough to work with Polymer80's jig.

The plastic used in Polymer80 lower is soft enough that a dremel with a router attachment plus carbide end mill (finish with a center cutting Rotozip bit) will make short work of the plastic. Use 1/8" end mills. I would do about the first 1/2" with the jig on, and once that's done I remove the lower from the jig, then using the finished cavity as a guide I continue deeper with the dremel. The last 1/4" or so requires me to use a Rotozip bit because it's the only thing available out there that's long enough to reach it.

I successfully did an EPArmory 80% polymer lower in a Modulus HD jig.  Worked great.  The Makita trim router I have with the Modulus supplied end mill cuts the polymer like a sharp knife in warm butter.  Much easier than aluminum.

Great info thanks guys.

The only known poly lower that will not work with our jig is the genesis brand. They have beefed up the buffer tube mount so much in an effort to keep them from breaking that they will no longer fit our jig as is. However we have had customers modify our jig to fit by simply opening up the top plate to fit.

There are a few poly lowers out there that seem to have very tight buffer tube mount threads, but our jig will still fit the majority of them. This issue is why our universal fit guarantee covers alloy lowers but not plastic. Even though it will fit most of them.

Hope this helps.
Max

thanks max.

you jig works great and was hoping to use it on a polly.