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Polymer80 subcompact build adventure

Overall the Polymer80 build is arguably the easiest of the 80% builds. However, that doesn’t mean that my Polymer80 subcompact Glock build went flawless. One of the biggest problems with the build is the directions. In our Polymer80 PF940SC completion using a drill press video, I am able to show you how to mill out the barrel block, as well as, the slide blocks using a drill press instead of using a Dremel. However, this is where the real adventure begins.

Polymer80 – Milling

On my speeds and feeds calculation, I calculated the mill will need to spin at 7800 rpm. However, my drill press maxes out at just over 3000 rpm. I knew that this would give me a lot of tool chatter and leave a less than perfect finish. So I decided to mill a little higher and take the rest off with the Dremel.

The second problem that I ran into was that the mill that comes with the kit is not long enough to cut out the barrel block. The chuck of my drill press rubbed on the front of the jig and you can see the damage on the jig. Fortunately, the jigs are single use and plastic. Even with the problems of the mill, I was able to finish the build with a Dremel and get the gun to the range and have a successful test firing.

P80 Jig Damage from MillI opened a ticket with Polymer80 on this situation and included pictures. It took them just over a week to get a response and they admitted that there are problems with their directions and advise on what drill presses that they recommend. Even though I didn’t really qualify for a warranty on the frame, they did warranty the frame and sent me a replacement. I had to cut the frame in half and send them pictures. I did purchase this frame from Brownells, however, I am not sure if I could have it covered under their satisfaction guarantee.



When I received the replacement, I began working on it so that I could show the completion using a Dremel. During the build of this second frame, I ran into a problem that the frame was not in the jig correctly when I drilled the holes. 

When I discovered the problem, I moved the frame in the jig and drilled the holes again and everything fit. However, this left me with a problem of having holes in the frame that didn’t need to be there.

Fixing the oops

Not being one to let a good disaster go to waste, I immediately went directly into how to fix an oops video. I bought some fast setting JB Weld and went to town fixing my screw up. I used the Dremel on one side of the frame and a hobby knife on the other so that I could show you two different methods of clean up the excess JB Weld that built up on the frame. 

The frame does have a texture that will be damaged from sanding down the JB Weld but I was not too worried about this since I am going to Cerakote the frame and the sand blasting that I needed to do would blend these areas to look normal.

When using a sanding drum on a Dremel to remove the excess JB Weld, you do want to go slow, use the finest grit and the lowest setting possible to maintain control and minimize gouging damage to the frame. When cleaning up the excess, using a hobby knife definitely keeps gouging down but took a little longer than the Dremel method (It took me about 6 minutes on one side). If you keep the knife blade at a shallow angle, you will find that the KB Weld will easily “scratch it off” and keeps the gouging damage to a minimum.

Fixing frame damage

When I was finished fixing the holes I wondered if you could fix damage from a slip of the Dremel when removing the tabs on the frame. Using the cut frame that I now had from the warranty replacement, I went into how to fix frame damage video. This is where I took a Dremel sanding drum to the frame and did a cut on the back. From there I filled in the damage with JB Weld and sanded it down.

The repair went well and the JB Weld adhered to the frame better than I had expected. Unfortunately, I did not film the testing of how well the JB Weld adhered to the frame. I took a pair of pliers and twisted, pulled and pried at the replied area. Eventually, I got it to break free but it took a lot of force. I plan on taking the frame that I repaired the holes on and make the same cut and repair. Once the repair is completed, we will take that frame out to the range and test fire the gun again to see how the repair actually holds up. 


Overall I had a lot of fun with this project even though there were some problems that came up during the build. However, I think that the problems actually made this a more enjoyable project in the long term. If you are looking at getting into 80% building, I definitely recommend that you start with a Glock build as they are pretty easy, parts are plentiful and they require the least amount of tools to complete. You can complete a frame with a Dremel (forget using a drill press), Drill and some sandpaper.  

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