80% dimension question

Joined
Dec 28, 2015
Messages
122
Likes
79
Feedback: 1 / 0 / 0
I'm trying to design my own jig and i have a question about the dimensions.

Some lowers have a small pocket in the back by the threads for the buffer tube where the rear takedown pin goes through, others don't. For the ones that do, anyone know the height/width of that pocket?

thanks
 
A pic of the spot would help - not sure what dimension you need? There are tons of prints available on the 'net too, should be able to find what you need on one of them. I can't post pics here or I'd just grab a section off my prints for you.

If you mean the countersink where the takedown pin head seats on the right side, it's 7/16" diameter, and the depth is .411" from centerline.

Or, if you mean a section is cut away on the inside of the lower where the takedown pin lug of the upper sits, that could vary by manufacturer, unless they had cut it to print size, which I'd doubt.
 
Last edited:
Hey all

I have drawings and prints for the completed lower. what I'm looking for is the dimensions for this pocket. I know its .620 deep and .500 high. I just need to know how far from the threaded end it goes. If all else fails I'll just measure an 80% when it comes in.
 

Attachments

  • cast.png
    cast.png
    60.3 KB · Views: 43
Hey all

I have drawings and prints for the completed lower. what I'm looking for is the dimensions for this pocket. I know its .620 deep and .500 high. I just need to know how far from the threaded end it goes. If all else fails I'll just measure an 80% when it comes in.
The PDF I sent you has the position for the FC pocket on it. You just need to look at the correct view and such. Everything indexes off the front take-down pin hole center (for those dimensions).

From what your attached image shows, that pocket isn't complete. It needs to almost hit the buffer catch hole. Again, all on the plans already sent to you.
 

Attachments

  • lowerBlueprint.pdf
    144 KB · Views: 36
So. My apologies if I'm not explaining myself correctly. I have that PDF and I know that the pocket I indicated in the photo isn't complete. I'm making my own jig and I was hoping not to make the router guide go farther back than needed if the 80% lower comes with part of the pocket already there. On the 80% I'm buying, the pocket goes back far enough and I was hoping to find out how far forward it comes. I'm thinking that that dimension varies by manufacturer as Archilocus said and I'll have to wait, or design the jig assuming there is no pocket at all so it works with whatever 80% lower I happen to buy in the future
 
The jig I have wasn't designed for use with a router, nor with any of the fire control group pocket machined at all. If you're going to make a jig, and you intend to sell it, then you're BEST off planning for the 80% lower to be 80%, not 82%. Don't assume that any part of the pocket will be already machined/cleared.

As for the back of the pocket, you'll need to be sure the bit used is long enough to clear the buffer tower. This kind of thing is EASY when you're using a milling machine.
 
Yea I could def throw it on a proto trak at work and it would be done in literally 5 minutes. But I don't want to be reliant on anyone else's equipment/tooling ultimately, and the thought HAD crossed my mind to sell them... Do you guys think there is/will continue to be a market for it?
 
Yea I could def throw it on a proto trak at work and it would be done in literally 5 minutes. But I don't want to be reliant on anyone else's equipment/tooling ultimately, and the thought HAD crossed my mind to sell them... Do you guys think there is/will continue to be a market for it?
IMO, there's already enough jigs out there for sale. The one I have is made by someone that's not doing it anymore. Which is a shame since it's a really great setup. Made to NOT be used with a router, since it was designed/made before that became a thing. IMO, using something that's held by a person is a easy way to F things up. I've actually seen the results of someone messing up with the router. Plus, getting the depth 100% correct is not easy to do with the router model. While there are +/- numbers in the plans, they're not all that large.
 
Gen ll AR15 receivers come with the rear shelf almost completely finished. But there is usually a couple thou (mostly in depth) left to be removed,. The finished shelf is .630 deep and .500 wide.
 
Back
Top Bottom