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Jigging up for an 80% lower with benchtop tools
- Thread starter pastera
- Start date
![[wink]](/xen/styles/default/xenforo/smilies.vb/002.gif "Wink [wink]")
pastera
NES Member
First hole:
Spotting the second hole
Selector hole:
Ream:
Houston we have a problem:
Buggered up the depth for the first hole but not hard to fix.
Just mount the lower loosely and let the drill center it in the hole before locking it down.
Spotting the second hole
Selector hole:
Ream:
Houston we have a problem:
Buggered up the depth for the first hole but not hard to fix.
Just mount the lower loosely and let the drill center it in the hole before locking it down.
pastera
NES Member
Now the questions start.
My lower is 0.870 wide, leaving only 0.090 walls if I mill the 0.690 spec for the fire control pocket.
My bushmaster lower is 10mil wider and has the right side wall at 0.103
Should I shoot for the low side of spec for the pocket to get thicker walls or is 0.090 fine?
My lower is 0.870 wide, leaving only 0.090 walls if I mill the 0.690 spec for the fire control pocket.
My bushmaster lower is 10mil wider and has the right side wall at 0.103
Should I shoot for the low side of spec for the pocket to get thicker walls or is 0.090 fine?
I think the .090 is fine. I used an ares armor jig and left .090 on the walls on the one I did. If your worried about it go for the thicker walls, you can always remove material if needed for the fire control group.
Sounds fine, whichever way you do it (don't go below spec though).
The forged lowers vary a lot, both in thickness, and in "centeredness" (just made up a new word I think
![[laugh]](/xen/styles/default/xenforo/smilies.vb/012.gif "Laugh [laugh]")
).If you ever do more, you'll probably end up needing to adjust or shim your clamping plates for each lower - I know I did.
Last edited:
Golddiggie
NES Member
According to the lower blueprint, milspec is .104" -/+.006". I checked some of the lowers I have, both factory made and one that I machined from an 80% lower. They are all between .090" and .098" on the side walls. You NEED the .690" for the pocket width. You can be a bit over there, but you don't want to be smaller. If it's .69x" you're ok, don't go .68x" or you'll have trouble getting the pins in for the FCG parts. I know one [at least two] NES members that machined his FCG pocket to less than .690 and had to widen it after in order for the parts to go in and work.
BTW, with all that you've gone through with machining the lower, making your own plates and such, you could have saved gobs of time by just using an actual lower jig. We have communal jigs made by aimsmall (from calguns). It's especially nice when you have the side holes already located for you. Typically, we use the reamer for the selector hole (to get 100% position) and then use DRO's to get all three holes drilled and reamed. Yes, we drill AND ream all three holes.
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pastera
NES Member
Thanks for the info - will cut to .690
I didn't ream the .156 holes but did ream the selector.
As far as a jig, thanks for the offer but I am doing this as a learning experience more than the need for a lower.
Having DRO's would make this a simple task but I am stuck counting turns.
I didn't ream the .156 holes but did ream the selector.
As far as a jig, thanks for the offer but I am doing this as a learning experience more than the need for a lower.
Having DRO's would make this a simple task but I am stuck counting turns.
Nice job! That came out nice.
If you have not already go to http://www.ray-vin.com/frtech.htm for help with machining the FCG pocket. There is so much variation in the pocket size from manufacturers, I just fit mine to my FCG (centered of course)
