Drill or make bushing?

[grasshopper579]

Ok I have read a lot of posts about putting a F/A lowere onto a S/A receiver and the trouble with the F/A lower having the 8mm pin. What is the opinion of everyone here about just drilling the lower to 9mm? This seems to be the easiest method, but how secure will this be?

 

[root]

I've done two for myself it's harder to weld in the blocking bar to keep it out of the FA position than it is to drill the lower out.
Lock up will be nice and tight
mine are super tight to the point that it needs a slight tap with a screwdriver handle to get the pin out.

later
Rich

 

[UZI SBR AWC]

I have a 45 lower, and a SBR' IMI "B"... I welded in the block to limit selector travel and ran over to Ohio Rapid Fire and had Todd pilot the hole with 5/16 (8mm) bit on the mill, swap bit to a 9mm, and drill the hole on the lower to 9mm. I bought a pin from Vector so both my lowers (std Uzi & 45) have their own pin.

 

[grasshopper579]

Sounds good now I just have to find a 9mm drillbit.Thanks

 

[suka5168]

Bosch make one , I got a 8mm and 9mm HSS bit.

 

[makoman]

Use the closest standard undersize drill bit there is, I forget what size it is, and finish the holes carefully with a dremel. Worked fine for me.

 

[chrisp929]

you need a # 'T' bit ... thats the right size.

 

[freedom5]

Use a undersized drill bit. .015-.020 smaller than 8mm (8mm = .315.). A 19/64 drill or a letter M drill will work. Then run a 8mm reamer through the hole at a slow speed. Buy slow I mean the reamer is turning slowly and you are not pushing with all of your might. Let the reamer pull itself through the hole. Use oil.
A letter O reamer is .316 thousandths of an inch. That would give you .001 clearance for the 8mm pin. This is taking into consideration that you ream the hole perpendicular to the lower and not at an angle, which would make the hole slightly larger.
If you are going to do it on a mill or drill press buy a letter O reamer.
I


You cannot make a more accurate, better finish, and perfectly round hole than this method.

 

[freedom5]

you need a # 'T' bit ... thats the right size.

With all respect,

A letter T bit is .358 thousandths of an inch.

8mm is .31496 or rounded to .315 thousandths of an inch.

A letter T bit would be .04304 thousandths bigger than 8mm.

 

[peabody]

Hey freedom5, you sound like a machinist! You are right about the nice finish done by a reamer.
We are actually trying to make a 9mm hole here.
We use a T bit and it works fine but if you want a really nice hole, you would follow freedom5's instructions but for a 9mm setup.

 

[freedom5]

OOPPPSS,

Sorry about that got confused with the 8mm and 9mm. But yeah reamers are made for making precision holes.

Yeah I am a Mac-11 owning machinist who is determined to become a UZI owning machinist.

 

[grasshopper579]

Alright I got the holes drilled to 9mm. now it seems the pin doestn't want to go through unless you beat it in with a hammer. The pin goes through the right side of the lower ok and the receiver lug but thats where it seems to go off to an angle. If you force it the rest of the way with a rubber malet then the trigger mechanism is hung up and doesn't work. Any ideas on this?

 

[root]

you will have to trim the sear feet to fit the semi reciever or trim the reciever to fit the FA sear feet.
also just take a round file and slowly file the side it's hitting on.
I mean little by little or you'll be welding and redrilling.
you want it tight but not hammer tight.
Sounds to me like you drilled it crooked.
later
Rich

 

[root]

see pix..
the one on the left is drilled blocked and sear cut to semi.
the one on the right is a un-modified FA lower I got from a board member haven't needed it yet so I haven't done anything with it.
note how the pads are MUCH smaller on the one on the left...
I didn't want to modify the reciever so I modify FA parts so semi spec.
I wouldn't want anyone saying "HEY THAT WILL ACCEPT FA SUCH AND SUCH"
it's not illegal to modify the sear pad holes I just don't do it
later
RIch