How do I make this hole?

[Kingjamez]

I need to put a 1" hole through a 2"x2"x8" block of aluminum. I have available to me a X3, an Emco Compact 8 lathe, and a 7x12 mini lathe.

I'm having a hard time finding a drill bit long enough ( that I can put in the mill or the headstock of my lathes), and don't think I should chuck up the 2x2x8 block and bore the hole with a super long boring bar.

Any ideas?

-Jim

[Geof]

How accurate does it have to be, is a drilled hole good enough?

You could get a Prentice drill, this is the type with a 1/2" shank. Clamp the block on the crosslide of your lathe and drill it with the drill in the chuck.

But first make an extension holder for the drill out of 7/8" round bar so you can go 8 inches deep with the drill. Little setscrews on the flats on the drill shank should hold it fine.

You would probably need to grind the full diameter portion of the drill, right at the end of the flutes, slightly below 1" so you did not get serious rubbing here when it was entering the drilled hole. Freehand grinding is fine you just want clearance.

The hole should be spotted first with a spotting drill so the 1" drill enters accurately on center. Without spotting it may start slightly off and then wander badly before reaching the full 8" depth.

Naturally you are not going to be drilling fast and when the drill is deeper than its length you will have to back out frequently to clear chips. Lubricant is essential for the chips to flow nicely.

[Kingjamez]

Thanks for the help. I'm really not sure of the absolute tolerance one the hole. I plan to ream it with a 1" reamer after the hole is made. The application is an AR-15 upper. I suspect that the tolerance is fairly large.

The drill extension is a good idea. I can do those things fairly easily on the lathe. I'll give that a try.

-Jim

[packrat]

Don't know if you've seen this site; CNCGUNSMITHING - www.cncguns.com - AR15 A3 Upper

Might give you some ideas.

[DareBee]

You can buy 1" taper shank 2' long (if you want).
4 Jaw chuck the part and drill it.

[M250cnc]

Originally Posted by DareBee 4 Jaw chuck the part and drill it.

I would drill from both ends too

Phil


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[Delw]

you can also build it on a lathe by
chuck the drill in the lathe chuck
bolt the block to the cross side of the table, ( you will have to use your Imagination)

that 1" dia hole is also used as a location hole as well, so it needs to be pretty close to accurate.

4 jaw is better and from both sides like mentioned above. another option is to give the block to a machine shop and have them drill and bore the hole properly then you can locate off it and know its correct.
having said all that I have read posts of guys useing a dremil tool , hand drill and files to finish 80% uppers and lowers on various guns so anything is will work.

cncguns.com has an excellet how to and instructions but there on a real machine

another one is Login

[nate]

line bore it on the lathe.

drill through with an undersized bit and then run a boring bar between centers and backwards as a line bore with the block fastened to the cairrage of the lathe.

an accurate 8" long hole in aluminum is a challenge. Running a 1" reamer all the way through an 8" hole will probably be an incredible challenge.

line boring is the best way to get an accurate hole of this length. but its only as accurate as the lathe you do it on.

actually, come to think of it, if you drilled through with an 7/8 drill bit and then chucked up the block and used a STOUT 10" long .750 solid carbide boring bar, you might be able to suxcessfully bore it on the lathe. IF your lathes spindle is very good and your allignment of the headstock is perfect and IF you take light finish cuts to counter deflection.