Making A Boring Bar

J

junk iron

Registered
Registered
Joined
Aug 4, 2014
Messages
63
My Tobin Arp line boring machine has a 1.125 dia. bar,I am making a smaller 1",tool bit is held in by hand screw in the end of bar pushing a 5/16 rod against the tool.
The end of bar is bored 9/16 dia.x 2.750 deep leaving 6-1/4" to drill for 5/16 rod,how would you fellows go about drilling 5/16 hole that deep?
Thanks Randalltobin arp 020.JPG tobin arp 023.JPG
 

Some of the gunsmiths should be able to give you an answer. 5/16" is very close to 30 caliber. The Modern Gunsmith, vol.2 by James V. Howe show a barrel drilling arrangement for 30 caliber on page 139. The drill is a 2" straight flute drill with an oil supply hole which is brazed to a tube used to deliver oil to the cutting surface as well as drive the drill. The holes allow the cutting oil to be presented at the cutting edge for cooling, lubrication and flushing the chips out through the flute. Coolant thru drills are available if you don't want the bother of making one.

The entire book is available as a free download at http://www.milsurps.com/showthread.php?t=27137 as is vol 1. I have had my copy for decades now and it is a valuable reference to machining as it pertains the gunsmithing.

If I were doing this, I would probably get a conventional taper length or aircraft extension drill and peck my way down, using plenty of cutting oil. A tedious process but doable.

Bob
 
Second that aircraft extension drill. Maybe start with a 12" 3/16 or 1/4 drill just to get the hole started, and then go back in with the 5/16. How clean/accurate does the hole need to be?
 
Thanks to all,the hole needs to be fairly straight so after setting tool bit rod pushes straight and doesn't move bitl.what does the aircraft drills look like?
 
Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356
 
I think RJ nailed it.
Just make a starter hole with a good jobber bit, then peck down with an aircraft drill.
An aircraft extension drill looks just like a regular drill, only longer
https://www.mscdirect.com/product/details/77426757
(random 5/16" extension drill, dunno about quality)

I have done this with mixed success on the lathe and with a hand drill. I have to move the tail stock in a out when it gets deep. Just clear the chips often, the moment the chips pack up is the moment the bit deflects and wanders off center.

-Josh
 
My buddy has some ext.drills with coolant holes ,will let you know how it turns out.
 
WellI got it finished and it turned out great!slooooow drilling and lots of oil! thanks to all.
 
You must log in or register to reply here.
Back
Top