Machinists - drill to use with taps

BigDanS

I do not have a 110 drill set.

I am going to attempt to tap the 30-06 case stuck in my die. I have the required 5/16-24 thread tap, bolt, washers and spacer tube, but I think the closest drill bit I have is 17/64 or 9/32. Looks like it calls for an "I" sized drill, but I am tapping brass, not steel.

Thoughts?

D

tennmike

Use the 17/64 drill. There isn't that much difference in size between it and an I size drill, around 0.050". Use a good oil on the tap and back it out every quarter to half turn in to break off the chip. It will be tight threading a smaller than normal hole, but go slow and you should be just fine.

You could use the larger drill, but the threads would be weaker from the larger hole.

Teach

Use the 17/64" drill bit and lube the tap well. Turn the tap in about 3/4-1 turn, then back it up and break off the chips you've created. This keeps the chips from jamming in the tap gullet and maybe breaking it off. You'll need to make 3-4 turns of the tap to get a good start before doing the forward/back maneuver, but if it gets hard to turn, don't force it. Taps are as hard as glass, and if one breaks off it's impossible to drill the pieces out. Use LOTS of lubricant for drilling and tapping- - - - cutting oil is cheap, tooling isn't! I like to use 90 weight rear end lube if a bottle of cutting oil isn't handy, but plain old 30 weight motor oil will do.
Jerry

Edit: It's hard to beat lard as a cutting lube, but a 5-lb. pail of it is about the smallest quantity you can buy. OK for a machinist like Mike or me, but that's several lifetimes' supply for the average gun tinkerer!
Jerry

BigDanS

Oddly enough I carry over 5 lbs of lard with me everywhere I go, but it is just not accessible. I will use some 30 wt.

Thank you again!

D

tennmike

Now Jerry! Lard isn't just for machining! Fried chicken, and biscuits made with lard, instead of vegetable shortening, are just a couple of goodies lard excels at as a cooking medium.

Favorite use of unsalted lard in the shop is to mix it with kerosene to make it the consistency of that runny hand cream in those pump bottles. Put it in a Nalgene squirt bottle and use it for cutting fluid for finish cuts in the lathe and mill, and as a tapping fluid. Thick enough to stay put and sliker 'n' snail snot!

Buford

I'm sold on Rapid Tap nothing better in my experience.