Drill/tap end of leadscrew, how to approach?

[bikemutt]

I need to drill and tap one end of a leadscrew 5/16-18. The end already has a hole drilled, presumably for some sort of tailstock center used during it's manufacture. While I'm used to making such a hole with a countersink or spotting drill, this one has an odd looking profile, almost as if it was made with a countersink that was drilled deep.

I don't want to face the part, it sits flush in a pillar block, prefer to leave it that way.

Anyway, I'm planning to hold the piece with a 4-jaw indicated off the outside and see if I can find the center with a small twist drill in the TS, if the bit settles down I should be able get on center and use successively larger bits up to tap size. If I don't find center this way, I'll need plan B.

It's not a Space Shuttle part, just want the 5/16" shaft extension to spin true with the leadscrew axis. Appreciate any ideas on best way to start, what to avoid, etc.

Below are a couple borescope pictures showing the hole opening and the hole bottom.

 

[hvnlymachining]

If your desire is a true to O.D. bore. Simple way is to drill to near, and safely undersized bore, finish to size with a ( small) boring bar. Viola! Quick and true without the risks.

Also I would avoid step sizing drills, that steel may be hard enough to eat drill corners or worse, risk snapping the drill in there.

 

[bikemutt]

If your desire is a true to O.D. bore. Simple way is to drill to near, and safely undersized bore, finish to size with a ( small) boring bar. Viola! Quick and true without the risks.

Also I would avoid step sizing drills, that steel may be hard enough to eat drill corners or worse, risk snapping the drill in there.

A "why didn't I think of that moment", thank you!

 

[Tyrone Shoelaces]

Turn and bore out a simple steel piece of bar to the same size as the end of the shaft. Drill your tapping drill hole in the bar. Slip it over the end of the shaft and use it as a drill jig.
Obviously you’ll need to move the end bracket out of the way a little bit.

Regards Tyrone.

 

[Clive603]

Turn and bore out a simple steel piece of bar to the same size as the end of the shaft. Drill your tapping drill hole in the bar. Slip it over the end of the shaft and use it as a drill jig.
Obviously you’ll need to move the end bracket out of the way a little bit.

Regards Tyrone.

+1 for this. Worked fine for me the three times I needed to do such a job. Made the guide bush as long as was practical to help ensure drill went in true. Be easier these days with a battery drill rather than the old 2 speed, 240V B&D I used. Smooth controllable speed makes all the difference for this sort of thing.

Made a second guide tapped through to help staring the tap square as the tap was on an extension shaft maybe 3" long to clear the back of the machine.

Still way less work than stripping it out.

Pity Mr Machine Maker didn't actually face the shaft ends dead square. Sigh. But Decon covers a multitude of sins.

Clive

 

[Tyrone Shoelaces]

+1 for this. Worked fine for me the three times I needed to do such a job. Made the guide bush as long as was practical to help ensure drill went in true. Be easier these days with a battery drill rather than the old 2 speed, 240V B&D I used. Smooth controllable speed makes all the difference for this sort of thing.

Made a second guide tapped through to help staring the tap square as the tap was on an extension shaft maybe 3" long to clear the back of the machine.

Still way less work than stripping it out.

Pity Mr Machine Maker didn't actually face the shaft ends dead square. Sigh. But Decon covers a multitude of sins.

Clive

Why do you need a second guide Clive ? Once you’ve drilled the tapping hole you can open up the hole in the jig bush up enough to accommodate your taps.

Regards Tyrone.

 

[Clive603]

Why do you need a second guide Clive ? Once you’ve drilled the tapping hole you can open up the hole in the jig bush up enough to accommodate your taps.

Regards Tyrone.

Wanted to save the first tapping drill size bush for another job or three I knew would be coming along soon. Second one with the thread was because I could see the end wasn't faced off square. Working more or less from the side with an extended tap in an extended T handle chuck type tap wrench I figured I needed all the help I could get if the tap were to run in square. Just not enough room to eye it up straight and only one spare hand for the tap wrench. If serial taps had been a common thing then I'd have bought some.

Bit of habit too as I always try to make any tools and guides first before starting on the job. Then stamp a label on when done to either keep as is or modify. Guess it comes from a combination of too many away from the shop fixit jobs and, back in the day, only having the one machine so when its down for repair bits can't be made.

Clive

 

[rons]

Anyway, I'm planning to hold the piece with a 4-jaw indicated off the outside and see if I can find the center with a small twist drill in the TS, if the bit settles down I should be able get on center and use successively larger bits up to tap size. If I don't find center this way, I'll need plan B.

Tried this kind of thing with a drill bit. Even with short stub bits the point wanders. A few times I could see the drill bit wiggle.
A small end mill in the TS to start things off worked better. Then use a 1/4" or larger center drill in the TS. Or whatever.

 

[bikemutt]

After examining the hole a bit more, and less closer, the outer chamfer looked pretty good. Got to thinking a 120 degree 3/8" spotting drill might just settle into it. I gave the spotting drill some wiggle room in the collet; I'll be darned if it didn't center up. Went in enough to give the 118 degree, 9/32" tap drill a good start, it bored in real nice, tapped the hole.

Made the leadscrew shaft extension with a decapitated 5/16" hex bolt, filed a flat, pinned the parts, runs like a top!

Thanks again for the help.

 

[Tyrone Shoelaces]

After examining the hole a bit more, and less closer, the outer chamfer looked pretty good. Got to thinking a 120 degree 3/8" spotting drill might just settle into it. I gave the spotting drill some wiggle room in the collet; I'll be darned if it didn't center up. Went in enough to give the 118 degree, 9/32" tap drill a good start, it bored in real nice, tapped the hole.

Made the leadscrew shaft extension with a decapitated 5/16" hex bolt, filed a flat, pinned the parts, runs like a top!

Thanks again for the help.

View attachment 382053

What does the extension do ? We normally used a 17/64” drill when we were tapping 5/16” holes that needed a good thread.
Just saying.

Regards Tyrone.

 

[bikemutt]

What does the extension do ? We normally used a 17/64” drill when we were tapping 5/16” holes that needed a good thread.
Just saying.

Regards Tyrone.

Originally, I wasn't planning on rotating the assembly in either direction, threading works fine CW. After I got it threaded I thought CCW might be nice, hence the roll pin. In retrospect, I could've bored and pinned an unthreaded extension. Hindsight is 20/20 .