WW Lathe tailstock drill modification--seems very clever

[LittleWatchShop]

I got this book by Rod Lloyd about fixing Atmos clocks.  He has a separate section on clock repair in general.

He presents this idea of taking a piece of 8mm round stock that fits in a WW tailstock and using the headstock, drills a hole that will fit a PCB drill bit.  By drilling the hole with the headstock, perfect alignment is guaranteed.  Now the thing missing is, how do you secure the drill bit.  The implication is that each runner is a one off bit.  Maybe I am wrong.

Why not put a set screw into the runner (would have to be removed to remove the runner, of course)?

Anybody done this?

I have a collet holder that fists my tailstock runner, but is not so precise.

OK...it appears Mr Lloyd is wrong.  I measured all of my runners.  7.6mm  He says they are 8mm which is easy to find 8mm rods. Hmmmmm

[nickelsilver]

As noted in this thread, there's no standard between makes (and even within makes) for tailstock bores. Checking with my normal supplier here, they have 7.50mm and then 7.70mm, haha, McMaster in the states only has whole metric sizes and then in inch they get close with 02.969", which would be sloppy, or 0.302" which would require lapping off almost 0.003" and that's a lot more than it sounds.

 

Just a note on drilling "perfectly concentric" holes- it's much harder than it seems. You have to think in terms of percentage; if I center and drill an arbor for a 0.15mm pivot, and the drilling wanders off center 2 %, that's a total of 0.003mm, which is almost imperceptible under 10x magnification and wouldn't adversely affect anything unless it was some crazy tiny watch. At circuit board drill size, 1/8", that 2% would be over 6 hundredths of a mm, and that's starting to be a lot. In the precision machining world if you want a hole on-size and on-location there are a number of steps you can take, from using highly specialized drills in awesome machines (with speeds and feeds optimized etc.), or you would drill undersize, bore about 1 diameter deep to just  the next drill size, which would be maybe 0.10mm undersize of final, and then ream to final size. You can also bore to final size if wanted.

 

Sometimes the drill really does stay centered, and even drill on size, and even make a round hole, but if you're counting on it it usually doesn't, haha.

 

I have a drill chuck that pretty much stays in my collet holding tailstock. It's not perfect; under the scope I can see it almost always holds the drill slightly off, but when drilling (using the scope), I just nudge the chuck with my finger and regularly drill 0.10mm holes without issue. I keep the drill chuck as it's fast, and otherwise the tailstock doesn't reach far enough with the slide rest in place, which I use as much as humanly possible.

 

The fellow's idea isn't bad though. If you want to do it, you could find an easily available rod size like maybe 1/4", and make up some rings out of Delrin that fit the front and back of the tailstock bore, so the rod is a light sliding fit. As for a set screw, there won't be much material to thread, and if the bore in your rod is just a little loose the screw will skew the drill. You could make a clamp that's just a ring with a set screw; if the bore is close (easy to get a 1/8" reamer) it should clamp fine without splitting the end, but you could also run a slit down the middle of the rod along the bore, and the clamp will squeeze the two sides together on the drill.

Edited July 12, 2022 by nickelsilver

[LittleWatchShop]

2 hours ago, nickelsilver said:

As noted in this thread, there's no standard between makes (and even within makes) for tailstock bores. Checking with my normal supplier here, they have 7.50mm and then 7.70mm, haha, McMaster in the states only has whole metric sizes and then in inch they get close with 02.969", which would be sloppy, or 0.302" which would require lapping off almost 0.003" and that's a lot more than it sounds.

 

Just a note on drilling "perfectly concentric" holes- it's much harder than it seems. You have to think in terms of percentage; if I center and drill an arbor for a 0.15mm pivot, and the drilling wanders off center 2 %, that's a total of 0.003mm, which is almost imperceptible under 10x magnification and wouldn't adversely affect anything unless it was some crazy tiny watch. At circuit board drill size, 1/8", that 2% would be over 6 hundredths of a mm, and that's starting to be a lot. In the precision machining world if you want a hole on-size and on-location there are a number of steps you can take, from using highly specialized drills in awesome machines (with speeds and feeds optimized etc.), or you would drill undersize, bore about 1 diameter deep to just  the next drill size, which would be maybe 0.10mm undersize of final, and then ream to final size. You can also bore to final size if wanted.

 

Sometimes the drill really does stay centered, and even drill on size, and even make a round hole, but if you're counting on it it usually doesn't, haha.

 

I have a drill chuck that pretty much stays in my collet holding tailstock. It's not perfect; under the scope I can see it almost always holds the drill slightly off, but when drilling (using the scope), I just nudge the chuck with my finger and regularly drill 0.10mm holes without issue. I keep the drill chuck as it's fast, and otherwise the tailstock doesn't reach far enough with the slide rest in place, which I use as much as humanly possible.

 

The fellow's idea isn't bad though. If you want to do it, you could find an easily available rod size like maybe 1/4", and make up some rings out of Delrin that fit the front and back of the tailstock bore, so the rod is a light sliding fit. As for a set screw, there won't be much material to thread, and if the bore in your rod is just a little loose the screw will skew the drill. You could make a clamp that's just a ring with a set screw; if the bore is close (easy to get a 1/8" reamer) it should clamp fine without splitting the end, but you could also run a slit down the middle of the rod along the bore, and the clamp with squeeze the two sides together on the drill.

Lots to chew on here. I did find some 7.6mm stock in China, so I ordered yesterday. I got enough to do experiments.

Your "finger nudge" method is the one I have used a few times. My tapered collet holder that fits in the runner is a little off.

[praezis]

There are issues with that method, not yet mentioned:

- after having bored the tailstock rod, you have to use it always in that same position (use a mark for alignment). With turning the rod, you will lose your center.