Calibrated Advancement

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monophoto

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Joined
Mar 13, 2010
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2,549
Location
Saratoga Springs, NY
Richard Kleinhenz buried a very useful hint in his classic book The PenTurner's Bible, something that I haven't seen mentioned anywhere else. Recently, I was making some hangers to hold hats, and found the suggestion to be very helpful.

The usual way to drill on a lathe is to mount the workpiece on the headstock, perhaps in a scroll chuck, and spin it a 300-800 r/min. The drill bit is held in a Morse taper-mounted Jacobs chuck in the tail stock, and is advanced into the workpiece. While this can be done by simply sliding the tailstock to the left, it is more typically done by locking the tailstock to the bedways, and then advancing the quill by rotating the tailstock handle.

Kleinhenz' suggestion is to know how far the quill advances for each revolution of the handle. Knowing that number, you then know how many turns of the handle are needed to achieve a desired drilling depth.

The challenge is in determining the initial calibration. The simple solution is to lock down the tailstock and rotate the handle to advance the quill. Since the amount of advance per revolution is quite small (on my 12" Turncrafter, I measured 2mm per revolution of the handle) it makes sense to give the handle a number of turns, measure the total extension of the ram, and then divide that total extension by the number of turns to determine how far the quill moves per turn. Once the quill starts moving, the amount of extension per turn should be fairly uniform, but there could be some backlash in the first revolution. So it might also make sense to conduct the measurement several times, and then take the average of the measurements.

My experience in using this approach to achieve a desired hole depth has generally been good, I have learned that it is possible for the tailstock to slip a bit when drilling which means that the hole might actually be slightly more shallow than the calibration would indicate. Actually that's a good thing in many cases - when I used this technique recently, I needed the hole to be deep enough to receive a tenon, but because I wanted the bottom of the hole to be as thick as possible, I didn't want the hole to overshoot. So the slippage essentially allowed me to sneak up on a final depth.

Incidentally, the way you know that the tailstock is slipping is to look at the dust and shaving accumulating on the bedways - if you see a clean area on the bedways to the left of the tailstock, you know that it has slipped.
 

howsitwork

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Joined
Jul 9, 2016
Messages
2,327
Location
Thirsk
Thanks for that. I shall measure and then write in on a label on my tailstock .

The metal,lathe has a digital,readout I installed but never bothered on the wood lathe so far.
 

greenacres2

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May 2, 2017
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1,698
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Northwest IN
Makes perfect sense, appreciate your pointing this out.

I bought some wood and a few tools from Richard in his last 6 months…swapping emails with him was a treat. His simple approach to life and problem solving truly belied his skill level. I've never had a desire to build a boat, but doing so with him would have been an experience to carry for life,

Thanks for resurrecting Rich's memories!
Earl
 

its_virgil

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Joined
Jan 1, 2004
Messages
8,147
Location
Wichita Falls, TX, USA.
Tailstock slipping? I would find out why and fix it.

Rich was a good friend and has lots of excellent information in his book. Thanks for sharing this piece with the group.
RIP Rich
Do a good turn daily!
Don
 
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