scale/readout on tailstock.

[marcros]

I have a jet mini lathe. Great bit of kit, however there is a modification that would make it even better.

I want a method of measuring the extension of the tailstock, so that I can easily tell drilling depth as I wind the handle in, without having to use bits of tape on the drill bit. This can be a graduated scale, something mechanical, or a digital readout. I need it to be capable of reading from zero to about 75mm.

Has anybody fitted anything to their lathe?

 

[Phil Pascoe]

It might need a calculator, but it would be fairly accurate - measure precisely the advancement of one turn of the handwheel, divide the depth required by that.

 

[Glynne]

I'd never have thought of that, but there again I don't do that amount of drilling on the lathe.
The one thing that comes to mind is that you would have to "zero" the tailstock at a set position i.e. the point the self ejecting kicks in (probably didn't explain that very well) otherwise you could get differing measurements. So perhaps you could scribe a line around the tailstock at that point and then measure the travel from there? A bit Heath Robinson but it should work.

 

[marcros]

the digital would be an advantage. For example, last night I needed to drill a 40mm hole at 6mm, then enlarge 26mm of that to something larger, then 2mm larger still, and 0.5mm even larger. This was to make part of a fountain pen, and whilst I am not likely to be able to drill accurately to a depth of 0.5mm, all in all that is a lot of counting turns.

Since posting, I have found http://www.micro-machine-shop.com/9x20_ ... ck_DRO.htm which is more complicated than I was thinking, but it may be a solution.

 

[Phil Pascoe]

Glynne, you could advance the drill bit to touch and count from there. Even if you have a mark on the barrel, you have to know its distance from the item to be drilled - its all very well knowing the travel, but if you don't know the drill bit's position relative to the item to be drilled it doesn't get you far.

 

[RogerP]

This sort of thing?

http://www.micro-machine-shop.com/9x20_Lathe_Tailstock_DRO.htm

 

[CHJ]

Simplest way to get a guide would be to scribe the tailstock quill at known distances.

But as anyone who uses a lathe with this facility will tell you it can only provide a rough guide.

Tailstock location, seating of drill in drill chuck, security of drill in drill chuck, assessing the Start datum etc. are all variables that are fine for general hole boring but useless for 'accurate' depth control.

Even fitting a tailstock with a DRO system is not likely to improve a great deal on the above variables.

This is why on a manually operated metal lathe the cross slide-compound slide and dial gauge are used to measure hidden bore dimensions.

You may be better off just looking into a dial gauge setup to determine the advancement of the drill but it is so fraught with variability that I doubt you would do better than using a gouge with a depth stop.

On one task I did some time ago I had a Allen key secured ring on a boring gouge that provided a positive stop rather than the eyeball one of a piece of tape, this still had a 1/2 to 1 mil. variability when checked with a vernier though due to wood density differences.

 

[marcros]

thanks Chas. 1/2 to 1mm variability would be suitable I think for what I need. Certainly 1/2 mm. It is a wood lathe rather than a precision metal working lathe and I appreciate the difference. I am using ebonite hard rubber for this task, so the density should be less varied than using different types of wood.

I would think that if the drill was in the chuck correctly, the jacobs chuck seated in the taper correctly and the drill bit moved to kiss the workpiece that would reduce some of the variables. The main advantage of a dial, or a DRO over a scribed scale is that it can be zeroed at the point where the drill starts to cut.

 

[chipmunk]

Am I the only one who doesn't snug down the tailstock 100% and ends up with it slipping when drilling biggish holes?

That's why the quill scale can only ever be a rough guide IMHO.

Another solution is a set-screwed collar on your drill bit which is a bit more hi-tech than masking tape ;-)

HTH
Jon

 

[CHJ]

Am I the only one who doesn't snug down the tailstock 100% and ends up with it slipping when drilling biggish holes?

No, happens all the time.


...

Another solution is a set-screwed collar on your drill bit which is a bit more hi-tech than masking tape ;-)

HTH
Jon

+1, the simplest and just as likely to provide the depth control needed as any other in a wood lathe situation using the tailstock IMO.

That's why Pattern Making Lathes have cross slides etc. for better dimension control.

 

[Random Orbital Bob]

rig up a jig with a cheap laser from Maplins which is calibrated to exactly the end of the drill bit. As the drill disappears inside the stock, the red dot from the laser remains visible on the outside of the wood where you can accurately mark your depth.

Yewtube made a similar jig for deep hollowing where the tip of the laser was calibrated to the end of his hollowing tool which was confined in a framework. So his had both stability and depth control built in. What I'm suggesting is much simpler, a means of tracking the whereabouts of the drill tip from outside the hole.

 

[Phil Pascoe]

Get a few different sizes of metal (or even plastic) tube, cut to different lengths and slip over the drill bit leaving the protrusion you require? You wouldn't have to worry about a marker or the the tailstock moving.

 

[CHJ]

This is the sort of thing I use as a depth stop if needed, having two grub screws gives a bigger working range for fewer rings.

 

[IHc1vtr+]

I have adapted a vernier caliper to fit my lathe, can post a pic if you are interested?

 

[marcros]

yes please. all ideas are welcome.

 

[woodpig]

I just chopped up an old caliper and bolted it to the tail stock of my metal working lathe. Works great. If you wanted to be picky it's probably no more accurate than .2 of a mm but as it only needs to be within 5 - 10 X that amount for what I do most of the time its close enough. :wink:

 

[Duncan A]

Or just do as woodpig but use a cheap vernier caliper such as at http://www.ebay.co.uk/itm/Brand-New-Ver ... 1377807909.
No batteries to go flat and more than accurate enough for woodworking purposes.
Apologies in advance if I'm stating the obvious, but, just in case you're confused by the terminology, calipers of this type are either digital or vernier - the so-called digital vernier calipers are actually just digital. "Vernier" refers to the way in which the scale is engraved and read on the non-battery calipers.

 

[woodpig]

You can of course just buy a digital scale but sadly they're over double the price!

http://www.machine-dro.co.uk/horizontal ... -inch.html