Setting Tool zero on fixed dial ring lathes

This topic has 14 replies, 7 voices, and was last updated 16 December 2013 at 15:05 by Russell Eberhardt.

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16 December 2013 at 08:59 #137939
richardandtracy
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@richardandtracy
I have a Warco WMT 300/1 combi lathe/mill, and is basically identical except in colour to the Clarke 500. The machine is better than I am, so I have no worries there, but I do have a question caused by it having a few shortcuts in its design.

The dial rings are fixed on the feed screws by woodruff keys, meaning you can't zero the axes or tool when it's in a position you want to return to. I have a work around of keeping a pad of paper and pencil next to the lathe to note down the diameter and feed reading for the tool, then work out the dial reading that should be the desired diameter, stop 0.5mm from that, re-measure and do the final cuts (the calculated and actual rarely coincide due to the tool not being absolutely 100% on the centreline, heating etc).

My method is pretty laborious though, and I wonder if anyone has more sensible work arounds?

Does anyone set their tool against a known diameter bar, so that (say) it's touching a 10mm diameter bar at 0 on the dial? Or have any better/quicker solutions?

Regards,

Richard
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16 December 2013 at 08:59 #6977
richardandtracy
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@richardandtracy
16 December 2013 at 09:09 #137942
jason udall
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@jasonudall57142
Strapping digital calipers to the slides seems popular…
16 December 2013 at 09:10 #137943
MICHAEL WILLIAMS
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@michaelwilliams41215
Where index dials are cylindrical fit a slip ring around existing dial . Can be calibrated or just have one fiducial mark to show datum on primary dial .

Set a dial gauge to detect the zero or any desired offset .

Full DRO is obviously best but many engineers worked for centuries without it .

You can set zero by touching a bar but any where I ever worked that would be considered a blacksmiths method .

The only real test ( in absence of sophisticated equipmemt ) is to skim work , measure and take this positively known diameter as datum for tool position .

MikeW
16 December 2013 at 09:26 #137945
richardandtracy
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@richardandtracy
Mike,

The latter skim method you suggest is what I do, I was hoping someone had a better (ie quicker & no less accurate!) method.

Regards,

Richard
16 December 2013 at 09:30 #137948
MICHAEL WILLIAMS
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@michaelwilliams41215
More :

Unless work is very small diameter minute errors in tool centre height do not affect cutting diameter very much ( nor as a matter of interest does it cause tapers to go crooked ). Most of the discrepancies between applied and measured depth of cut are due to accumulated small errors of human observation , poor cutting action and to variable backlash spring in work and machine .

Professional workers doing fine work are often pedantic about setting tools , taking measurements and using experience to compensate for known minute defects in machine .

Just try setting your tool by dial very accurately – using a glass if needs be and get a good feel for using a micrometer properly . Don’t do this every time but just have a trial to see how much difference things like this can make .

As regards reading micrometers don’t just apply to work and hope for the best . Observe and feel position of micrometer – find the true maximum/minimum diameter by taking several measeurements . Common fault is that the micrometer is held askew by small amount and reading is then too big . Also many micrometers have huge radius but spherical anvils – again find the true reading point in the centre .

MikeW
16 December 2013 at 09:30 #137949
Russell Eberhardt
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@russelleberhardt48058
A CD marker pen is useful for marking the dial for the final cut position.

Russell.
16 December 2013 at 10:26 #137959
Ady1
Participant
@ady1
Strapping digital calipers to the slides seems popular…

Press a button, get 0.00

Gives you a fixed datum which is independent of any machine errors/backlash, VERY useful for screwcutting when hundredths of a mm really matter

Edited By Ady1 on 16/12/2013 10:37:38
16 December 2013 at 10:55 #137968
richardandtracy
Participant
@richardandtracy
Mike,

In practice I use a vernier calliper more often than not. The accuracy I need is to 0.05mm, the calliper precision is to 0.02mm. I mostly work with plastics, which have a noticeable spring in the diameters I use (down to 8.5mm), especially when cutting with carbide inserts (I do this because the finish is better than with my home ground HSS tools and the chips come away as a nice even spiral, when using a less 'pushy' geometry the surface tears). I do use the calliper 2 or 3 times at the mid point of the turning to get the largest diameter and then take the smallest reading. These plastics do expand considerably when heated by working, with rates of expansion easily 1000x that of metals, and the various coloured acrylic alloys I use seem to be much worse than polyesters or 'sensible' engineering plastics. The size of the work precludes a fixed steady, and the travelling steady that came with my machine would have a support point necessitating a doubling of the work length – so no gain there at all. Using a micrometer is problematical on these plastics: I have noticed that there is about 0.1mm compression of the plastic before the micrometer clicks, and if anything my one at home clicks more easily than the ones at work, so it's not faulty, just designed for more rigid materials.

Sorry, I'm drifting from the point.

A sort of consensus is appearing: If I don't use a fixed digital calliper attached to the machine to act as a DRO, then carry on as I am. Ah well, it's nice to see that I had a reasonable work around to the problem.

Regards,

Richard.

Edited By richardandtracy on 16/12/2013 10:57:12
16 December 2013 at 11:03 #137971
Ady1
Participant
@ady1
It's really the time saved, as well as the accuracy

If you do do a lot of ME stuff then picking bits up and aligning them to get a decent reading eats up time, and over many years this adds up to a LOT of time

Glancing at a DRO and tweaking the leadscrew means more time spent as machine time
16 December 2013 at 11:37 #137982
mechman48
Participant
@mechman48
For final cuts fix a tyre depth DRO gauge to your crosslide with earth magnets ( see my album photos) set 0 & away you go without fear of backlash problems… 0 -1" DRO tyre gauge off eBay for £ 5-6.

George
16 December 2013 at 12:41 #137997
richardandtracy
Participant
@richardandtracy
I like the tyre gauge idea. I really like it. I shall go away & investigate. Thanks.

Regards,

Richard
16 December 2013 at 13:08 #138000
John Stevenson 1
Participant
@johnstevenson1
Set your top slide at a slight angle say 10 degrees or so.

Take test cut and measure, then advance the top slide a bit and do another test and repeat.

This way you get zero on the dial to match up with a workable number.

There is a setting on the top slide, can't remember what it is but it works out that 10 units advances on the top slide is equal to one unit on the top slide, supposed to be for very accurate work when the wind allows.
16 December 2013 at 14:09 #138017
richardandtracy
Participant
@richardandtracy
Hmm. 'Tis a thought. But I do seem to be fiddling with the compound slide quite often. In pen making (which currently comprises 95% of my lathework), 3 degree tapers seem very popular, along with 7.5, 10, 15 and 75 degrees, so all the setup goes out the window every time I take a taper.

Regards,

Richard
16 December 2013 at 15:05 #138025
Russell Eberhardt
Participant
@russelleberhardt48058
Posted by John Stevenson on 16/12/2013 13:08:16:

There is a setting on the top slide, can't remember what it is but it works out that 10 units advances on the top slide is equal to one unit on the top slide, supposed to be for very accurate work when the wind allows.

5.7 degrees.

Russell.
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