DRO on lathe cross slide accuracy/resolution

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DRO on lathe cross slide accuracy/resolution

This topic has 49 replies, 23 voices, and was last updated 3 April 2015 at 14:12 by Bob Brown 1.

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30 March 2015 at 17:58 #184981
Stuart Bridger
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@stuartbridger82290
I am looking at a DRO for my lathe. The DRO vendor is offering 5um resolution scales with an accuracy of +/- 0.005mm which is +/-2 tenths on radius or +/-4 tenths on diameter, on the cross slide. This doesn't sound that great? I am currently waiting a quote and accuracy spec on 1um scales.

What is everyone else using?

Thanks in advance for your response

Stuart
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30 March 2015 at 17:58 #17658
Stuart Bridger
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@stuartbridger82290
30 March 2015 at 18:24 #184983
Michael Gilligan
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@michaelgilligan61133
Posted by Stuart Bridger on 30/03/2015 17:58:48:

I am looking at a DRO for my lathe. The DRO vendor is offering 5um resolution scales with an accuracy of +/- 0.005mm which is +/-2 tenths on radius

?
30 March 2015 at 18:25 #184984
JasonB
Moderator
@jasonb
I suppose it depends on what accuracy you feel you need to work at. I would say for 99% of what I make then 5/10ths would be fine and for anything better than that I'll get out the mic with 10ths on it.

I mostly use the mitutoyo callipers to measure on the lathe and they only read to 0.0005" and all my engines seem to run OK and develope good compression.

What sort of things do you usually tend to make?

J
30 March 2015 at 18:31 #184985
Tony Pratt 1
Participant
@tonypratt1
In the real world do you think using a 1um scale will be practical? This is a lathe not a cylindrical grinder you are talking about.

Just trying to save you money.

Tony
30 March 2015 at 18:37 #184987
Stuart Bridger
Participant
@stuartbridger82290
Posted by Michael Gilligan on 30/03/2015 18:24:36:

Posted by Stuart Bridger on 30/03/2015 17:58:48:

I am looking at a DRO for my lathe. The DRO vendor is offering 5um resolution scales with an accuracy of +/- 0.005mm which is +/-2 tenths on radius

?

I know I am mixing units here, but I can visualise old school better.
The comment on radius was that the DRO is going to read absolute position of the cross slide, so if I am understanding correctly any error will be doubled on diameter. 4 tenths is getting close to half a thou, which to me sounds significant. I suppose if I have to get a mic out for the finer work then so be it?
30 March 2015 at 18:39 #184988
Stuart Bridger
Participant
@stuartbridger82290
Posted by Tony Pratt 1 on 30/03/2015 18:31:35:

In the real world do you think using a 1um scale will be practical? This is a lathe not a cylindrical grinder you are talking about.

Just trying to save you money.

Tony

Tony, that is why I am asking In reality I guess I am concerned about accuracy rather than absolute resolution
30 March 2015 at 18:46 #184990
Nick_G
Participant
@nick_g
Posted by Stuart Bridger on 30/03/2015 17:58:48:

What is everyone else using?

Stuart

.

What lathe are you using.?

Basically the question I am asking is can the lathe you are intending fitting it to achieve and maintain that level of accuracy.?

Nick
30 March 2015 at 18:47 #184991
Stuart Bridger
Participant
@stuartbridger82290
1963 Chipmaster, which is much better than I am.

Mostly making stationary engine models

Edited By Stuart Bridger on 30/03/2015 18:49:55
30 March 2015 at 18:55 #184993
JasonB
Moderator
@jasonb
So lets assume there is a bit of wear in the lathe, you put a bit of 1" bar in the chuck and take a 0.050" cut, take another 0.005" cut to form a slightly smaller spigot on the end

Do you trust the DRO that it has given you two dia of 0.900" and 0.890" as the DRO cannot allow for the possible tool deflection caused by a cut 10 times deeper than the second?
30 March 2015 at 18:56 #184995
Mike Poole
Participant
@mikepoole82104
On a hobby type lathe I think turning to tenths of a thou will be affected by other factors like machine rigidity, tool edge, work temperature, workpiece flex and tool lube. Lapping parts is often the process used to achieve tight tolerances and high surface finish in the home workshop.

Mike
30 March 2015 at 18:57 #184996
Stuart Bridger
Participant
@stuartbridger82290
Good point Jason, on that basis are you saying that there is little point installing a DRO on a lathe?
30 March 2015 at 19:10 #184997
blowlamp
Participant
@blowlamp
Do you have the option of getting a higher resolution scale for just the cross slide?

Martin.
30 March 2015 at 19:15 #184999
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Stuart Bridger on 30/03/2015 18:37:04:

I know I am mixing units here, but I can visualise old school better.

The comment on radius was that the DRO is going to read absolute position of the cross slide, so if I am understanding correctly any error will be doubled on diameter. 4 tenths is getting close to half a thou, which to me sounds significant. …

.

No problem with that Stuart

I do wonder, however, [just out of curiosity] what the original spec was, for the Chipmaster cross-slide feedscrew.

MichaelG.
30 March 2015 at 19:24 #185000
KWIL
Participant
@kwil
5 micron on the cross slide is more than sufficient. My Super 7 and M300 are so fitted. I do have a special with 5 micron fittted to a Super 7 topslide, but that is another story
30 March 2015 at 19:38 #185001
Stuart Bridger
Participant
@stuartbridger82290
All, excellent feedback, I am thinking that 5um will suffice. Experience will tell once installed with regular checking with the mic. how much spring and deflection I am getting.

Thanks

Stuart
30 March 2015 at 19:53 #185005
Bob Brown 1
Participant
@bobbrown1
To top it off there is temperature.

There was a program on the TV with Guy Martin fitting fitted bolts on a Spitfire which although they had been machined to the correct size Guy holding one meant it did not fit as he had warmed it up.

I doubt if that sort of precision is required for stationary engine, which have been made successfully before all these electronic aides.

Bob
30 March 2015 at 20:08 #185007
JasonB
Moderator
@jasonb
Posted by Stuart Bridger on 30/03/2015 18:57:32:

Good point Jason, on that basis are you saying that there is little point installing a DRO on a lathe?

No but putting one on won't make your work 10 times more accurate overnight though I can see where they do have their advantages.
30 March 2015 at 20:23 #185009
Nick_G
Participant
@nick_g
Posted by JasonB on 30/03/2015 20:08:21:

Posted by Stuart Bridger on 30/03/2015 18:57:32:

Good point Jason, on that basis are you saying that there is little point installing a DRO on a lathe?

No but putting one on won't make your work 10 times more accurate overnight though I can see where they do have their advantages.

.

I have DRO's and very pleased with them I am.

However I do have an 'old school' pro machinist friend. (who of course uses DRO's) But he is totally adamant that I should not have fitted DRO's until I was totally proficient without them.!

With that in mind would I ever be tempted to switch mine off.? ………………. No chance.

Nick
30 March 2015 at 21:04 #185014
Neil Wyatt
Moderator
@neilwyatt
> There was a program on the TV with Guy Martin fitting fitted bolts on a Spitfire which although they had been machined to the correct size Guy holding one meant it did not fit as he had warmed it up.

Which bolts? I can't believe they would have turned out many like that in war production!

I remember reading that they made couple of spits with flat-head rivets (much less drag) They then stuck split peas on the rivets to find out which ones made the biggest difference, so they could make production planes with as few flat head rivets as possible.

Neil
30 March 2015 at 21:16 #185017
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Wyatt on 30/03/2015 21:04:49:

> There was a program on the TV with Guy Martin fitting fitted bolts on a Spitfire …

Which bolts?

.

The ones that hold the wings on

MichaelG.
30 March 2015 at 21:23 #185019
Nick_G
Participant
@nick_g
Posted by Michael Gilligan on 30/03/2015 21:16:01:

Posted by Neil Wyatt on 30/03/2015 21:04:49:

> There was a program on the TV with Guy Martin fitting fitted bolts on a Spitfire …

Which bolts?

.

The ones that hold the wings on

MichaelG.

Rubbish.!

The Spitfire I had used rubber bands and 1/4" wooden dowel to hold it's wings on with.

Nick
30 March 2015 at 22:04 #185022
Stuart Bridger
Participant
@stuartbridger82290
I already have a DRO on my mill and there the advantage is much more obvious, no more counting handwheel turns and functions like divide by 2 are invaluable. What I am looking for on the lathe is primarily to increase productivity rather than accuracy. I am thinking that it will help on the carriage more than the cross slide. When i did my apprenticeship some 35 years ago we had no DROs then… I am relearning my lathe skills after a 30+year break, productivity is improving (and scrap rates are decreasing), but my thoughts are a DRO will really help.
30 March 2015 at 22:14 #185024
jason udall
Participant
@jasonudall57142
a couple of things..

the guy martin "bolt" was a between center cylindrical ground pin.

it may have been that close a fit.

the other thing.. adding a dro will make your life easier.

more fun even.

it will even help controlling your TOOLPATH.

.it depending , on wear elsewhere, will not guarantee your parts dimentions..

that said.. more resolution is always nice..but may just serve to make you more unhappy about the machine its attached to..

I would not look for better than tenth of the hand scales….(if say 5 thou scale then 0.5 thou dro)

..unless un upgrade is in the offing……

Edited By jason udall on 30/03/2015 22:17:58
30 March 2015 at 22:35 #185027
daveb
Participant
@daveb17630
Posted by Neil Wyatt on 30/03/2015 21:04:49:

> There was a program on the TV with Guy Martin fitting fitted bolts on a Spitfire which although they had been machined to the correct size Guy holding one meant it did not fit as he had warmed it up.

Which bolts? I can't believe they would have turned out many like that in war production!

I remember reading about fitted bolts that held the wings on, they were always a good fit but later marks needed the bolts cooled (LOX?) before they would enter the holes, Vickers were not impressed with the fitters who made the holes bigger.

Dave
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