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Setting lathe top slide angle accurately.

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Geoff Causon25/12/2018 09:07:05
8 forum posts
2 photos

Does anyone have a clever idea to set the lathe topslide to a precise angle. My top slide swivels 360 deg & the crude plastic dial goes +/-50deg. Anything other than that I use my protractor but this means eyeballing the ruler to the edge of the cross slide. There must be a better way.

JasonB25/12/2018 09:14:28
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Moderator
16045 forum posts
1684 photos
1 articles

Plunger type DTI and a bit of trig then you can measure how much the needle moves over a given distance so that gives you two sides of the triangle and the angle you know so just adjust until the dti shows the correct amount of movement.

Must admit that I seldom get the calculator out these days when I need to know an angle or side of a triangle, easier to sketch the two known items in Alibre and let it give the third.

Ady125/12/2018 09:21:47
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3463 forum posts
513 photos

For accurate angles on a hobby machine use a DTI

Fiddly but accurate

Michael Topping25/12/2018 09:37:33
73 forum posts
5 photos

I always use a Sine bar and slips against the side of the top slide, then clock along the bar. Guaranteed accuracy.

Michael

Clive Foster25/12/2018 10:00:38
1807 forum posts
59 photos

Two separate issues here.

First one is actually moving the topslide accurately and repeatably through a small angle to home in on the setting. The two pusher screw device advocated by Geo. H Thomas seems the best answer to that. Theoretically the screws could be calibrated but that's probably guiding the lily to little practical benefit.

Enlarging on the comments from Jason and Ady1 about using a DTI. My way was to set up a straight bar, calculate the topslide movement needed for a sensible DTI deflection then run back and forth until I get the right deflection. If you use a couple of inches of topslide movement the errors will be very small. Probably best to standardise on a topslide movement length so the job becomes very fast. Once you get the pusher screw movement needed for a given change in DTI deflection dialled in you will be there in two or three tries. Obviously you always work between the same calibration marks on the topslide dial.

Clive.

John Hinkley25/12/2018 10:10:03
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749 forum posts
252 photos

For no other reason than to set myself a problem to solve, I made a device for setting the lathe topslide angle using a Wixey-type angle gauge. The saga is one of my albums ( page 2 ) entitled "Top slide angle setter". The photos aren't very clear, I'm afraid, but it was written up for publication in MEW, with drawings, etc. I can't find it in the various indices, but it must have been sometime after 2011! My original drawings got lost in the great hard drive crash of 2018, but there is a jpeg of the general layout in the album.

John

Edit:  I think I said in the article that it was probably a sledge-hammer-to-crack-a-nut solution, but it was more of a brain teaser than anything else. But, Hey-Ho!, it works.

 

Edited By John Hinkley on 25/12/2018 10:12:54

John Haine25/12/2018 10:16:37
2591 forum posts
133 photos

Since you usually set over the topslide to cut a taper, if you have a taper to match, fit that in the chuck and set the DTI to get no movement as you run the tip up and down the taper. DTIs are great at indicating small movements and errors but not necessarily well calibrated.

SillyOldDuffer25/12/2018 10:31:28
4597 forum posts
987 photos

Depends on how precise you need to be - see Sine Bar and DTI solutions above for good answers.

In a home workshop cruder methods may be more appropriate. I use a CAD package to draw a right-angled triangle with the wanted angle, print it, and then use it as template to align the tool-post. Sticking the template on card makes it less floppy and easier to use but it's not necessary.

The triangle can be drawn manually, in this example I chose 30mm as the baseline, any number will work.

template.jpg

This calculator may help. Note the slider switch between Rad and Deg

Dave

Chris Trice25/12/2018 10:37:12
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1362 forum posts
9 photos
Posted by Michael Topping on 25/12/2018 09:37:33:

I always use a Sine bar and slips against the side of the top slide, then clock along the bar. Guaranteed accuracy.

Michael

That's what I do too. It's the most consistently accurate way I know.

Chris Evans 625/12/2018 10:49:26
1450 forum posts

Plus 1 for sine bar method although for most common angles I have a set of accurately ground setting "Wedges" from my toolmaker days.

larry phelan 125/12/2018 10:53:58
482 forum posts
11 photos

I made two simple gauges for setting my top slide for screw cutting,one for 55*,one for 60*,since I found it difficult to read the scale. They were made from off cuts of Ali sheet,nothing fancy,but they are fast and they work.

There are pictures of them in my album. Would be easy to make a few for the angles you use most.

Glyn Davies25/12/2018 11:37:43
113 forum posts
21 photos

If I need to set the top slide to match an existing taper, such as a Morse taper, I hold some silver steel bar in the chuck and use a DTI to check that the top slide is set to zero by running it along the silver steel. I then slacken the nut clamping the Dickson tool post body to the top slide and bring the plain face of the body into contact with the silver steel. Then lock the tool post. I next fit the taper I’m trying to match into the chuck, release the top slide lock screws and bring the plain face of the tool post into contact with the taper. Then lock the top slide and turn my taper.

Joseph Noci 125/12/2018 12:01:56
536 forum posts
832 photos

I have used this method a few times - Still basic Trig and it works really well and becomes second nature after a few times.

The presenter ( Joe Pieczynski) , contrary to his normal style, did waffle a little at the start, but hang in there - the method is neat.

**LINK**

If you have DRO's, it's even easier when setting the cross slide to measure the triangle 'drop'

The method does require that the tailstock quill is parallel to the ways in all ways..If not, and if you have a test bar with center pips at the end, fit the bar between centers and DTI over its length till parallel and use that as the reference.

He mentions right at the end to ensure that backlash is taken care of when measuring - important.

Joe

Lambton25/12/2018 12:02:11
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679 forum posts
2 photos

+ for using a sine bar and slip blocks.

May I refer any one interested to:

  1. Model Engineer 4328 article by Maurice Turnbull on how to make a simple jig for using these items :and:
  2. Model Engineer 4346 my follow up article about the use of Maurice's article.

If carefully made this jig enables very accurate setting of the top slide for cutting small angle.

Eric

Gary Wooding25/12/2018 12:33:03
572 forum posts
137 photos
Posted by Joseph Noci 1 on 25/12/2018 12:01:56:

The presenter ( Joe Pieczynski) , contrary to his normal style, did waffle a little at the start, but hang in there - the method is neat.

**LINK**

I know this reply is slightly off-topic, but thought I'd mention it anyway.

Joe's videos are usually interesting, and this was no exception, but those adverts!!!

The advertisers must be oblivious to the fact that incredibly mistimed interruptions do not endear viewers with good feelings about the content of the interrupt. Personally, it turns me off, and I wouldn't contemplate buying whatever they're pushing.

Kettrinboy25/12/2018 19:36:39
75 forum posts
39 photos

Don't think anybody's mentioned it yet but whatever way you set a precise angle on the top slide it wont be cut precisely if the tool is not set dead on centre height , if its out either way the angle cut will not be exactly as set.I found that out when I used to have to machine a precise 20 deg angle on water pump impellers for Mercedes F1 engines.

regards Geoff

Chris Trice25/12/2018 20:34:51
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1362 forum posts
9 photos

I forget where I read it but an error of a few thou above or below makes negligible difference when you do the trig except on VERY small diameters. Obviously spot on dead centre is to be aimed for as the ideal.

Michael Gilligan25/12/2018 22:03:11
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13823 forum posts
603 photos

Chris,

This may not be appropriate reading for Christmas evening, but if you want to work through the trig. it's in here:

**LINK**

http://jeteas.scholarlinkresearch.com/articles/AN%20EXPERIMENTAL%20STUDY%20OF%20THE%20EFFECT%20OF%20WRONG%20POSITIONING%20OF%20CUTTING%20TOOL%20ON%20TAPER%20TURNING%20OPERATION.pdf

Apologies for the ridiculously long URL

MichaelG.

Kevin F25/12/2018 22:34:35
96 forum posts
24 photos

Do you still work for Mercedes F1 team , it was always my dream to work in F1 as an engineer , I guess having made parts for F1 power boats is a close second

Posted by Kettrinboy on 25/12/2018 19:36:39:

Don't think anybody's mentioned it yet but whatever way you set a precise angle on the top slide it wont be cut precisely if the tool is not set dead on centre height , if its out either way the angle cut will not be exactly as set.I found that out when I used to have to machine a precise 20 deg angle on water pump impellers for Mercedes F1 engines.

regards Geoff

Hopper26/12/2018 05:06:59
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3657 forum posts
72 photos
Posted by Chris Trice on 25/12/2018 20:34:51:

I forget where I read it but an error of a few thou above or below makes negligible difference when you do the trig except on VERY small diameters. Obviously spot on dead centre is to be aimed for as the ideal.

ISTR Geo. H Thomas conducting experiments/ calculations on the topic in one of his books and concluding that centre height was not as critical as sometimes previously supposed. I think the smaller the diameter, the greater the influence of centre height becomes.

It's all horses for courses though. For offsetting the topslide to 29 degrees for screwcutting, simple protractor gauge will do. For offsetting topslide to cut a Morse taper that works, the dial indicator method/s is best used.

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