Setting lathe top slide angle accurately.

[Geoff CausonParticipant @geoffcauson89285]

[Geoff CausonParticipant @geoffcauson89285]

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.

[JasonBModerator @jasonb]

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.

[Ady1Participant @ady1]

For accurate angles on a hobby machine use a DTI

Fiddly but accurate

[Michael ToppingParticipant @michaeltopping17870]

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

Michael

[Clive FosterParticipant @clivefoster55965]

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 HinkleyParticipant @johnhinkley26699]

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 HaineParticipant @johnhaine32865]

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.

[SillyOldDufferModerator @sillyoldduffer]

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.

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

Dave

[Chris TriceParticipant @christrice43267]

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 6Participant @chrisevans6]

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 1Participant @larryphelan1]

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 DaviesParticipant @glyndavies49417]

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 1Participant @josephnoci1]

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

[LambtonParticipant @lambton]

+ 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 WoodingParticipant @garywooding25363]

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.

[KettrinboyParticipant @kettrinboy]

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 TriceParticipant @christrice43267]

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 GilliganParticipant @michaelgilligan61133]

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 FParticipant @kevinf]

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

[HopperParticipant @hopper]

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.

[Geoff CausonParticipant @geoffcauson89285]

Thanks everyone for your help. I have decided to make some "wedges" for the commonly used angles (like 29 1/2 deg) that don't need extreme precision & use Joe Piezinski's method for more accurate jobs. His method doesn't need a long travel DTI & I have a DRO on the cross slide. He also has a good video on milling angles on wedges. A good result all round, thanks again.

[Chris Evans 6Participant @chrisevans6]

Geoff, do you have a sine bar ? If so when making your wedges it will pay to make lots of common angles. Keep them small and then they can be used in the vice on the mill for setting workpieces. I have most angles from 1/4 degree up to 45 degree. Made up over the years I find them very useful.

[Tim StevensParticipant @timstevens64731]

A brief caution regarding printing a drawing: Check that the printer actually produces the same scale in both directions. Most are near, but not all are bang on. And do not rely on paper or card being really stable in moist or dry conditions. They can shrink or stretch more one way than the other.

Not really a problem unless you are after accuracy – but sometimes, we all are.

Seasonable Yuletide wossnames

Tim

[John ReeseParticipant @johnreese12848]

I don't use the any method consistently.

If I have a sample taper to match I mount the sample in the lathe and sweep the taper with a dial test indicator. O adjust the angle of the top slide until the indicator reads the same at both ends of the taper.

If I have no sample to go by I use a sine bar. I have a 2.5" sine bar that can be locked in position. Once set with gauge blocks I can remove the blocks and take the sine bar to the lathe. One leg of the sine bar is magnetic so I can stick it to the tailstock spindle or to the face if the chuck.

If I am cutting long tapers by setting over the tailstock I check diameters at both ends of the work and adjust the tailstock accordingly.

If I am setting the top slide for threading I use the graduations on the cross slide. I set the angle about 1/2 deg. less than half the flank angle of the thread.

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