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Setting angles

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mike mcdermid27/08/2012 00:15:52
97 forum posts

How would one precicely set an angle on a lathe top slide

15 degrees and so many minutes in "imperial"


15.3 degrees in metric

I would use a sine table on the mill but accuracy on the lathe has always puzzled me?

Springbok27/08/2012 05:03:51
879 forum posts
34 photos

Pleaseexplain to do what.

Thor 🇳🇴27/08/2012 05:56:21
1630 forum posts
46 photos

Hi Mike

For small angles may be this site will be helpful? I suppose you could use the same principles as a sine table uses to set the topslide accurately. Like this or this?


Edited By Thor on 27/08/2012 05:59:14

Edited By Thor on 27/08/2012 05:59:35

Edited By Thor on 27/08/2012 06:04:15

JasonB27/08/2012 07:33:59
22751 forum posts
2653 photos
1 articles

Yes as Thor suggests in his first link.

Use a bit of trigonometry to work out the lengths of a triangle with angle of 15.3deg and a base of 1" length.

This will give the short side of 0.274"

Put a DTI in the chuck, roughly set your ange and put the point of the dti on the side of your topslide.

Feed the carrage exactly 1" along the bed and adjust the topslide until it reads 0.274 over the 1" distance.

If you can't feed the carrage accurately do the same calcs for an angle of 74.7 (90-15.3) and use the cross slide.


Ady127/08/2012 09:20:07
5091 forum posts
736 photos


Use a DTI over a fixed distance, usually the TPI of the leadscrew, or 2xTPI


Works well for tapers too

Edited By Ady1 on 27/08/2012 09:21:25

Andyf27/08/2012 09:20:59
392 forum posts

Hi Mike,

Thor's suggested method is the one I use, though it does rely on the side of the topslide which the indicator bears on being parallel to to the dovetail within, and care needs to be taken to mount the indicator horizontally. For anyone who (like me) was daydreaming during the trig lessons, the Right-Angled Triangle calculator HERE can be useful.


PS. The longer the distance over which you take the measurement, the better. Do the trig for as big a triangle as the length of your topslide permits.

Edited By Andyf on 27/08/2012 09:29:27

MadMike27/08/2012 09:45:00
233 forum posts
4 photos

In simple terms imagine that your lathe is no more or less that a vertical mill lying on its side. The same techniques are used, only the macine position has changed. Of course this presupposes that you can set the angle on a milling machine table I guess. HTH.

Clive Foster27/08/2012 11:45:06
3135 forum posts
109 photos

I set a true running bar up in the machine and measure off that. A taper fitting test bar is ideal although I usually just put a known straight rod up in a collet.

Precise adjustment is hardest thing using the usual push, tap, curse method. Best to make some sort of opposed push screw thingy to fix on the cross slide and give positive, controlled, movement both ways. Geo. H. Thomas recommended 2 BA screws for pusher duties. That or 10-32 UNF seem a good compromise between stout enough to push and fine threaded enough for accuracy. 4 mm is nearly double the pitch and a bit too coarse.

Its advisable to have a good scrub up and lubricate under the topslide before attempting precise setting. Swarf, bits and general grunge do tend to work in there and the shop gremlins will take great pleasure in nudging the contamination into just the right place to ensure that things shift a bit when you tighten down after getting the setting just so. Push from the side locking systems, such as the circular wedge and angled pusher used by Boxford, Southbend et al suffer more in this respect than the simple through bolt or Tee nut in slot variety.


mike mcdermid29/08/2012 22:39:25
97 forum posts

Hi chaps thanks for the tips and techniques,Completely honestly it was for setting up a vertical slide on the lathe i figured it might still involve a sine bar on its side so tu speak but was just wondering if there were any new tricks out there....always something to learn


That patented idea in the links was pretty interesting for a project and i did have a bit of a doh/ how simple is that once thor had posted a link ,funny how you dont think of stuff when its laid in a different axis

Edited By mike mcdermid on 29/08/2012 22:44:16

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