# Angle Of Compound Question On Lathe



## Investigator (Aug 24, 2016)

I hope I can say this correctly, or at least say it so that they way I understand it makes sense and can ask my question.
Regarding a metal lathe;
I understand that the saddle only moves in the linear direction of the length of the material relative to the work.  Also, the cross slide moves at 90* to the work.
The compound however can be set at any angle relative to the work.  And on top of the compound the tool holder can rotate.

So, I see that the compound is 'routinely' set at 29.5 or 30 degrees.  Does that mean that the tool holder is also at that angle?  Or is the tool holder and therefore the cutting bit always set at 90* relative to the work?

Does that make sense?


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## JimDawson (Aug 24, 2016)

Investigator said:


> Does that make sense?




Yup.  You are correct that the compound is normally set around 30°  That is for threading, but also it's a convenient position to get it out of the way.  The tool needs to be set to the work at an angle that gives adequate clearance to the non-cutting edges.  This is normally done by rotating the tool holder to the correct angle to achieve this.


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## Investigator (Aug 24, 2016)

Great.  So two thoughts, tell me if I'm on the right track;

The angle of the tool holder and cutting bit are within a fairly narrow range relative to the work, and that angle is determined based on work piece shape and direction of cutting, and clearance.

The compound angle and angle of the tool holder are related although independent of each other.


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## JimDawson (Aug 24, 2016)

Investigator said:


> The angle of the tool holder and cutting bit are within a fairly narrow range relative to the work, and that angle is determined based on work piece shape and direction of cutting, and clearance.
> 
> The compound angle and angle of the tool holder are related although independent of each other.



The angle that the tool cutting edge is presented to the work is the controlling factor, the angle of the tool holder is not important.  With the exception of threading or cutting tapers with the compound, angle is not important and is not related to the tool holder or tool bit angle.


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## Investigator (Aug 24, 2016)

got it! thanks!


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## mike sr (Oct 21, 2016)

I also have cut non critical tapers with the compound, the tool needs to be set dead center of the work as well.


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## 12bolts (Oct 21, 2016)

Depending on the lathe, (age/wear/quality) it can be beneficial to lock the saddle and use the compound, (set parallel to the ways) to make the longitudenal cuts. But yes the tool post is just rotated to present the tool to the work at the ideal, (or required) angle.

Cheers Phil


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## Wreck™Wreck (Oct 21, 2016)

Rotate the compound to the angle that makes it most user friendly when not in, use which is most of the time.

Push the tail stock against the back of the carriage and then rotate the compound so that it just clears keeping the compound control wheel and the cross slide wheel as far apart as possible (so that you are not whacking your knuckles). 

With manual lathes using modern tooling I have found when making small threads advancing the tool at 30 Deg. is unneeded, leave the compound where it is.


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## Glenn Brooks (Feb 20, 2017)

+1 on what others have said above.  Took a long time to unlearn that one must set the compound at 29.5*.

For example, my 1919 Dalton Lathe needs the compound set to at around 45* just for the handles on the (small) compound to clear the cross slide.  Also, on Myford lathes, apparently the compound often is set to 90* because of similar clearance issues.


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