How to read the angle on the compound

[Investigator]

I need some explanation please.
When setting the compound angle, which part of the scale do I read? Am I reading included angle? If it helps, I need to make some cones that are 60 degrees, as well as some that are 50 degrees.
I have a strange set up in that I have a Southbend compound mounted on a Logan 12" lathe. It's a double turret tool post cross slide with a compound mounted on top.
The compound has a scale around the front going from 90-0-90. When the compound is set so that it's movement is at 90 degrees to the ways, the scale lines up at the 90-0-90 marks. I'm trying to understand how to set it to cut accurate tapers with the compound.

I hope that makes sense. So for instance I will soon need to cut a 6 degree taper or 12 degree included. How do I read that on the scale?

 

[Alexander McGilton]

Any photos? How did you get the two manufacturers components to fit to one another? For threading I set the compound to 29* or one less than half the thread angle. For taper turning I don't trust the protractor. Use a sine bar or outside protractor and an indicator.

Setting Compound Rest Angles - Home Shop Machinist

Setting the compound rest angle on a lathe can be frustrating since the engraved protractor scale is frequently hidden from view by the compound rest.

www.homeshopmachinist.net

 

[Investigator]

Any photos? How did you get the two manufacturers components to fit to one another?

That's actually a bit of a story. I've taken photos along the way, and plan on showing what I've done in an upcoming post. Long story short the previous owner of the lathe made an adapter so the lathe would have a compound. I made a better one.

 

[RJSakowski]

I wouldn't trust the compound scale to set up for cutting an accurate taper.

A better way is to set up a dial indicator or test indicator on the compound. Mount a bar in the chuck and run the compound in to a point close to its end of travel. Run the cross slide in and zero the indicator and zero the cross slide. Make a mark with a Sharpie on the bar so you can return to the same spot on the bar. Now back the compound out by a known amount (one, two, or three inches are convenient numbers). run the cross slide in to zero the indicator, moving the carriage to make contact at the Sharpie mark. The cross slide distance divided by the compound distance is the sine of the angle between the compound and the spindle axis.

Better yet is to use a sine bar. In theory, you should be able to set angles to better than .01º using a set of gage blocks. Tom Lipton, Ox Tools, did a video on using a sine bar to set accurate compound tapers.

 

[T Bredehoft]

I have a 30 60 90 triangel I made during my apprenticeship, I use it and the face of the chuck to set for threading. That won't help you on 6 and 12 deg, but setting the tool post parallel the face of the chuck with a 1-2-3 block will get you zero, then move off 78 deg for your 12.