What is correct? 29.5 vs 30 vs 59.5 vs 60 vs 60.5 compound setting?

[schemer]

Too much reading makes a person question if he is doing something the most correct or best results kind of way. I have Grizzly G4003G Gunsmith lathe and haven't really cut any threads on it until recently although I have cut threads many years ago on an unknown lathe. Being a bit out of practice, I cut a 3/8-24 thread that worked great and only had to do it once. Then I was reading (due to yet another thunderstorm keeping me stuck in the house) about the correct angle on the compound. I have mine set to 29.5 degrees. Of course I could run down there in the rain and check with my protractor but I am going to ask here to stay dry. Should the angle using a protractor be measured from the side of the compound and the face of the chuck to see if my Chinese graduated scale is accurate and set to 29.5 degrees? Or does anybody have a Grizzly G4003G and know the answer? I am thinking I need to set mine to 60.5 degrees (or 59.5 or 60 etc) as I have a feeling the graduations are measured off of the cross slide to the compound.
Thanks,
schemer

 

[awander]

You want to measure the angle as if zero degrees is "perpendicular to the work". As you suspected, some lathes compounds are calibrated the other was, with "zero degrees parallel to the work".

Don't sweat the 1/2 degree, you really can't set it that accurately using the calibrations on the compound anyway.

 

[schemer]

Ok, that is what I thought. Just wanted to be sure. Sometimes reading too much just throws a wrench into the picture. anic:
Thanks,
schemer

 

[chips&more]

I don’t worry about setting the compound to a specific angle. Because, I do not feed the compound when threading. When you set to 29.5° and feed the compound the tool bit cuts on one side of the thread way more than the other side. When you use a carbide threading tool, this can be a problem because of the uneven cutting pressure on the carbide. If you have galling problems, it’s tuff to clean up the side that doesn’t get cutting depth. It’s a pain to set the compound…I can go on with reasons, but having senior moments. Anyway, I just feed in with the cross feed noting the advances on the dial. This method cuts the same amount of material on both sides of the thread and this is why I prefer this method for the last 40 years. I can also do a very sexy stop thread and the end of a thread because the point of lead does not change with this method…Good Luck

 

[schemer]

I don’t worry about setting the compound to a specific angle. Because, I do not feed the compound when threading. When you set to 29.5° and feed the compound the tool bit cuts on one side of the thread way more than the other side. When you use a carbide threading tool, this can be a problem because of the uneven cutting pressure on the carbide. If you have galling problems, it’s tuff to clean up the side that doesn’t get cutting depth. It’s a pain to set the compound…I can go on with reasons, but having senior moments. Anyway, I just feed in with the cross feed noting the advances on the dial. This method cuts the same amount of material on both sides of the thread and this is why I prefer this method for the last 40 years. I can also do a very sexy stop thread and the end of a thread because the point of lead does not change with this method…Good Luck

I thought that was the Old School way of cutting threads. :thinking: I am using HSS so that is not a problem for the cutting pressure etc. I guess I could try it that way too, but I always read about the 29.5 and compound method as the new school way of thought cutting on the one edge and no curls coming back around etc. I know both methods work as you are not the only one I read that does it that way. Sounds easier to set up, but not by much. The sexy stop has my attention though. )
Thanks,
schemer

 

[dave2176]

The angle depends on whether you measure from perpendicular or parallel to the work piece. I would say 29.5 from perpendicular so the compound moves to apply the cutting force on the leading edge and that half degree just keeps the trailing edge clean. I have the same lathe so it would read 59.5*.

Dave

 

[schemer]

The angle depends on whether you measure from perpendicular or parallel to the work piece. I would say 29.5 from perpendicular so the compound moves to apply the cutting force on the leading edge and that half degree just keeps the trailing edge clean. I have the same lathe so it would read 59.5*.

Dave

Dave,
So you are saying the scale is correct and set to 29.5 on the compound? I just checked and with the compound at "0", it it perpendicular to the face of the chuck so the setting at 29.5 is correct? My scale doesn't go up to 59.5 on the compound or maybe if I jam it all the way.
Thanks,
schemer

added: So looking at the bottom of this page, the tool this guy made is the correct way to set it correctly right?

http://dezignshack.com/blog/?cat=3

 

[tertiaryjim]

Can't add anything to all the good explanations of the others but will mention that I grind my bits using the leading edge of the tool stock as a reference.
That way it's edge is perpendicular to the work and makes it easy to line the tool up to the face of the work.
It's just a bit more accurate and faster than using a thread tool, at least for me.
29 deg when cutting a 60 deg thread has been the standard for a long, long time.
Just remember to adjust the compound angle should you cut a different thread style.

chips&more
Didn't know about the pressure problems using carbide.
Thanks for mentioning it.
Wonder if more load on the trailing edge of a HS tool would work better when cutting acme threads.
The last acme I cut one using a 14 deg compound setting and HS tool gauld a bit on the trailing edge.
Will be trying that one again in a few weeks as I need it to be rite.

 

[chips&more]

chips&more
Didn't know about the pressure problems using carbide.
Thanks for mentioning it.
Wonder if more load on the trailing edge of a HS tool would work better when cutting acme threads.
The last acme I cut one using a 14 deg compound setting and HS tool gauld a bit on the trailing edge.
Will be trying that one again in a few weeks as I need it to be rite.

Please do not sound off, I totally know all about its hazardous effects and you should too! But there are moments when the best is not always the safest. I’m talking about using white lead. If you are having problems with threading and galling and if you happen to have any white lead, that stuff works! If any of you know of a safe chemical or recipe of safe chemicals that also work well, than please chime in, I would like to hear from you…Good Luck

 

[chips&more]

chips&more
Didn't know about the pressure problems using carbide.
Thanks for mentioning it.
Wonder if more load on the trailing edge of a HS tool would work better when cutting acme threads.
The last acme I cut one using a 14 deg compound setting and HS tool gauld a bit on the trailing edge.
Will be trying that one again in a few weeks as I need it to be rite.

Don’t know the scope of your acme threading project. But, for starters try setting the compound at 90° and scoot the cutter from cutting side to side. And do all the feeding with the cross. That way you relieve half of the tool pressure and have a better control on how much to cut and control galling…Good Luck.