29.5 Deg. Angle Tool For Lathe

[Baithog]

Just some confusion in my old brain, but up there in the LL picture - If you use a standard 60deg. ground tool and set the compound at 27 or 26, or something like the picture title says, wouldn't you screw up the angle being cut on the left side of the tool, too? Half a degree is a wash, but several degrees starts to make a lopsided thread. Wouldn't it be better to have a tool ground with clearance on the trailing side. You guys with fancy carbide threading tools would have a hard time doing that, but those of us with more modest means and HSS threading tools can grind whatever angle we want... And I have done that by mistake

 

[randyc]

Nice work on your project. But this subject gets pounded to death on angle this and angle that. And I’m still gonna say, ”I go straight in with the cross slide only”. And I’ve been doing it that way for about 40 years now. Look at all that time I have save not messing around with the compound angle adjusting. And my threads look great. And my lead does not change so I can do trick things to the end of the thread too. And threading up to a shoulder is easier because your tool does not creep to the left. Try it, you might like it…Good Luck, Dave.

While personally, I use the angled compound to cut threads, I imagine a lot of people use the cross-slide, like Dave does. As an example, I have an old book that came with my Sheldon EXL-56B that's similar to the South Bend book. BUT there is no mention at all of angling the compound when cutting screw threads. In fact, quite the contrary.

On the Sheldon, there is a little gizmo attached to the cross-slide that looks like this:



This arrangement is used for cutting threads in production. The stop that is mounted to the carriage is rotated up so that it is over the threaded rod and between the two sets of lock nuts and locked into position. The lock nuts are adjusted so that cross slide travel is limited to the thread major and minor diameters (by cutting a trial thread presumably).

It's a PITA to describe how to set up and use this tool but at no time does the operator have to look at any dial and make any adjustment other than feeding the cross-slide a fraction of a turn. I've never used this feature so I can't attest as to how quickly threads can be produced with it.

The point of this post is to note that Dave's technique may be used far more often than the rest of us think. And obviously with success

 

[randyc]

....Wouldn't it be better to have a tool ground with clearance on the trailing side. You guys with fancy carbide threading tools would have a hard time doing that, but those of us with more modest means and HSS threading tools can grind whatever angle we want... And I have done that by mistake

You could do that but then the compound would have to be set at exactly thirty degrees because the rear flank of the thread would be produced by the compound infeed, not the shape of the cutter. Also, to produce a good finish, the infeed would have to be very, very small which would take a l-o-n-g time to produce a screw thread.

 

[RJSakowski]

I would think that the ability to go straight in without chatter will depend to a great extent how rigid the lathe is. For a small lathe, making the cut from both sides can be a problem. At least it was for me.
The bottom line is whatever works is OK. As has been pointed out, there are many ways to skin the cat. From my personal experience, my threads are much nicer using the 29.5 feed angle.

 

[randyc]

I would think that the ability to go straight in without chatter will depend to a great extent how rigid the lathe is. For a small lathe, making the cut from both sides can be a problem. At least it was for me.
The bottom line is whatever works is OK. As has been pointed out, there are many ways to skin the cat. From my personal experience, my threads are much nicer using the 29.5 feed angle.

That is the main thing, the chattering problem, and the reason that I also use the compound technique on my two small lathes. I've tried feeding with the cross-slide but I have to run the spindle in back gear to keep the chatter down - it's a slow process and sometimes the finish is less than optimal.

FWIW - and this is not based on a lot of testing - I think that I get better thread finish when I run the spindle faster.

 

[JR49]

Just some confusion in my old brain, but up there in the LL picture - If you use a standard 60deg. ground tool and set the compound at 27 or 26, or something like the picture title says, wouldn't you screw up the angle being cut on the left side of the tool, too? Half a degree is a wash, but several degrees starts to make a lopsided thread. Wouldn't it be better to have a tool ground with clearance on the trailing side. You guys with fancy carbide threading tools would have a hard time doing that, but those of us with more modest means and HSS threading tools can grind whatever angle we want... And I have done that by mistake

Baithog, I think what's confusing you is that you're assuming that when the compound gets angled to 29.5 deg., that will alter the angle of the tool bit. That is not the case. You set the compound to 29.5 deg. first. THEN, you turn your tool post so that the threading tool bit is perfectly perpendicular to the work. Then as you advance the compound to take successive cuts into the thread, the tool remains perpendicular (at a right angle) to the work being threaded. Hope this helps, JR49

 

[RJSakowski]

Great Stuff!
i always rounded off to 30*and use a small 30*60*90* triangle gage to set it.
it seemed a lot simpler albeit less than correct.
the function is fine for the class of fit i'm accustomed to.
the error is small on my lathe(s) in reference to the triangle.

thanks for sharing!

Thanks for the like.

I believe that the rationale for the slightly less than 30 degrees is that you want to make a very light shaving cut on the right-hand side of the thread to clean it up. From what has been said, the angle isn't critical.

My G0602 protractor is not that accurate and the divisions are 2-1/2 degrees and hard to read so I would use a triangle or adjustable angle square as well. It was too difficult for my arthritic hands to try to juggle a square, a spacer, and the compound while clamping it down; hence the gage.

If I were using your method, I would set it to 30 degrees with the 30/60/90 triangle and bump it a little to be slightly under. I used a 30/60/90 triangle to check the machining cut when I made the gage.

 

[RJSakowski]

Just some confusion in my old brain, but up there in the LL picture - If you use a standard 60deg. ground tool and set the compound at 27 or 26, or something like the picture title says, wouldn't you screw up the angle being cut on the left side of the tool, too? Half a degree is a wash, but several degrees starts to make a lopsided thread. Wouldn't it be better to have a tool ground with clearance on the trailing side. You guys with fancy carbide threading tools would have a hard time doing that, but those of us with more modest means and HSS threading tools can grind whatever angle we want... And I have done that by mistake

No you won't mess up the left side. When you set you compound angle, you set the angle at which you advance the tool. You then adjust the angle of your tool in your toolholder with the fishtail gage so the cutting bit is perpendicular to the thread axis. As you advance the tool, the cut surfaces are always 60 degrees to the thread axis. The left side is making the bulk of the cut while the right side is making a very light cut, almost scraping. Think of like cutting a double bevel.

If you ground your tool bit with clearance on the right side, the thread angle on the right side would be whatever you set the compound angle at. Take it to the extreme and set the compound angle a zero. You are now advancing the tool straight in. The left side will give you a 60 degree bevel while the right side be perpendicular to the thread axis.

Sorry Baithog, Your post came up on top and I thought it was new. I should have looked at the post date. I also should have my morning coffee before reading or replying.

 

[kingmt01]

Nice tool. If you don't have nothing else to do why not make a tool that you can be proud of? Now if you notched a 60 in it to square the tool youd have a two in one.

 

[The Liberal Arts Garage]

Great Stuff!
i always rounded off to 30*and use a small 30*60*90* triangle gage to set it.
it seemed a lot simpler albeit less than correct.
the function is fine for the class of fit i'm accustomed to.
the error is small on my lathe(s) in reference to the triangle.

thanks for sharing!

. If I remember correctly, the missing half
degree is there to concentrate the cutting action on the leading edge.
If I remember correctly, the cutter is to be set at thirty degrees for the
last " polishing" pass. Please correct if I am misled.......BLJHB.