29.5 Deg. Angle Tool For Lathe

[RJSakowski]

A 29.5 degree angle is most likely the most used angle set on the compound on a lathe. The Grizzly G0602 lathe has a difficult to read dial with 2-1/2 degree graduations. My solution was to make a gage that would provide easy and accurate setting of this important angle.
I made mine from a piece of 2" x 2" x 1/4" 6061 aluminum angle that I had in my scrap bin. I used my CNC to mill the piece but could have just as easily made it with a rotary table or by setting my milling vice at a 29.5 degree angle to the y axis. I roughed out the piece on a band saw and finished the milling with a 1/2" end mill. The entire project was an easy few hours
Because I was using some scrap for the piece, my version is not exactly to the drawing. Additionally, it works for the 0602 but the maker should check that the dimensions fit his or her particular lathe and make adjustments accordingly.
Enjoy!

 

[Ken_Shea]

That is a good idea RJ, it a pain setting exactly the 29.5.

 

[T Bredehoft]

It's more work, but I set up my compound close to 30°, set an indicator to register movement of the saddle and another to measure movement of the compound in the Y coordinate. For .050 in X it should read .0246 in Y. Once you've achieved these readings, you KNOW it's right. The marks on my Clausing/Atlas are off by 1 1/2 marks, more or less.

Oh. Sine 29.5° = 0.49242. 0.49242/20 = .0246.

Tom

 

[Ulma Doctor]

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!

 

[RJSakowski]

That is a good idea RJ, it a pain setting exactly the 29.5.

With the CNC, I started at an offset from the apex of the triangle I set that at 0,0 and ran G1 X-6 Y-3.3946. then X0 Y0. Then I moved to X-.1 and set to 0. I repeated until I had cleaned up the edge to my satisfaction. The actual location of the apex is not critical.
If using a rotary table set your vice up with the jaws parallel to the x axis. I use and edge finder but a test indicator will work as well. Note the reading on the rotary table and rotate 29.5 degrees from there to cut the angle.
If you don't have either of those options, use a sine bar to set the vice. The block stack for a 5" sine bar is 2.462". If you don't hahe a sine bar, a 30-60-90 drafting triangle with a shim at the 30 degree vertex will give you the required 29.5 degrees. The shim is 8.73 thousandths for every inch of separation between the two contact points.
There isn't anything really sacred about the 29.5 degree angle. Its intent is to shave a small amount of the left hand side of the thread as you advance the cut. The South Bend book "How to Run a Lathe" recommends a 29 degree angle.

 

[randyc]

Holy cow ! Some of you guys are even more obsessive/compulsive than me and that's impressive ! 29-1/2 degrees is a time-worn standard but it's really not all that critical. At least I haven't found it to be - cranking the compound around so that my aged eyes detect that the angle is somewhere slightly less than 30 degrees seems to be satisfactory.

If the cutting tool shaves the flank of the thread, doesn't chatter and produces a nice finish, the exact angle doesn't matter. For example, this particular reference from "Machinery's Handbook" suggests 29 degrees (the extra half degree was left by the wayside - SACRILEGE):

http://www.kanabco.com/vms/eng_mhandbook/eng_mhandbook_06.html

Here’s an illustration that I snatched from the internet.




Note that the lower left illustration suggests that compound angle can be adjusted over a fairly wide range provided that it is less than 30 degrees. The object is to lessen the stress on tool/work, cutting NOT like a forming tool, that must remove ALL material from both thread flanks.

The better alternative, as we know, is to remove most of the material from the leading edge while just shaving the training edge. Cutting pressure is reduced and surface finish consequently improved (no chattering).

The angle of the compound – within reasonable limits and always less than 30 degrees – can be adjusted to the point that chatter starts to occur given a reasonable DOC (usually less than .015) then backed off slightly to achieve satisfactory results.

Just my experience, of course -

 

[RJSakowski]

Randy, I believe I said that in the last post. However, with my G0602 anyway, the dial has 2-1/2 degree graduations and is buried where it is difficult for me to read. On top of that, it has an offset as well. Being able to loosen the bolts, slide the gage in and retighten is worth the hour or so spent machining the gage.
Interesting that the title on the lower left illustration says "15 to 29-1/2 Degrees Infeed Angle" while the illustration says 1 -3 degrees.

 

[RVJimD]

RJ, Could you show me a picture of where/how you use this on your 602? I have the VFD version the that lathe and would like an easy way to set it for threading. I know exactly what you mean about hard to see/read the dial on the compound.

Jim

 

[darkzero]

Nice, I like that. I use a dedicated preset bevel square but I think I'm going to have to make something similar. Thanks for sharing.

 

[RVJimD]

Will,

Thanks for the photo! It was late last nite when I saw the angle and my brain wasn't showing me a good picture of how it was used!

Jim