What do I need to make this thread?

Djl338

Djl338

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It’s 8 tpi square thread, never did one f these before so not sure how to grind a tool to cut it. Does it need to be angled or a particular angle?
Thanks
295468
 
Yes, the tool has to be the proper width, and have side clearance adequate for the spiral angle of the thread on the side advancing into the thread, and can be made almost vertical on the trailing side. The angle on the advancing side should be several degrees in excess of the spiral angle.
 
How do you determine the angle on the advancing side?, is it a trial and error method or is there a formula. Using the compound at 29° or is this a different way of threading all together? Tried searching around and getting conflicting confusing info
Thanks!
 
Make it a degree or two more than the helix angle
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also , make your tool a tad too narrow. Set compound at 90. advance it to get width just right.
 
Ok, that’s what I need thanks! Nice to learn a new skill/technique
 
Djl338 said:
How do you determine the angle on the advancing side?, is it a trial and error method or is there a formula. Using the compound at 29° or is this a different way of threading all together? Tried searching around and getting conflicting confusing info
Thanks!
Click to expand...
 
The compound angle would be straight in for a square thread, which is 90 degrees to the axis; 29 degree thread is the acme thread, not a square thread, for it, the compound is set at 14 1/2 deg. If the thread you are dealing with has an angle to the axis, likely it is Acme, not square. If it is square, you can take a piece of stock the root diameter of the thread, and take a vee threading tool and trace a threading cut on it, and that will be the spiral angle; yes, there are formulas, but the "seat of the pants" approach works fine too; determine that spiral; angle, and add several degrees to it and grind the leading side of the tool to that angle, and as I previously said, the following angle can be nearly vertical and have sufficient clearance on it; if it is a square thread, feed straight in with the compound for each successive cut, for an Acme thread, feed in at 14 1/2 degrees with the compound.
 
The 1st thing you would need is an optical comparator to check the thread and grind your tool.
 
benmychree said:
The compound angle would be straight in for a square thread, which is 90 degrees to the axis; 29 degree thread is the acme thread, not a square thread, for it, the compound is set at 14 1/2 deg. If the thread you are dealing with has an angle to the axis, likely it is Acme, not square. If it is square, you can take a piece of stock the root of the threadi, and take a vee threading tool and trace a threading cut on it, and that will be the spiral angle; yes, there are formulas, but the "seat of the pants" approach works fine too; determine that spiral; angle, and add several degrees to it and grind the leading side of the tool to that angle, and as I previously said, the following angle can be nearly vertical and have sufficient clearance on it; if it is a square thread, feed straight in with the compound for each successive cut, for an Acme thread, feed in at 14 1/2 degrees with the compound.
Click to expand...

Well, it doesn’t seem to have any angle to it, and I like the sound of a “seat of the pants” approach. I have a has parting tool that is about the same width I was thinking of working with as a starting point, and have lots of 4140 5/8”stock to practice with (outside diameter). Probably not purchasing an optical comparator, the magnifying glass seems a bit more practical for my level. Thanks for the great explanation
David
 
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