Lathe operation question

[tigtorch]

I am making an ER40 chuck for my lathe. It requires internal threads to be cut for the spindle threads and also for the nut (I am going to make my own nut, or at least try). This is a wonderful learning experience for me and so far I have succeeded in my efforts (haven’t started the nut yet). Both internal threads call for a relief cut behind the threads and the drawing I am following shows this cut with sharp corners. What is the proper way to do this? For the main body of the collet, behind the spindle thread location, I ground a piece of HSS with square corners on both sides (i.e. rectangular looking down from the top) with relief angles. I then plunged into the inside side wall using a boring bar to hold the HSS cutter. It worked but it chattered somewhat and I couldn’t help thinking maybe there is a better way to do this?

 

[Ray C]

Shoulder reliefs are cut with a grooving tool which are either square or round (for inserting O-rings). You can make them as you described or purchase inserts. It's usually a noisy proposition. BTW: When I cut shoulders for threading, I cut them the depth of the desired thread then, do the threading. When the tip first makes a scratch in the shoulder, you're assured proper thread depth. Do a few spring passes to clean-up the threads then, re-cut the shoulder to clean-up the scratch marks. Doing it this way ensures the bolt threads won't bang into a shoulder that's not cut deeply enough.


Ray

 

[tigtorch]

Thank you, Ray. I guess my instincts were correct, it just seemed to be complaining a little too much but after your response that sounds normal..

 

[Ray C]

Fortunately those cuts are usually not prolonged but, if it's really driving you crazy, try angling the insert up or down or raise it a tiny bit higher than center. A drop of cutting oil may help too. You might not get it perfectly quiet but you might tweak it enough to prevent your dog from hating you every time it sees the lathe turn on. -

Ray

Thank you, Ray. I guess my instincts were correct, it just seemed to be complaining a little too much but after your response that sounds normal..

 

[Tom Griffin]

The tool you use needs to have some side relief to prevent chatter. If you leave it square, there will be too much tool in contact with the groove and it will chatter. Try grinding 5º-10º of clearance on the sides and about the same amount of back rake on the top and see if that helps. It should look something like the cut-off tool in the crumby image below. Also be sure to use as large a boring bar as possible, keep the amount of tool overhang and the corner radii to a minimum. All of these things will help prevent chatter.

Tom

 

[Boswell]

wrong thread.

 

[P. Waller]

The relief is where the tool stops after a thread cutting pass when threading manually, it often has no other function..
A poor finish on the undercut surface will have no effect on function.

If threading to a shoulder on a part that will be screwed into a mating threaded hole where the shoulder is tightened against the surface the undercut removes any potential for incomplete threads to interfere.
Shoulder bolts are a fine example of this https://www.boltdepot.com/Product-D...MI24TD6L7K3wIVQsDICh3N6QMMEAQYCiABEgKHY_D_BwE

 

[Kroll]

If you get a change post couple pics,this sounds like an awesome project.Never threaded before but want to