Member postings for Mike Rolly

I really appreciate the informative and passing along of knowledge given in the post gents, it's a remarkable source of knowledge for me and I have been spending the best part of a day thread cutting using methods described from your posts..

I have no source for thread chaser at the moment, even Australian eBay (where I live ) has very slim pickings. The required chasers can be found on UK and US eBay though. Looks like I will be buying some from overseas in the near future. My knowledge of thread chasing was skim, I remembered some talk of them in 'Lathework- A Complete Course' by Harold Hall in his practice series 34. I had a good read of his use of chasers, he seems to be a big advocate of them.

I also went the under diameter method mentioned by a couple of posters and went to Trev67 advice of .618", also tried the 'zero/ zero method as mentioned by Clive Foster. Must admit, I was a little doubtful going off the dial readings to hit diameter due to backlash compensation and any tool tip variations. Very happy to see that I was within .003" ! All the stuffing around setting up 0-1" dials on mag bases ensuring that the stylus tip is square to the tool post was perhaps a bit unnecessary.

As I do not have chasers on hand I tried a few methods to flatten the vees on the crests, mill file, emery paper and used a honed sharp HSS cutter and a round nose finishing tool also in HSS. Out of all the cutting/ filing, the nicest threads came from the finish tool being used to shave the crest followed by 300 grit wet and dry. I used the wet and dry folded in half then let it run up along the threads on the roots, happy days.

Thanks very much fellers, I will be building up some thread chasers in the very near future and have become that little bet more better in thread cutting for precision requirements.

Regards,

Mike

Edited By Mike Rolly on 21/03/2016 10:06:33

Thanks again for the information, I priced up full form inserts in 24, 28 and 32 TPI this afternoon and received some sticker shock. I would probably be in for three new threading bars to hold the inserts in a tool holder on my BXA sized QCTP on my Colchester Master as well. FYI the master is running a 3hp, 3 phase motor controlled with a VFD.

I understand your explanation John and it makes sense with the added advantage of not buying new tooling at this stage. I do have ring gages in 24,28 and 32 TPI for the corresponding TPI for UNEF threads. I agree with the unsuitability of using a DTI for measuring, I do use a DI in a mag base for this duty.

I recall seeing a bloke showing me his thread cutting method some time ago. I doubt if I have the technique remembered correctly though. If my memory serves; it was based on using the crosslide to feed in on the thread, however I remember he still was using the Top slide? The thing that sticks in my mind was the cross slide movement along the Z axis. He was alternating between a feed of approx 2 thou in the +Z and then adjusting for backlash, feeding the slide 2 or so thou in the -Z . I remember thinking tat it seemed like a fair bit of mucking about with the cross slide and never tried it myself.

I do wonder though if there maybe some merit in this technique ? I imagine I have not remembered the sequence of ops correctly yet I imagine some one may have heard of a method that sounds vaguely familiar to this.

My thinking is maybe he is starting his threads on the Major pitch diameter and cleverly manipulating the cross slide in a way that gave him UNEF threads?

Thanks,

Mike

Thank you for the information regarding full form inserts, this is the first I have heard of them. Sure enough they are the answer to my threading form, excellent inserts to have in the UNEF pitches I am working with.

Thanks for showing me these gents,

Mike

Hello all,

I am wondering on how best to go about cutting a thread to dimensions in the thread tables is achieved.

Example: I wish to cut an external thread on a round of 4140 annealed steel.

The thread is 5/TH " x 24 TPI 60 degree UNEF Class 3A. Max major diameter is listed as .6250", the minor, .6178". No allowance given due to thread tolerances. With pitch. major listed as .5979" and minor as .5949". UNR minor diameter is .5754" for the external thread.

OK, all looks good on paper and I apply (attempt to) the necessary cuts to get my diameter to .6250", my major diameter. It's from here I have problems. I set my compound to the required 29.5 degrees and use a hand honed 6mm HSS toolbit with the 60 degree angle ground and it at the work piece on centre and perpendicular to the work piece.

Using the correct gearbox ratios I cut my thread with a dial indicator against the face of the toolpost to dial my thread depth in, then checked with 3 wires.

This is when I invariably end up with dimensions different to the listed table values, my pitch major diameter is always larger than the listed .5979" although I mange to hit the minor pitch diameter either dead on or within a thou or two.

I am baffled, my thread does not look like a UNEF thread form, my threads are more pointed than the UNEF thread that have a round crest.

What am I doing incorrectly here gents ? Do I need to run a flat file over my major pitch threads to round the crests and decreases size? I cannot see that being conducive to accuracy through. I have looked at purchasing a set of thread files to see if I can correct this diameter issue.

Although, I maybe doing something wrong in my execution, hence my request for assistance.

Thanks,

Mike