Another screw cutting question

[firebird]

Thank you Arnold.

I mentioned earlier that i had a few TCT, these are the ones



Some are gold coloured some are grey. Some of the gold ones are marked KC730

Some of the grey coloured ones have what looks like screw cutting profiles on 2 of the points but don't look like 55° or 60° but I'm not sure how to measure the angle of such a tiny tip



Also the are not flat across the top but have turned up points.



Any ideas??

Cheers

Rich

 

[arnoldb]

Hi Rich

I don't use TCT - so below is more of a collection of thoughts than a true answer...

All the TCT tips I've seen for threading looks like the bits here on Chronos's site (scroll down a bit) - they have well-defined threading tips, and come as either left or right handed for all faces, and in 55 or 60 degrees for the tip.

The angles on the grey tips you show are definitely far smaller than 55 degrees that would be used for Whitworth thread form and looks to be hand-ground. On the other hand, the angles appear to be larger than the normal 20 degrees that would be used for ACME threads...
I'm basing this on the photo; an equilateral triangle (as is the overall shape of all of the tips you show) has angles of 60 degrees at all corners. With the cut-outs on the tips at just below half the full tip angle - i.e. leaving more than 30 degrees carbide - and less than 55 degrees, I don't know of any threading standard suited to that.

The gold tip you show held in your fingers with the raised profile - well, it's difficult to judge its true cutting angle, but it appears more for general use than thread cutting. From the profile shown, it would not cut at a true 60 degrees, and anyway, it would be pretty useless for threading close to a corner with a flange next to it - as is needed so often.

As to measuring the angle for threading tips (and I use these to grind up my own HSS tips) - you need a thread angle/fishtail/centering gauge. I just grind up my own HSS bits and use the appropriate gauge (55/60 degree) to check the angle for the toolbit - as well as setting the tool up in the lathe.

<Off topic>
And lastly, I'll openly admit that, while I've cut quite a couple of internal and external threads of Metric, Whitworth and ACME forms, I don't think any of them would stand up to "true" quality control tests... - I only needed them to be close enough to work; which they did and still do. IMHO there's too much of a theoretical boo-hah raised by people (most of whom never show their own examples), when it comes to threading on the lathe - which scares off a lot of very capable folk from trying it in the first place. It's not difficult at all, and entirely acceptable results are possible for anyone that's willing to put some effort in to try.
</Off topic>

Kind regards, Arnold

 

[firebird]

Hi Arnold

That's a very good reply. I'll stick to general turning jobs with the tips, I have already made a holder for them and they work quite well. As for your off topic comment I think your bang on the button. I really appreciate all the info that has been posted, very interesting but a bit beyond me. If I can cut a male and female that screw together that will do for me for now.

Cheers

Rich

 

[moconnor]

Hello Arnold,

If you are referring to the advice and responses that I have tried to provide here, first I did show examples of the threading tools that I made and use. And second, I tried to provide information that is not easy to find in any one place and answer questions to the best of my ability. In no way was I trying to make the topic of single point thread cutting more difficult. On the contrary, I was trying to make it simpler by providing the formulas that will give you the numbers to control the process. I have taught machine tool technology for more than ten years and have been a machinist and toolmaker for almost thirty years. In that time I have taught hundreds of students how to cut threads on a lathe.

I am really sorry if I have wasted anyones time here with all this "technical boo-hah" raised by someone who did show some examples and was only trying to help.

An appropriate quote by Lord Kelvin: "When you can measure what you are speaking about and express it in numbers, you know something about it; and when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind."

Kind regards,
Mike

 

[Maryak]

Mike,

Perhaps you have fallen for the same trap that most of us have experienced from time to time. "The written word is subject to misinterpretation when not accompanied by facial expression or tone of voice."

I am sure Rich is grateful for everyone's input to his threading question and I am sure that Arnold was not casting aspersions at individuals who have contributed.

Relax mate, it's a hobby and we do it for fun.

Best Regards
Bob

 

[arnoldb]

Thank you Bob.

Mike, please accept my apologies. I in no way meant to offend you or anybody else who contributed - input is always welcomed.
I think I used inappropriate wording when I said "technical boo-hah".

Threading can be a very complicated subject - so much so that I feel a lot of hobbyists are scared away from trying it in the first place just by the sheer amount of information and methods available to do it.

Like many operations, the biggest hurdle to overcome in threading is to just try it for the first time and getting passable results on the workpieces and seeing how the lathe behaves while doing it. After that initial start, all the other information and accuracy comes into play and will actually be understood better.

As to the quote from Lord Kelvin - Yes, I agree, but then again we all have to start somewhere with no knowledge at all and learn from the ground up. It becomes a marriage of theory and practice; no amount of theory will guarantee a practical result, and without a practical workpiece to try and apply the theory to one would get nowhere either, as there is then no way to even try to measure it

The main thing is that nobody should be scared to try to cut those first threads - it's really not difficult.

Kind regards, Arnold

 

[firebird]

Hi Mike

I work in the motor trade and one thing you learn very early on is NEVER REFUSE INFORMATION! While some of what you have posted is a bit beyond me at the moment it has been printed out and put into a screw cutting folder. I'm Quite methodical in that way, I have folders for everything I do. I love my computer but I do prefer printed hard copies in my workshop. These folders are referred to regularly. As I progress and my skills improve I may well need that vital bit of information. So please, if anybody posts a question and you have information you are willing to share do not hesitate to post it.

Cheers

Rich