AL960b metric threads not quite right

[Wilson85]

Hello everyone,
i just wanted to ask others who own a AL960b if they have any trouble with their metric threads not being quite right?

i have tried to cut a 2.0mm pitch thread with the 30 tooth change gear installed. It is close but not right. My thread pitch gauge doesn't line up with what it cuts

I am cutting threads in a bit of a 'unconventional' way as I am threading up to a shoulder and the lathe doesn't have a foot break. I have an internal threading bar coming onto the back of the work and running it in reverse so I can leave my half nuts engaged.

If anyone can see what I am doing wrong, please tell me.
cheers

Anthony

[Stustoys]

Hi Anthony,

Think we are going to need a little more info.
Imp leadscrew?(I think some 960s had metric)
What change gears you have on and what gears you have selected on the QCGB.

Stuart

[variant22]

Imp leadscrew?(I think some 960s had metric)

Mine has an imperial leadscrew (unfortunately).

I had the issue you mentioned when I did not back the tool off for the reverse. The other time I experienced it was when I tried setting the compound angle to 29.5 degrees. Now I just square it up and plunge in at 0 on the compound angle. I get decent threads every time. PDW mentioned it might be that the compound angle needed to be double recommended 29.5 due to the position of the zero on the AL960b. I think that was what he said but he mentioned it in passing so I could be wrong on that.

[Wilson85]

Thanks for the replies gents.

My machine has an imperial lead screw. Found this out when I tried to use the thread dial.... A multi start thread.....

Yes I am plunging my tool at 0 deg, just taking it pretty easy when doing it. The thread looks nice.

I am only a hobby machinist. I do have a good mate that is a very good machinist that I will probably call upon to come over and have a look.

I cannot see what I am doing wrong.

[Michael G]

What change gears have you got? To get an accurate thread there needs to be a 127t gear in the train but some manufacturers cheat and use a 63t gear - it's close but...
If I understand what you have written so far, you can cut a thread but it is the thread pitch that is not right?

Michael

[KBs PensNmore]

I had this problem on my C2 mini lathe, thought it had a metric lead screw, but had the imperial one instead. Sticker for cutting threads said for metric screw 1.5 use XX XX gearing, that's OK on a metric lead screw, but when you get imperial it's a whole different set up. Maybe that is where your problem is?
Kryn

[Gavin Newman]

The AL960 has the "correct" 127 tooth change gear, at least mine does. If you can let us know the gear set up you are using and the gearbox settings I'll try it on my imperial AL960 and see what I get. How far out is the thread?

[variant22]

The AL960 has the "correct" 127 tooth change gear, at least mine does. If you can let us know the gear set up you are using and the gearbox settings I'll try it on my imperial AL960 and see what I get. How far out is the thread?

Gavin, whilst you're here can you let me know how you set the compound angle? Do you go to 29.5 or ~60? Maybe our graduations are different but mine never cut a proper thread at 29.5 degrees as measured on the compound.

[Gavin Newman]

Gavin, whilst you're here can you let me know how you set the compound angle? Do you go to 29.5 or ~60? Maybe our graduations are different but mine never cut a proper thread at 29.5 degrees as measured on the compound.

I set it at around 29-30 degrees on the scale (ie around 30 degrees to the cross-axis and 60 degrees to the bed direction). Having said that I've also cut threads with the compound left as-is and just using the cross slide.

These days I generally use the zero degrees method unless cutting deep coarse pitch threads.

[variant22]

I set it at around 29-30 degrees on the scale (ie around 30 degrees to the cross-axis and 60 degrees to the bed direction). Having said that I've also cut threads with the compound left as-is and just using the cross slide.

These days I generally use the zero degrees method unless cutting deep coarse pitch threads.

Thanks Gavin. I will have to give it another shot with the compound angle and see if I can work out what's up. 0 degree plunge has not failed me. More just an issue of curiosity.

[pipeclay]

Seeing that you don't have a great deal of experience it might be good if you describe in detail your method of cutting this thread.

[Maxi77]

Gday Anthony,
I have a AL960B. I often cut metric threads including 2.0mm. No problems, Just make sure the threading tool is exactly parallel to the job.
I also have the cross slide set at zero(parallel with bedways) and use the top slide dial. Light cuts.
Another trick threading to a shoulder is to thread under power and then turn off and use the Chuck key to manually rotate the chuck.

[Stustoys]

I also have the cross slide set at zero(parallel with bedways) and use the top slide dial.

I think you have that back to front.

Another trick threading to a shoulder is to thread under power and then turn off and use the Chuck key to manually rotate the chuck.

Something you really shouldn't do, more so in low gears, more so with 4 jaws. Every seen a chuck with one side of the square broken out? now you know how it happened*. Of course I do it , but mostly out of gear. Just don't say you weren't warned

Stuart

*Well so I was taught. But then at the time I was also using lathes with screw on chucks, maybe it was people undoing chucks that was half the problem?

[Maxi77]

Yes just realized back to front opps,
As far as using the key in the chuck, I don't see a problem for the amount I do it(upto a shoulder) Also of course make sure the key is in properly. Where only talking a couple of revolutons of the chuck. Probably where the jog button would come in handy

I have done a reasonable amount of theading(metric) and this is just what works for me

[pipeclay]

For the size of that bolt pictured you should of been able to machine to the end rather than manually doing it.