Thread: aL336-D

Firstly, Welcome.

Secondly, Just to be sure, you say tpi, does the lathe have an imp leadscrew? if not you cant use the dial(I think the new ones are imp but they also bought in metric ones I believe)

Thirdly, are you getting the tpi you expect?

What tpi are you cutting? with something like 24tpi(any muliple of the leadscrew pitch so 4, 8, 16, 24 etc) you should be able to "pick up anywhere"

Stuart

p.s. are you saying you can pick 15tpi ok?

G/day Clive, I have a AL336, a few years ago I was attempting to cut a thread on a 3 MT arbor, I put the arbor
in a 5 MT adapter and put that into the spindle and turned to the required diameter.
I changed the gears to suit the required thread engauged the half nuts and did a light cut, I was nearly ready to disengage
when the lever disengauged by itself ummm ?
The problem was that the half nuts run out of thread on the lead screw, as soon they hit the unthreaded part of the leadscrew
they were forced apart and damaged.
Those half nuts have never been the same since that day and if I use that lathe to cut a thread I now start the cut
1/2" or more away from the job as sometimes they don't engage fully and this gives a different start position.
You will be able to work out if this is the problem with yours just by noting if the half nut lever travels the full distance,
often I will engage the lever and it may only go half way and the carriage takes off and I have to quickly disengage
and have another crack at it.
One day this problem might even make the to do list

shed

Originally Posted by Stustoys

Just to be sure, you say tpi, does the lathe have an imp leadscrew?

G/day Stuart, they have an 8 TPI leadscrew.

Originally Posted by Stustoys

Firstly, Welcome.

Secondly, Just to be sure, you say tpi, does the lathe have an imp leadscrew? if not you cant use the dial(I think the new ones are imp but they also bought in metric ones I believe)

Thirdly, are you getting the tpi you expect?

What tpi are you cutting? with something like 24tpi(any muliple of the leadscrew pitch so 4, 8, 16, 24 etc) you should be able to "pick up anywhere"

Stuart

p.s. are you saying you can pick 15tpi ok?

Stuart, it does this on any thread.. As I said it has only just started doing this. I cut threads two weeks ago absolutely normal, but last week I was cutting a 32 tpi and it started tearing the thread off, looke like a rat had been chewing it.
i have been in this trade for 52 years and cut hundreds of threads but this is the first time I have ever seen anything like it. As already mentioned it is an imperial leadscrew.
the dial is just a shaft with a gear on one end and a dial on the other, no wear and everything was tight, no slop anywhere.

I would think if you have no problem with the halfnutsi when left engaged that there probably isn't a problem with them.

You say that you have checked the dial and the Gibson,not sure what part the Gibson would play in this scenario.

When you checked the dial have you disassembled the dial to check that nothing may of come adrift,have you also checked to make sure that the gear wheel on the dial is engaging correctly on the lead screw.

One other thing that might be useful to test may be to take the carriage to wards the tailstock,engage the halfnuts and apply finger pressure to the dial and see if there is any slippage.

May be another test could be to put a piece of stock in, set for thread cutting,engage the halfnuts,as the tool commences cutting shut off the power withdraw the tool and take not of where the dial is,leave the nuts engaged and reverse and then repeat and see if the dial is in the same spot as the previous,if not this should indicate that the problem is somewhere in the dial.

I think I might have solved it, I'll try it this evening Andrew post the results.

Originally Posted by clive hugh

last week I was cutting a 32 tpi and it started tearing the thread off, looke like a rat had been chewing it.

Shouldnt you be able to pick up 32tpi with your eyes closed? e.i. its got nothing to do with the dial, its somewhere else. But with any luck it looks like you've found the problem.

Stuart

No, not that. I thought maybe the gears had too much backlash but it wasn't the cause. I wonder if the lever mechanism where it engages has moved/slipped and is causing it.
i havent checked the 24 and 48 tooth gears to see if the keys have sheared but that would have caused problems with ordinary turning which is fine. Plus I would have heard something like that, I'm deaf but I'd have heard that.

Not something simple like left a 127t gear in the train instead of the 120t or something?
Michael

Originally Posted by Michael G

Not something simple like left a 127t gear in the train instead of the 120t or something?
Michael

I checked it but I'll go and have another slower look.

Originally Posted by Michael G

Not something simple like left a 127t gear in the train instead of the 120t or something?
Michael

Buggeration! Silly old git! It is a 24 driving a 127 driving a 48. Some idiot looked at the 24 and the 48 and left the 120 in the train. So it was the 120 driving the 48.
Many thanks, i think I'll go and beat myself around the head a few times.
clive

So how could it cut the correct pitch with the gear train set up incorrectly even if you did not disengage the half nuts?

Originally Posted by Techo1

So how could it cut the correct pitch with the gear train set up incorrectly even if you did not disengage the half nuts?

OK, first, check my edit of the previous post, it requires a 24driving a127 driving a 48. I had the 127 in there but the final drive of the 48 was off the 120.
i had cut the 32 tpi and it was horrible but it fitted the nut but not well. Next I cut a 3/8 -16 but this was done with the nut constantly engaged. It turned out well, again it was a short length thread for a nut so possibly with a longer thread it might not have fit. Possibly the fact that the 127 was in there made it possible. I will put the correct gears in place tomorrow and see how it goes.
i was under the impression that the leadscrew is imperial. The normal train of gears for regular turning is 24 driving 127 on the same shaft as 120 which in turn drives the 48.
In this'll train the feeds are shown as imperial, ie .002 per revolution.
this train stays the same for metric threads, it's only on the imperial threads you take the 120 out of play so maybe it is metric. Tomorrow I'll check that too.
If I wasn't confused before I am now