Help with thread cutting - cutting wrong pitch

[19brendan81]

Hi all,

I have an Al340-D that I have had for a while now. The last few times I have cut a thread on it I have noticed that the pitch is slightly out from what I intended. As an example. I just went down and set it up for a 19 TPI imperial thread, using the gear chart printed on the front of the lathe. After taking a scratch pass, I measured the threads and its 21 TPI.

Any ideas what I am doing wrong? I have the 60 tooth gear driving the 127 which drives the 57 on the lead screw (meteic 3mm pitch i think).

Photos refer. Cheers, brendan.

[jack620]

I’m counting 20 tpi. But that still doesn’t solve the issue!

[elanjacobs]

Stupid question, but have you checked the number of teeth on the gears? I know of one instance where the number marked was one tooth off the actual count.

[Reidy41]

I am trying to look at the photos but can't make a few things out.

My first thought is the 60 should be driving the 120 and the 127 driving the 57. It may be that way. Out of curiosity what does the 60 driving the 127 and the 120 driving the 60 achieve. If I did not have a headache I would do the maths.

For me the diagram on the lathe is not great.

Steve

[Reidy41]

I went to the hare and forbes manual and found this picture. I think you have your 120 and 127 around the wrong way.

https://images.machineryhouse.com.au...n%20Manual.pdf

Steve

[Zsteve]

have you got the 60 tooth running on the 120 or 127? looks like its on the 127.

[Ray-s]

Brendan, If you have a metric leadscrew then I would have thought you should have both the 120 & the 127 used to get the metric/inch conversion.
I think that would be the 60 driving the 120 with that ganged to the 127 and the 127 driving the 57?

The little drawing on the table (the one above the imperial table) isn't very clear as to the order of the 120 & 127 with a&b but I think that is right.
Ray

PS. Sorry to add to the confusion - a lot can happen while you are typing.

[SurfinNev]

Brendan, If you have a metric leadscrew then I would have thought you should have both the 120 & the 127 used to get the metric/inch conversion.
I think that would be the 60 driving the 120 with that ganged to the 127 and the 127 driving the 57?

Not a gear expert, but I tend to agree with this.

[19brendan81]

Fixed thanks fellas. User error was the issue (doh). I had both change gears connected to the 127. The 120 may as well have not been there. Once I introduced it into the fray I was bang on. Whilst I feel like a goose I'm also blaming the crappy diagram on the lathe.

[steran50]

I just had a look at the manual for this and it looks like it could have either an metric or imperial lead screw so you need to ascertain as to whether your leadscrew is metric or imperial. I assume you have a manual for it, but if not just go here https://www.machineryhouse.com.au/L179E# and then to downloads and download the instruction manual or simply here https://images.machineryhouse.com.au...n%20Manual.pdf If your lathe has an imperial leadscrew and your using it thinking that the leadscrew is metric then this would cause a pitch variation.

[SurfinNev]

The diagram is a little unclear.

[OxxAndBert]

Glad you got it sorted, and while you might feel like a goose - likely you’ve helped someone else in the process.

I’m assuming you’ve got thread pitch gauges and just used the calipers to illustrate the issue, but if you haven’t then I’d highly recommend splurging $10 on eBay to get some.
They’re so much easier than counting threads!!

Steve

[steran50]

I must have been posting at the same time.
Great to hear that you got it sorted out. I've done something like that in the past whilst thread cutting except my issue was I had the feed gearbox levers set wrong. Just out of interest how do you find the AL-340D lathe ?, I ask, because I bought a AL-340A years ago but the transport company dropped it in Bairnsdale and broke it so I never got to see or use it apart from the pictures.

[racingtadpole]

I’m just having a quiet chuckle that you’ve labelled the 57 tooth gear with a bow tie

[19brendan81]

I must have been posting at the same time.
Great to hear that you got it sorted out. I've done something like that in the past whilst thread cutting except my issue was I had the feed gearbox levers set wrong. Just out of interest how do you find the AL-340D lathe ?, I ask, because I bought a AL-340A years ago but the transport company dropped it in Bairnsdale and broke it so I never got to see or use it apart from the pictures.

Sorry for the late reply!

I love the lathe. I have only owned 2 lathes, and used maybe two more on top of that, but I was immediately machining to tighter tolerances when I got the 340D. I really like the DROs and the larger spindle bore compared to my small old kirloskar lathe. I don't get on it enough lately, life has been in the way. But every time I do i enjoy using it.

Brendan