Thread: AL-250G Lathe - Threading Indicator Table

Can anyone out there shed some light on the threading options for this lathe?
The thread chasing dial comes with alternative gears, 32 teeth and 35 teeth. It is clear that for correct registration there are some specific thread pitches that require the gear to be changed.
The indicator table shows which specific pitches are associated with each gear. Simple eh???
Unfortunately the table also shows a dash in the "Z" (gear) column and shown against this is another range of pitches with an infinity symbol in the "Scale" column.
Surely this doesn't mean that if no gear is used it is possible to obtain registration in an infinite number of positions, that would be just plain silly.
So, what does it mean?
There is a photo of this Indicator Table in the group of photos for this lathe on the Hare & Forbes site.

I don't have one, but I had a look to see if I could figure it out.

If I had to guess what it means, I'd suggest any threads in the "dash" row can't be cut using the threading dial, only by leaving the halfnuts engaged (same as metric threading on an imperial lathe).

Then the threads in the "32" row can be picked up at any number on the threading dial, from 1-8.

And finally, the threads in the "35" row can only be picked up at "1" on the threading dial.

Hopefully someone else can confirm or deny, but that's what it suggests to me.

Like Jeckyl, I don't have one,but I interpret the table in the same way.

Thanks Jekyll & Hyde. I suspected that leaving the half nuts engaged might be the answer. Not what I wanted to hear, so maybe someone else has other ideas.
I will attempt to add an image of the indicator table. Maybe easier for others instead of going to the H&F site.

Not sure what its trying to say. But, don't forget that thread pitches either the same as the leadscrew or multiple thereof will be able to be picked up in any position.

For example, for a 3mm leadscrew you can use ANY dial position for a 3mm, 6mm 9mm etc etc pitch thread.

Perhaps that's what the infinity symbol is for?


Just looked at the pic you attached. I can't see anyway on their website what pitch the leadscrew is, I suspect its 2mm. Hence why a 2mm pitch can be engaged any location.

I think you may just have to have a play and see what it does.

Simon

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Originally Posted by Fatfettler

Thanks Jekyll & Hyde. I suspected that leaving the half nuts engaged might be the answer. Not what I wanted to hear, so maybe someone else has other ideas.

I actually had a look at the indicator table on my AL335 while I was out there before. Never looked before, as it's got imperial screws and I've only ever cut metric threads! Looks like I can't use the threading dial for 8, 16 or 24 TPI - just has a slash through that spot. So unfortunately, I think you might be out of luck.

To be honest though, I've never understood how you'd manage to pick up a thread with the dial anyway, I reckon I'd miss it every time with the jankiness of my halfnut lever, and I'd probably just leave the halfnuts engaged if I WAS cutting imperial threads...

Originally Posted by Jekyll and Hyde

To be honest though, I've never understood how you'd manage to pick up a thread with the dial anyway, I reckon I'd miss it every time with the jankiness of my halfnut lever

Nah, I think you'd be surprised. Just for fun, have a play with it with nothing in the lathe and see how it feels, keep the speed down to a few hundred rpm so you have a decent window to catch the mark you want.

Ok, update time.
I spent some time in the shed running a few threads and I now know what the indicator table is trying to say.
The thread pitches for the dash can be registered at any numbered mark on the dial, and also for the unmarked mid-points between the numbers.
This is true for both the 32 and 35 tooth gears. (I tried them both.)
I only confirmed this for 0.6 and 1.5 pitches but I am confident it will apply to the other pitches listed against the dash.
Out of interest I fitted the 35 tooth gear and ran a 1.75 pitch. The indicator table says to engage at the 1 mark, and I ran a scratch pass using this.
Registration for this pitch was definitely only possible at the 1 mark, so lots of waiting time. (That 1 is slowww to come around.)
I have left the 35 tooth gear fitted, as it will give me the greatest number of pitches. Only need to change it for 0.4, 0.8, and 2.0.
Jekyll, I am so glad that I don't need to leave the half nuts engaged.
Thanks for your replies guys.

Originally Posted by Jekyll and Hyde

To be honest though, I've never understood how you'd manage to pick up a thread with the dial anyway, I reckon I'd miss it every time with the jankiness of my halfnut lever, and I'd probably just leave the halfnuts engaged if I WAS cutting imperial threads...

Granted it sounds like its not much of an issue for you but maybe this will help someone else. It's possibly not jankiness in the lever. It can help to "time" the indicator rather than just tighten the gear up any old place. If you run the lathe, engage the half nuts, turn off the lathe, then set the indicator on 1 with the gear loose on the indicator shaft, engage that in the leadscrew and tighten the gear. This means the halfnuts drop pretty much straight in without hitting the top or flanks of the leadscrew. Maybe you know this and it is just jankiness

There may be some advantage to "advancing" the indicator a little so that you are past the crest of the thread and sliding down the trailing flank, but I thread that slow that I have never bothered to try it.