Crazy Threads...

John Hasler said:
The threading dial moves one tooth for each revolution of the leadscrew. Any integer will work but a multiple of two is most convenient. One would work ok.

Suggestion: count the TPI of your leadscrew and then set up to cut that TPI. Then the spindle and the leadscrew should be running at the same speed and you can start on any leadscrew thread.
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So I tried that, and got this hot mess...

IMAG0676.jpg
 
16 pitch = one tooth every .0625 inches. Metric threads, 1.75 pitch = one tooth every .6889 inches or 1 3/4 mm. which is awfully close to 15 pitch, (.0666).
Methinks you're cutting metric threads,

14 teeth on on the thread dial doesn't compute with Imperial threads, ....
 
So is it looking like the wrong lead screw?
 
I should note, when I got the lathe the metric gearing on the side we're engaged. and there is a half chipped tooth of that metric gear. suggesting the use of metric threading
 
I did try to measure metric threads on the less screw, nothing really lined up. hoe should I be measuring it tho?
When I measured the 8tpi on the lead screw, it was almost dead nuts 8 teeth I'm the inch on the ruler
 
Hukshawn said:
I did try to measure metric threads on the less screw, nothing really lined up. hoe should I be measuring it tho?
When I measured the 8tpi on the lead screw, it was almost dead nuts 8 teeth I'm the inch on the ruler
Click to expand...

Place a metric ruler along side the leadscrew and count 10 turns. How many mm did that measure out to? It should come out to a number like 20, 30, 40 etc. It will not come out to a partial like 33 mm. Supply a photo of this showing the ruler along side the leadscrew.

On the side of the headstock, you have the gear train, if one of the gears is off by 1 tooth ALL the threads and feeds will be off. Most lathes use a 127/120 gear set to change from Imperial to Metric. Can you supply a photo of these gears? Also a better picture of the plate showing the gears to be used.
Pierre
 
bfd said:
I agree half nut engagement. find a place where the halfnut engages solidly. it does not matter where it is. then shut the lathe off and with a felt pen make your own mark use this mark to machine these threads.
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Ok, but you shouldn't need to make a new mark. The thread dial has to have an adjustment for this. Mine has a friction clutch but there might be a set screw.
 
pdentrem said:
On the side of the headstock, you have the gear train, if one of the gears is off by 1 tooth ALL the threads and feeds will be off.
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Sure, but he'd still get good threads. They just would not have the intended TPI.
 
Hukshawn said:
BIG update...

so that nice perfect thread i did with the half nut engaged the whole time is NOT what i had the machine set up for... i had it set for 16tpi, put a thread gauge to it and the 15tpi gauge fits reasonably nice... so theres that.
also, i counted the teeth on the thread dial, 14...
also, someone asked if i get the same 1.75" per one revolution of the thread dial everywhere on the bed, yes, i tried about 10" away from my first attempt and got the same 1.75" per rev.

so lets recap... the lead screw is 8tpi, the thread dial is 14 teeth, i carved a "16tpi" on that piece of stock, the result is 15tpi...... soooooo.... i have no freaking idea whats going on. im wondering if this lathe is a Frankenstein...
Click to expand...
If the threading dial gear is really 14 tooth it has to be intended for a metric lathe with a metric leadscrew. If you have an 8 TPI leadscrew you need a 16 tooth gear. Those gears are easy to make though as they carry no load. I made the one on my threading dial out of nylon on the lathe using a dremel strapped to the toolpost and an indexer cobbled up with one of the change gears.

The 15 TPI is a puzzlement, though. Again I suggest that you set up for 8 TPI. Then everything is one-to-one and it should be easier to see what is going on.

[Edit] Could the previous owner have installed metric interpolating gears? I can imagine someone installing them so he can cut metric threads and then thinking that he should also install a metric threading dial. 15 TPI is real close to 1.75mm pitch.
 
You may have a Metric Treading Dial with an Imperial Lead Screw. A metric lathe I used, many years ago, had a tread dial with multiple gears, depending on the pitch you would change the gears to match. If I remember correctly a 14 tooth was one of them. Attached is a description of Threading Dial similar to the Metric Lathe I once used.
Metric Tread Dial.jpg
 
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