The widest gear spread this lathe comes with is 30 and 40 tooth gears. With the 40/40 combo it can do 4 TPI, so without special gears the best you can do is 3 TPI.
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PM1236T: Are custom change gears available?
- Thread starter macmccaskie
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- Sep 16, 2019
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I just remembered I have a 7 X 22 grizzly that needs to be sold, I'll play with that and see what it can do. Otherwise I'll seriously un-stubborn myself and go with 3 TPI.
A tip of the hat to Ischgl99, most likely height adjustment will be infrequent.
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- Aug 3, 2017
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Making gears is easy enough with a rotary table and a milling cutter, so if the machine would take it, a 10 tooth gear would work. (or a 12 and 48).
EDIT: THe module of the gear is probably pretty 'off the shelf' so you could probably pick up the gears on mcmaster.
@macmccaskie
So you want to make a spiral ....
I do not really know the physical limitations of your external gears fitting together on your lathe. So my numbers here maybe unreasonable. But I have been developing this spread sheet to calculate the TPI and FEED rates for several lathes and with various exchange gears. So I took @Ischgl99 comment and played with the center exchange gear ratios for you while using the max and min that he mentioned for the top and bottom.. @Ischgl99 and I worked out some TPI for his lathe which I think are the same as the PM1340GT.
Assuming you set the levers to the largest thread A-1 then put the 30T at the top and the 40T at the bottom. Then in the center position use the 120T to touching the top and put in a 60T to touch the bottom gear. This will yield a 1.5TPI. In my spread sheet I can put in any external gears that you have or might want to have and generate the TPI and FEED rates very quickly. However, in general you want to put the smallest gear at the top and the largest that will fit at the bottom and still reach the exchange gears in the middle. In between for the exchange gear, the largest at the top and the smallest at the bottom.
Tell me what gears you have available or might have and I will generate a table for you of all possible combinations of gears to get all possible TPI values. If the 127/120 comes apart then you will only need to find one gear to put together with one of the 120/127 gears. If I figure that right then you only need to find a smaller gear that can still be reached.
By the way, if you use the 127 instead of the 120 the TPI becomes 1.417. If you can get things to fit with a 127T/40T change gear arrangement you will drop the TPI down to 0.945TPI. At 120T/40T at the center it works out to a nice even 1.0000TPI.
Dave L.
So you want to make a spiral ....
I do not really know the physical limitations of your external gears fitting together on your lathe. So my numbers here maybe unreasonable. But I have been developing this spread sheet to calculate the TPI and FEED rates for several lathes and with various exchange gears. So I took @Ischgl99 comment and played with the center exchange gear ratios for you while using the max and min that he mentioned for the top and bottom.. @Ischgl99 and I worked out some TPI for his lathe which I think are the same as the PM1340GT.
Assuming you set the levers to the largest thread A-1 then put the 30T at the top and the 40T at the bottom. Then in the center position use the 120T to touching the top and put in a 60T to touch the bottom gear. This will yield a 1.5TPI. In my spread sheet I can put in any external gears that you have or might want to have and generate the TPI and FEED rates very quickly. However, in general you want to put the smallest gear at the top and the largest that will fit at the bottom and still reach the exchange gears in the middle. In between for the exchange gear, the largest at the top and the smallest at the bottom.
Tell me what gears you have available or might have and I will generate a table for you of all possible combinations of gears to get all possible TPI values. If the 127/120 comes apart then you will only need to find one gear to put together with one of the 120/127 gears. If I figure that right then you only need to find a smaller gear that can still be reached.
By the way, if you use the 127 instead of the 120 the TPI becomes 1.417. If you can get things to fit with a 127T/40T change gear arrangement you will drop the TPI down to 0.945TPI. At 120T/40T at the center it works out to a nice even 1.0000TPI.
Dave L.
These are module 1.25 gears. I posted a link earlier where he can get gears close to what he needs, but they will need to be modified to fit. These are not off the shelf gears as far as I have found. To make them would get pricey if he did not already have the tooling to do that, but he then would have the tools for future projects.
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- Aug 3, 2017
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Ah, I missed that!
Fortunately he has a lathe and could bore out the center if that is all there is! A file gets you the keyway if necessary (or a shaper, or a broach & arbor press/etc), so I suspect shopping for gears is the hard part
You’re welcome, hopefully the 3 tpi turns out to work fine and you don’t need to make the 1 tpi
Yes, the website I posted is painfully slllooooooowwwwww. LolAh, I missed that!
Fortunately he has a lathe and could bore out the center if that is all there is! A file gets you the keyway if necessary (or a shaper, or a broach & arbor press/etc), so I suspect shopping for gears is the hard part