- Joined
- Feb 13, 2017
- Messages
- 2,128
To get true metric conversion on an Imperial lathe will require a 127 and 120(or 100) tooth pair. Any gear will work so long as it is this tooth count. Where things get complicated is the tooth size and/or form that will mesh with what you have on your machine.
Size is determined by Diametrical Pitch (DP, US) or (more likely, metric) Modulus. It either matches. . . or it doesn't. Tooth form is a matter of pressure angle. On straight cut spur gears, 14-1/2 degree will run a little quieter, 20 degree is stronger. There's always a Pro-Con in any situation. Metric gears, Modulus, generally tend to be 20 degrees. Generally, not always. Different PAs will almost mesh, but not close enough to trust for threading. And certainly not well enough for power transmission.
There are some combinations that will give "almost" metric threads. 44 and 52 are a common combination for my Atlas/C'man machine. I don't use them, for several reasons. Foremost because I have another machine that does do true metric threads. And I have a plastic pair for the Atlas that works well enough the little I need it. But the gears are easy enough to acquire if I did want them.
Such a combination will cut almost metric threads that are usable for fasteners and other short threads. But they are not recommended for long threads such as "all thread". A metric 1.0mm pitch is 25.4 TPI. If you were to cut 25.3 or 25.5 threads you would cut smooth enough to use on a foreign car. But for a lead screw on something, it might or might not work. It would depend on how many threads were in the follower.
Threading gears do not transfer power, they are only "timing" gears. As such, many people use plastic gears that are 3D printed. But unless you have a 3D printer and proper gear software and know how to use it, compensating someone else for making them will cost about the same as buying steel gears from a vendor. And truth be known, I would prefer metal timing gears. Just old school, me.
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Size is determined by Diametrical Pitch (DP, US) or (more likely, metric) Modulus. It either matches. . . or it doesn't. Tooth form is a matter of pressure angle. On straight cut spur gears, 14-1/2 degree will run a little quieter, 20 degree is stronger. There's always a Pro-Con in any situation. Metric gears, Modulus, generally tend to be 20 degrees. Generally, not always. Different PAs will almost mesh, but not close enough to trust for threading. And certainly not well enough for power transmission.
There are some combinations that will give "almost" metric threads. 44 and 52 are a common combination for my Atlas/C'man machine. I don't use them, for several reasons. Foremost because I have another machine that does do true metric threads. And I have a plastic pair for the Atlas that works well enough the little I need it. But the gears are easy enough to acquire if I did want them.
Such a combination will cut almost metric threads that are usable for fasteners and other short threads. But they are not recommended for long threads such as "all thread". A metric 1.0mm pitch is 25.4 TPI. If you were to cut 25.3 or 25.5 threads you would cut smooth enough to use on a foreign car. But for a lead screw on something, it might or might not work. It would depend on how many threads were in the follower.
Threading gears do not transfer power, they are only "timing" gears. As such, many people use plastic gears that are 3D printed. But unless you have a 3D printer and proper gear software and know how to use it, compensating someone else for making them will cost about the same as buying steel gears from a vendor. And truth be known, I would prefer metal timing gears. Just old school, me.
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