Acme Thread Worm Gear

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croyleje

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Hello Everyone,

I am trying to find a worm gear that will mesh with an acme thread lead screw. Does anyone know if there is such a thing or any ideas on what would work? The acme lead screws are 1/2 - 10 and I want to add a handle to move the carriage out of the way faster then just running the power feed or turning the leadscrew handle. To do this I need a worm gear that will mesh into the acme threads so I can quick traverse the length with just a few turns of the hand wheel. The best idea I have come up with so far is using a 10 pitch spur gear then use a 1/2" endmill and cut a slight concave in the teeth so it will contour to the shaft better and that along with the 14.5 degree PA on the spur gear and the 29 degree included angle on the acme screw I am thinking it should mesh pretty well but I don't have any 10 pitch gears around and they are not the cheapest things so I do not want to buy one unless I have high confidence it will work. So I was hoping someone could point out where my logic is wrong or verify my concept? Well any help would be greatly appreciated.

Thank you,
Jason
 
Are you are trying to create a rapid traverse on a lathe carriage, if so how much does it weigh?
 
Similar concept yes but it is actually an horizontal milling machine and the table weights a good bit but weight is carried by slides but I am guessing its around 50 pounds. The amount of weight needed to move the table is minimal.
Jason
 
croyleje said:
Hello Everyone,

I am trying to find a worm gear that will mesh with an acme thread lead screw. Does anyone know if there is such a thing or any ideas on what would work? The acme lead screws are 1/2 - 10 and I want to add a handle to move the carriage out of the way faster then just running the power feed or turning the leadscrew handle. To do this I need a worm gear that will mesh into the acme threads so I can quick traverse the length with just a few turns of the hand wheel. The best idea I have come up with so far is using a 10 pitch spur gear then use a 1/2" endmill and cut a slight concave in the teeth so it will contour to the shaft better and that along with the 14.5 degree PA on the spur gear and the 29 degree included angle on the acme screw I am thinking it should mesh pretty well but I don't have any 10 pitch gears around and they are not the cheapest things so I do not want to buy one unless I have high confidence it will work. So I was hoping someone could point out where my logic is wrong or verify my concept? Well any help would be greatly appreciated.

Thank you,
Jason
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Jason,

If I understand what you are trying to do, you want to drive the lead screw via a gear engaging the threads. The lead screw engages a nut which moves the table by turning the lead screw. You cannot cause a lead screw to turn by means of a gear which engages the lead screw thread.

A ball screw, by virtue of its greatly reduced friction, can be run in reverse but an a conventional lead screw has too much friction and the mechanical advantage is wrong. There are some high pitch multi-start lead screws which can be run in reverse (driven rather than driving) but they would not be suitable for moving a mill table or lathe carriage as the distance/turn is quite large.

A better approach would be to use something like half nuts on a lathe to disengage the table from the screw. A rack and pinion gear can then be used for your rapid traverse.
 
I believe he is trying to use the lead screw as a rack. I may be misunderstanding as well, however.
 
That is correct Jester966 the acme leadscrew will be the rack and I need a gear that will mesh with the threads on the leadscrew like a pinion. I know it has been done before I just can not find one or find the information needed to make one. I was just hoping someone might know where I could get one but if not I fairly certain this logic works to make one. Acme thread 29 degrees included angle (helix angle unknown) then I could cut a 14.5 degree PA spur gear 10 pitch with a matching helical angle that matches that of the acme thread helix angle. Then after it is cut use a 1/2 end mill to contour the teeth to leadscrew.
 
I seem to remember seeing or reading about using a lathe as a hobbing machine, with a tap as a hob. Once engaged, the spinning tap rotates the workpiece. If you get a 1/2-10 ACME tap, this method would yield a perfect gear to mesh with the lead screw.
 
Don't know how you would do it on a lathe, but I have done it on a mill. Once you get the blank made, it is bolted to a 1-2-3 block or something similar so it can rotate as the tap cuts it.
 
That youtube i sware theirs a video on nearly everything :)


Stuart
 
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