Thread: home made worm drives - clever

Thought this was clever - there are a few different versions of it on youtube and other web pages.

http://www.youtube.com/watch?v=J0o3W4_LRBw

http://www.astronomyasylum.com/gears.html

What puzzles me is that neither of these people seem overly concerned about the diameter of the wheel - one actually says that you just keep cutting until it works.

Will have a go.

Bill

Bill I was shown this on MEM forum some months ago and tried it on a scrap piece of aluminium that I had and yep works well.
Pete

Thanks for this Bill, very interesting and would never have thought of using a tap.
Kryn

Very clever. It would probably be worth turning a concave groove close to the radius of curvature of the tap drill size first and then taking if from there. It should reduce the amount of metal that needs to be removed.

Originally Posted by steamingbill

What puzzles me is that neither of these people seem overly concerned about the diameter of the wheel - one actually says that you just keep cutting until it works.

In this case they are only using the worm as a reduction gear and don't care about the ratio. For something like a rotary table where the ratio is important because that is how you keep track of where you are for fractions of a degree you would have to hob things properly. For a bit of hobbing action, try this -

http://www.woodworkforums.com/showth...78#post1661078

Michael

When this was discussed it was suggested to gash it first then the ratio is correct. The guy was making a gear for a specific uzd
Pete

Sent from my GT-P5110 using Tapatalk

I did a lot of research into hobbing gears for worm screw drives, a couple of years ago. My intention is to build a rotary table. Some of the best information came from Telescope sites. If you cut your own hob you can make it identical to the worm shaft.

Here is a nice rotary table build from MadModder. Worm gear cutting starts at Reply #19.

http://file:///L:/Documents/Workshop...le%20Build.htm

Dean

Originally Posted by Oldneweng

I did a lot of research into hobbing gears for worm screw drives, a couple of years ago. My intention is to build a rotary table. Some of the best information came from Telescope sites. If you cut your own hob you can make it identical to the worm shaft.

Here is a nice rotary table build from MadModder. Worm gear cutting starts at Reply #19.

Dean

No link Dean...actually i've noticed a few of your post seem to be missing links....

Ew

Originally Posted by Michael G

In this case they are only using the worm as a reduction gear and don't care about the ratio. For something like a rotary table where the ratio is important because that is how you keep track of where you are for fractions of a degree you would have to hob things properly. For a bit of hobbing action, try this -

http://www.woodworkforums.com/showth...78#post1661078

Michael

Its not the ratio that bothers me, although I can see that is important, its the fact that one of them implies that the cuts will be in exact synchronisation after going 360 degrees around the wheel, ie once you have hobbed the teeth to 359ish degrees around the wheel then the next "cut" " will line up exactly into the very first cut.

Isnt this going to be a bit like knurling, where if you are not careful you can just make a mess if things dont line up right after you have gone around 360 degrees ? (have only read about it not done any knurling yet)

Have to test it in shed.

Bill

Originally Posted by steamingbill

... its the fact that one of them implies that the cuts will be in exact synchronisation after going 360 degrees around the wheel, ie once you have hobbed the teeth to 359ish degrees around the wheel then the next "cut" " will line up exactly into the very first cut.

That would be a concern if you only had a small number of teeth on the worm gear, but given the pitch of the tap and the number of teeth on the gear it is probably not going to be a problem in reality - as the guy said you go a bit deeper (that is make the PCD smaller) until it works.

Michael

Originally Posted by Ueee

No link Dean...actually i've noticed a few of your post seem to be missing links....

Ew

I wonder if links to other forums are filtered.... I seem to remember they were at some stage.

Ray

Did anyone pick up on the lathe spindle speed? It increased speed from the initial cutting through to the finish full depth cut. I did not notice adjustments made for speed change ,but it may have been edited out.

The spindle speed change was not to be confused with the frequency of the noise from the turning tap lobes. The duration of noise from each lobe strike increased as it cut thread ever deeper, in the wheel as thread became deeper.

The material chipped like brass but I don't recall any mention being made of the material, but as a worm wheel, I imagine it had to be softer than the worm shaft.

Grahame

Im thinking that the cutter / wheel should be positioned at full depth and then the wheel fed in along the x axis, otherwise the tooth count around the perimiter of the wheel wont divide properly. That said, does anyone know how to calculate the pitch circle of a worm wheel? Is it just treated as a normal gear calculation at the root of the gear?

Originally Posted by Ueee

No link Dean...actually i've noticed a few of your post seem to be missing links....

Ew

Whadja talking bout?

Are you suggesting I am missing a few links?

I wonder if links to other forums are filtered.... I seem to remember they were at some stage.

I reckon there is some filtering going on, but it may actually be a bit closer to home. Iv'e been working long hours. That's my excuse and I'm.......

Dean

Originally Posted by Grahame Collins

Did anyone pick up on the lathe spindle speed? It increased speed from the initial cutting through to the finish full depth cut. I did not notice adjustments made for speed change ,but it may have been edited out.

The spindle speed change was not to be confused with the frequency of the noise from the turning tap lobes. The duration of noise from each lobe strike increased as it cut thread ever deeper, in the wheel as thread became deeper.

The material chipped like brass but I don't recall any mention being made of the material, but as a worm wheel, I imagine it had to be softer than the worm shaft.

Grahame

The spindle speed changed several times up to a much faster speed than at first. I had the impression that it was a variable speed lathe and I thought I saw a hand movement towards the headstock at one stage.

Its not the ratio that bothers me, although I can see that is important, its the fact that one of them implies that the cuts will be in exact synchronisation after going 360 degrees around the wheel, ie once you have hobbed the teeth to 359ish degrees around the wheel then the next "cut" " will line up exactly into the very first cut.

Isnt this going to be a bit like knurling, where if you are not careful you can just make a mess if things dont line up right after you have gone around 360 degrees ? (have only read about it not done any knurling yet)

Have to test it in shed.

Bill

Quite correct Bill, but don't imagine I am an expert. I have not put any of this into practice. A lot of the research I have done discusses this very problem. Some people have said that at the start you get an extra tooth, which will disappear when full depth is achieved. This is due to the different PCD's as the thread depth increases. Michael has put it in a slightly different way. A whole extra tooth would depend on the number of teeth on the circle. The disk should be calculated with the PCD at the full depth of the tooth I believe.

I have ideas to produce a 72 tooth gear so I get 5 degrees per rotation of the handwheel on a rotary table. This seems to be a nice middle point.

Dean