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View Full Version : Making a worm and gear for a Sheldon lathe



Bill Pace
06-09-2012, 09:38 PM
Seems the hot topic lately is gears ... so I thought I would share a bit of how Lane and I managed to keep my M model 13x36 Sheldon that Im rebuilding from being useless with a badly worn apron worm and its mating gear.

The worms teeth, being hardened, seemed OK, but Sheldon made their worms with a 'built in' key, and it was about worn away. The gear was almost to the point of the teeth breaking off completely - just worn out! Both had to be replaced...

From our figuring, they were 18dp, and while there are a lot of combinations of worms/gears out there from Browning, Boston, etc - there wasnt any with 18dp! And obviously, there wasnt any to be found elsewhere.

The worm had a double start 5tpi thread, which meant we would have to be able to cut 2 1/2tpi - and neither of our lathes had that capability.... Sooo, we just gonna have to cut a conventional 5tpi. After carefully taking the measurements off the original worm, we used a piece of 1 1/2" O-1 steel. Lane chucked it up with enough exposed to get the left hand worm and the hob threaded. This was pretty straight forward Acme thread cutting. Finishing the thread, bored the end portion that was to be the worm out for the 7/8" lead screw to slide in, and cut that portion off. Taking the hob portion over to the mill and using an indexer cut 5 flutes with ball end mills, carving out the profile needed to cut, then doing some stoning and filing for some nice cutting teeth, we heated it up and gave it a bath in oil.

Back to the worm - we had to figure out how to get a key in it. Sheldon had a practice of making the key integral to the worm - using a round broach with a slot in it?? Decided to broach a conventional 1/8" key way in the worm and then mill a little 'pocket' on each end of the key slot to accept "ears" (like a South Bends key) I then made up a key to snugly fit in this manner. That worked really well.

The gear blank was made up with a piece of cast iron (as was the original) Had to kinda guess at the outside dimensions, it was so worn - and to get a curved pocket. Mounting the blank in the indexer we used a slitting saw to 'gash' the 40 teeth so the hob could get something to get its first bite in. Then mounted the gashed blank in a 5C spin indexer so it would rotate and eased the hob in. After a bit of a jerky start, the hob settled in and started making a rather nice profile of teeth - turned out rather nicely.

I had already finished the repair of the apron and it just needed the worm slipped in and the lead screw run through. Turning it by hand it appears to work beautifully (still got lots more to do to run under power!)

Some pics ---

Didnt get any pics of the threading ...

Heres the hob just out of the mill ready to be dressed - stoning, filing, etc. (when the gear was finished , we looked at the hob and it had lost one tooth...)

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear2.jpg

The gear blank in the indexer getting 'gashed' (its at a slight angle - I cant remember what we came up with)

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear3.jpg

The hob gnawing away at the gear blank.

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear4.jpg

Then the finished worm and gear with the old one

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear5.jpg

sasquatch
06-09-2012, 10:42 PM
Thanks for posting this, and congrats on a great rebuild of that lathe!!

Optics Curmudgeon
06-10-2012, 12:40 AM
Well done, but be aware that since the original was a 2.5 TPI double start and the new one is a 5 TPI single your apron feeds will be half of what they were originally.

Bill Pace
06-10-2012, 01:25 AM
your apron feeds will be half of what they were originally.

Yes, we discussed this and decided that would be a minor inconvenience compared to the alternative....

oldtiffie
06-10-2012, 02:38 AM
Seems the hot topic lately is gears ... so I thought I would share a bit of how Lane and I managed to keep my M model 13x36 Sheldon that Im rebuilding from being useless with a badly worn apron worm and its mating gear.

The worms teeth, being hardened, seemed OK, but Sheldon made their worms with a 'built in' key, and it was about worn away. The gear was almost to the point of the teeth breaking off completely - just worn out! Both had to be replaced...

From our figuring, they were 18dp, and while there are a lot of combinations of worms/gears out there from Browning, Boston, etc - there wasnt any with 18dp! And obviously, there wasnt any to be found elsewhere.

The worm had a double start 5tpi thread, which meant we would have to be able to cut 2 1/2tpi - and neither of our lathes had that capability.... Sooo, we just gonna have to cut a conventional 5tpi. After carefully taking the measurements off the original worm, we used a piece of 1 1/2" O-1 steel. Lane chucked it up with enough exposed to get the left hand worm and the hob threaded. This was pretty straight forward Acme thread cutting. Finishing the thread, bored the end portion that was to be the worm out for the 7/8" lead screw to slide in, and cut that portion off. Taking the hob portion over to the mill and using an indexer cut 5 flutes with ball end mills, carving out the profile needed to cut, then doing some stoning and filing for some nice cutting teeth, we heated it up and gave it a bath in oil.

Back to the worm - we had to figure out how to get a key in it. Sheldon had a practice of making the key integral to the worm - using a round broach with a slot in it?? Decided to broach a conventional 1/8" key way in the worm and then mill a little 'pocket' on each end of the key slot to accept "ears" (like a South Bends key) I then made up a key to snugly fit in this manner. That worked really well.

The gear blank was made up with a piece of cast iron (as was the original) Had to kinda guess at the outside dimensions, it was so worn - and to get a curved pocket. Mounting the blank in the indexer we used a slitting saw to 'gash' the 40 teeth so the hob could get something to get its first bite in. Then mounted the gashed blank in a 5C spin indexer so it would rotate and eased the hob in. After a bit of a jerky start, the hob settled in and started making a rather nice profile of teeth - turned out rather nicely.

I had already finished the repair of the apron and it just needed the worm slipped in and the lead screw run through. Turning it by hand it appears to work beautifully (still got lots more to do to run under power!)

Some pics ---

Didnt get any pics of the threading ...

Heres the hob just out of the mill ready to be dressed - stoning, filing, etc. (when the gear was finished , we looked at the hob and it had lost one tooth...)

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear2.jpg

The gear blank in the indexer getting 'gashed' (its at a slight angle - I cant remember what we came up with)

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear3.jpg

The hob gnawing away at the gear blank.

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear4.jpg

Then the finished worm and gear with the old one

http://i22.photobucket.com/albums/b301/pace1980/Sheldon%2013x36%20lathe/WormGear5.jpg

Bill and Lane.

Nice job nicely done.

I can see all the detail in the hob which I presume is an acme form (pic 1).

I can see the dividing head tilted by the helix angle while the hob teeth gaps are preliminarily gashed with a woodruff/key-seat cutter at each indexing point (pic 2).

I can see that the gear blank is tranferred to a "spindexer" with zero tilt and that the helix angle of the hob will match that of the gear (blank) so I guees the gear blank and the Spindexer spindle were free to rotate and were driven by the hob so that the gear blank was "free-wheeling" as the tooth form of the gear was cut (pic 3).

I also notice that Lane has a rotating base under his machine vice (pic 3) when so many here say/think that rotating bases are a big "no-no" and should never be used but should be scrapped. Perhaps given the example set that some of the more strident and "me too" members need a cold shower as well as a re-think at least.

lane
06-10-2012, 09:57 PM
Yes Tiffy I would not use a vise with out a swivel base . When I want to turn it for some reason I have no time to wast. Get It Done and stop fooling around. Time is money even when you are playing.

oldtiffie
06-10-2012, 11:46 PM
Sorry Lane I wasn't taking a shot at you at all as I really do respect what you do and how you do it.

I leave my base on the vise so that I can find it and as its there I use use it.

That was a nice use of the ubiquitous "Spindexer" that so many ingnore or "rubbish" but I find mine very useful too.

The vice (with base) and a "Spindexer" in it are a very useful combination as you've shown very clearly.

Congratulations to you and Bill for a very fine job and for the really good pics

lane
06-11-2012, 08:12 PM
Sorry Lane I wasn't taking a shot at you at all as I really do respect what you do and how you do it.

I leave my base on the vise so that I can find it and as its there I use use it.

That was a nice use of the ubiquitous "Spindexer" that so many ingnore or "rubbish" but I find mine very useful too.

The vice (with base) and a "Spindexer" in it are a very useful combination as you've shown very clearly.

Congratulations to you and Bill for a very fine job and for the really good pics

Do not be sorry at me .I have been fussing at people for years about why the take the swivel base off their vise and then having to spend extra time putting it on when needed. If you are going to worry about 1 more inch in room under the spindle You NEED a bigger machine are smaller parts its that simple.