Need Help With Rotary Table

[DougD]

I have a 12" rotary table. I would like to get it operational. It only (only is the BIG operational word) needs the drive worm and worm shaft. The table is in good shape for its age. It does not have a name plate on it so I do not know what brand it is. Economy is large factor, so I do not want to have the worm made. From looking at various worms available through a google search, the price is very reasonable if I can determine the correct one to get. Although the RT is larger than I need, it was given to me by a friend who has since passed away, which adds to my motivation to restore it to operation.


From what I can surmise I need to get a drive worm to match the RT driven worm gear, and then fabricate a shaft for the worm.


I looked in the machinery handbook, and in an old Boston Gear catalog for information on worm gears, and realized that it was way, way over my understanding. From the information given/needed for the gears and the formula's to derive them I was totally lost. I believe to be able to look up or order a worm, I need to know the gear "throat" diameter, lead angle, and the axial, circular, and diametrical pitches. I might as well be trying to decipher a foreign language.


I have attached pictures of the RT, the RT top, and a sketch (not to scale) of the RT dimensions. The hole for the worm shaft is 1.5". The threads are right handed. The number of teeth is 90. Measuring the angle of the teeth at 86 degrees, the tooth angle should be 4 degrees. On the sketch, I have attempted to sketch the tooth width as well.


I am hoping someone can point me in the right direction as to the gear I need or from the dimensions I have can give me the above so I can try and order the necessary worm. If any other dimensions are needed, I would be happy to attempt to get them. Thanks in advance for your help.

doug

 

[Uglydog]

I believe I understand your desire to save this RT.

I cut my first spur gears a few months ago and hope to progress to cutting a worm. Regardless, I gotta do the simple stuff first.
I've been reading several texts on cutting gears. Including several which were way beyond my understanding.
I wish I would have started with: Gears and Gear Cutting by Ian Law
http://books.google.com/books/about/Gears_and_gear_cutting.html?id=5opONwAACAAJ
If you do an engine search for the title you'll find some pretty cheap original copies available.

Likely you will get some expert help here at HM, regardless I believe its good to understand the principles.
Even if you never intend to cut a gear, I'd encourage you to understand the principles before ordering, as you are more likely to get it right the first time.
While I fumble with the math, it is all doable.

Daryl
MN

 

[Smithdoor]

The worm is not hard to make on lathe
You to find out the DP or MOD and the angle of the worm gear so you can set up the lathe to cut the worm
From the photo you just missing a few part that can be easily made the shop
From the photo it looks like a old Palmgren they work great.

Dave

 

[Uglydog]

Dave,
You are likely 100% accurate identifying that it is easily made in a home shop by a HM.
I am still working through the concepts.
Do you have specific recommendations for me and DougD?
I am just beginning Laws cutting chapters.
I haven't read anything on the actual cutting of worms yet as I've been focusing on spur gears and math.

DougD, would you consider cutting your own worm if we can get the guidance here at HM?


Thank you,
Daryl
MN

 

[Smithdoor]

Yes I give more detail but I Need to know more on the worm gear
Odds are the worm is less than 1" od and the 1 1/2 is eccentric for smaller worm

Dave

 

[DougD]

Daryl, thanks, I agree on having the understanding in helping ordering the right one the first time.
I will look up laws book.
Dave thanks, although I have to admit one of the "scariest" statements to me is "ah it's easy"!! Lol That has got me into trouble many a time. That said, I have not been afraid to do regular threading, but had "assumed" not to be ready for worms.
Daryl, yes I would be willing. However, in restoring the operation of the RT I was not planning on turning the worm, but yes I was planning on turning the shaft fo the worm.

 

[Uglydog]

Perhaps with Daves help and other wizened contributors/moderators we can learn to do worms.
Are you game to consider it?
Worst case we are out some time and some steel, and have created precision scrap to show for it.

Daryl
MN

 

[chips&more]

The worm is not hard to make on lathe
You to find out the DP or MOD and the angle of the worm gear so you can set up the lathe to cut the worm
From the photo you just missing a few part that can be easily made the shop
From the photo it looks like a old Palmgren they work great.

Dave

Yes correct, it’s not a hard lathe job. BUT, make sure your lathe can cut the pitch. A lot of lathes are limited at the coarser pitches…Good Luck, Dave.

 

[DougD]

Dave, I too assume the worm will be somewhat smaller than the 1.5 opening for the shaft in the casting. This one has no provision in casting for the back of the worm shaft to be adjusted for engagement like some of the Bridgeport RT's I have seen. By the opening there are two machine bolts. I assume one will lock in the shaft for in-out movement, and assume the other will provide some movement of the shaft for engagement. That, the assumptions was as far as I got as at this point I had been concentrating on the worm.
doug

 

[DougD]

Daryl, as an "old dog" I can attest that I CAN be taught new tricks. And, I have never been afraid to produce "scrap".
As I said in my original post, from my initial search, it appears the worms are readily available and reasonable in cost
($20-$35). But the problem is in knowing the correct one.
Dave (chip&s'more) my lathe is a SB heavy 10.

doug