Where to get worm and gear 1:40 or 1:60 for indexinng?

[PekkaNF]

I have a small rotab. I alsko have some indexing disk 10-49 holes. They do not really fit together.

I would very much leave my rotab as it is and would like to build something different for indexing.

Next project is screaming of micrometer type dial, and I'm very tempted to try to line the dial on the lathe and index the mandrell. Probably I will construct a direct indexing feature when I will update the lathe AC motor and VFD. Meanwhile I could cobble up something at the tail end of the lathe, but would very much to use proven brass gear / steel worm construction.

So, where I could get a ready made steel worm and brass gear for indexing apparatus?

I would like to have 1:40 or 1:60 ratio to put the indexing plates into a good use.

I probably could go nonstandard ratio and use stepper motor, driver, and indexer but prefer mechanical solution here.

Any pointers? I tried to google, but found some industrial gear units and then some toys.

Pekka

[velocette]

Hi Pekka
You can cut a worm wheel on your lathe using a spiral flute tap in the chuck an suitable gear blank mounted on the tool post.
I have read this on a forum somewhere but for the life of me the location eludes me now.
You have to calculate from the thread pitch the diameter, then add the thread depth
Eric

[PekkaNF]

Thanks

I have been reading ocassionally about this type of free hobbing and even tried it once. It's pretty labor intensive for end result.

http://pounceatron.dreamhosters.com/shop/hob/index.html
http://bedair.org/Worm/Worm.html

Some did not have this good results.

If these parts would be available at reasonable quality/price I rather would buy them. If I had proper material and worm (trapezoidal bar?) ready I probably would give it a try.

Found this one, but pretty expensive:
http://www.hemingwaykits.com/acatalog/Compact_Indexing___Dividing_Attachment.html#aHK_202135


Pekka

[chipenter]

Straight spure gears work with a largeish worm at an angle ,the angle is related to the diamiter of the worm my one can use myford change gears up to 45 teeth , or http://www.beltingonline.com/gears-racks-366/worm-wheels-374/bronze-0-5-2-0-mod-474/ .

[PekkaNF]

Thank you, that shop good, but shipping of a gear pair would cost £32.50, which is ridiculous. Most UK mail order companies that weight would be about 6-8 GBP.

Pekka

[drmico60]

Hi Pekka
I would like to make two comments:
1. I would not rule out using plastic gears. These are cheap and light. They are not as  strong as metal gears but an indexing unit the usually has some facility to lock the spindle so the gears are under no stress during machining.
2. I would not worry to much about helix angle of the worm. As long as the  worm and gear mesh then one turn of the worm will advance the gear by one tooth. This means that you can use an ordinary spur gear for one component and make a worm to match which is a simple turning job. If you make the worm a good size then the helix angle will be small anyway.
I hope this helps.
Mike

[Pete W.]

Hi there, Pekka,

Have a look here:

http://www.hpcgears.com/n/products/4.worms_wheels/worms_wheels.php

Usual disclaimer, no connection except that I have used them (for helical gears) in the past.  They have an extensive stock range and will also quote for specials. 

[PekkaNF]

Thank you very much. This helps a lot. I have something realistic to toy with.

I read Gears & Gear Cutting (Workshop Practice Series 17)  again and I thought that I'm sorted and then I found this:
http://www.hpcgears.com/pdf_c33/27.48-27.60.pdf
 

Nope, It didn't cut it. Soo... I eyballed... and questimated and module 0.8 looks about right
http://www.hpcgears.com/pdf_c33/15.10-15.13.pdf
For a small stepper motor driven indexer, where accuracy is important, but not much forces are expected. Unless they have no-thank-you p&p price looks right too.

For middle size lathe I would need MOD 2 would clear spindle - and my wallet! Way over 100 GPB. That would require careful consideration.

They have a "budget" model too:
http://www.hpcgears.com/pdf_c33/21.5.pdf
Price is right, but really MOD1 would be too small in 1:40 gear ratio. Even nonstandard biggest 50 tooth wheel would not clear even the smallest lathe spindle I have.

How much compromize really I would be looking at MOD1 60 teeth straight spur gear coupled with MOD1 1 start worm?
http://www.hpcgears.com/pdf_c33/23.28-23.33.pdf
OK, I know putting it to oil bath and using it for circular milling is out of question, but when it comes to indexing would I loose on accuracy?
If I get it right worm should be at lead angle (MOD1 - 3°35´) to wheel? MOD1,5 looks like a good possibility.

Pekka

[chipenter]

I would go for a 90 tooth wheel gives you 4 divisions on the indexing per rev , and greater accurarcy and more divisions with youre plates .

[PekkaNF]

Thanks. Now I only need to aproximate what I want

I basically have two more immediate needs: To index few dials for lining (probably something 40-100 divisions) and simple division plate on lathe (maybe 60 or 24 division?).

If I get it right, it does not make much difference between 40/60/90 tooth wheel and and a single start worm when it comes even divisions?

I have a set of indexing plates, arms and handle for 1:40 ratio (Plate #1 has 15, 16, 17, 18, 19, and 20 holes. Plate #2 has 21, 23, 27, 29, 31, and 33 holes. Plate #3  has 37, 39, 41, 43, 47, and 49 holes). Therefore I was rushing into 1:40 division.

I have to check the divisions, but I don't think I'm missing any small divisions, no matter which 40/60/90 ratio I take.

Pekka

[steampunkpete]

If you haven't already chosen a supplier, Davall Gears at Hatfield is one I've used in the past. Down-loadable pdf catalogues of stock gears can be found here:

http://www.davall.co.uk/stock-gears/davall-stock-catalogue/gears/

Good luck and happy machining,

Peter

[RotarySMP]

www.Mädler.de is also a good source and has a good website.