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250 divisions on a indexable super spacer ?

garychipmaker

Cast Iron
Joined
Dec 2, 2005
Location
ia
Hi Is it possible to get 250 divisions on a indexable super spacer with a 90 to 1 ratio. this is for a infeed gear on a cylindrical grinder It has some teeth that are worn. I would make a new gear but the chart only goes to 100 divisions for my indexer. I did make a new racheting pawl and it is working for now. the gear is only 7.086 in diameter so the teeth are very fine Thanks
 
use the SS to make 10 divisions (every 36 degrees) holes in the face.

Use the SS to make 25 divisions per rotation, advance to blank to next hole,
and go around again.

Lathe, rinse, repeat 10 times.
 
Or if you are into making index plates - Yuasa's 90:1 jobs would do 100 hole new plate using 27 on the 30 hole plate, then use 36 on the new 100 hole job to get the 250
 
250 = 2 x 5 x 5 x 5.

90 = 2 x 3 x 3 x 5

So the 90:1 worm has the first two factors of 250: 2 and 5. You need two more 5s or 25. Those two fives can be in a 25 or 50 division plate. Or you can use some other scheme to get them.

Most sets of plates tend to have numbers that introduce additional prime numbers to the mix so you see things like multiples of prime numbers like 7 or 13 (3x7 = 21, 2x13 = 26, etc.) So even if you have a set of plates, you probably do not have a 25 or 50 division ring. There are several ways to make a 25 or 50 division plate if you don't have one.

You need to understand that if you use a hole ring on a plate on a indexer or RT, any errors in that ring of holes will be REDUCED by the worm factor when you use it. So if your hole circle has errors of 1 degree, a big error, then the divisions made with it will have errors of no more than 1/90 degree or less than 1 minute.

You can lay it out by hand and just drill as accurately as you can. With care you can have errors of less than 15 minutes (1/4 degree) in that plate which, when you use it, will give you an accuracy less than 8 seconds. That is probably more accurate than your worm.

Another method of making a plate with hole circles would be to make a scratch plate as accurately as you can (above) and use that plate to make a second plate which will be 90 times more accurate. If you are going to use the plate on the indexer or RT, there is little or no reason to carry this process any further.

So, the answer is YES, you can make a 250 division part, but it will take some extra effort.

This will work for ANY number of divisions and for any worm ratio. You can, with a little work, have hole plates with any number of holes that are just as accurate as your worm gear is. The magic factor is having a good, high quality worm gear set.
 
That's another good way of getting those two additional fives.

Actually you could use any plate that has a multiple of 5 in a ring. 5, 10, 15, 20, 25, 30, 35, 40, etc. Just the number of holes for each successive position changes.



Or if you are into making index plates - Yuasa's 90:1 jobs would do 100 hole new plate using 27 on the 30 hole plate, then use 36 on the new 100 hole job to get the 250
 
Yep - less work (than 100 holes) would be a new 50 hole plate (using 1 turn plus 24 on the 30) - then 18 on the new 50 for the 250 divisions
 
I have a 60:1 indexer with 4 plates and it'll do loads of divisions but still I'll get called on to do a real oddball sometimes. For a one-off I'll just stick a paper disk to a plate with white glue, it holds fine and comes right off too. There's usually a blank area near the rim that the index pin can reach, draw up in cad a ring of circles the size of the pin at the appropriate diameter and an outer circle the size of the index plate diameter, print at 1:1, cut out and stick it on.

You just eyeball the pin location over the dots, at 90:1 you'd have to be way off for it to matter. For this job I'd use 9 holes in 25. Don't forget you're moving 9 holes so set your sector arms at 10.
 








 
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