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Old 02-13-2018, 02:45 PM   #1
AFCarbon15
 
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Default Old Indexing/Dividing Head (Rebuild) Missing Parts

I picked up this old Brown and Sharpe #249 indexing / dividing head in pretty good shape but missing some parts. I can't find any info on it. No pictures or manuals of this model or one very close. I don't even know what the parts are called. Since I didn't have a dividing head prior to picking up this one, if it were complete and functional, I won't have any issues finding uses for it.

I had to make the mount for the worm gear and a mount to hold it. I'm working on an adapter plate to hold a 4" chuck. I'll probably add some T slots if there's room. If not, I'll just add some extra threaded holes. Not sure if I will make or buy a index plates and a lock to engage the plate. Will figure out a better turn wheel / handle when I figure out the plate.

Hopefully this link works.
https://plus.google.com/u/0/collection/01UyRF


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Old 02-13-2018, 08:36 PM   #2
Buchanan
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Dividing plates are easy to make on the dividing head its self. You only have to approximately accurate with drilling as when you put the plate on the crank side any error is reduced by the worm ratio. You could make your self a master plate with a hole drilled every, say, half turn of the crank. A 60 :1 worm will give you 120 holes.
Then work out how many holes you need to index to get the number of divisions you want, and round up or down to a whole number. Make sure you do not get an accumulating error. This will produce an acceptably accurate division plate, 120 holes times 60 turns gives you 7200 divisions= one revolution. That is 0.0026 inch on the circumference of a 6 inch diameter gear. So you holes on your dividing plate will have a maximum error of 26 thou if your holes are on a 6 inch circle. When you use this plate on the dividing head you will reduce that error again by 60 , so you will have an error of max 0.00004 inch on a 6 inch diameter part. it should pass.
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Old 02-20-2018, 05:48 PM   #3
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Quote:
Originally Posted by Buchanan View Post
Dividing plates are easy to make on the dividing head its self. You only have to approximately accurate with drilling as when you put the plate on the crank side any error is reduced by the worm ratio. You could make your self a master plate with a hole drilled every, say, half turn of the crank. A 60 :1 worm will give you 120 holes.
Then work out how many holes you need to index to get the number of divisions you want, and round up or down to a whole number. Make sure you do not get an accumulating error. This will produce an acceptably accurate division plate, 120 holes times 60 turns gives you 7200 divisions= one revolution. That is 0.0026 inch on the circumference of a 6 inch diameter gear. So you holes on your dividing plate will have a maximum error of 26 thou if your holes are on a 6 inch circle. When you use this plate on the dividing head you will reduce that error again by 60 , so you will have an error of max 0.00004 inch on a 6 inch diameter part. it should pass.
Thanks for the reassurance. I didn't do the math on paper but quick numbers in my head it seemed like I would be reasonably accurate. I haven't counted the teeth, but it's just over 6", and 6TPI, so quick math tells me that's over 18" Circumference. Roughly 108 teeth around (error on the low side) One rotation of the handle will move one of those teeth. So guessing roughly 120 to 1 ratio. I think I'm even safer than your "reduce that error again by 60" I'll find out. While it will take some time, I have a few feet of 6" 3/16 plate to make some index plates out of.

I haven't checked my runout yet, but it should have a little adjustment for that anyway. Here she is with a temp handle but the chuck is mounted.

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