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Cutting a 365 tooth gear

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Engine Builder13/05/2011 16:41:53
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267 forum posts
I am having trouble getting my head around this problem.
Can anyone advise how to index 365 divisions with a dividing head with 60:1 ratio?
Plates with the following hole numbers are available but I could make up a custom one if necessary.
120, 100, 96, 80,72, 60, 22, 42, 91, 77, 49, 45, 38, 34, 32, 47, 46, 43, 42, 41, 37, 31, 29, 26, 64, 84
David
 
Andrew Johnston13/05/2011 17:14:08
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I don't think you can do it with the plates you have. For 'n' divisions of the circumference, and a 60:1 worm ratio, then the crank handle movement, 'a', for each index is:
 
a=60/n
 
or in this case:
 
a=60/365
 
Simplifying gives:
 
a=12/73
 
Since 73 is prime no further factorisation is possible, and since you don't have a plate with 73 holes, it would seem that you have lost your paddle! I think you'll have to make a plate with 73 holes, and turn the crank past 12 holes per index.
 
Regards,
 
Andrew
 
PS: I did the maths in a hurry while taking a break from the TIG welder, so check the maths before using it!
mgj13/05/2011 18:58:15
1017 forum posts
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What kind of head do you have? If its a complete VDH you can do it using the secondary worm and work in angular measure, which will save making a plate
Engine Builder13/05/2011 19:26:01
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267 forum posts
I am quite familiar with the process , I have done it many times, it's the question of how many holes in the plate and how many turns I am seeking help with.
David
JasonB14/05/2011 07:29:56
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David, I think you are a member of MHEM, have a look through Marv's (mklotz) usefull little programmes, I'm sure he has one for dividing heads - punch in the No of holes and your 60:1 ration and it will spit out whats needed. You can get to them from his profile.
 
Or treat yourself to a Division Master
 
Jason

Edited By JasonB on 14/05/2011 07:31:51

Engine Builder14/05/2011 09:22:36
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267 forum posts
Thank you Andrew
I agree with your calculation. I can easily make a 73 hole plate on the mill using coordinates and a little program I have to give me the positions.
 
Jason.
Thanks for that , I don't belong to MHEM allthough I do read the posts sometimes.
David
ady14/05/2011 10:18:35
612 forum posts
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For a newbie looking in here what just happened was.
 
He has a cog with 60 teeth on a worm with a dividing plate with a wee handle to crank the worm around.
Crank the handle around once and the cog moves forwards 1/60th.
 
He wants this 60 tooth cog to make a 365 tooth cog.
 
so we have 365/60= 6.0833333
This is the number of stops which each turn of his worm handle has to achieve.(gulp)
 
the problem is the 0.0833 we need it to divide into a whole number so that the holes in the division plate move the worm the correct fraction of 1/60 each time
 
1.0 / 0.08333 = 12 times looks good for hitting a whole number
 
So we expand the 6.083333 up to a divisible whole number of holes
 
6.083333 x 12 = 72.9999996 or 73 holes with a weensy error.
 
So each time he cuts a tooth he moves the division plate controlling the worm around 12 holes, locks the work, cuts a tooth and then moves another 12 holes round.
 
If he does this 365 times he will have made a 365 tooth cog from a 60 tooth cog.
 
Magic!
ady14/05/2011 10:21:00
612 forum posts
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...or should that be 364 times...
JasonB14/05/2011 11:11:31
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Dave, its in here somewhere on Marv's site.
 
If you have a DRO that should do 73hole PCD easily enough.
 
Or borrow a set of plates from a 90:1 8" or 10" rotary table, they a 73hole plate
 
J
Andrew Johnston14/05/2011 11:32:50
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Ady,
 
Your arithmetic is at fault, the answer is exactly 73, no error, weensy or otherwise.
 
Regards,
 
Andrew
ady14/05/2011 11:41:49
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Just testing
blowlamp14/05/2011 11:53:59
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Posted by JasonB on 14/05/2011 07:29:56:
Or treat yourself to a Division Master
 
Jason

Edited By JasonB on 14/05/2011 07:31:51

Isn't that bordering on CNC and therefore too easy?
 
Martin.
Stovepipe14/05/2011 12:17:06
196 forum posts
Ady,
Thanks for clarifying this. Although not interested in clock making, I found your consolidation of the procedure very interesting and informative.
 
(We are assuming of course that "Engine builder"'s hands haven't dropped off after his (say) 257th turn of the wheel, or RSI hasn't set in !!)
 
Dennis
JasonB14/05/2011 13:15:42
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Blowlamp, I'm keeping quiet on the CNC debate. Can't see what all the fuss is about I have to put up with in excess of three articles about trains in every issue of ME that don't really apeal to me
 
J
blowlamp14/05/2011 13:46:44
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1885 forum posts
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Posted by JasonB on 14/05/2011 13:15:42:
Blowlamp, I'm keeping quiet on the CNC debate. Can't see what all the fuss is about I have to put up with in excess of three articles about trains in every issue of ME that don't really apeal to me
 
J
You have responded and that is enough
 
Martin.
Richard Parsons14/05/2011 16:38:29
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645 forum posts
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Engine builder There is a very cheap answer to your problem. Get out your steel toe caped flippers, snorkel and mask and go ‘Skip Diving’. What you want is a nice length of steel case strapping! Measure it and allow about ½” (13mm) from each end. Now divide that distance by 366 and remember the result (Yes you will need an overlap when you join ends together). Now make a punch system with Two holes in it a little bit less (about ½ ‘smidgen’ or 8 ‘gnats’ that the than the remembered distance. Punch one hole near one end of the strip (remember the ½” allowance). Move your newly punched hole to the second hole and pop a nicely fitting pin into it. Repeat the move, pin and punching until you have all 366 holes punched.


Now join the ends with the 366th hole overlapping the first. You now have the outside of a hoop with 365 holes in it. All you need to do is knock up a centre for your hoop and an indexing pin and away you go. The bigger the hoop within reason the better and more accurate you will become.


My dad used this idea to help him drill some 151 rivet holes in a flattened steel loop some 15’ in diameter for a broken mill wheel.


It works


Dick

Engine Builder14/05/2011 21:14:46
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267 forum posts
Nice idea Dick, but if the holes were say 3/16" apart with 365 divisions you would end up with a hoop 21.79" diameter. Try fitting that on your mill!
Would work for a smaller number of divisions but the advantage of a dividing head is that any error in the hole spacing is greatly reduced by the worm reduction.
David
John Olsen15/05/2011 02:37:38
1294 forum posts
108 photos
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Well, he doesn't actually need a dividing plate with 365 holes, one with 73 will do the trick, and that might be more practical for the hoop idea, or for marking out and drilling, or coordinate drilling. It doesn't matter if the initial plate is a bit inaccurate, since it can be used, with a worm dividing head, to make a more accurate one. The eventual limit on accuracy becomes the errors in the worm and wheel, and any wander in the drill used to make the holes.
 
But rather than make a new dividing wheel every time an unusual number needs to be divided, I adapted my Vertex BS0 to allow differential dividing. With this adaptor and a set of standard Myford change wheels I can divide by any number that is ever likely be wanted, including the above 365. Vertex actually do make a differential dividing head, the BS3, but it is a bit big for most amateur machines, although I know someone who has one.
 
regards
John
Richard Parsons15/05/2011 13:54:13
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645 forum posts
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May be I should have explained more. OK the hoop is 21.79” diameter. Actually that is nice as I think you could snug it nicely into a 20” bike wheel. I would then make an extension which fits into the headstock of the lathe. There you can either use directly or make a dividing plate. It has another advantage; the ‘hoop’ can be used to make ‘things’ with fewer steps.
You could even use the method to make your 73 hole plate (Do not forgrt you will need to make 74 holes!) 
Dick

Edited By Richard Parsons on 15/05/2011 13:56:26

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