MadModder
Gallery, Projects and General => How do I?? => Topic started by: doubleboost on August 30, 2015, 05:23:53 AM
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Hi
I have borrowed a 63 tooth change wheel to use as a conversion (metric to imperial)
This works very well
I want to make my own but can only get 64 teeth with my deviding head
As the 63 is half of a 127 (should be 63 1/2 )
How much difference would a 64 make
John
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Could you rig something to use the cog you have borrowed to do a straight copy?
I also could use a 63 probably the same as yours since I believe you also own a Harrison so if you figure it out I would be interested. Also I would be interested to compare the tooth counts for the gears you have now.
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Hi
I have borrowed a 63 tooth change wheel to use as a conversion (metric to imperial)
This works very well
I want to make my own but can only get 64 teeth with my deviding head
As the 63 is half of a 127 (should be 63 1/2 )
How much difference would a 64 make
John
Can't you make an adapter for the Sparey dividing head?
Regards, Matthew
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John,
What is your proposed gear train?
And what is your leadscrew pitch?
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How many holes do you have in your available dividing plates? As the difference you were asking 360degree divided by 63=5.714 Your thinking of cutting the nearest to that you can get with your available tooling 64teeth so 360 divided by 64=5.625 a difference of .089 of a degree.Which is less than 1/10th of a degree -so your pitch on your 64 teeth would be 1/10th of a degree closer than they should be ,not much,but be easier and more precise with the correct plate-take it you are going to do this on a mill.
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Well if you're comparing to a 127, 63 is half a tooth off, and 64 is a half a tooth off, both in opposite directions. So the amount of error is the same, just depends on whether you want the pitch slightly long or slightly short.
I'm not a mathematician, so apologies if this is simplistic and inaccurate.
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John can't you just strap the change wheel to the back of the dividing head, rig up a locking pin against the teeth and grind a form cutter to suite the teeth? no maths and an exact copy?
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127 by the way is half of 254, which is the usual approximation of the number of mm in ten inches. That's how it converts the pitches.
63 and 64 are both as close as each other to half of 127 (63.5). I don't think there's much to choose between them, unless there's some other reason one is better.
127 would be better than either, but then you get into a pretty big gear to fit the trains of some lathes. That's why they go to approximately half that.
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Can you not use the 63 gear to make a 63 ring for the divideng head ,
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The easiest way would to borrow the apropiate plate. Formula : 40/n -40/63 so a plate such as a 126hole plate would be ideal but any plate divisable by a number that can go into 63 would cut 63 teeth.Its approx 5/8turn of the crank
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John,
What size is the 63 teeth gear on the OD and bore details.
I have a box of old change wheels here from auctions and college clearouts, might just have one.
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as said by others, for a short thread I doubt it will make much difference.
lead screw pitch and other gear tooth numbers would be needed to calculate the resulting screw thread and thus the actual error.
alternatively, there are a few online gear train calculators about, might be easier to use one of them to work out what thread can be cut with a 64 tooth gear. must be one around for a Harrison
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Does any of your buddies have a cnc mill?
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Is not the thread pitch error going to be constant when expressed as a percentage of nominal? So 0.5 tooth out of 63 is:
(0.5 / 63) x 100 = 0.79% as an error in pitch so a nominal 1.0 mm pitch would be 1.0079mm etc :scratch:
So if you work out how long the thread that you are cutting is, you can easily see if the error is to much to tolerate.
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John, I think you can make a 63 hole indexing plate!
Just cut a plate to size and clamp your borrowed 63 tooth gear centred over the plate then drill an index hole as close as you can in line with each tooth of the gear. You now have a 63 hole divider plate. It will not be terribly accurate but if your dividing head is 40:1 your errors will be divided by that. If you are still not happy with the accuracy use your first plate to index and drill a second plate which will have errors 1/1600 compared to your first manual drilling.
John
(I hope I am right! :Doh:)
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John
There is a easy / expensive option fit a stepper motor to your dividing head get a division master or similar then you can divide any division or any degree you like
Stuart
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For odd number of teeth Iv used band saw blade round a ply former. Not very elegant but works for my simple needs
cheers
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John,
Is your dividing head the BS0 type with a 40:1 worm and wheel?
If you have a division plate with 29 and 33 holes you could use compound indexing.
You need an extra detent plunger to engage with the 33 hole hole circle. (I made mine with a piece of stiffish spring steel and rivetted a pin in the end. The division plate is not bolted - it is free to rotate and the extra detent (in the back of the plate) stops it rotating.
To get 63 divisions you index 4 turns and 19 holes on the 29 hole circle and then 14 holes on the 33 hole circle by moving the plate. This doesn't give an exact division - the maximum error is 0.027 degrees.
The downside is that the chances of getting something wrong are high unless you're very, very careful.
A better solution would be for me to drill you 63 holes in a plate on my CNC mill. If you want one tell me what OD and ID. It would have to be in 3mm MS because, other than 16mm boiler plate, that's all I have. 63 holes would be very tight on a BS0 plate so the holes would have to be a bit smaller - meaning a smaller pin.
Cheers.
Phil.
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Phil
Could not John use his DRO on his mill to do a PDC with 63 holes or any factor of the same say 21
Stuart
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Phil
Could not John use his DRO on his mill to do a PDC with 63 holes or any factor of the same say 21
Stuart
Stuart,
I could easily generate a table of coordinates for John to do that - I'd just need to know the pcd of the holes. (It would be easier for me than making a plate. :thumbup:)
Edit - See Below
Cheers.
Phil.
Coordinates for holes on 100mm pitch circle with the plate centre at 0,0
X Y
1 0.000 50.000
2 4.978 49.752
3 9.907 49.009
4 14.738 47.779
5 19.422 46.074
6 23.913 43.911
7 28.166 41.312
8 32.139 38.302
9 35.793 34.912
10 39.092 31.174
11 42.001 27.127
12 44.494 22.811
13 46.544 18.267
14 48.131 13.542
15 49.240 8.682
16 49.860 3.737
17 49.984 -1.247
18 49.612 -6.217
19 48.746 -11.126
20 47.396 -15.924
21 45.575 -20.564
22 43.301 -25.000
23 40.597 -29.187
24 37.489 -33.084
25 34.009 -36.653
26 30.190 -39.857
27 26.072 -42.665
28 21.694 -45.048
29 17.101 -46.985
30 12.338 -48.454
31 7.452 -49.442
32 2.492 -49.938
33 -2.492 -49.938
34 -7.452 -49.442
35 -12.338 -48.454
36 -17.101 -46.985
37 -21.694 -45.048
38 -26.072 -42.665
39 -30.190 -39.857
40 -34.009 -36.653
41 -37.489 -33.084
42 -40.597 -29.187
43 -43.301 -25.000
44 -45.575 -20.564
45 -47.396 -15.924
46 -48.746 -11.126
47 -49.612 -6.217
48 -49.984 -1.247
49 -49.860 3.737
50 -49.240 8.682
51 -48.131 13.542
52 -46.544 18.267
53 -44.494 22.811
54 -42.001 27.127
55 -39.092 31.174
56 -35.793 34.912
57 -32.139 38.302
58 -28.166 41.312
59 -23.913 43.911
60 -19.422 46.074
61 -14.738 47.779
62 -9.907 49.009
63 -4.978 49.752
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Phil
Could not John use his DRO on his mill to do a PDC with 63 holes or any factor of the same say 21
Stuart
21 won't work.
For one thing 21 is a standard hole sequence on dividing plate but the formulae is
40 / 63 which will not break down any lower.
We needs answers off John but he's having a lie in.
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Iff you mount the 63 gear to the indexing side then every 40 teeth drill a hole in the new plate will give you 63 .
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Thanks John
Had a brain fade , goes to show when you have a divisionmaster you forget the basics and just punch in the numbers , just like a calculator
Eg. Type all on one line into a calculator. 1 plus 1 divided by 2 you will get 1.5 not 1 as you expected
Reason they use BMDAS put brackets around the 1plus1 and you get 1 as you should
Moral do not trust them
Stuart
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Iff you mount the 63 gear to the indexing side then every 40 teeth drill a hole in the new plate will give you 63 .
But if you mounted a 63 tooth to the indexing side then every 40 teeth cut a tooth in a blank you'd have a gear.
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Thanks for all the comments
It would seem the 64 is no worse or better than a 63
As I am new to gear cutting I will have a go at cutting a 64
John
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John,
What size is the 63 teeth gear on the OD and bore details.
I have a box of old change wheels here from auctions and college clearouts, might just have one.
Thanks for the kind offer John I will have a measure up
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John,
Is your dividing head the BS0 type with a 40:1 worm and wheel?
If you have a division plate with 29 and 33 holes you could use compound indexing.
You need an extra detent plunger to engage with the 33 hole hole circle. (I made mine with a piece of stiffish spring steel and rivetted a pin in the end. The division plate is not bolted - it is free to rotate and the extra detent (in the back of the plate) stops it rotating.
To get 63 divisions you index 4 turns and 19 holes on the 29 hole circle and then 14 holes on the 33 hole circle by moving the plate. This doesn't give an exact division - the maximum error is 0.027 degrees.
The downside is that the chances of getting something wrong are high unless you're very, very careful.
A better solution would be for me to drill you 63 holes in a plate on my CNC mill. If you want one tell me what OD and ID. It would have to be in 3mm MS because, other than 16mm boiler plate, that's all I have. 63 holes would be very tight on a BS0 plate so the holes would have to be a bit smaller - meaning a smaller pin.
Cheers.
Phil.
Thanks for the offer that would be the ideal solution a direct plate
I will go with the 64 tooth gear and compare the results to the 63
Then decide from there
John
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You can only try John if you havnt got the correct plate for your D/Head if it was me I would go slightly deeper on the depth
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That'll be 24 hole plate, index every 15 holes John.
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well I wood just mack a adapter to fit the 63 tooth onto the divider and set up a detent on the mill bed :)
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I will be very disappointed John if you do not make a 63 hole indexing plate. :coffee: You make the first one then make another from it and each time you do that the errors are averaged until you have the accuracy you require.
Thats what Henry Maudslay would have done! :bow:
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Yes John as has been said 15holes on a 24plate it is 5/8turn you want if your going to put up with a 64tooth gear,or multiply 5/8 by whatever you have( 5/8x3=15holes24plate)5/8x4=20holes 32plate(5/8x8=40holes 64plate) etc-Good Luck