Dividing Head Question

[BigBoy1]

I've just gotten a dividing head and have been playing with it, learning how to use it. For one of my projects, I need cut a gear with 97 teeth (it has to be 97 for the other things to work out). This equates to a ratio of 40/97 or 0.4123. The closest ratio I can get is to use 14 holes on a 34 hole circle which is a ratio of 0.4117.

Did I do this correctly? If I used 14 holes on the 34 hole circle, I will get my gear with 97 teeth? Appreciate any assistance. Thanks.

[John Stevenson]

Sorry, no can do because 97 is a prime number, it can't be divided by anything other than 1 or 97.

two ways are
[1] get a plate with 97 on it or some variation of that theme [ not going into this ]
or
[2] use differential indexing where you move forward so many holes in one circle and so many forward or back in another circle.

There are other way but most will be a variation on [1] above.

Know anyone with a CNC local to you who can spot you a 97 plate ?

.

[SGW]

By my calculations, you'd get a gear with 97.143 teeth, which is probably undesirable.

What John said -- you need a 97-hole plate, or a way to work in some kind of compensatory movement.

If you have a rotary table, you could make a 97-hole plate by figuring out the angular position for each hole. Or, possibly, make the gear using the rotary table.

[oldtiffie]

I've just gotten a dividing head and have been playing with it, learning how to use it. For one of my projects, I need cut a gear with 97 teeth (it has to be 97 for the other things to work out). This equates to a ratio of 40/97 or 0.4123. The closest ratio I can get is to use 14 holes on a 34 hole circle which is a ratio of 0.4117.

Did I do this correctly? If I used 14 holes on the 34 hole circle, I will get my gear with 97 teeth? Appreciate any assistance. Thanks.

Bill.

John S is quite right as regards prime numbers etc.

There is another way. It may well be tedious but it will get you there. It involves using the hand-wheel calibrations and vernier - and not the indexing plates on your rotary table.

I prefer/use this method in preference to the indexing dials and arms etc. for small jobs.

First of all, set your rotary table to zero on the scale on the side of the rotating table. Next, set the hand-wheel dial and vernier to zero. Turn the hand-wheel half a turn anti-clockwise ("back-wards") then clockwise ("forward") - back to zero - and lock the table. This is your zero or reference point.

Next, set the job up on the table. If you have to move the table it is no problem as long as you re-set it to zero - and lock it.

It is important that the rotary table and the hand-wheel settings be approached in a clockwise direction and locked/clamped during your gear-cutting. Use the main scale on the side of the rotating table to check and keep check of the hand-wheel settings.

I have enclosed the dial settings in both decimal degree as well as in the usual degree/minute/second format. It is in a one cut/tooth per line format.

I got the info from one of Marv Klotz's utilities.

Here is the data - sorry about the number of lines, but it is bigger than the PM message 5,000 character limit. I suggest that you print it out and rule off each tooth/line as it is completed.

Best of luck.

[Edit]
Bill,
I just re-read John S's post as regards a 97-hole dividing plate. You can use this method to make a 97 hole plate on which the indexing arms are set at 40/97.
[End edit]

Number of divisions = 97

DIVISION degdec deg min sec
0 0.0000 0 0 0
1 3.7113 3 42 41
2 7.4227 7 25 22
3 11.1340 11 8 2
4 14.8454 14 50 43
5 18.5567 18 33 24
6 22.2680 22 16 5
7 25.9794 25 58 46
8 29.6907 29 41 27
9 33.4021 33 24 7
10 37.1134 37 6 48
11 40.8247 40 49 29
12 44.5361 44 32 10
13 48.2474 48 14 51
14 51.9588 51 57 32
15 55.6701 55 40 12
16 59.3814 59 22 53
17 63.0928 63 5 34
18 66.8041 66 48 15
19 70.5155 70 30 56
20 74.2268 74 13 36
21 77.9381 77 56 17
22 81.6495 81 38 58
23 85.3608 85 21 39
24 89.0722 89 4 20
25 92.7835 92 47 1
26 96.4948 96 29 41
27 100.2062 100 12 22
28 103.9175 103 55 3
29 107.6289 107 37 44
30 111.3402 111 20 25
31 115.0515 115 3 6
32 118.7629 118 45 46
33 122.4742 122 28 27
34 126.1856 126 11 8
35 129.8969 129 53 49
36 133.6082 133 36 30
37 137.3196 137 19 11
38 141.0309 141 1 51
39 144.7423 144 44 32
40 148.4536 148 27 13
41 152.1649 152 9 54
42 155.8763 155 52 35
43 159.5876 159 35 15
44 163.2990 163 17 56
45 167.0103 167 0 37
46 170.7216 170 43 18
47 174.4330 174 25 59
48 178.1443 178 8 40
49 181.8557 181 51 20
50 185.5670 185 34 1
51 189.2784 189 16 42
52 192.9897 192 59 23
53 196.7010 196 42 4
54 200.4124 200 24 45
55 204.1237 204 7 25
56 207.8351 207 50 6
57 211.5464 211 32 47
58 215.2577 215 15 28
59 218.9691 218 58 9
60 222.6804 222 40 49
61 226.3918 226 23 30
62 230.1031 230 6 11
63 233.8144 233 48 52
64 237.5258 237 31 33
65 241.2371 241 14 14
66 244.9485 244 56 54
67 248.6598 248 39 35
68 252.3711 252 22 16
69 256.0825 256 4 57
70 259.7938 259 47 38
71 263.5052 263 30 19
72 267.2165 267 12 59
73 270.9278 270 55 40
74 274.6392 274 38 21
75 278.3505 278 21 2
76 282.0619 282 3 43
77 285.7732 285 46 24
78 289.4845 289 29 4
79 293.1959 293 11 45
80 296.9072 296 54 26
81 300.6186 300 37 7
82 304.3299 304 19 48
83 308.0412 308 2 28
84 311.7526 311 45 9
85 315.4639 315 27 50
86 319.1753 319 10 31
87 322.8866 322 53 12
88 326.5979 326 35 53
89 330.3093 330 18 33
90 334.0206 334 1 14
91 337.7320 337 43 55
92 341.4433 341 26 36
93 345.1546 345 9 17
94 348.8660 348 51 58
95 352.5773 352 34 38
96 356.2887 356 17 19
97 360.0000 0 0 0

[juergenwt]

Bigboy1 - Do you have a universal dividing head with gears? That is what you need. If not - have someone who does make it for you.

[Pherdie]

All you have been told to date is correct, however I offer another approach which I used to make a metric conversion gear (127 teeth). Make a blank dividing plate of the appropriate size. Then find someone with a CAD program to make you a drawing incorporating 97 equidistant radii for the diameter size of your plate. Glue the drawing to the plate and center punch the radii near the outer circumference of the plate.

For greater accuracy, use the CAD based plate to make another plate. Each successive plate generated will have less error.

Fred

[BigBoy1]

I'm glad I asked the question and pointed in the "right" direction.

As I see it, I have two ways to go -- First use my rotaty table and do angular measurements. Second, I can look at the hole circle function on my DRO and make a plate with 97 holes.

At this point, making the 97 hole plate looks to be the easist and less chance for error way to go.

[Robin R]

You could also use your original method to make a plate with 97 holes, but with the error as calculated. Using this plate will I believe, reduce the error by a ratio of 40. If you want to get closer, use that plate to make another one with 97 holes, I would think at that point you are good to go.
Save the original plate, but clearly mark it as wrong, you can then use it as a blank for the next set of holes you don't have. You would then transfer that set of holes, to the good plate you made up.

[Quetico Bob]

Robin is correct and second the method.

Cheers, Bob

[clutch]

If the OP has a mill with dro's, why not plot out the x y coordinates and drill a wheel that way?

Clutch