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gear cutters

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bricky04/06/2018 20:14:32
378 forum posts
47 photos

I am wanting to cut two gears a 25 and 50 tooth at 24DP. Will one cutter do for both gears or do I have to have two.In the Advanced Machine Work book there is a table for the cordal thickness of both gears and there is so little difference that I wondered if I could get away with one cutter.

Frank

Andrew Johnston04/06/2018 20:39:40
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4847 forum posts
543 photos

You'll need two cutters. The circular pitch, and thus the circular thickness of a tooth, for a given DP is constant, irrespective of the number of teeth. The chordal thickness varies slightly with number of teeth but it's a geometric issue, not fundamental to the tooth shape. However, as the number of teeth varies the shape of the teeth varies considerably above (addendum) and below (dedendum) the pitch circle. So even though the circular pitch is constant you still need different cutters to cope with the different tooth shapes. For 25 teeth you need #5 and for 50 teeth you need #3, using the Brown and Sharpe notation.

bricky04/06/2018 20:48:35
378 forum posts
47 photos

Thank you Andrew, I will have to buy both or make the cutters myself.

Frank

Pete Rimmer05/06/2018 00:38:56
416 forum posts
18 photos

If you get stuck Frank I could possibly cut those gears for you, though you would have to cut any keyways required as I have yet to lay my hands on a broaching cutter set.

Alan Charleston05/06/2018 08:11:53
76 forum posts
19 photos

Hi,

Gear cutters used to be a fearsome price but I have had good experiences with cheap cutters from Aliexpress. Here is a link for a full set (8 cutters) of DP24 14.5 degree pressure angle cutters for a bit over US$70. I can remember paying about that for one cutter about 20 years ago. The DP gears are hard to find on Aliexpress as most of them are module cutters but a search for "gear cutters 14.5 degrees" digs them out.

https://www.aliexpress.com/item/DP24-modulus-Pressure-Angle-14-5-degrees-1-8-8pcs-let-HSS-Gear-cutter-Gear-Milling/32825653274.html?spm=2114.search0604.3.26.7ba324c4dEKGwO&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_5722815_10342_10547_10325_10343_10546_10340_5722915_10548_10341_5722615_10696_10084_10083_10618_10307_5722715_10059_100031_10103_10624_10623_10622_5722515_10621_10620,searchweb201603_25,ppcSwitch_5&algo_expid=9eebc2d2-a942-49cb-b1a5-3847d5b60140-4&algo_pvid=9eebc2d2-a942-49cb-b1a5-3847d5b60140&priceBeautifyAB=0

Regards,

Alan C.

not done it yet05/06/2018 10:52:47
3338 forum posts
11 photos

If you are cash strapped and the duty is light and slow, a number 4 is only three tooth counts from the optimum of a number 5 cutter. A bit of a gap to a 50 tooth gear, but that same No.4 cutter might make a satisfactory 50 tooth gear in delrin, which might soon ‘wear in’, possibly with a bit of care. Might also depend on what each gear is on either side of the replacements.

Involute cutters are used over a certain range, so are a close enough approximation for the outliers of the range and only perfect for the median tooth size (if even that!). Ideally, a cutter for every tooth count would be best, but 8 cutters from rack to 12(?) is a compromise already. Andrew would be in a better position than me to tell you if it would work.

bricky05/06/2018 12:15:43
378 forum posts
47 photos

Thank you Pete that is a very generous offer but I do want to cut the gears myself.

Frank

Neil Wyatt05/06/2018 14:28:25
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Moderator
16556 forum posts
687 photos
75 articles

Cutters made using circular silver steel 'button' to approximate the involute shape work well.

I found that it's easier to use one button and cut both sides of the cutter independently - less chatter and easier to move the button accurately using the cross slide than drill two holes and exact distance apart for a twin button cutter.

24 dp isn't far from 1 mod, if you can substitute the metric gears by changing centre distance (I'm assuming you need the 2:1 ratio) the cutters are likely to be cheaper. 26:52 in 1 mod might be another option.

Neil

Pete Rimmer05/06/2018 18:31:06
416 forum posts
18 photos

You don't even strictly need a button. I made my first single-point cutter by first making a fly cutter of the same diameter as a button then cutting both sides of a piece of gauge plate with the head of my mill tilted to give the form with some relief.

bricky05/06/2018 20:45:49
378 forum posts
47 photos

I would have had to buy gauge plate and 5/8" silver steel and as these items are expensive and the effort needed to make the cutters I ordered two cutters from RDG at 42 pounds delivered.Thanks to all for the advice.

Frank

Andrew Johnston06/06/2018 07:53:31
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4847 forum posts
543 photos

An additional note; B&S style gear cutters are exact for the lowest number of teeth in the range they cut. I'd hazard a guess that this is because the tooth shape becomes more curved as the number of teeth decreases and a tooth with a bit too much curvature, rather than too little, is less likely to bind.

Andrew

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