Gear cutting problems

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Wino1442

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Hi all….this more like a Part 2 to my original post (Gear cutter Depth of cut)

I’m going to try to keep this short and still provide enough info to get some ideas or opinions.

I bought two 32DP gear cutters..#3 and #6 to cut a 20 tooth and 40 tooth gear. Cutters are marked #3 Z35-54 and #6 Z17-21. I cut the 40 tooth gear with the #3 and it was spot on when measured across wires. I then cut the 20 tooth gear with the #6 and this is where things went wrong. I fed in .0674 and the teeth came to a point. Knowing that the numbering of the import cutters is suspect I cut a second 20 tooth gear with the #3 (feeding in the same .0674) and got a gear that looked right and also measured across pins within a 1/2 thou. I then cut another 40 tooth gear (feeding in the same .0674) with the #6, thinking the cutter numbers were wrong, and the teeth on this gear came to a point. So now I’m confused as hell. I’ve checked and re-checked my math and setup and am satisfied it’s good. I got my depth of cut of .0674 from 2.157/32. There are markings/numbers on the #6 cutter and a number which appears to be “26” stamped on one side of the #3 cutter. I’m sure those numbers mean something, but I can’t figure it out. I’ve tried working those numbers in the markings to see if they mean something in metric or imperial and can’t get anything that makes sense.

I have attached photos of the cutters (both sides), the cutter profiles, and the gears made. I’m hoping one the many experienced guys on here can help me out and point me in the right direction. Thanks
 

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I think one of the cutters was made wrong (or mismarked?)
 
I was thinking something along those lines. I think one of them is possibly mislabeled because the profiles look different to me.
 
Somewhere, perhaps on a Mr. Pete video, I recall seeing that some old gear catalogs (e.g. Boston Gear) used to have full-size images of different gears that could be used for comparison. I don't have any, but maybe there are some downloads?

Here is a .dxf gear generator. Never used and don't know how accurate but it may provide a profile image for compariison: https://evolventdesign.com/pages/spur-gear-generator
 
Sometimes the china cutters are numbered backwards from the US cutters. That may be your problem. If you have a gear from that tooth range see if it matches up with the cutter profile.
 
I'm in the same boat. I'm still not sure what the depth of cut should be based on past experience. When I was making my beer bottle capper, I used the formulae to depth of cut, but the tops of the teeth were very pointy. I wound up eyeballing it until it looked right. Not the best solution! This was a module 1.25 gear.

Now, I'm working on a clock with LOTS of gears and I'd like to know the depth of cut. These will be module 1 gears. my "Machinery's Handbook"(25th edition) shows: Whole Depth (Preferred) = 2.25/P for 20 and 25 degree pressure angle. I can't find the equation for 14.5 degree pressure angle.

I also have the book "Gears and Gear Cutting" by Ivan Law. It shows D+f = 2.157/DP and doesn't state a pressure angle.

Then, I found this on the web:
Whole Depth = 2.157/P for 14.5 degree pressure angle and 2.250/P for 20 and 25 degree pressure angle. So, I'm totally confused myself.

So, for a metric gear, this becomes 2.157*M (14.5*) and 2.250*M (20*, 25*)?

Can someone verify what is correct?
 
E
Nutfarmer said:
Sometimes the china cutters are numbered backwards from the US cutters. That may be your problem. If you have a gear from that tooth range see if it matches up with the cutter profile.
Click to expand...
European cutters also follow that (un) convention. funny thing is that cutter is stamped for the number of teeth range that would be appropriate for the gear that was cut.
 
In practice, one seldom sees module gears in 14 1/2 deg. PA, they seem to be a thing of the past. I have only ever seen one in my days, that being on a cooperage stave saw that I worked on long ago.
 
john.oliver35 said:
Somewhere, perhaps on a Mr. Pete video, I recall seeing that some old gear catalogs (e.g. Boston Gear) used to have full-size images of different gears that could be used for comparison. I don't have any, but maybe there are some downloads?

Here is a .dxf gear generator. Never used and don't know how accurate but it may provide a profile image for compariison: https://evolventdesign.com/pages/spur-gear-generator
Click to expand...

Boston Gear have lots of dxf files you can download

https://www.bostongear.com/ecatalog?page=search&cid=spur_gears_02&filter=Diametrical_Pitch:2:32.0#

Stu
 
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