Steel gear cutting

[DPittman]

I've cut a few brass and nylon gears but had never cut a steel one until now.

I recently noticed one of the gears in my reverse tumbler mechanism on my lathe had several chipped teeth. I'm pretty sure that was caused by a dumb head operator move engaging the gears while rotating. I had noticed the gears were noisier than normal but I kind of ignored that.

I'm always a bit nervous when getting near full circle cutting when I'm sure the last few teeth are not going to fit. And then I am surprised when the last tooth gets cut perfectly.

Question for the more experienced gear cutters.... do I use the same cutter rpm calculation for determining correct cutter speed based on the gear cutter diameter just the same as an end mill? My gear cutter is 2" diameter and I ran it at about 175 rpm. Steel material is the same as I often use....who knows mystery salvage steel.

 

[John Conroy]

I don't know what the correct cutting speed would be bit I assume it would be normal sfm calculation for HSS. Glad your gear turned out well, I'm about to make a couple as soon as my cutter arrives from China

 

[Susquatch]

Assuming your cutter is HSS, I believe the correct calculation is for the speed of the cutter tip for HSS in whatever material you are cutting.

In practice, I have not found that the speed is critical and mostly tune the speed for the best sounding/feeling cutting experience. Your mileage may vary and I am no expert. I've cut a lot of teeth, but farm gears are not exactly precision things!

 

[DPittman]

mostly tune the speed for the best sounding/feeling cutting experience

That's exactly what I did. When I cut the brass and nylon gears I ran higher rpm and cut dry, this steel one I squirted with oil.

 

[RobinHood]

I'm always a bit nervous when getting near full circle cutting when I'm sure the last few teeth are not going to fit.

One way to reduce the anxiety to near zero is to do a “blank pass”. Set everything up as usual and blue (or whatever your favourite colour is) the blank and just touch off the cutter (kind of like a trial pass when threading). Now just concentrate on the indexing as you go all the way around the blank making little ticks at the edge. After you are done, check for proper spacing and number of teeth. If all is a-ok, cut the gear for real. You now have a visual indication at each position and you will know for sure that the spacing is correct.

If you mess up during the trial run, just colour the blank again and start over. Nothing is lost by the first go around as the little ticks will all be gone once you chamfer the teeth when done.

Worked great when I did my 127T using differential dividing for the first time. Yes, it was an extra step, but this way I was assured that everything would work the first time while cutting for real.

As far as speeds and feeds - I do what you did (calculation) and then go as @Susquatch suggest: listen and observe. If machine is happy, the operator is happy.

Job well done.