Arduino Gear Hobber

[Dave SParticipant @daves59043]

Coming to this a bit late, but is the aim of the project to cut gears, or to make a hobber?

Bit of a left filed suggestion, but why not dispense with the threaded hob and make a rackform cutter.

With x,a and z axis you could cut whilst also 'rolling' the gear and simultaneously raising the z axis. Like a gear planer, but with a rotary cutter.

That is potentially doable by just plugging in a grbl to the 3 axis and figuring out the g code.

Dave

[John PParticipant @johnp77052]

Posted by Dave S 27/11/2020 19:10:55

Coming to this a bit late, but is the aim of the project to cut gears, or to make a hobber?
Bit of a left filed suggestion, but why not dispense with the threaded hob and make a rackform cutter.
With x,a and z axis you could cut whilst also 'rolling' the gear and simultaneously raising the z axis. Like a
gear planer, but with a rotary cutter.
That is potentially doable by just plugging in a grbl to the 3 axis and figuring out the g code.

Dave

Hi

You are correct in thinking about using a rack type cutter in this way , using a rotary cutter,the photo's
here show this type of cutter in use to produce an internal gear form ,this was done just as a
try out ,the cutter is fixed in the spindle of the machine and does not rotate the work is
fixed in the chuck mounted to the rotary table ,the table moved a few deg and the X,Y movement
of the machine table keeps time with the movement of the rotary table,the Z movement moves the
cutter up and down.It is a very slow operation but eventually produced the internal gear form
as can be seen.
Moving on from this Richard Bartlett produced a file for me to run on Compucut which is
designed to use a shaper, by using 2 rotary table motions and a 20 tooth cutter form
every tooth number internal and external up to the physical limit of the machine
including all of the prime numbers could be made .For example using the ratio of 6.35 between one rotary table and the other would produce a 127 tooth gear with no errors .

John

[Dave SParticipant @daves59043]

I was thinking of the cutter in the spindle, and rotating, more like this

Where the cutter traverses in x, and the blank rolls on the a (? Think that's x axis roll) axis synchronised with plunge in the z.

Spindle revs are then independent of the cutting of the tooth form.

Dave

[John RutzenParticipant @johnrutzen76569]

Hi Dave S, so am I right in thinking that the only thing that detemines the number of teeth is the diameter of the blank? I 've seen and read about those rack form gear cutters before but didn't appreciate that you could roll the blank to generate the gear.

[Dave SParticipant @daves59043]

Yes. It's much like Hobbing in that respect.

All these were cut with the same cutter:

The pinions are profile shifted to avoid tooth undercutting.

There is potential to make 'better' than hobbed gears this way too.

If you don't roll the blank at all you get roughly 5 facets. With a hob you get a number of facets that is equal to the number of teeth on the hob. With coordinated Z and A you can get equivalent to the step resolution number of facets.

Dave

[BazyleParticipant @bazyle]

Dave, where does the 'roughly 5 facets' come from?

Really like this idea

[John RutzenParticipant @johnrutzen76569]

Dave S, surely though you can only roll it so much. Then you would have to step it round to the next tooth.

[Dave SParticipant @daves59043]

The facets come from the adjacent teeth on the cutter shaving the flanks / tops of adjacent teeth on the gear blank.

There is a bit of a thread here: Gear cutting with more pictures.

Yes the rolling will ultimately lead to the next tooth, but with a (say) 7 tooth cutter the roll can be completed from entry to exit of the “rack” at the target tooth. The adjacent teeth will also get shaved. Once rolled far enough then index to the next tooth and reset the Z to the start and do it again.

I planned to gear the roll to my TOS spindle somehow as that’s a fully manual machine, but I haven’t got round to it yet, and if I can get my baby cnc to work reliably the I was going to fix up a rotary axis and do it with cnc – but that’s a way off yet – the CNC nearly works, but so far it hasn’t really cut a complete part due to other distractions.

Dave

[BazyleParticipant @bazyle]

thanks, I forgot the cutter as a rack would have more than one tooth. I guess an old horizontal mill, small one as once used in small parts production, would be a good starting point for a dedicated machine.

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