Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: JohnHaine on February 01, 2014, 01:49:12 PM
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Hi all, I've decided it's time I cut some gears and want to make some cutters. There's a standard method of making cutters where you profile turn arcs of a circle on the edge of a bit of gauge plate, using a form tool which has two hardened circular buttons fixed to a plate with the right spacing and diameter. Now it seems to me that with a CNC lathe it ought to be possible to form the arcs directly with the right G Code.
So I have found the formulas for the cutter dimensions, but I just thought that I'd ask here if anyone else has done this and has any tips (or even some G code they can share)?
Thanks, John.
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Now it seems to me that with a CNC lathe it ought to be possible to form the arcs directly with the right G Code
Somewhere i have the article your refering to..........
Yes, one could machine the profile...actualy it should be ground...and it needs to done accurately.
Wish ya luck.
Frankly i would just buy a gear cutter that for the job. ;)
BUT
One must have fun, so see threads below how I made some for a fly cutter and then used the indexer with the mill to cut the gears.
http://www.machsupport.com/forum/index.php/topic,8118.msg51321.html#msg51321
http://www.machsupport.com/forum/index.php/topic,8120.msg51325.html#msg51325
RICH
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Fun is the name of the game!
Another question. In writing the g code for this it will be convenient to operate the lathe in radius mode and zero the X axis off the periphery of the tool blank rather than the rotational axis. Is there anything I should beware off doing this please?
By the way the code will be generated using an excel spreadsheet.
John.
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So, success! I have developed a method of making form relieved gear cutters similar to the "button method". The difference is that the circular profile of the tooth, which generates a circular approximation to the involute, is formed by a few lines of G-code which make the lathe tool trace out a circle centred at the appropriate point relative to the cutter blank. Took a while to figure out the geometry and how to generate the code, but in use it's a lot faster than making buttons and the mount to space them the right distance apart. When I get time I'll post more details of the method if anyone is interested.
Here are some pictures of the formed blank mounted on a fixture in my collet chuck; the cutter after gashing out the teeth; and the cutter and the fixture, sitting on my big manual mill table.
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Heck YEAH ! Keep posting more details ... I'm interested. :)
I like this method MUCH better than the two slugs.
So you mount the blank on the fixture 8 times, right ? and do all turning from the same (out) side ?
Nifty !
Nice work !
Thanks,
Russ
:)
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Thanks Russ! Yes, that's exactly right.
There's quite a lot to write up, I want to make sure I understand how I've done this, will be a while before I can post much more.
John.
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PM'ed you John.
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Your gear cutter sure looks familar. Live Steam Magazine ? a long time ago had an article about making them.
RICH
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Yes, there have been at least 3 articles in the UK model engineering press as well as several on the web about using form tools ("buttons") to shape the circular profile. I haven't seen anything about using CNC but there is little new under the sun! CNC saves the trouble of making the buttons and a holder, and can make a much wider range of sizes.
John.
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Hey John, are you familiar with Gearotic ?
Art had a Tool Wizard utility in there at one time, (not sure of it's current state), that would generate the Gcode to machine a profile to match a selected gear form using a mill with a 4th axis.
I'd thought about entering the lathe tool tip rad(dia) in place of the endmill dia., generate the code, then delete all but the one side and the tip of the finished profile. Then by replacing the X and Y with Z and X. Using a few G52 offsets for the roughing, then a smooth finish pass.
Should be a perfect form with the too tip rad. comp. all taken care of.
But, never got around to trying it.
Seemed like a relatively easy task at the time though.
Thanks john,
Russ
:)
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That would be a good approach too. Maybe a gearotic version for the lathe could be generated? Turning the profiles, you can as easily generate a true involute as a circle I guess. The reasons I didn't do that were, first, the approximation of using a circular profile are probably less than the inevitable tolerances, and second, for the case of a circular profile only, I am pretty sure you can ignore tip radius compensation as the direction of cut is always a tangent to the tip. Cutting an involute I'd have had to get to grips with cutter compensation on the lathe which I gather doesn't work too well in Mach?
John.
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