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Cutting Spur Gears -- A neat technique

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AdeV:
OK, so in lieu of actual machines, I broke out SolidWorks as well  :lol:

Unfortunately, I just can't get mine to work properly  :scratch:

Please look at the 3 attached pictures:

The first picture shows my "cutter" lined up with a gear blank. The dimensions are all taken from Helicron's site, namely: 4.32mm maximum depth-of-cut (assuming pointy-tipped cutter). 1/2 way point between (2.16mm) is the contact point (gap & tooth width equal), so I assume this is my PCD. Actual DOC (assuming pointy cutter) is 3.41mm (again, taken from Helicron's site). And finally I've lopped off the top to 1.4mm above the PCD (red circled dimension).

This results in the "gear" as seen in the 2nd picture. Looks to me like the teeth are too skinny, have an odd "dink" where the tall cutter is catching just inside the PCD, and a strange "pit" at the bottom where the cutter is at max depth.

So... I reduced the cutter height-above-PCD to 1mm... and got the result in pic 3. The teeth still look too skinny, but at least that "dink" has gone away. Still got the weird pit though.

Obviously, I've mangled something somewhere. Can anyone set me back on the right track? The measurements are all based on Module 1 gear (as far as I understand Module...) & 20 degree pressure angle.

I've attached a ZIP containing the Solidworks (2013) part, so if someone fancies fixing it for me! Note that I'd like to use Helicron's method (i.e. simple 40-degree included angle pointy tool) to actually cut the cutter.

Thanks!

BillTodd:
Your rack still does not look quite right . The width of the V at the circumference of the blank should be at least equal to the flat at the top of the rack.  it looks like the flat is too wide given the depth of the cut.

Bill

AdeV:

--- Quote from: BillTodd on May 20, 2017, 05:23:11 AM ---Your rack still does not look quite right . The width of the V at the circumference of the blank should be at least equal to the flat at the top of the rack.  it looks like the flat is too wide given the depth of the cut.

--- End quote ---

Doh! You're quite right of course... I got the cutter blank diameter wrong - I was working with an outside diameter of 48mm, not a PCD of 48mm...

Re-set the diameter to 50.50mm (PCD + 2x 1.25mm), and it's looking better. I increased the cutter depth back to 1.4mm, as the tooth looked a bit shonky at 1mm.

Still got that "pit" at the bottom, is that because 1.4mm is too deep a cut? Or because it's only an approx tooth form?

Thanks for the prod anyway, made me realise what I'd done wrong  :thumbup:

AdeV:
Well... they mesh... more or less...

Might need a spot of virtual grinding paste in there to smooth things off a bit  :lol:

BillTodd:
They don't look too bad  :D

what happens if you do another cut with the rack and gear half a tooth around (if you see what i mean).?

Bill

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