Gallery, Projects and General > How to's
Cutting Spur Gears -- A neat technique
RussellT:
Hi Ade
Helicron suggests the DOC below the PCD should be 1.25*MOD and you seem to have 1.4. I haven't gone any further investigating but I think that might deal with the pit at the bottom of your teeth.
Russell
AdeV:
Hi Russell,
Every time I look at this again it makes my brain ache... For the pics I did above BTW, I did reduce the cut to 1.25mod (i.e. 1.25mm), it reduced the "pit" but didn't eliminate it.
So, attached is another pic of the cutter sketch.
The four dotted lines, starting with the top one are:
- My maximum depth of cut (note the triangular peak marked 3.41 - that's the theoretical DOC if the cutter were infinitely sharp)
- The next dotted line is the PCD (point where tooth & gap are equal, exactly half of the absolute maximum DOC, 4.32mm approx)
- The third dotted line is the outer edge of the gear blank, and represents the point where I stop cutting
- The fourth and final dotted line is the bottom of the cutter (=bottom of the rack).
Now... according to Helicron's site, the total DOC should be 3.41mm based on a 2.16 + 1.25 cut. But I'm not cutting as deep as 2.16, is that a problem??
Thing is, if I go full depth (i.e. the full (theoretical) 3.41mm cut, I end up with vampire teeth (pic 2)...?
:scratch: :scratch: :scratch:
A bit more information:
Gear blank is 50.5mm diameter (increased to 52.32mm to account for the increased DOC)
I'm "cutting" a module 1 gear, so 48 teeth.
20 degrees pressure angle.
AdeV:
Ignore that last one... my DOC's gone all wonky...
No... don't ignore it... the DOC is actually 3.41mm from the base dotted line to where I've trimmed off my cutter.
Last modification....! Do ignore it, I've got my blank WAY too big. I'd missed the bit where the OD of the blank is N(o of teeth) + 2 in mm... i.e. 50mm.
I've still got a "pit" though. I can only assume it must be because it's an approximation rather than an actual involute.
RussellT:
Hi Ade
Don't forget there are two DOCs here. The first one is for making the cutter - 3.41*MOD as you show. The next one is the DOC when cutting the gear blank which according to Helicron is 2.25*MOD or 2.4*MOD for fine gears.
It may not help but I attach the spreadsheet I used to calculate the numbers when I tried this method - I wanted to make some 14.5deg PA gears. :smart:
Russell
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