making a gear cutter using ordinary milling cutters

[wheeltapper]

Hi all

I've been trying to make a single tooth gear cutter using a form tool with hardened buttons and got nowhere.
I read on another forum someone used a cone drill to form the cutter shape but I didn't have much luck with that either.

so I thought' if I can't tilt the milling cutter tilt the blank.

so this is what I did,

first I fixed my dividing head to the mill with packing under the l/h side to give 5 degrees of tilt to the spindle.

then I held the blank in a collet

then I fixed a 120 tooth gear to the div head and indexed the spindle so the blank was square to the bed and took a skim across the end

then I fitted a normal milling cutter of a diameter equal to the dia of the button you would use doing it the other way, indexed the spindle 1 tooth which is 3 degrees,fed the cutter up to the blank and fed in the recommended cutting distance.

I placed the cutter on the side of the blank which would put the leading (widest) edge of the tip at the bottom and took a cut.

when it's across far enough, raise the cutter, index 2 teeth the other way and take the other cut.

finally index back to zero then go round 180 degrees which puts the cutting edge on top and take a skim across the top with the end of the milling cutter to relieve the tip.

here's the finished cutter

here's an aluminium gear done as a test meshed with a change wheel.

the advantage of this is you can use any ordinary cutter.

there is a sad ending to this tho, I was so pleased that it worked I tried it on a steel gear blank , unfortunately I was in such a hurry to try it out I hardened the cutter but forgot to temper it and 5 teeth into the steel blank I chipped the end off.

but I can make another one.
so I did,

any comments welcome.
Roy

 

[kjk]

Positively brilliant. This posting goes into my tips file.

 

[Maryak]

Positively brilliant.

I agree,

Best Regards
Bob

 

[Captain Jerry]

Good job. You got all the angles covered. I particularly like the packing under the RT. I don't think I've seen that before but it does give the needed radial relief. Even more might be good if you could stabilize the setup.

Jerry

 

[ttrikalin]

very nice,
thanks for the tip!

 

[John S]

The problem is finding a milling cutter with the correct diameter as the button.

An alternative would be to use a boring head and then it could be dialled in to any size needed.

John S.

 

[shred]

The problem is finding a milling cutter with the correct diameter as the button.

An alternative would be to use a boring head and then it could be dialled in to any size needed.

John S.

Good thought John. I was thinking that without CNC, it could be a bit tricky getting the desired diameter. With a CNC it could be pretty simple to pop these out, though there are other ways if you want to go that route.

 

[GailInNM]

It is not a bad as it might seem to use standard cutters. The button cutter diameter calculations normally published are to make a set of 8 cutters and are spaced accordingly. The tooth form for a particular cutter is most accurate for the smallest number of gear teeth for a particular cutter and is still acceptable for the largest number of gear teeth that can be cut with that particular involute cutter.

If we turn our thinking around a bit and calculate the range of teeth that can be cut with a particular button cutter diameter then we find that we can cut almost the entire range of gear teeth using standard milling cutters to make the gear cutters. OK for at least for higher pitch diameter gears. For lower pitch diameter gears the milling cutters will start to get fairly large.

The attached Excel program will help. Enter the pressure angle and DP and then the number of teeth. It is not obvious, but you can change the number of teeth in fractional increments and watch the cutter diameter change to creep up on a standard milling cutter size and it will calculate the rest of the coordinates as well as the maximum number of teeth that the resulting cutter will cut. Of course a fractional number of teeth can not be cut, so this number has to be rounded up. Not the most convenient way of doing it, but it works. The second file attached shows how this was done to generate a 48 tooth gear cutter using a 5/16 diameter cutter.

I had a similar program written years ago that allowed entering the milling cutter diameter, pressure angle and DP and it would output the range of teeth that the resulting cutter would cut along with the other information to make a cutter. It disappeared in the great computer crash of 5 or so years ago and I have not rewritten it. Future project, maybe?

If you use the attached program, you will notice that the upper range of gear teeth that can be cut does not exactly correspond with standard involute cutter sets. It is close enough however. I think that Brown and Sharp through in some fudge factors to make the upper end come out integers and I have never chased the equation down.

Gail in NM


View attachment GearCutters.xls

View attachment GearCutters2.xls

 

[wheeltapper]

Good job. You got all the angles covered. I particularly like the packing under the RT. I don't think I've seen that before but it does give the needed radial relief. Even more might be good if you could stabilize the setup.

Jerry

Hi Jerry
yes I agree about more relief, I discovered when I cut the gear I had to stone a bit more.

Roy


while I'm here, thanks for all the nice feedback guys an gals.

 

[bob ward]

That really is very clever Wheeltapper, thanks for sharing. And as is often the case an idea sets the brain cogs whirling and I think I can see an adaptation of your method to produce multi tooth gear cutters. I'll try to do a mock-up and take photos in the next day or 3.

Thanks too for your insight Gail, why not indeed look at the diameters of the stock buttons (milling cutters) we have and work backwards from there to see what gears can be made from them? Playing around with Gail's spreadsheet you can make a lot of different gears with up to a 3/4" mill.

 

[shred]

If we turn our thinking around a bit and calculate the range of teeth that can be cut with a particular button cutter diameter then we find that we can cut almost the entire range of gear teeth using standard milling cutters to make the gear cutters. OK for at least for higher pitch diameter gears. For lower pitch diameter gears the milling cutters will start to get fairly large.
...
Gail in NM

Ah, that's clever thinking. You may end up with more cutters to cover the whole range, but if you can make them with standard tooling, that's not a big deal.

 

[Lakc]

I would have never thought about taking an endmill to a cutter. Maybe because all I have laying around are pre-hardened 5% colbalt types, and I suspect the collision would end in an explosion of some sort. Did you use plain square oil/air/waterhard toolsteel?

 

[wheeltapper]

Hi
yes, we Brits call it silver steel, and judging by the price of the dam' stuff I think it's got silver in it. :big:

Roy

 

[Lakc]

Thanks for the clarification. That's one of the good things about forum's is the ideas you would have never thought of for some reason or another.