Spacing of buttons for making involute cutters

[Martin KyteParticipant @martinkyte99762]

Posted by bernard towers on 20/10/2021 18:38:06:

I used the single button method with a twist , the button was a length of carbide mounted tangentially and 1 side of the blank machined then taken off the mandrel and reversed and the second side machined. This was for Wildings turret clock which works very well.

Given that you say your method worked , why did you not traverse the crosslide and topslide to turn the second face?

regards Martin

[John HaineParticipant @johnhaine32865]

Because you only have to get one feed right.

[John HaineParticipant @johnhaine32865]

Actually this raises an interesting point. Since all the gears in a clock famously rotate only one way, it shouldn't be necessary to machine a symmetrical profile on each tooth. The other side could for example just be a buttress to give reasonable tooth strength. Then you need to assemble the gears the right way round to make sure the teeth mesh on their "right" sides.

[egaParticipant @ega]

I recently acquired a profile lathe tool with a 12mm diameter carbide insert – an instant single button tool, perhaps?

[John HaineParticipant @johnhaine32865]

Indeed, but quick calcs using Mike Cox's formulas says that for a 20 tooth 20* PA gear the mod would be 1.7542mm. You can choose 3 of button diameter, PA, teeth or mod, but not all at once alas.

[bernard towersParticipant @bernardtowers37738]

Martin, The reason being that you would need another tangential toolholder of the other hand. Plus the blank is butted up to the collet chuck nut so no room to get to tother side

[John PParticipant @johnp77052]

Button form tools used on the Eureka device can be a problem
to make in the sizes above cutter No 4 the radius is so large
that it would interfere with the body of the device , see here the photo
of 6 off 20 DP 20 pa cutters and tooling to make them .
Only a small part of the circle is needed to form the cutter in the
sizes 3 to 1.

These illustrations taken from an old book shows how this used
to be done and may be of some interest especially if you have
a shaper ,i don't need to add any more the pages show it all.

John

[Howard LewisParticipant @howardlewis46836]

There was an article in M E dated 2nd September 1994 which dealt with gear cutting and in which there were some a table giving button sizes and spacing, which may be of help.

Howard

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