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MEW No. 285 Gear Cutters and Gear Cutting

...a simpler option?

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Kiwi Bloke17/09/2019 11:32:58
250 forum posts
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I've just received MEW No. 285. The idea of incorporating relief into single-point gear cutters by using conical milling cutters to make them is superficially attractive. However, it seems to me to be an unnecessary elaboration of a simpler technique, and it comes with two problems: 1, the need for conical cutters, depth-setting collars, look-up tables (or real maths), etc., and 2, most serious, the resulting cutter is not form-relieved, thus it can't be sharpened without changing its shape.

If, as the author suggests, it is acceptable to make a cutter with profiles that are slightly part-elliptical, rather than part-circular (and it should be), then a form-relieved cutter can be made using cylindrical milling cutters (rather than conical ones), by tilting the blank nose-down (or -up) in the way that has been suggested for providing positive rake, towards the end of the article.

The advantages are: 1, it's easier; 2, the resulting cutter can be sharpened by grinding its top surface and 3, there's no need to buy conical cutters, so you can spend the money saved on beer.

OK, this method also comes with problems: 1, the form-relief is not arcuate, as, for example, a Eureka device would produce, but, providing the 'tilt' chosen for its manufacture provides enough heel clearance in use, that doesn't matter; 2, the correct diameter cylindrical cutter will probably have to be made, but that's easy; 3, you still have to look up or calculate the diameter of that cutter.

Neil Wyatt17/09/2019 12:33:57
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Posted by Kiwi Bloke on 17/09/2019 11:32:58:

I've just received MEW No. 285. The idea of incorporating relief into single-point gear cutters by using conical milling cutters to make them is superficially attractive. However, it seems to me to be an unnecessary elaboration of a simpler technique, and it comes with two problems: 1, the need for conical cutters, depth-setting collars, look-up tables (or real maths), etc., and 2, most serious, the resulting cutter is not form-relieved, thus it can't be sharpened without changing its shape.

If, as the author suggests, it is acceptable to make a cutter with profiles that are slightly part-elliptical, rather than part-circular (and it should be), then a form-relieved cutter can be made using cylindrical milling cutters (rather than conical ones), by tilting the blank nose-down (or -up) in the way that has been suggested for providing positive rake, towards the end of the article.

The advantages are: 1, it's easier; 2, the resulting cutter can be sharpened by grinding its top surface and 3, there's no need to buy conical cutters, so you can spend the money saved on beer.

OK, this method also comes with problems: 1, the form-relief is not arcuate, as, for example, a Eureka device would produce, but, providing the 'tilt' chosen for its manufacture provides enough heel clearance in use, that doesn't matter; 2, the correct diameter cylindrical cutter will probably have to be made, but that's easy; 3, you still have to look up or calculate the diameter of that cutter.

I think the clever bit is using a taper cutter to get an exact diameter, as making the 'correct diameter' cutter is a bit fo a challenge for most and is probably harder than making buttons..

Neil

BW17/09/2019 13:23:11
245 forum posts
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I think the clever bit is using a taper cutter to get an exact diameter, as making the 'correct diameter' cutter is a bit fo a challenge for most and is probably harder than making buttons..

I have always thought that post #8 in this thread was a brilliant bit of lateral thinking. It means that you can make single point gear cutters using the radii of standard sized end mills.

Its explained very well in the post .... no point in me rehashing it ........ have a read and then copy the spreadsheet.

Bill

Michael Gilligan17/09/2019 14:20:12
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Posted by Neil Wyatt on 17/09/2019 12:33:57:

I think the clever bit is using a taper cutter to get an exact diameter, as making the 'correct diameter' cutter is a bit fo a challenge for most and is probably harder than making buttons..

Neil

.

A rather fine clockmaking acquaintance of mine simply machines a half-round tool [with relief], on the Rotary Table of his Hauser jig-borer, and then uses this [twice] to machine the wheel-cutter blank. ... no buttons, no spacing them on a holder.

MichaelG.

Neil Wyatt17/09/2019 15:48:57
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Posted by Michael Gilligan on 17/09/2019 14:20:12:

A rather fine clockmaking acquaintance of mine simply machines a half-round tool [with relief], on the Rotary Table of his Hauser jig-borer, and then uses this [twice] to machine the wheel-cutter blank. ... no buttons, no spacing them on a holder.

MichaelG.

A less refined artisan of my 'aquaintance' has been known to file a bit of gauge plate to match the gap between the the of a matching gear

Ironically this is includes one of the few gears made by a forum member which has been copied and put into industrial production...

Neil

Michael Cox 117/09/2019 18:43:16
515 forum posts
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Niel has already pointed out that one benefit of using conical cutters is that it is easy to make any diameter of cut out using only a limited range of conical cutters. The other benefit of using conical cutters is that they provide relief all around the cut out arc. Using cylindrical cutters and a tilted blank only provide relief in one direction.

The cost of the tapered drills is relatively small and one set can be used to make cutters to match a big range of MOD and tooth counts.

Mike

BW18/09/2019 00:30:18
245 forum posts
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Posted by Michael Gilligan on 17/09/2019 14:20:12:

.

A rather fine clockmaking acquaintance of mine simply machines a half-round tool [with relief], on the Rotary Table of his Hauser jig-borer, and then uses this [twice] to machine the wheel-cutter blank. ... no buttons, no spacing them on a holder.

MichaelG.

Hey Michael,

Am struggling to understand "half round tool" and how your friend uses it.

Is that shaped like a half round file and then mounted on a machine spindle

Bill

Michael Gilligan18/09/2019 08:03:57
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Posted by BW on 18/09/2019 00:30:18:
Posted by Michael Gilligan on 17/09/2019 14:20:12:

.

A rather fine clockmaking acquaintance of mine simply machines a half-round tool [with relief], on the Rotary Table of his Hauser jig-borer, and then uses this [twice] to machine the wheel-cutter blank. ... no buttons, no spacing them on a holder.

MichaelG.

Hey Michael,

Am struggling to understand "half round tool" and how your friend uses it.

Is that shaped like a half round file and then mounted on a machine spindle

Bill

 

.

No, Bill ... Just a round-nosed lathe tool, used for form cutting.

I wrote "half-round" to stress that it's symmetrical.

.

Using this lathe tool to make a cutter follows the same principle as when using the "buttons' ... but he makes two separate cuts.

MichaelG.

.

Edit: This chap is doing something similar, but using a special fixture in the lathe:

https://m.youtube.com/watch?v=JAaowOG2l0c

Edit: ... [ with a  'Machine Porn' warning ] ... Here's a Hauser M1 in action:

https://m.youtube.com/watch?v=AhUoZ1mMwfQ

Edited By Michael Gilligan on 18/09/2019 08:12:46

Edited By Michael Gilligan on 18/09/2019 08:29:17

JasonB18/09/2019 08:39:47
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I suppose as you don't use more than half a button then there is no need to make a full circle cutter. Though a lot easier for most to just turn a bit of Silver Steel to a diameter than make jigs for tool grinding which is the good thing about teh button method.

I have also used the Stub Mandrel method though opted for the offhand grinder on an HSS bit referring to a printed out tooth profile, results can be seen in my last video in the "Electric traction engine" thread.

Unless making very small gears as per Michael's last link you can also get any diameter cut on a single point tool using a boring head and that will also cope with larger radii than a cone drill. And as for those of us who now have CNC (hint hint Neil) just about any shape is possible and clearance easily obtained by using a taper flute milling cutter.

Edited By JasonB on 18/09/2019 08:41:13

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