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Gear cutters

This topic has 25 replies, 10 voices, and was last updated 13 September 2010 at 18:18 by Michael Cox 1.

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1 July 2010 at 15:03 #16563
Michael Cox 1
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@michaelcox1
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1 July 2010 at 15:03 #53044
Michael Cox 1
Participant
@michaelcox1
I am interested in making some gear cutter using the button method.

I have two reference to this method. The first is Ivan Laws book “Gears and Gear cutting” and the second in John Stevensons article in Metal Web News (http://www.metalwebnews.com/howto/gear/gear1.html) . Both of these highly respected authors give tables for the button diameter, button spacing and infeed for various gears with a 20 degree pressure angle. However the numbers given in both tables are very different . For example for a gear cutter for 55-134 teeth Ivan Law quotes a button diameter of 32.15, a button spacing of 31.6and an infeed of 11.47. the corresponding numbers from John Stevensons table are 18.81, 19.07 and 3.415.

How can they both be correct? Is it that they assume a different tooth count to be the centre of the range for a particular cutter. Can someone please explain.

Mike
1 July 2010 at 15:28 #53045
John Stevenson 1
Participant
@johnstevenson1
I wish I had a pound for every time I answered this

First off both tables are correct but you either have to use mine or Ivan’s, they can’t be mixed up.

Where the difference is is how the buttons are infed.

On Ivan’s he touches the front of the button onto the blank, moves sideways and feeds in.

the first part of the infeed is in fresh air until the two edges touch the blank.

On mine the two edges are centralised onto a blank of calculated width, then infed.

It’s where the infeed starts that gives the different sizes.

I did draw Ivan’s and mine out in CAD and place them on top of a correct gear and the differences were so slight it was hard to say which one fitted better.

John S.
1 July 2010 at 21:01 #53054
Terryd
Participant
@terryd72465
I would like to try gear making and would make 18 DP gears. If I wished to make a number 5 cutter, according to your table John, I need pins (buttons) of 46.17mm dia for the form tool. Is that correct?

Could these be made from gauge plate (hardened and tempered ) rather than silver steel? That sort of diameter ss is very expensive for experimenting, but I have some 1/4″ ground stock that I could make the discs from.

Terry
1 July 2010 at 21:29 #53056
John Stevenson 1
Participant
@johnstevenson1
Terry,

You take the size of the buttons for the cutter needed which are in the table at 1DP scale and divide by the DP so in your case it’s 7.18 / 18 = 0.399″ or 10.13mm

Not sure where you got 46.17 mm from ?

You can use gauge plate if needed, it’s only the flat version of silver steel.

John S.
1 July 2010 at 21:57 #53057
Terryd
Participant
@terryd72465
Thanks John,

You’ve cleared up my misunderstanding, a light has just switched on in my head!!

I was looking at the no 1 cutter in table 2 on your site which gave me the 46.17 figure, so am I right in saying that if I wished to make a No 1 cutter for an 18 dp gear, greater than 135 teeth my buttons would have to be 46.17 / 18 = 2.565″ or 65.15mm dia for example? That would be a large piece of silver steel!

Terry

Edited By Terryd on 01/07/2010 22:05:18

Edited By Terryd on 01/07/2010 22:07:51

Edited By Terryd on 01/07/2010 22:09:48
1 July 2010 at 22:30 #53058
John Stevenson 1
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@johnstevenson1
Yup you have got it.

The table is in inches that’s why you divide by DP .

2.565″ is quite large but you don’t need a full circle, you could mark out in gauge plate and cut and file a 1/4 quadrant. the rest of the circle does nothing.

Sometimes when the two radii are greater than the centre to centre distance you have to flat the buttons off where they touch anyway to get them in.

John S.
2 July 2010 at 05:15 #53061
Terryd
Participant
@terryd72465
Excuse My ignorance John, this area of engineering is new to me, but does the DP affect the ‘pin centres’ and ‘feed in’ in the same way?

Terry
2 July 2010 at 07:55 #53064
Michael Cox 1
Participant
@michaelcox1
Thanks for your reply John. I sat down last night with pencil and paper and confirmed your numbers from the geometry. I still cannot understand where Ivan laws numbers come from.

Mike
16 July 2010 at 22:47 #53470
Michael Cox 1
Participant
@michaelcox1
I have added a page to my website on making gear cutters. You can find it at

http://mikesworkshop.weebly.com/making-gear-cutters.html

Mike
18 July 2010 at 22:17 #53553
Sub Mandrel
Participant
@submandrel
Sorry if it seems partisan John, but I prefer the Ivan Law method. Why?

I just use the discs to take a tiny skim off the blank, then I KNOW I have an accurate zero to feed in from, also I’m not too confident I can part off discs of silver steel to an exact thickness – fine if you make disks from gauge plate.

Neil
16 August 2010 at 21:06 #54356
wheeltapper
Participant
@wheeltapper
I wonder if someone could help with the trouble I’m having with this gear cutting caper.

I’ve got Ivan Laws book and I followed the instructions for making a button tool for making a cutter.

I made the cutter exactly to plan ( and boy, did it give my little lathe a pounding)

I hardened and tempered the cutter, made an aluminium blank to try it out and would it cut,…….would it heck as like.

I tried everything I could think of, different speeds, very light feeds,all sorts, made no difference, the tool just hammered away at the ali and tore chunks out.

the cutter just didn’t seem to want to take an edge.

It looked like the one in the book, I made sure I had the spacer in the tool holder in the right place for forming and cutting.

the cutter is now at the bottom of the garden and I am totally confused.

I was hoping to attempt a clock but if I can’t even make a cutter what Chance have I got.

incidentally, why are the prices of cutters so stupidly variable, RDG sell them for £20-00

Chronos for £12-00 and I found one place on the net selling them for ….£136-00, no its not a misprint, £136-00.

Roy.
17 August 2010 at 00:03 #54364
Michael Cox 1
Participant
@michaelcox1
Hi Wheeltapper,

I too have been through the frustration of making gear cutters by the Ivan Law method. The John Stevensons method is much simpler and I have had good results. See my web pages:

http://mikesworkshop.weebly/making-gear-cutters.html

http://mikesworkshop.weebly/designing-gear-cutters.html

Mike
17 August 2010 at 08:47 #54368
Pierre EHLY
Participant
@pierreehly19171
john,

Have you an version for 14°1/2 PA ?

pierre
17 August 2010 at 11:59 #54373
wheeltapper
Participant
@wheeltapper
Sorry Mike but neither of those links work for me.

Roy
17 August 2010 at 12:26 #54375
Keith Long
Participant
@keithlong89920
Hi wheeltapper

Same problem for me – try putting ” .com” after the “weebly” – should work then I think.

(note there is a “dot” before the com)

Keith

Edited By Keith Long on 17/08/2010 12:27:33
17 August 2010 at 12:32 #54376
wheeltapper
Participant
@wheeltapper
works for me too, cheers.

looks like a good idea too.

Roy
17 August 2010 at 15:56 #54384
David Clark 13
Participant
@davidclark13
Hi Wheeltapper,

I too have been through the frustration of making gear cutters by the Ivan Law method. The John Stevensons method is much simpler and I have had good results. See my web pages:

http://mikesworkshop.weebly.com/making-gear-cutters.html

http://mikesworkshop.weebly.com/designing-gear-cutters.html

Mike

Edited By David Clark 1 on 17/08/2010 16:02:35

Edited By David Clark 1 on 17/08/2010 16:03:07
17 August 2010 at 22:21 #54400
Sub Mandrel
Participant
@submandrel
Hi wheeltapper,

I have cut gears in EN24T (tough steel) using Ivan Law cutters.

I guess something is going wrong with the geometry of your cutters OR you are running them far too fast.

This is a cutter from gauge plate, but the geometry is the same:

Look how the cutting edge passes well to the right of the centre of the arbor. This ensures postive rake on the cutting edge BUT the cutter must be mounted to allow relief – move the cutter (not rotating) until its tip can just touch the work – the ‘back’ must not touch the work when the tip just touches.

I run the single point cutters at between 60 and 100 rpm feeding manually about 5 thou per cut in brass or EN1a (free cutting steel), slower feed for hard steels. I brush the cutter with cutting fluid before each cut.

In aluminium the cutter should work freely and easily.

Good luck

Neil
22 August 2010 at 12:56 #54561
wheeltapper
Participant
@wheeltapper
Hi all

I tried making a cutter using a cone drill but the angle of the cutter seemed far too steep and it wasn’t leaving enough material at the tip so I thought, why not turn the problem on it’s head.

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.

Edited By wheeltapper on 22/08/2010 13:09:57
22 August 2010 at 19:56 #54576
Sub Mandrel
Participant
@submandrel
An interesting new technique!- It does depend on having the right diameter of cutter, but I get the feeling that the diameter isn’t too critical, as long as you get the spacing and infeed correct for whatever diameter you are using.

Neil
23 August 2010 at 08:12 #54594
John Olsen
Participant
@johnolsen79199
The diameter is supposed to be a close approximation to the ideal involute curve, so I suppose in theory there would only be one “best fit” diameter. I suspect that for a lot of applications it is not all that critical, eg if the gears are not all that heavily loaded. After all, ordinary gearcutters only have 8 or so to a set at most, and each of those is actually only right for one size of gear.

You could use a diamond * to adjust the size of a small mounted point to the desired diameter if you wanted to get close to a particular size that was not otherwise easily available.

I can still remember dropping a nice little home made cutter just after hardening and before tempering.

*An industrial one, not the one you gave your wife all those years back… (if you have a wife that is…)

regards

John
23 August 2010 at 08:47 #54597
John Stevenson 1
Participant
@johnstevenson1
An alternative is to use a boring head and dial in the correct diameter.

This will also cover for the larger pitches and hight count teeth that need large diameter cutters.

John S.
23 August 2010 at 21:16 #54645
Anthony Ashgrove
Participant
@anthonyashgrove58555
Hi all,

I have not actually cut any gears yet ! ! But have studied Ivan Law’s book and together with info found on the web written an exel spreadsheet to calculate the ‘button sizes’ and infeed to make form cutters for ANY DP and ANY PA. It calculates the data for each gear so you need to ‘average’ the cutter for the range of teeth youn require. If anyone wants a copy please e-mail me aashgrove@yahoo.com.

Hope this might clear up some confusion with the way it is presented in the book.

Tony Ashgrove
23 August 2010 at 21:25 #54646
wheeltapper
Participant
@wheeltapper
the main reason I tried this in the first place was because making a cutter with buttons hammered my poor little lathe to death and I thought there has to be a gentler way.

Roy
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