Speaking of making gears.....

[BCRider]

There's been a few threads recently about making gears or indexing for making gears. And along comes this interesting short on forming an involute single point cutter from Clickspring.

Making An 'Involute' Profile Fly Cutter - YouTube

Obviously the radius would need to be adjusted for different ranges. So it might not be practical to make the buttons from drill rod or similar like he shows. But there are options. Perhaps like this idea for holding two 1/4" HSS blanks ground to the proper radius. Then spaced with a shim and held secure with an upper "bridge" that ensures both cutters are held firmly. The holder being just the usual 1/2 or 5/8 wide Aloris style holder.

[Huub Buis]

Grinding HSS accurately for making gear cutters is not so easy. I make gear cutters and gears for a long time on the mill and on the lathe. I think the method for making the gear cutters on the mill is quit easy and accurate.

[djc]

And along comes this interesting short on forming an involute single point cutter from Clickspring.

What is he showing that was not already detailed in Ivan Law's book and discussed and refined here by Sir John?

https://bbs.homeshopmachinist.net/forum/general/43078-a-form-tool-for-gearcutting?t=42051

https://bbs.homeshopmachinist.net/forum/general/63055-gear-cutter-via-2-button-method

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

https://www.homemodelenginemachinist.com/threads/spread-sheet-for-button-formed-gear-cutter.5859/

If the two HSS bits are only clamped from the top as you show, as soon as you present them to the work, they will spread.

[BCRider]

I'd not run into that book or the method of using round buttons before. So it's new to me.

As for the clamping? You have a pretty poor expectation from your clamping setup if you think they would spread.

I do like the buttons idea since starting with round cutters ensures easy size radii. But for bigger radii needed for higher tooth counts using round buttons I suspect that it would be more viable to grind some square HSS blanks as shown. Just need some accurate radius template to work with.

I'll be taking advantage of the links.

And to Huub, I'm half way through your video. It all seems just great.

To my thinking the idea of Clickspring's where he uses a spacer first on the one side then on the other is nice because it sets up the cutter to receive the needed clearance angles very easily. That appears to be the big take away from his video.

[J Tiers]

The round buttons are an approximation. They generally do work, I understand, although I have not used them.

Whether the approximation is better or worse than the use of a Browne & Sharp type cutter over a range of tooth count, I do not know. There is a difference between a circle and an involute curve, but the difference can be subtle in specific cases.

[Huub Buis]

The round buttons are an approximation. They generally do work, I understand, although I have not used them.
Whether the approximation is better or worse than the use of a Browne & Sharp type cutter over a range of tooth count, I do not know. There is a difference between a circle and an involute curve, but the difference can be subtle in specific cases.

If you cut a 12 teeth gear using a T12..T13 Brown & Sharp involute cutter, the gear is more accurate than using a "button cutter" designed for a 12 teeth gear. If you use the T12..T13 Brown and Sharp involute cutter to cut a 13 teeth gear, this gear is not as accurate as the gear you make using a "button cutter" designed for a 13 teeth gear. At higher teeth counts, the involute Brown and Sharp cutters have a more accurate profile than a "button cutter" designed for this teeth count. Both methods produce gears that are usable for most applications.
If you have a CNC machine, you can make involute cutters for a specific teeth count. I make gear cutters having a "button method profile",on my CNC lathe. I don't change it to the involute profile because for me, there is nothing to gain. At the moment, I can spend the time it takes better on other wishes.
You can compare the shape of the involute cutter and the button method cutter in a CAD program. You can see the difference in profiles and compare it to the play between gears.

[J Tiers]

The 12 and 13 tooth case is special. That size is really not quite properly cut by any rotating form cutter no matter how made.

One aspect of the usual button method is that it makes a one-tooth cutter, which is a nuisance to use. (Not the fault of the buttons) You need more equipment to make a relieved cutter, or you have to make a "bent" cutter as shown in the Goodrich watch lathe book (for making watch gear cutters).

Also, there is a tilt to the button cutter that changes the cut profile to something more like an involute.

I have made gears with hand-ground cutters, where I had a gear to match the tooth form to. Those were used on a shaper, to make bevel gears. The form was near perfect for the spot I matched on the example gear, but it was a good deal of work to get the right form, and also to manage the shaper when cutting..

[djc]

The 12 and 13 tooth case is special...

I think you have missed his point. A B&S cutter (any one of the eight in the series) is correct for the lowest number tooth count of its range. A button cutter made for a specific tooth count that is at the upper part of a B&S cutter's range could be more accurate than the button cutter.

It is possible to write a little python program to work out (x,y) coordinates for a specific involute curve (Wikipedia has the parametric equations). Knowing the centre and radius of your approximate arc, you can work out the error between the correct point and the approximate arc.

It would be instructive for you to read and digest this article:

https://www.geartechnology.com/articles/21023-approximating-an-involute-tooth-profile

[The Artful Bodger]

Cutting gears on a shaper? Time to bring this out again...

http://neme-s.org/Shaper%20Books/Michael_Moore/shaper%20gear%20cut.pdf

It is a few years old but it might be worth looking at doing it with a couple of steppers and a control micro.

[BCRider]

Cutting gears on a shaper? Time to bring this out again...

http://neme-s.org/Shaper%20Books/Michael_Moore/shaper%20gear%20cut.pdf

It is a few years old but it might be worth looking at doing it with a couple of steppers and a control micro.

Rustinox set up for doing that on his shaper and managed to make a couple of nice gears.

To my thinking it's a LOT of work to make up all that stuff to just make a gear or two. I think I'd rather make up the curvy single flycutter style cutter. Or for a module that I'd use reasonably frequently even just buy the set of cutters.

[Rich Carlstedt]

The round buttons do an amazing job of reproducing a In-volute curve , if you use the right table---and there are a few out there


To start, You want a 5 to 7 degree angle on the buttons, so mill your stock at that angle by using this easy setup in your vise.
One Degree of angle is .017" per inch, so 5 degrees is .085" and if you use a 3/8" Toolbit, set the parallel at 4 3/8" and then place the button holder
in the vice and mill the 5 degree angle and then mill a slot and the two appropriate holes for the desired pitch center for the buttons

Now make the appropriate buttons with a pilot for the holes, so they can be silver soldered and tempered at the same time.

After mounting the button, grind them down flat with a belt sander and you automatically have a 5 degree relief and a closer involute curve

Grind the buttons and holder on a belt if you do not have a surface grinder , make the cut edge on the trailing end and use a sacrificial shim for step grinding

The picture below shows a very small gear cutter button set up .
Trying to hold two buttons with a clamp is a fools game in my opinion. you never know when or "if" they move. and using pilot holes for spacing assures the desired size
and the tapered holder produces great cutter relief .
Rich

[J Tiers]

I think you have missed his point. A B&S cutter (any one of the eight in the series) is correct for the lowest number tooth count of its range. A button cutter made for a specific tooth count that is at the upper part of a B&S cutter's range could be more accurate than the button cutter....................................

He actually said that, so, no, I did not miss the point. The formed cutter is a known and accepted compromise to minimise the number of different cutters required. Making a reasonable approximation to correctness for a specific number of teeth is bound to be better. A hob cuts theoretically correctly (aside from faceting, which is due to a finite number of cutting edges), and it will cut ANY number of teeth, at the price of a specialized machine.

For that matter, the cutter for 55-134 may be better, or no worse, at cutting 54 teeth as the one "officially labeled for" that count.

But those particular two tooth counts (12 & 13) really are "on the edge" of not being effectively cut by any formed cutter. At low tooth counts there begins to be an undercut needed, which the rotary formed cutter simply cannot cut. The required shape alters radically with tooth count, so much so that the cutter only cuts those two counts reasonably well, where the 55-134 cuts a huge range.

My point was that the 12 - 13 covers a relatively wide range in just two integers....it is a special case. There is a reason why the range covered in integer tooth count goes up with the tooth count. The actual change of ideal tooth shape is less and less per single integer difference in tooth count as the number of teeth goes up.

Oh, yeah, there are MORE than 8 cutters in that series. There are half step cutters which improve the form somewhat.

[Rich Carlstedt]

Continued coverage

The process covered in Law's book is great , but the process started earlier I believe in a article by Mr. Unwin in Model Engineer in the 1960's
and then followed by our own John Stevenson, then Laws, and Mikes Work Shop , so there are 4 variations that I am aware of
I did a study of the variations in the involute curves and compared them to the bible of gear measurement, the Van Keuren tables
The generated curves are quite good and this is a comparison made on a 44 tooth -16 pitch gear.
The variations change according to the tooth and pitch numbers , so each case is slightly different as you can see in picture # 2 .
The differences are very small
You can see in the last drawing that the cutter had to go .009" deeper compared to the other formula even though the difference in Pitch was only .0019" per side. That .009" may have been called out in those formulas, but Van Keuren is the goal for accuracy
Hope this helps !
Rich

[J Tiers]

You showed a thing resembling a gear cutter in your picture. Not clear, but implied by the picture that it was made with the button tool.

If that was made with the button tool shown, did you do relief? It looks as if a short "tooth" is being used in place of a true relief.

Goodyear has the cutter wheel slit and the teeth bent inward to form the relief. Forming a true relief would obviously be better.

[Rich Carlstedt]

My multi-tooth gear cutter all have tooth relief with a process that I developed years ago and have taught when I did Gear Seminars at the NAMES show in Detroit
Never seen it done before by anyone, not published. and it really works if you follow this process, which I will show in the following pictures
You turn the blank with the Two buttons and then cut the teeth , and then return to the Lathe and do the relief process . It does require a good
Tool Post and holders for repeatability, which my Aloris does well, and a way to sort of lock the spindle. I use low backgear for that ( explained later)
First is cutting the teeth. Set the cutter as a disc in the vise and have a rigid stop on the left side ( but not seen here) which is needed for repeatability for a 8 tooth cutter
Place the gear in the vise against the left side stop and place a dowel in the bore, this will give a constant height !
Now with a radius endmill , come in and cut to the center of the cutter to give you a 90 degree tooth ( not positive or negative ) ( ie to half the diameter - Mill depth to your desire)
This is a re-created photo, so the dowel and center line not exact , but you get the idea - note, the area you see the endmill in is called the 'Void" area in my explanation


Do not use the lathe under power !
If your lathe has a brake-- use it , or else place the spindle in lowest back gear and put the chuck key in the socket
Line the button cutter to the profile and set a carriage stop so the button tool returns to centerrline or set the DRO to zero
Now set at it Lathe centerline in height then bring it into the cutters voided area sufficiently
- and then by hand,rotate the chuck until the cutter tooth hits the top of the two buttons ( this is very important !
Now, make sure the spindle does not move (!) , and withdraw the button tool , and then mount a blank tool holder backwards ( now using the back end as a stop )
as seen in the following picture , raise the blank tool slowly and using a feeler gauge , sneak up to a .002" shim measuring the distance from the cutter tooth to the locked blank .. perfect.
now remove the feeler and and lock the setting of the blank bar , which is now a height setting for relief cutting
Now rotate the cutter to touch the top as seen here , and which places the cutter at .002" below center (!)


retract the carriage towards the tail stock swap holders and bring to "0" and then feed in thee button holder.\It will hit the tooth .002" too high -perfect !


now with the right hand , crank in the cross-slide-hard ! and with the left hand on the chuck wrench , pull down.
You will shave a perfect relief on that tooth .
It's what I call 'rotary shaping"
Repeat on next tooth , setting bar, then button and pressure as seen below

Good luck, and if you feel ( not needed really) that you want a totally relieved tooth,
just stone off a few thousandths off the face of each tooth.
Then heat treat your cutter and you are ready to go. no special tooling and very fast relieving
Rich

PS You will get tapered chips as the buttons enters the tool tooth -