Gear cutters for clock wheels

Dear forum members,

Could you have a look at my album “Radius tool for gear cutter”?

I am open for comments and suggestions.

Accuracy of tooth thickness of gear cutter has to be improved, at least.

Regards,

Jouke

Well thats an interesting twist. You are a little limited on diameter with that method. What's wrong with turning tapered buttons in silver steel. With a parallel waist they can be accurately positioned in holes drilled in the end of the button holder, whitch is put in on the mill will correctly separate two buttons to give the correct thickness to the gear cutter. High Strength loctite to cement in place means that you don't loose the polish on the buttons as you don't have to apply heat to silver solder them in place.

regards Martin

Posted by Jouke van der Veen 07/02/2022 21:42:17

Dear forum members,

Could you have a look at my album “Radius tool for gear cutter”?

I am open for comments and suggestions.

Accuracy of tooth thickness of gear cutter has to be improved, at least.

Regards,

Jouke

Varying tooth thickness ,cause the sides of the cutter blank not
parallel.

Build a Eureka device and or make a two button tool
to cut both sides of the gear cutter at the same time.

John

Hallo Martin,

I considered the method you described more than once.

I recognise that having such a tool woul result in e constant tooth thickness but I think I willl not be able to postion two buttons at a, lets say, precise distance of 3x1.57 = 4.71mm. How precise has this to be? What do you exactly mean with a parallel waist?

Regards,

Jouke

Hallo John,

I think you are right. On the other hand I think an Eureka device is a step to far for me.

I preshaped the gear cutter with a “standard” cutting tool in 8 steps to a tooth thickness of (approx.) 1.7mm.

Then I changed over to the radius tool and needed again 8 steps, of course, to reach the final thickness of 1.57mm

With this method I had to repostion the gear cutter on the excentric mandrel several times.

It was my second trial. I started with a M1.27 in mild steel with a less precise result. The second trial was the M1.0 shown in this topic. I am convinced that I can do better. But remember, I have to do this on an Emco Compact 5.

How accurate should tooth thickness be?

Regards, Jouke

Edited By Jouke van der Veen on 07/02/2022 22:37:25

I assume you are making involute gear cutters using the "button method".

I make single tooth versions on my CNC lathe. I measure the tooth thickness using a caliper. I set the caliper to the requested diameter + 0.1 mm. The cutter tip should "lock" between the "legs" (don't know the English word) of the caliper. Then I set the gap 0.1 mm smaller than the requested size. Now it should not be possible to "lock" the tip of the gear between the "legs" of the caliper. By changing the gap between the "legs", I can "measure" very repeatable the tip of the gear.

I also made these cutters on the milling machine. An end mill is used as "Button". Instead of calculating the button diameter for the gear cutter to make, I calculate the the number teeth, based on the end mill diameter.

A 4 mm end mill can make a Modul 1 cutter for 12 (11.7) teeth and more.

A 5 mm end mill can make a Modul 1 cutter for 15 (14.6) teeth and more.

A 20 mm end mill can make a Modul 1 cutter for 59 (58,5) teeth and more.

Edited By Huub Buis on 07/02/2022 22:48:35

Using the analogy of a buttercup flower where the tapered sided button is the 'cup' and the waist is the much smaller 'stem'. If you drill your locating holes on the mill they can be located with precision using the dials or DRO.

regards Martin

Given that clock gear designs have quite a lot of clearance, how precise does the width have to be?

I measured the original thickness of the gear cutter at the “foot” of the teeth. Thickness varies between 4.72 and 4.77mm. So, the cutter blank is not optimal parallel, as John said.These differences cause a varying and larger offset of the tooth tips when the gear is mounted in its 4 positions. This needs improvement, at least.

Huub, I have to study your method before coming with a proper answer. My restriction is that I have to work with an Emco Compact 5 including its milling column in their original outfit. As many clock builders did. 😉

Double

Edited By Jouke van der Veen on 08/02/2022 09:15:01

John,

That is also my question. Cutter dimensions are specified two digits behind the point.

Example: M1: 1.57mm tooth tip, etc. But where do gear cutter makers end up with their final product?

In other words, my cutter, after some additional improvement, may be good enough. I would like to get some response on this.

On the other hand it would be a bad experience to have made a set of clock wheels, and then, after assembling, coming to the conclusion that they are not accurate enough!

Edited By Jouke van der Veen on 08/02/2022 10:07:09

You might look at this website. It designs "cycloidal" gear pairs based on standard profiles.

You can see immediately the clearance that the standards recommend. I've built a gear train based on the dxf files this generates, exported to a CAM program to actually generate g-code for a CNC mill, and they work well direct from the mill using the calculated centre-centre distance.

If you have the use of a 3D CAD program (such as Solid Edge or Fusion 360) you could import the dxfs and animate the gear pair to investigate the impact of tolerances.

Your cutting depth = D+f = 2.16 for a Modul 1 gear. The 0.16 (extra cutting depth) creates play between the gears. If you have a 20° pressure angle, this results in a clearance at 1 flank of (tan 20 x 0.16) 0.06 mm. At the 4 flanks there is 0.23 mm clearance total.

A 12 teeth Module 1 gear has a tip of 1.10 mm.

A 60 teeth Module 1 gear has a tip of 0.82 mm.

Posted by Jouke van der Veen 07/02/2022 22:35:10

Hallo John,

I think you are right. On the other hand I think an Eureka device is a step to far for me.
I preshaped the gear cutter with a “standard” cutting tool in 8 steps to a tooth thickness
of (approx.) 1.7mm.Then I changed over to the radius tool and needed again
8 steps, of course, to reach the final thickness of 1.57mm
With this method I had to repostion the gear cutter on the excentric mandrel
several times.It was my second trial. I started with a M1.27 in mild steel with
a less precise result. The second trial was the M1.0 shown in this topic. I am
convinced that I can do better. But remember, I have to do this on an Emco Compact 5.
How accurate should tooth thickness be?

Regards, Jouke

A lot of your problems can be resolved by boring and facing one side
of the cutter blank and marking that side and later on using this side
as the datum for mounting the blank of the finished cutter on the arbor.
The other side of the blank must be parallel to the datum side to
0.00 or as close as.

Secondly a two button tool will automatically give a constant width
on all of the cutting teeth. Referring back to the photo in my previous post
these 2 button tools some have parallel turned buttons that are hardened
and then loctited into the holder,in the absence of a dro system a cheap
clock gauge about £10 from China can easily be set up to give the
required spacing, a metric clock gauge reading in .01 can be easily
read to subdivide that to half or quarters.
The holder seen here is the one in the book Gears and gear cutting
and the clearance is provided by the 5 deg angle on the front.
The only problem that you face then is the minimum spindle speed
of your lathe which seems to be around 200 rpm ,to cut silver steel
with hardened silver steel tooling at the diameter that you have you would
need to be below 50 rpm , if you are unable to make adjustment to the
machine to get down to these speeds the next best thing is to
use a mandrel handle.Coating the tooling and cutter blank with RTD
will make it a lot easier.

John

Hallo Huub,

I understand that with your caliper check you can work wit an accuracy < 0.1mm for measuring gear tooth thickness, but not down to 0.01mm.

In the milling method you describe tooth foot radii are shaped with the appropriate end mill diameter.
I did not yet check if I can reproduce your method. For instance, I do not understand how you can make a M1 58 teeth gear cutter with a 20mm end mill. Is this a typing error?

in your following response you speak about gear tips of 1.1 and .82mm I expect these are for involute gearsand not cycloidal.

Regards, Jouke

Dear John H,

I have to study the website you refer to. It will be helpfull. I have no experience with CAD/CAM software. Thank you for the information about how get a better insight in tolerances for gear wheels.

Regards, Jouke

Dear John P,

I will apply your proposed cutting sequence on the next gear cutter to be made: pre-cutting followed by finish cutting on one side of the blank and then repeat this on the other side, starting from a real parallel blank. I think I will do this with my “one-button” tool. This tool has the benefit of giving a precise radius after a simple grinding step.
If this does does not work at all for me than I should switch over to the two-button cutter. But I know that generations of clock makers must have used methods equivalent to the one-button method.
I have a measuring clock available, and a digital caliper that can be magnetically clamped on the lathe.

I think, I have now a lot of input that will help me to improve accuracy of my working methods and to give more insight in required tolerancies. Thank to all the contributors. I will keep you informed.

Regards, Jouke

Edited By Jouke van der Veen on 08/02/2022 20:23:44

Your cutters look very serviceable and will give consistent tooth geometry. A deviation in tooth thickness of a few hundredths of a mm from perfect is really not an issue. I have now built quite a few clocks and my experience is that they are quite forgiving of tooth geometry. Unless you are building an unusual very low-power or long duration clock it just won’t matter.

To be honest though, I have gotten bored of making cutters myself and just buy them from PP Thornton. They last for ages (for ever if your are an amateur constructor) and can be resharpened easily. You can then get on with the task of making the clock...

Hallo Huub,

Now I understand your large end mill diameters. They are inherent to involute gears.

I think I understand the effect of using a spacer for getting clearance on the side cutting edges. As you understand my cutters do not have a clearance for the parallel parts of the teeth. I think, however, they should have to get a “smoother” tooth cutting in brass.

It would be nice to see some pictures showing your two ways of making gear cutters. These YouTube movies I just find on the Internet are yours I assume! I will have a look. Ijust saw something about gear cutting!

You are right about making the parallel parts of cutting edges larger then specified length to start with. This will make measurements easier. As a last step you can turn the parallel parts down to the specified length. By the way I measure with a micrometer.

Where do you live about in The Netherlands?

Regards,

Jouke

Edited By Jouke van der Veen on 09/02/2022 20:36:22