Gear cutters for clock wheels

Huub,

You will find it in my other album “Tangential cutter”. I added a photo of a sheet with handwritten text in Dutch about radius calculations of an elliptical cross-section of a round toolbit. I made this about 8 year ago and it should be improved by explaining wat the intentions were, and in English of course.

Regards, Jouke

Youke,

I have found your calculations and this is an interesting approach.

My first thoughts are that you want to mill an ellipse by placing the mill (button) at an angle. This way you can approach the desired tooth form more accurate than by using a mill or button the common way.

Question:

How do you know the dimensions of the ellipse that best fits the required shape.

Making such a cutter is not so simple but doable:

If you rotate the head of the mill, you will lose your position and setting the right position is very difficult as I experienced some time ago.

Placing one button at the right angle is doable. Placing the other button at the same angle is also not a problem, just reverse the tool 180°. Getting the right distance between the two buttons is very difficult, but using 2 separate tools is not a problem. So I think it is doable.
You could also mill one side of the two seperate tools until the distance between the buttons is OK and than bolt them together.

The benefit:

I expect that the extra accuracy you gain by making an ellipse will be lost once you cut different tooth sizes (12,13) using the same gear cutter. So the real gain will be only for the first gear in the range. Because making a cutter on the CNC lathe is so easy, I make a cutter specific for each tooth count.

If I look at the tolerances the cutters a made (D+f = 2.16) I expect that in the end the gain is little. The tolerances on clock gears are even greater.

How to check the result:

A way to check the real benefit is to design the gears in CAD made in different ways and check the differences.

Regards, Huub

Huub,

I had a quick look at your spreadsheet. Nice work. It needs more attention from my side.

Years ago I thought it was not such a good idea to make a cutter by grinding a radius by hand and then to check this radius against a known radius in a thin plate. The latter is made by drilling a hole in a plate and cutting a quarter away. Many clockwheel makers made their radius tools in that way I believe.

The idea was to make a well defined radius by cutting a round toolbit under a known angle. The part of the ellips with the highest curvature (direction of long axis) could be used as a cutting edge. The radius of that edge is surprisingly constant over many degrees. So you do not use a round button for cutting but the elliptical shape with a rather constant radius.

You start with a horizontal tool holder in which a round toolbit is clamped under a known angle from the vertical. You can always use a toolbit with the constant diameter D.The top part of the toolbit is machined down to a smaller diameter d which will become the short diameter of the ellips you need. This ellips is made by cutting the top of the toolbit parallel to the tool holder.
The curvature (or 1/r) of the ellips in the direction of the long axis is now fully determined by diameter d and angle of toolbit from the vertical. As said above: radius r is rather constant along a considerable angle of the “tip” of the ellips.

Depending on the radius r you need you machine a toolbit down to a corresponding diameter d.

The elliptical cutter was intended to be used feeding perpendiculer to the gear cutter blank axis. I agree that moving away from this direction may give undefined shapes.

A lot of words about a shape tool I never really used and in principle the same as a tangential cutter with a round toolbit I was not familiar with at that time. So “invented” by myself 😉.

Jouke

Gentlemen,

I tried to improve parallelism of a gear cutter blank with diameter 30mm having a thickness variation of 0.05mm by applying the super glue chuck method. It decreased to 0.03mm, so not so much improvement. I bonded the blank to an aluminium plate, faced after mounting in the independant 4-jaw, by applying 4 droplets of super glue (between the 4 small holes, I will add a picture to the album). The blank was quickly pressed against the chuck by means of a mandrel in the tail stock. After debonding in boiling water I found two thin disks of glue back on the aluminium. I measured thickness of these and found 0.09 and 0.08mm, respectively. Rather thick in my opinion. I wonder how an a constant and minimum thickness of the glue film can be achieved. I used Ever Build Stick 2 Super Glue GP Industrial Grade, set time 5-15s. I think it is so called medium viscosity.

Regards,

Jouke

Jouke,

Gentlemen,
May women not reply

The blank was quickly pressed against the chuck by means of a mandrel in the tail stock.
If you do this, you have to use very little pressure because the raw blank it self is not flat. Have you removed the burs from making the mounting hole? Have you removed the burs from making the chamfer?

It decreased to 0.03mm, so not so much improvement.
From 5 to 3 is 40% better, you are on the right way

My procudure for this would be:

• Face the blank, drill the hole (- 0.1 mm), chamfer the blank, chamfer the hole, do a last facing pass.
• Turn the blank to do the other side
• Face the blank, chamfer the blank, chamfer the hole, do a last facing pass.
• Ream or drill the hole to remove the burs from chamfering and get right the diameter
• Give the blank on both sides a few manual grinding passes using an old worn 400 grid diamond grinding plate (1 mm thick)

I have checked a M20 washer 40 mm diameter, 4.83 mm thick, that I faced using the above procedure a few months ago. Thickness spread 4.82..4.83 mm. This was done using a taper in the spindle bore as I explained before.

• Have you faced both sides of the blank using the super glue method
• Did you use a HSS tool or Insert (Carbide)
• RPM
• Cutting depth
• Thickness of the blank
• Has the blank a really smooth finish
• Have you checked the cross slide play. Any play will lead to thickness variations.

Regards, Huub

Edited By Huub on 14/02/2022 22:26:50

Huub,

Your first point: I realised it too late to correct it. I apologize for it.

Of course there was some 40% improvement and you can improve it to below zero 😉 but you can make it worse.

The sequence of operations you describe should be the one I should apply next time.

I am not sure if a low pressure during bonding to the face place would work for me. The small blank is in vertical position when it is placed in position and it should in center I suppose. Perhaps I should use a thinner glue.

I used a 4.5mm thick blank that had already the final central hole and the 4 3mm holes. Burrs were removed from all edges. I did not polish before facing. One side was faced in glued position. I still can do the other side but I can also start again from the beginning on this blank.

Carbide insert with radius .6mm for this facing (the glued side was with HSS).

Rpm was 550.

Cutting depth appr. 0.05mm. Not a really smooth surface.

I did not lock the saddle and dit not correct cross slide for play.

So many things to improve. I could repeat an improved procedure on the same blank but could also start from the real beginning by cutting new blanks from silversteel bar stock.

Regards,

Jouke

Edited By Jouke van der Veen on 15/02/2022 09:30:20

Edited By Jouke van der Veen on 15/02/2022 09:58:48

That was what I meant.

Jouke

Jouke,

I still can do the other side but I can also start again from the beginning on this blank.
Just use the same blank until you get it right.

Not a really smooth surface.
If you are targetting the 0.01 mm range the surface should be really smooth. That is the first to achieve. Start by using a softer steel to get a feel for it. Check the tip of the tool using a 10X magnifier. Some damage is hard to see by eye.
You should play with the RPM, cutting depth and feed. Depending on the insert, you can't do a shallow cut. Depending on the rigidity of the lathe, you can't do a thicker cut. If there is an unbalance in the chuck (or bad bearings), you can't run high RPM.
Listen to the sound the cutting makes. You can hear if the cutting is smooth or rough!!!
Make notes of the metal type, turning conditions, tool data and the result. Buildup experience!!!

I did not polish before facing
I just give it 2 passes in 2 directions to remove any burs or high spots (from impurity's).

Rpm was 550.
That is pretty slow for carbide. I have a Vc (Velocity at the outer diameter) of 180 mm/min!!!

My test on the small lathe
I faced an other 40 mm washer on the small lathe (HB300) using the glue method (cheap Super glue from the Action store). I faced a 20 mm register to loosely centre the washer. I gently pressed the washer against the mandrell using my fingers.

I faced both sides CNC using a carbide insert, nose radius 0.4 mm, RPM 1400, Feed 60 mm/min, 0.05 mm cutting depth (final pass).
Spread 4.045 .. 4.055 mm, the same as on the bigger (HBM BF290)

Then I faced one side again, but now manual (on the same lathe)
Spread 3.925..3.920

So I can repeat the results on both lathes manual and CNC.

I boiled the glued washer for 6 minutes (microwave) but couldn't separate the washer from the mandrel. It took a bit force (screw driver) to get is lose. So I couldn't measure the thickness of the glue but I estimate around (0.02..0.05 mm).

Normally I heat up the mandrel using a torch!!!

Edited By Huub on 15/02/2022 13:07:36

Edited By Huub on 15/02/2022 13:08:06

A lot of improvement here!

I started with polishing the “faced” gear blank (see earlier) on a 800 diamond coated steel disk. Of course this does not improve parallelism (0.03mm) but does show all features on the surface.

Thereafter I faced the other side of the blank by bonding it to a freshly faced alu disk in the chuck. Again I applied 4 droplets of super glue to the blank surface, between the 4 small holes. Then I put the blank on a 8mm mandrel in the tailstock and pressed it against the chuck. Facing was done in two steps of approx 0.05mm with a carbide insert with radius .4mm (not .6mm) with 950rpm.

After appr. 15min in boiling water the blank came off. I measured thickness between the 4 holes a close as possible to the outer edge, with following results: 4.30(3); 4.30(5); 4.30(7) and 4.30(5)mm.

To my opinion this result is more than good enough to proceed to the next operation: profiling of the blank on the excentric mandrel. When starting with new blanks I will follow a more consequent sequence of operations, as Huib Buis proposes.

The glue remainings are still on the alu disk. I tried to remove it for thickness measurents (as I did earlier) but I could not peel it off. Perhaps I should leave it longer in water but that may increase thickness by swelling. It should be dried before measuring. It is for sure that this thickness must be very constant, otherwise the above reported parallelism is impossible.

With thanks to the forum and Huub especially.

Regards, Jouke

Jouke,

with following results: 4.30(3); 4.30(5); 4.30(7) and 4.30(5)mm.
Great to see results are improving. Turning within 0.01 mm on a hobby lathe is not only good but excellent.

To my opinion this result is more than good enough to proceed to the next operation
I agree, you have the base for a good gear cutter.

I am looking forward to see the finished gear cutter and the gear you made using this cutter.

Huub

Edited By Huub on 17/02/2022 21:46:05

Intention was to measure thickness of glue between cutter blank and alu chuck face.

After 1/2 hour in boiling water the glue remainings still did not release. Therefore I decided to peel it of with a sharp blade. It came off in tiny thin pieces and not in one part. Not to measure but also with the conclusion that the super glue layer between blank and face was now (much) thinner than in my first trial (.08 to .09mm). I am convinced that this improvement must have helped me in getting the parallelism reported above.

Good progress.

Tooth shape has been machined on the cutter blank.

First on side of the blank was shaped into its final cycloidal shape and then the other side.

First a pre-shape was made with a standard 0.4mm radius carbide insert with steps following the final contour of theradius. This radius was made with the “half ball” radius tool described at the start of this topic. On the first side it was done with 200 rpm and feeding the radius tool with the cross slide. This suffered from some vibration and resulted in visual roughness in the radius. Therefore, this shaping was repeated by cranking the chuck by hand (as John P proposed!), resulting in a much better surface. This radius procedure was repeated on the other side of the blank but now in 3 steps, to get a nominal tooth thickness of 1.57mm.

Final result was a tooth thickness varying between 1.56(7)and 1.58(1)mm (measured with micrometer), not bad I think.

Next steps will be cutting the 4 teeth of the gear cutter, pregrinding the front of these teeth and then to harden it. First I will do some exercise on the cutter with less accurate shape made earlier.

When turning using form tools, the cutting edge is often large. This gives a heavy load on the tool (post), comparable when doing threading. Let the tool stick out as minimal as possible and keep the tool above the tool post. If the tool shatters, reduce the RPM. Some times also to shallow cuts can cause chatter.

If you use the "Tangential cutter" you need to let the tip stick out as minimal as possible.

I keep the stick out of my tools below 12 mm. Only when turning between centres, I need more stick out. Because then the load is quit small, it is not a problem.

Final result was a tooth thickness varying between 1.56(7)and 1.58(1)mm (measured with micrometer), not bad I think
This is more than adequate for cutting gears.

Next steps will be cutting the 4 teeth of the gear cutter,
If you want to polish the flank of the cutter, do it before cutting the teeth.

Edited By Huub on 20/02/2022 23:10:45

Huub,

i think you are right to do it in that order.

Which method would you follow to polish? There are people who make a wooden contra shape of the tooth and let the blank rotate through it while a polishing paste is applied.

I think you should avoid to round the corners of the tip of the tooth.

What is your advise?

Regards,

Jouke

Youke,

Which method would you follow to polish
I use in this order:

• 400 grid sand paper, sanding by hand (this dust is killing for the lathe ways)
• steel wool (safe to use on the lathe)
• dremel and polish paste (this dust is killing for the lathe ways)

I think you should avoid to round the corners of the tip of the tooth.
It would make the teeth a bit stronger but I never do it.

The CNC turned cutters have an excellent finish and are good enough as is.
From the the milled cutters, i only remove the burs by scratching with my nails. The finish is not as good as the turned cutters, but good enough.

After hardening (I only harden for cutting aluminium and HPL, not for plastics, don't cut steel) I only give the flat cutting face a few strokes on a stone (800 grid I think)
I don't relieve the 25 mm long fly cutters after hardening. I want them as hard as possible. I do not quench in oil (anymore) but use water.

Appreciating that I am rather late to this thread, and my apologies for slightly straying from the original post, but this may be of interest to someone...

There is a really excellent book that covers much of this and far more besides:-

"Wheel and Pinion Cutting in Horology" by J Malcolm Wild FBHI.

First published in 2001, second impression 2005.

ISBN 1 86126 245 0

It is a very good read as it also covers the historical side as well as the practical. The presentation is unusually clear and it is very well illustrated. Of most importance of course is the fact that the information conveyed is accurate and very practical, and the methods put forward are based on long experience and work as suggested. Whether you wish to make your own cutters of various types or to use the splendid Thornton ones this book is a very useful resource.

Hallo Lauri,

Yes, I am aware of this book but I do not have it and had never the opportunity to look into it.

I agree, it could be very helpful in choosing proper techniques for wheel and pinion cutting.

Regards,

Jouke

Hallo Jouke,

Yes it is always nice to be able to have a good look at a book before deciding whether to purchase it.

If it helps at all I have found that the publishers Crowood Press do have copies, as do a number of English bookshops as found on abebooks.co.uk website. Perhaps of more use if you are in Holland is that Amazon also carry copies.

Good luck with your cutter making, I am sure your hard work will pay off.

Regards,

Laurie.

If you need a flavour of J.Malcolm Wild’s knowledge and skill, have a look at his website: **LINK**

http://www.j-m-w.co.uk

… and particularly this article [which is linked on that page] : **LINK**

http://www.j-m-w.co.uk/HJ%20Published%20ArticleNEW.pdf

MichaelG.

Jouke,

I finally finished the video about gear making. I started a separate topic and I hope it will get you on the way.

Topic

Video

Regards, Huub