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Hydraulic rc Liebherr excavator: gear cutting query

Help needed to cut internal gear for planatary gear box

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rebekah anderson22/06/2012 12:36:47
135 forum posts

Hi every one,

I am in need of your help.

I need to cut internal gear rings for my final drive on my rc excavator. (sprocket drive sys)

Internal diameter is about 20mm. The scraping of each tooth is fine but I am struggling with the actual tool. More the lack of it.

So I'm wondering if any one can help me.

I need a cutter to cut small 1mm wide teeth.

So either advice on how to make one (materials method) or someone make one for me.

I own a lathe, milling machine and rotory table with chuck. I can make a holde etc...i can design anything just the making is at times an issue.

Many tthanks becky

John McNamara22/06/2012 16:40:19
1313 forum posts
113 photos

Hello Rebekah

I wonder If instead of cutting the teeth one by one it would be easier to make a broach/former and form them all at once?

The tool would need to be hardened. I would be tempted to leave it full hard and not temper it

With one mm teeth the depth of cut is very small I would be tempted to try a toothless broach/former; mill the teeth along a length of bar the correct diameter say 200mm long plus a 50mm undersize section at the large driven end. A small fly cutter ground to the correct tooth profile would do, together with the rotary table for indexing.

Then grind the bar to a taper You could use fine emery strip in the lathe if you do not have a grinder, to enable the broach/former to start in the hole of the Ring gear blank. As it is pushed through the teeth will be progressively formed.

Commercial broaches have teeth, Maybe you can cut a series of rings to form teeth with a very sharp tool, although it might muck up the teeth form on the broach.

You would need a small press to force it through and plenty of oil on the tool, pork fat is great for this type of job.

If it the ring gear is thin you may have to press it in a larger supporting collar. to stop it stretching, it can be removed later.

Many commercial ring gears are broached.



Edited By John McNamara on 22/06/2012 16:41:21

Edited By John McNamara on 22/06/2012 16:58:49

Michael Gilligan22/06/2012 16:42:06
16420 forum posts
715 photos


That sounds an interesting project! More information and some Photos would be appreciated.

... Is it this one?


The "Bible" is probably "Gears for Small Mechanisms" by W. O. Davies ... this covers the theory, and geometry in great detail, but not much on the practical side.

From your comments, I presume that you intend to Plane/Shape the teeth with a single point tool.

A few questions:

What material are you using for the gear?

How many teeth?

What profile?

How thick is the gear?

Do you already have a "Keyway Cutting Attachment", or do you plan to use the TopSlide on the Lathe?


Let us have a liitle more detail, and I'm sure this forum will help.



Edited By Michael Gilligan on 22/06/2012 16:50:14

rebekah anderson22/06/2012 17:32:47
135 forum posts

Hiya both good ideas but my resources are limited so tool to do all in one go is not within my capability.


No it's this. It's a scratch build to 1/14 making it a lot larger than that.

the depth of the ring is about 10 to 15 mm. The number of teeth I couldnt say but I will try and work that out. I believe it would be mod 0.5

The profile I would say would be a standard triangular possibly convexed .


I haven't got an attachment yet but I might make one. Untill then it's the lathe.

Ideally if some one was up for making just the cutting tooth then that would be amazing. I would use it to make the external gears too.

to the left you can see the design it's a double planatary gear system to drive the sprockets

Edited By rebekah anderson on 22/06/2012 17:35:13

Michael Gilligan22/06/2012 17:54:09
16420 forum posts
715 photos

Wow, that's impressive.

... I will have a think.


Les Jones 122/06/2012 19:51:17
2162 forum posts
149 photos

Hi Rebekah
Have you considered using the gearbox from a cordless screwdriver or drill to save all the work in making all the gears yourself.


Michael Gilligan22/06/2012 20:17:55
16420 forum posts
715 photos

An excellent idea, Les ... certainly worth investigating.


Becky; if you decide to make a Slotting Attachment ... this design is excellent.

But; for occasional work, you can just remove the feedscrew from the lathe topslide and add a lever.


Edited By Michael Gilligan on 22/06/2012 20:28:02

John Stevenson22/06/2012 21:24:21
5068 forum posts
3 photos


If you are talking 0.5 mod and an internal diameter, root in this case, of 20mm then you are looking at 42 teeth.


Right click and view image for a larger picture.



The tool used to form an internal gear, cannot be used for an external as the form is reversed.


One method of making one is to buy a small pinion say 15 tooth as in the picture, harden this grind the front face and holding this in the mill with the spindle locked use the quill as a vertical planer.


Work mounted on the rotary table underneath and feed in to depth, back out rotate the Rt by one tooth and start again. You may have to go a tad deeper to make up for the fact it will not generated the correct involute but it will be very close.


John S.

Edited By John Stevenson on 22/06/2012 21:25:20

rebekah anderson22/06/2012 22:21:25
135 forum posts

Hiya guys,

Superfast with the replies and chuffed with the answers.

Great idea about the gearing from the screw driver. Funny enough I did find this idea via you tube whilst looking for planetary gears. I tried to find either Knackered screw drivers or actual parts and no joy.

The idea of using a pinion gear seems the best one so far. I do have one that fits the bill. You mentioned harden, do you mean a process to harden it some how. Is this heating and cooling it in engine oil? Also grinding, in what way? Is this the angle of the flat side at the intended cutting face?

I would like to know what software you used as above because it looks rather useful for me. Many thanks and I will post a thread about my progress.

Huge thank you you to you all


JasonB23/06/2012 10:32:12
18924 forum posts
2082 photos
1 articles

Could you not get it done on an EDM, this guy makes some nice small internal gears or have the smaller pinion type cutter that JS suggests cut out of gauge plate which will be easier to harden.


Michael Gilligan23/06/2012 10:37:39
16420 forum posts
715 photos

Further to John's suggestion about using the Mill and Rotary Table:

I just found this little gem, made by Marvin Machine Products Inc.

... what a useful project it would be, to build a replica!




More info here

Edited By Michael Gilligan on 23/06/2012 10:42:36

Michael Gilligan23/06/2012 10:44:15
16420 forum posts
715 photos
Posted by JasonB on 23/06/2012 10:32:12:

Could you not get it done on an EDM, this guy makes some nice small internal gears or have the smaller pinion type cutter that JS suggests cut out of gauge plate which will be easier to harden.


That's pretty


AndyB23/06/2012 10:47:20
167 forum posts
7 photos

Hi Becky,

Just a thought...

I found an idea ages ago, and I can't remember where, that I intend to make up.

It is a small hand shaper made out of an old top slide. I have got an ML7 topslide for it; you need the base and the slide. Mount a pivot are at the back of the cross slide with a bracket mounted at the back end of the topslide where the feedscrew mounts; this is for the hand lever. Use the tool holder to set your tool height. Mount the topslide towards the front of the cross slide and adjust to where you need to cut your teeth; divide off the bull wheel if possible. An HSS tool ground to shape will do the rest with a planing action.

Like I said, I can't remember where I saw the idea but it was very old. Looking at hand shapers should give the idea of what I am trying (dismally) to describe.

The work you have done so far looks amazing in the photographs; good luck with the rest.


rebekah anderson23/06/2012 14:22:55
135 forum posts

Wow, that guy can make some small gears. Now that would be the perfect solution. However the machine, from what I've seen, is expensive. So I can't go for that.

The manual option is the only one I can use unless there's a budget machine option. Might try and make that Marvin machine. Shouldn't be to difficult.

The only other thing I would like to put out there.

Is any one willing to make the cutting element for me?

I don't have a proper grinder and technique. In the mean time I am going to use the pinion method.

Thanks guys, am sure there willbe more questions.


rebekah anderson23/06/2012 14:44:28
135 forum posts


I thought I'd share my project. It's a fully hydraulic excavator.

this is it.¤t=fcbef7e9.jpg

A lot of it I have to design and build my self. Designing isn't a problem, I just need to make it all.

This is the valve block and the axial hydraulic motor¤t=59b36af4.jpg

Like this¤t=87c799c2.jpg

Just to give you an idea of size¤t=4ac07753.jpg



Edited By David Clark 1 on 23/06/2012 15:42:53

Donald Wittmann23/06/2012 15:43:37
40 forum posts

Hi Rebekah,

That is a very interesting project you have there. It certainly makes a welcome change from all the steam on here. Will the hydraulics be fully functional? Have you ever contacted Liebherr? I feel sure they would be very interested in your model If you were to contact them direct in Germany I feel sure that they could provide you with some more info that would be of use to you.

Keep up the excellent work.



Edited By David Clark 1 on 23/06/2012 15:43:54

rebekah anderson24/06/2012 12:03:04
135 forum posts

Hiya Donald,

Yes it is going to be fully hydraulic. The only parts I am buying ready made is the pump and the cylinders. I'm making 3 hydraulic motors, the valve block and the slew joint (allow hydraulic power to the undercarriage and stil rotate beyond 360 deg)

I have spoken to Liebherr and they have helped a little. You can buy hyd excavators models but only one of them makes them fully hydraulic.

The hydraulic motor is going to be unique. It's literary a scale version of the real one one the diggers. Once I know it works I can use them for the pump.



John Stevenson24/06/2012 13:56:57
5068 forum posts
3 photos


PM sent.

look under My Messages top left.

John S.

rebekah anderson24/06/2012 20:15:11
135 forum posts

Well had an hour to spare and made a hub for the final drive.

Photobucket Pictures, Images and Photos

Edited By rebekah anderson on 24/06/2012 20:16:06

Edited By rebekah anderson on 24/06/2012 20:16:22

Jeff Dayman24/06/2012 21:03:35
1896 forum posts
45 photos


The hub looks great. However, I have no idea how big or small British cigarette packages are these days, because I am living in North America, so I have no sense of its' dimensions. If you want to include an object for a visual scale reference in a photo, how about using a 6" or 150 mm rule? Or a digital caliper's scale? or a 1/2" or 13 mm twist drill? (or anything whose size is truly understood worldwide?)

Thanks again, looking forward to watching your project progress.


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