Author Topic: Cutting internal gear teeth  (Read 37334 times)

bogstandard

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Cutting internal gear teeth
« on: October 03, 2009, 05:26:58 AM »
This is one thing I have never attempted.

I went in search on the web to see how it is achieved, and it looks like that it is done with a single tooth cutter, like cutting a keyway slot, but going around the internal diameter to produce the number of teeth required (looks to be a good job for a shaping machine).

To all those more experienced than myself, is it a feasible proposition to do this by hand using a dividing head and a hand powered keyway slotter, or is there an easier way?

Bogs

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #1 on: October 03, 2009, 06:21:31 AM »
About the only way John,
If the gear is big enough inside another way is to get a small gear of the same pitch turn it dished, harden it, hollow grind it and use this as a cutter indexing round one tooth at a time.

Advantages are finding a ready made gear of the right profile may be easier than hand grinding an involute. As you also cut one tooth you also part cut the teeth to the side. As you index round the multiple cuts will generate a nearly perfect involute.

This is the way it's done commercially but the blank and gear rotate in sync each straoke of the ram.

John S.
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bogstandard

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Re: Cutting internal gear teeth
« Reply #2 on: October 03, 2009, 07:56:41 AM »
No worries on that score John, I had delivered this morning a set of module hobs from Arc Euro.

They managed to get me a full set together, even though it says they are out of stock. :clap:

What nice people to deal with. :thumbup:

So not only will I be able to cut normal spur gears, I should be able to make the cutter as you suggested.

It sounds like a bit of a long job, but what you have told me, instills me with confidence that I will be able to do it. :ddb: :ddb:

Many thanks.


John

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #3 on: October 03, 2009, 08:06:21 AM »
You will be please with them, they are very good quality.
When they got the samples in they passed me a 20 DP hob for testing as I have a gear hobber, well I love testing other peoples gear  :zap:

So found a nice laser cut blank still with the outer scale on and dross from cutting, dialled in a reasonable high speed and feed and ploughed  thru.

No problems, nice gear good finish and no damage to the hob, might sound rough but someone is going to do the same and moan if it shags all the teeth off.

I'm still using the same cutter to cut all the 20 DP gears I have to produce and so far it hasn't needed retouching.

How are you going to drive these ?

John S.
John Stevenson

Offline DeereGuy

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Re: Cutting internal gear teeth
« Reply #4 on: October 03, 2009, 08:37:49 AM »
John's do either of you have a link to the hob  you are talking about?

bogstandard

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Re: Cutting internal gear teeth
« Reply #5 on: October 03, 2009, 08:53:15 AM »
Bob,


http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Gear-Hobs



John,

After seeing that DVD about gear cutting a few months ago, it gave me a good idea to try.

Very similar to using a freewheeling blank on the lathe for cutting a worm wheel. See attached C-o-C.

I am contemplating stacking gear blanks together, or make long blanks and part off to the thickness required.

The gashing doesn't need to be too deep or long, it is only there until the spiral of the hob starts to work like a worm spindle thread and drive the blank while it is being fed along it. Once the intial cut is done, it is a matter of going back to the start, put a little more cut on, re-engage the teeth and take another cut.

I think it has every chance of doing a good job, but if not, I will most probably make a small hobbing machine.

http://www.collegeengineering.co.uk/Castings/582.htm

The cost of small gearing is the only thing holding me up on a lot of projects I already have a desire to do. They are ridiculously expensive. If this works satisfactorily, then the cost of the hobs, and if needs be, the small hobbing machine, will soon be recouped by the savings made. This set also contains the correct module for the change gears, and other gears on my lathe, so then that opens up other areas to be explored.


John

« Last Edit: October 03, 2009, 09:02:10 AM by bogstandard »

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #6 on: October 03, 2009, 09:09:40 AM »
Don't see any reason why that won't work although I'd go for full depth at one pass, light cuts have more chance to bounce about wheras a deep cut into a pre gashed blank should hold tit steady, use a sacrificial gear at the start and end as that's were all the errors getting started and ending will occur.

Personally I wouldn't bother with the CES hobber as once the method is established I'm sure a more robust / universal machine could be fabricated up at 1/4 of the cost.

John S.
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bogstandard

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Re: Cutting internal gear teeth
« Reply #7 on: October 03, 2009, 09:31:36 AM »
I will suck it and see John. It will be a few months before this project gets to the front of the queue, so I have a little more time to search for answers before then.

If this works OK, I won't even bother with a dedicated hobbing machine. I am not going into production, just making gears for everything I want to do. I reckon if I can cut eight pairs of gears, maybe less, then the hobs will have paid for themselves.


Bob,

Unlike what most people think, they aren't great big stonking beasts of a cutter, but very genteel and superbly made pieces of engineering wonderment.

This is the largest (1.25) and smallest (0.3), the largest is shown against one of my change wheels off the lathe, the cutter is in fact shown upside down.




John

Offline ScroungerLee

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Re: Cutting internal gear teeth
« Reply #8 on: October 04, 2009, 07:17:24 PM »
About the only way John,
If the gear is big enough inside another way is to get a small gear of the same pitch turn it dished, harden it, hollow grind it and use this as a cutter indexing round one tooth at a time.

Advantages are finding a ready made gear of the right profile may be easier than hand grinding an involute. As you also cut one tooth you also part cut the teeth to the side. As you index round the multiple cuts will generate a nearly perfect involute.

This is the way it's done commercially but the blank and gear rotate in sync each straoke of the ram.

John S.


I have a question about this, using one gear to cut another won't cut deep enough to reach the base circle, will it?

Lee

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #9 on: October 04, 2009, 07:32:27 PM »
Technically no, the cutters used in industry have been modified to allow clearance.
In the home shop use you can fudge the calculations by adding the clearance to the pitch circle, it will add a gnats cock of backlash to the gear but it will still be a serviceable gear.

To be honest on small model engine gears like wot John is after you would probably be hard pressed to measure any inaccuracy.

One point about involute gears is that even though centre distance and or diameters can be out the gears will still mesh correctly and run OK even though they may have excessive clearance.

John S.
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bogstandard

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Re: Cutting internal gear teeth
« Reply #10 on: October 04, 2009, 11:01:17 PM »
Very interesting info coming out here guys.

Keep it up and I will be starting sooner than you think.

Just joking of course, this is a rather large subject to absorb quickly, but every little snippet of information all helps in seeing the big picture.

Reading technical information is OK to a point, having personal experiences to read is even better. There is a great difference between theory and practice.

John

Offline John Hill

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Re: Cutting internal gear teeth
« Reply #11 on: October 04, 2009, 11:19:12 PM »
John, are you going to be able to cut internal gears with those hobbing cutters? :scratch:
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bogstandard

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Re: Cutting internal gear teeth
« Reply #12 on: October 04, 2009, 11:58:39 PM »
John,

This is what we have been discussing.

The hobs won't cut internal teeth directly, only external.

But with the hobs I have, I will be able to make a cutter fairly easily, and that will then allow me to broach the internal gears to the correct profile using a hand cranked keyway slotter.

John

Offline John Hill

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Re: Cutting internal gear teeth
« Reply #13 on: October 05, 2009, 02:42:04 AM »
Oh right!  Sorry I must have been a little switched off!  I think if you want to cut model size internal gears you should call around here and use Sally Shaper. :coffee:
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Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #14 on: October 05, 2009, 03:13:26 AM »
John,
Not sure what you mill looks like on the back end but many have a slotter position.
Some years ago a friend of mine, now dead, wanted to do similar but for keyways, I scrounged him a big angle plate, slide off a machine and a motor and gearbox and he built a slotter to suit.






Sorry about the state of the pictures but they were done with an early camera phone and I never got any decent ones but I thing you get the idea.

One of these and a RT and you have a gear planer.

John S.
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bogstandard

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Re: Cutting internal gear teeth
« Reply #15 on: October 05, 2009, 03:30:43 AM »
John S,

Mine does have the sliding head, but no machined area at the  back to bolt things to. I think it is designed more for the machine to be used like a radial arm rather than a two headed machine. Besides, even if it would fit, the way the machine is sited, I don't think there is enough room to swing the head around by 180 degs. I have enough trouble swinging the cat.

John H,

Being able to use Sally would be great, but the cost of air fair is a bit offputting.

I have yet to make the slotting tool, but I already have the designs for it in my head. Normally it would be used on the lathe, but to do this job, it would need to be able to work on the mill, so as usual, with my interchangeable tooling idea, I will need to mount the lathe compound slide and toolpost onto the mill, to give me the adjustment for cutting when the part is mounted into the dividing head.

I suppose I could use the mill's own quill as a slotting head, but I don't fancy the idea of loading the quill like that, plus I would have to fix up some method of stopping the spindle turning, and it might be very tight on throat dimensions as well. So that idea hasn't even been considered past the thought stage.

As one problem is solved, another one rears it's ugly head. But what would life be like without it's little problems.

John

Offline John Hill

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Re: Cutting internal gear teeth
« Reply #16 on: October 05, 2009, 03:48:11 AM »
John,  yes air fares can be a challenge at times. Living where we are it is a significant air fare to get to anywhere,  three hours is the minimum trip and that only gets one to Australia, its about 13 to the US and I think 25 or more to the UK.  One trip I did to Europe was 46 hours door to door because of diversions due to weather then aircraft problems.

I suppose with some sort of jig you could remove about 75%, maybe more, of the metal by drilling a small hole at the base of the tooth and a bigger drill above it?  Maybe with a dividing head you could drill the teeth without a very complex jig? :coffee:
« Last Edit: October 05, 2009, 03:50:23 AM by John Hill »
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Offline sorveltaja

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Re: Cutting internal gear teeth
« Reply #17 on: October 05, 2009, 04:15:03 PM »
I wonder, what is to be expected. Interest plays main role. Set of planetary gears maybe?




Offline cedge

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Re: Cutting internal gear teeth
« Reply #18 on: October 05, 2009, 04:31:32 PM »
John
Have a look at Evan's solution to the hand "hobber/shaper/slotter".  http://metalshopborealis.ca/hobber/hobber.htm

Steve

bogstandard

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Re: Cutting internal gear teeth
« Reply #19 on: October 05, 2009, 04:58:36 PM »
Sorveltaja,

There are a lot of engines that use complex internal and spur gear setups. By doing it this way, I will be able to expand the range of engines I have the opportunity to build, purely because the cost of ready made gears is so prohibitive. Being able to make my own will put them within financial reach.

This is a simple example of what I am on about.

http://www.billreichart.com/images/epicyclicengine_lrg.jpg

Steve,

That is almost what I had in mind, but because it would be very dificult to set up indexing on my lathe to do all combinations of internal gears, I will be setting up the same sort of operation on the mill using my dividing head to give me the exact tooth spacing, and the compound to put the feed for the cut on.
Many thanks for the link, that will come in handy when I start to build the slotter, it is now in my 'favourites'.


John

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #20 on: October 05, 2009, 05:12:52 PM »
Best move the handle to work sideways, not vertical.
Unless you are 7 foot tall it becomes very tiring working over the top as opposed to working at waist level.

John S.
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Offline cedge

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Re: Cutting internal gear teeth
« Reply #21 on: October 05, 2009, 05:56:56 PM »
John
You're getting lazy...LOL. I added an indexer to my smaller lathe spindle long ago and it worked like a charm. Now that I've got to know the bolt circle thingy on my DRO, making up custom plates wouldn't be much of a job.

I can envision using the DRO to make the gear blank work as it's own indexer by drilling the required number of holes of the right size at the proper radius. Seems like that would cut down on the hand slotting work too. Trust me.... I'm not trying to teach an old dog to suck eggs.... just tossing out ideas that I too might need for building the same machine. When your box has a hole in it large enough to fall through, you wind up thinking outside of it..... even if you don't want to....(grin) You've gotten my head going off in new directions, so I guess I can't complain too much.

Steve

Offline John Hill

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Re: Cutting internal gear teeth
« Reply #22 on: October 05, 2009, 06:03:24 PM »
John Bogs, I think you have some sort of vertical filer machine?  You have a power hack saw too I think?

Perhaps you could sit down with a cup of tea and design some sort of jig for either rmachine to hold your blank while something like a shaped file or a form tool cut the tooth?

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Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #23 on: October 05, 2009, 06:14:05 PM »
John
You're getting lazy...LOL.
Steve

 :thumbup: Not really Steve, the odd keyway especially into alloy isn't bad but steel is another ball game.
I got back into the workshop game making parts for my racing bikes, at the time close ratio gears for Nortons were like hens teeth so I used to make my own.
Putting 6 splines into gear steel on 3 different gears per box soon teaches you the most comfortable way.
I had my lever horizontal and at elbow hight  so my fore arm was straight, the lever was about 24 " long and any less would have been a right pain.

The £400 I paid for my first slotter was money very well spent.

John S.
John Stevenson

Offline cedge

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Re: Cutting internal gear teeth
« Reply #24 on: October 05, 2009, 06:58:23 PM »
Sorry John S.... That one was actually targeted at the Bog-o-lounger....(grin)

Steve

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #25 on: October 05, 2009, 07:34:22 PM »
OK no problem, I'm actually thinking of adopting John [ bogs ] so I can legally change his name.
If it pans out I'll call him Bandit and Bandit will become Bogs, what do others think ?

John S.
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Offline cedge

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Re: Cutting internal gear teeth
« Reply #26 on: October 05, 2009, 08:05:08 PM »
Man.... are you ever gonna pi$$ Bandit off with that idea....LOL

Steve

bogstandard

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Re: Cutting internal gear teeth
« Reply #27 on: October 06, 2009, 08:07:34 AM »
Hey, you two, pick on Bog's time is it?

Unfortunately, Bandit doesn't want anything to do with me at the moment, that is why I am having trouble coming up with new ideas.


Anyway, back on track to put you straight, but first, this turned up this morning, I had forgotten to order it when I ordered the hobs.

A nice shiny 8mm arbor that fits the hobs perfectly. So part way along with the project.




Back to reality, and thinking INSIDE the box.

As I have already explained to John in private and everyone else now, plus having to come up with reasons for not using what has been suggested. I have a lot of thinking time on my hands at the moment, but not a lot of machine time, so even though your ideas are good, I have come up with my own. The main problem was getting the cutter made, and John has solved that for me.

My way of thinking.

WHY make life difficult for myself when I have most of the items available at my disposal? It also keeps the costs well down.

The first, accurate indexing. I have my dividing head to do that,

Putting an accurate cut on. I have the compound slide off the lathe to do that. Plus if I really wanted super accuracy, I can just plug the compound read head into the mill display, and I could, if I wanted to, be working to the nearest 0.00005" (or even more accurately if I decide I want to swing the compound round a little).

So what else needs to be done. The slotter, which has to be made anyway.

Then a support block for the compound to mount it onto the mill square and at the correct height.
Much easier to make than some sort of indexing bits for the lathe.

Can you think of anything I have forgotten?

Does the well know phrase or saying spring to mind - KISS.



Do I hear any mumblings in the background? Or are we going to extract the urine out of Bogs once again. :lol:


Bogs Bandit

Offline Darren

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Re: Cutting internal gear teeth
« Reply #28 on: October 06, 2009, 08:11:25 AM »
Very nice John, very nice indeed ......  :bow:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Bernd

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Re: Cutting internal gear teeth
« Reply #29 on: October 06, 2009, 08:51:00 AM »
Bogs,

Been following this thread silently. Very interesting. The place I worked at, as you are well aware of, was a gear cutting machine manufacture.

So, in one of the departments were they cut gears for our own use on machines, they had several internal hobbing, for lack of better terminology, machines. The arangement is like yours only verticle and all machine powered. If I recall right the cutter also revoled as it was cutting the internal teeth. This brings a question to my nind, does your cutter also have to rotate while you rotate the gear you are cutting?

I would think that if you rotated the gear a few degress you would cut all the metal and not be left with any teeth. Or am I missing something here that I don't see clearly.

Don't bother trying to explain in words to me now. I'll understand better once you have the set up done and are actually cutting gears. I work better with pictures than words. :)

Bernd
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bogstandard

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Re: Cutting internal gear teeth
« Reply #30 on: October 06, 2009, 10:13:49 AM »
Bernd,

As explained to me by John S, the cutter is made to the same profile as a small spur gear.

The central tooth on one side is the one that does the main cutting, and the teeth either side of it (depending how large the cutter is made) partially shapes the other teeth that are due to be cut either side of the main cut.

So basically to reduce the manual loading while cutting, you make a small cutter, so that say only one either side gets shaved, whereas if you made a large cutter with many teeth, you might be shaving say 8 or 9 at the same time (this will put more load on the cutter and of course the arm that is operating it).

I hope that is the way John meant it to happen.


Bogs

Offline tinkerer

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Re: Cutting internal gear teeth
« Reply #31 on: October 06, 2009, 01:31:03 PM »
This is a very interesting topic. I thought the cutter was shaped round like a gear, so it would turn with the piece you are cutting to cut the clearance profiles as it turned. Looking forward to your pictures of the process.
Tink

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Offline dsquire

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Re: Cutting internal gear teeth
« Reply #32 on: October 06, 2009, 07:10:32 PM »
John

Here is a link on gear cutting that may or may not be of interest to you. It is on a site by a new member Joachim Steinke from Germany. There are lots of other goodies there as well.

http://www.metallmodellbau.de/GEAR-CUTTING.php

Cheers  :beer:

Don
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bogstandard

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Re: Cutting internal gear teeth
« Reply #33 on: October 06, 2009, 08:04:35 PM »
Don,

The method Achim is using on the mill is what I was describing the other day, only he is cutting teeth one at a time using a straight cutter, whereas I will be cutting the whole blank in one go by freewheeling the blank using a spiral cutter, and how he has explained the cutting of adjacent teeth is what I posted earlier, but mine was a lot less technical.

He is having some very good results there. If mine turn out that well, I will be a very happy chappie.

Unfortunately, that is all concerned with external tooth cutting, of which there are a lot of techniques to achieve the same results.

There is very little on the net for the home machinists about cutting internal teeth, which is what I am trying to solve as easily and cheaply as possible.

It seems that very few people have even tried, and lived to tell the tale.

Bogs

Offline John Hill

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Re: Cutting internal gear teeth
« Reply #34 on: October 06, 2009, 09:40:50 PM »
John,  I have just about scratched out the last few strands of hair on my head trying to imagine how a rotating cutter could be used to cut an internal gear without the axle of the cutter getting in the way, unless the gear were is to be very big. :scratch:

Maybe if the cutter had a very coarse thread it would be possible to swing the axle enough to clear the gear while keeping the cut parallel to the axis of the new gear.  Then maybe that was what you have in mind anyway? :coffee:
« Last Edit: October 06, 2009, 09:43:17 PM by John Hill »
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Offline tinkerer

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Re: Cutting internal gear teeth
« Reply #35 on: October 06, 2009, 10:28:09 PM »
Are you saying you are trying to cut all of the internal teeth full profile in one whack? Wouldn't that take a drophammer? It might be able to be done. he support of the gear would be tough. maybe sandwiched in a holder of some type with only the effected area exposed. I hope you take a video of the process.
Tink

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Prov 13:19

bogstandard

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Re: Cutting internal gear teeth
« Reply #36 on: October 06, 2009, 11:07:37 PM »
John,

I am just wondering where you got the information that the cutter rotates.

The cutter is only round because that is the easiest way to make it with the cutting hobs I have, e'g make a spur gear out of high carbon steel (silver steel, drill rod) instead of say brass, then harden the cutter, and grind the cutting edges to shape afterwards. It is then locked onto the end of the ram with one cutting tooth perfectly horizontal.
The rest of the teeth except say two below and two above the main tooth could be ground away as they play no part in the cutting action.

The first tooth is cut by the slotting action of the cutter, then the blank is rotated to the next position and another tooth is cut, and so on until the inside gear is cut. Like cutting multiple keyway slots in a bore.

If you only used a single tooth cutter, then you wouldn't get the involute shape to the tooth form, it is the secondary cutting action of the above and below teeth, being 20 degs out from the major cutting tooth position that forms the involute 'shape'. It won't be a perfect involute because the two shaving cuts are in fact flat rather than curved, but close enough for the gear teeth to operate as though they were true to form.


John

Offline John Hill

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Re: Cutting internal gear teeth
« Reply #37 on: October 06, 2009, 11:25:15 PM »
Thanks John, I guess even Bandit would have understood it but not me! :doh:
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Offline tinkerer

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Re: Cutting internal gear teeth
« Reply #38 on: October 06, 2009, 11:48:55 PM »
The dog is smarter than I am too.  :( (now I know why my dog looks at me the way she does) On the referenced site, the cutter is spinning and he is cutting most of one tooth and parts of a tooth on either side. The full profiles are completed as he works around the gear. I see now that you will be doing the same interior cutting, but with the action a shaper makes. I am probably still shagging balls, but it exercises however many cells left between my ears.
Tink

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Offline andyf

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Re: Cutting internal gear teeth
« Reply #39 on: October 07, 2009, 03:56:00 AM »
Bogs, your idea of making a hardened gearwheel to use as the cutter looks brilliant to me  :clap:. The great advantage over a single point one is that if the tooth which is doing most of the work loses its edge, you can rotate the cutter, remesh it with the part-done job, and start off again with a fresh tooth.

BTW, you mentioned at one point that gearwheels at popular prices were hard to find. The cheapest I could find for my dedicated fine feed banjo were here:
http://www.technobots.co.uk/acatalog/Online_Catalogue_Gears_365.html  (usual disclaimer), and they are thick enough (15mm) to cut up and get two approaching 7mm thick for the price of one, as in the first pic here: http://andysmachines.weebly.com/fine-feed-banjo.html

Andy
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I've cut the end off it twice, but it's still too short

bogstandard

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Re: Cutting internal gear teeth
« Reply #40 on: October 07, 2009, 05:50:45 AM »
Andy,

I have used Technobots before now for gears, unfortunately the module sizes are a little on the large size for some models I have in mind. I have a very big box of metal gears, but most times I can find one spur gear but not the other in the size I want, and internal cut gears with matching spurs the right size are like rocking horse s**t, impossible to find.

Unless you are willing to have them cut in the materials you want (very expensive) you are usually stuck with either plastic or ferrous gears, and of course, the outside shape, if I make them myself, is only limited by my imagination.

http://www.hpcgears.com/newpdf/internal_gears_1.0mod.pdf

http://www.davall.co.uk/documents/davall_catalogue_048.pdf

Please, no further links like the two I have shown, otherwise the post will end up like a shopping trip, not how to make them yourself.

Quote
The great advantage over a single point one is that if the tooth which is doing most of the work loses its edge, you can rotate the cutter, remesh it with the part-done job, and start off again with a fresh tooth.

Andy, I have given this a lot of thought, and when I make the slotting tool, I will make it with a resettable holding nose so that what you have suggested will be easily done.
Also, if I put a little more thought into, and find an optimum diameter for the cutter, I will only need to make one of each module size to do all expected internal sizes.

Of course, this is still many months away, but I do like to have all the information in place before I start anything, and the response from the members on here has been great, and has solved a lot of my envisioned problems without too much difficulty.

Lots of minds are better than one.


Bogs

Offline Bernd

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Re: Cutting internal gear teeth
« Reply #41 on: October 07, 2009, 10:18:51 AM »
Bogs,

I did a bit of research into the cutting of internal gears. I contacted a friend that I used to work with. He was the head of the gear cutting department. I asked him about the cutting of internal gears. He cleared up several questions I had, plus the big one of rotating the cutter while cutting the internal teeth.

I had forgotten that there are two methods of forming gear teeth. One is called "generating" one is called "shaping". The generation of a gear allows a true involute, were as the shaping of the gear the cutter needs to be made very accurately to cut the tooth profile.

So your method of shaping the internal gears on the lathe will work with an accurately made cutter.

Below is a link to some interesting info on shaping gears. Scroll down through and you'll see all sorts of cutters used in gear manufacturing.
http://www.gearshub.com/gear-cutting.html

I've also found some pictures of Fellows Gear cutting machines.

The first pic is similar to the gear shapers we used at work.


This second pic is of a smaller gear shaper. The size a home machinist won't mind having.


The last three are of a medium size gear shaper.




Who ever set the machine up didn't get the gear ratios right between the cutter and the blank. As you can see there are no teeth, just razor sharp edges. Ask me how I know about razor sharp edges on teeth and not getting the gear ratio right between cutter and gear blank.


I hope this info has helped some in the questions always asked about gear cutting.

Regards,
Bernd
Route of the Black Diamonds

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Re: Cutting internal gear teeth
« Reply #42 on: October 07, 2009, 03:38:28 PM »
Many thanks for all that info Bernd. It was an eye opener.

It looks like my settup will end up being a lot more basic and a little less bulky than the machines you have shown.

The way I am looking at this project, is that, in the beginning, someone must have started off making these internal gears, just like I am trying to achieve.

They wouldn't have had the modern sort of machinery available to them. So those original artisans must have started, as I am attempting to do, with the least amount of basic equipment to get the job done. It was from those humble beginnings, that the modern day automated machines evolved. It would only be one step away to fit a windscreen wiper motor fitted with an arm, to push and pull the slotting tool handle, then a ratchet onto the cut feed and you are almost there. But that is getting much too complicated for where I want to be.

I think what I am doing is called reverse engineering. Starting with the finished article, and working out how to make it.


John

Offline Bernd

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Re: Cutting internal gear teeth
« Reply #43 on: October 07, 2009, 03:52:07 PM »
I just hoped it would benefit those who have never seen these machines before. It should give them some idea of what they look like next time somebody mentions interl gear cutting.

A google search on fellows shapers will bring up a history of the man that engineered the Fellows Gear shaper. As you said he started out with very basic machine.

As they say "not very many people can start with a blank sheet of paper".

Bernd
Route of the Black Diamonds

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #44 on: October 07, 2009, 05:35:58 PM »
John,
Slight alteration to your C- o - D drawing to save your arms.  :med:



John S.
John Stevenson

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Re: Cutting internal gear teeth
« Reply #45 on: October 07, 2009, 06:43:52 PM »
John,

That is definitely a good idea. AFTER the system has been proven to work manually.

Quote
It would only be one step away to fit a windscreen wiper motor fitted with an arm, to push and pull the slotting tool handle, then a ratchet onto the cut feed and you are almost there. But that is getting much too complicated for where I want to be.

After a little more brain time I have hit a problem :bang:
 
The slotting head would have to have total control of the rotation of the ram, with no play allowed at all, and would be a little difficult to do.

However, I do have a few precision linear slides that could do the job for me. I will have to measure them up, to see which would be best size wise.

John

Offline John Stevenson

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Re: Cutting internal gear teeth
« Reply #46 on: October 07, 2009, 06:56:55 PM »
John,


 
The slotting head would have to have total control of the rotation of the ram, with no play allowed at all, and would be a little difficult to do.


John

I have often wondered why most people follow the same paths ?
Like stepper motor mounting, everyone stands them off on 4 pillars which has to be the most inapt way, was everyone a watchmaker in earlier lives ?

Same with slotting heads, always round rams and bushes and a silly pin to stop rotation, why bushes anyway they don't run at 10,000 rpm.

What about a length of square silver steel in a brass block with vee's machined in and clamp bolts to set preload.
this way the whole of the 4 sides are load bearing AND guide the bar.

1" round bar in a 4" housing has a surface area of 12.56 square inches but a location of minute proportions on the index pin.

A 1" square bar has a surface area of 16 square inches and every one of those locates it.

John S.
John Stevenson

Offline andyf

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Re: Cutting internal gear teeth
« Reply #47 on: October 07, 2009, 08:01:16 PM »
Yes, I see it all in my mind's eye   :coffee: . John S's square ram with an offset mounting on its end for the gear-shaped cutter, leaving some of the end surface exposed when the cutter is in place. To that exposed surface, fit some sort of detent to go between the teeth of the cutter opposite the tooth which is doing the hard work, so the cutter can be rotated, if it is necessary to bring a fresh tooth into play. In effect, the cutter indexes itself. To provide rake and relief, the cutter blank to be dished on the front and slightly tapered in side view. No, that would only help at the tip of the cutter
I'm only posting this because I may want to make an internal gear myself in the not too distant future, so if I'm getting it wrong, please stop me now and prevent  :bang:

Andy
« Last Edit: October 08, 2009, 04:25:01 AM by andyf »
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline NickG

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Re: Cutting internal gear teeth
« Reply #48 on: October 14, 2009, 09:18:42 AM »
The slotting attachments I've seen are usually a dovetailed affair akin to the ram on a shaper. Infact, someone from the club gave me just a slotting attachment when I was thinking about making a vertical head for my horizontal milling machine. I think I gave it back when I bought my vertical one though. I don't like keeping things of other peoples if I'm not really going to use them ... somebody else may have given it a good home by now, or it could be sat under his bench still.

Nick
Location: County Durham (North East England)

Offline sbwhart

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Re: Cutting internal gear teeth
« Reply #49 on: November 06, 2009, 05:37:54 PM »
Ok this is just an idea to get you thinking who knows where it will lead too

When I was using the small arbour press to test out the leather hole punches I looked at it and though square ram,  :scratch: if you turned it on its side, clamp it to a verticle slide put the tool at the other end you could use it to shape out internal gear teeth.

Here's a press this one may be a bit big but you can get smaller ones.

http://www.mscjlindustrial.co.uk/CGI/INSRIT?PMRQIT=BIJT3-33710M&origin=VIRTUAL:VIRTUAL_CAT&PMAKA=BIJT3-33710M&returnurl=&partnerURL=http://catalogs.shoplocal.com/jlindustrial/index.aspx%6Fpagename=listpage%50circularid=15737%50storeid=1039181%50uniqueid=%50fsid=%50jsessionid=%50pagenumber=1%50deptid=%50title=%50keyword=press%50returnurl=

Her's a C-0-C of the idea




You may have to cut the press up a bit to get it fitted but they are dirt cheep, I bet you could fix them to a lathe as a key way slotter.
 
:proj: :proj: :proj: :proj:

Have fun chewing this one

Stew


A little bit of clearance never got in the road
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Re: Cutting internal gear teeth
« Reply #50 on: November 06, 2009, 05:46:54 PM »
I am going to have serious words with you Stew, if you get here tomorrow.

Just joking of course.

I was in fact, only this afternoon, whilst resting in my swarf hole, pondering on the way this problem will be sorted.

I think I have come up with the ideal solution, and it will get rid of a bit of junk I've had hanging around for a while now.

All hush hush at the moment until the project is ready to be restarted.

But it won't be too long.

Bogs

Offline Gerhard Olivier

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Re: Cutting internal gear teeth
« Reply #51 on: November 07, 2009, 03:33:36 AM »
John Something else to think about

your cutter is going to be a gear -smaller than the hole that your going to be cutting the teeth into.

Rather that moving the cutter into the cut you could take a 20 tooth gear and remove .5mm from tooth 2- and 1 mm from tooth 3 1.5mm from tooth 4-etc until you have a gear that has 1 very small tooth next bigger etc. until the last is full size.

Use the smallest tooth for first cut -index and first cut all the teeth.  Then rotate cutter to the next size up and cut all the second cuts and again and again til the last cutter gives the complete shape.?????????

Gerhard
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bogstandard

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Re: Cutting internal gear teeth
« Reply #52 on: November 07, 2009, 05:03:52 AM »
Actually Gerhard, that is very similar to what will happen when using a full circle cutter.

On the first tooth, if you cut to full tooth depth, and depending how large the internal diameter is, adjacent teeth will get a partial cut at the same time. So after the first tooth is cut to full depth, the next tooth should be well on it's way to being finished.

I think I will be using something like a 24 tooth cutter, that will be able to be rotated by three teeth at a time, when the first three get worn. That way, the middle tooth will be doing most of the cutting and the tooth either side will be partial cutting, and depending on the internal size, other teeth might also start to be cut.


John