What's new
What's new

I need a tiny invoulte gear cutter, aprk .25 dia?

kustomizer

Diamond
Joined
Aug 17, 2007
Location
North Fork Idaho
I need to make a small quantity of pinion gears about 3/16 dia with 10 teeth and a 1/4 gear to mesh with it, .6 c-c. I don't have much gear experiance but I am thinking I would like something like a 1/4 dia 4 flt carbide cutter. Where might I find such a critter?
 
Yes I would like a small milling cutter.
By 1/4 gear I mean it is not round but only about 90 degrees of the gear in kind of an odd triangle shape.
The cutter needs to be small in diameter
 
I'm no gear expert, but cutting gears that small is going to be very difficult.

1) You can cut spur gears with an indexer and B&S-style milling cutters, but this is smaller than any I've seen. If you try to profile it, you won't be very accurate. I've profiled some gears before, but they were bigger (mod 4) and I had incredibly sloppy accuracy requirements.

2) A 10 tooth pinion is going to have a lot of undercut. I've always been told to stay above 15 teeth, preferably over 17. What's driving you to the small number of teeth, the ratio of pitch diameters is what determines the gear ratio, so going to more, smaller teeth won't affect your ratio. There is a strength hit to smaller teeth, but your undercut teeth will take a big strength hit as well.

3) SDP (sdp-si.com) sells off the shelf small gears, down to 120DP. I would look at buying the small gear complete. For the large gear, buy a whole gear and cut it into quarters. If you wire it, you could get 4 pieces, otherwise just mill 3/4 of it away, they're dirt cheap. WM Berg also sells small gears.
 
Yes I would like a small milling cutter.
By 1/4 gear I mean it is not round but only about 90 degrees of the gear in kind of an odd triangle shape.
The cutter needs to be small in diameter

A, You have not given NEARLY enough information for us to be helpful to you.
B, your "1/4" gear is called a Sector Gear or Gear Segment.
C, You will not easily find Involute Form Mills in the size range you think you want.
D, Milling teeth with a Form End Mill poses more than one issue, from the relative dismall accuracy provided to the cost of a single custom end mill, to the fact that 99% of the custom mill houses will not guarantee an Involute Form End Mill's accuracy. Many will not even do it.
E, You should start by reading the Gear section of your Machinery's Handbook. All of the questions you have not even realized that you have are already answered, in it.
F, If you have specific questions, the forum can likely help you.

You will want to figure out what you want to accomplish, the ratio you think you need, the exact center distance of the two gears, and then derive the Pitch of the gears so that they can be specified correctly. Understand that a custom Form End Mill like you think you desire is going to run $275 and up. It will be good for ONLY ONE SPECIFIC TOOTH COUNT of gear, and it will make very poor gears.

Take the advice given and look at SDP and the like.
 
kustomizer,

OK... understood now. I'd have to guess that the PD of your 10t gear may be around .160" or so depending on the DP. That means a PD of a possibly just over 1" on the segment gear. So I'm guessing you're targeting a ~7:1 gear ratio or so?

As stated by DanielG, you're going to see a *LOT* of undercut on that 10t pinion, so I would highly recommend that the pinion be designed substantially oversized, and the segment gear correspondingly undersize. That is the common method to avoid substantial undercut and strengthen the pinion.

Depending on the thickness of the gears (I'd assume something this small will be quite thin), you might consider just having them cut via wire edm out of flat material. I would probably cut this with .004" wire. With the sizes you are talking about, this should not take long to cut, and the results will be super accurate compared to any other method. If your target is an initial proof of concept or something along this lines, wire edm might be the easiest solution initially.

Here is an example of a wire cut gear that I made out of heat treated flat plate for a customer's prototype project.

42t.jpg
 
I will work no providing better info, I removed the pinion, it has 15 teeth and is 3/16 in diameter as best as I can tell. the pivot holes between the pinion and the sector are .67 c-c. I will start looking at my machinery handbook this evening.
I was hoping to side mill as opposed to endmill with something like this:
thd mill.jpg
The cost you are talking about for cutters is fine, If I take this job it will have to all be made here, 9 small parts per assy, 65 assy's. I have been telling them "no" for months but they are talking about enough money now that I thought I would look into it some. I prefer to make stuff I am familliar with.
 
I am running some little stepped bushings about the size of the gear laying on that penny and am only able to find about 75% of them as the others vanish after part off
 
To prevent undercut on small toothcount one can chance the pressure angle to 30 dgr or even bigger
In handtooling you often find 4 teeth without undercut
If you wire edm it would be easy to change the pressure angle


Peter
 
Horological Cutter Makers - I started there but the cutters are really a lot bigger than I am hoping to use, the customer wants the gear and shaft to be one piece if possible
 
kustomizer,

OK... understood now. I'd have to guess that the PD of your 10t gear may be around .160" or so depending on the DP. That means a PD of a possibly just over 1" on the segment gear. So I'm guessing you're targeting a ~7:1 gear ratio or so?

As stated by DanielG, you're going to see a *LOT* of undercut on that 10t pinion, so I would highly recommend that the pinion be designed substantially oversized, and the segment gear correspondingly undersize. That is the common method to avoid substantial undercut and strengthen the pinion.

Depending on the thickness of the gears (I'd assume something this small will be quite thin), you might consider just having them cut via wire edm out of flat material. I would probably cut this with .004" wire. With the sizes you are talking about, this should not take long to cut, and the results will be super accurate compared to any other method. If your target is an initial proof of concept or something along this lines, wire edm might be the easiest solution initially.

Here is an example of a wire cut gear that I made out of heat treated flat plate for a customer's prototype project.

View attachment 261945

I really need to take some pics like this. We do some tiny ass stuff, but nothing really puts it into perspective like a coin, or an everyday object...


Move along, nothing to add to the OP's question. LoL
:D
 
I'm a watchmaker and make loads of gears and pinions all the time. In watchmaking the norm is epicyclic gearing. The theory is there's less frictional loss in the gearing (watch and clock geartrains always go slow-fast with a corresponding loss of torque). In epicyclic gearing a pinion of 6 teeth is commonplace. I don't know what the OP is doing but can assume it's with involute gearing. Zahnrad will have the best advice, hands down, but, if, in the end he wants to cut tooth-by-tooth Dixi Polytool will make you a cutter to your drawing (to an accuracy you can't measure unless you're Wayne Moore) in any diameter you want, as long as it's physically possible. I get customs from them with integral shank for about 275 bucks, 7-10 days. This would be a "disc" cutter, not endmill. They'll do a disc with hole if you want too.

Do you have drawings? Accurate?
 
110 yo you're probably outside of any realistic norm, you'll need to get/make drawings at the least. What sort of function does this perform? If it's delivering power or delivering "motion" makes a huge difference in how hardass you need to be.
 
Hi kustomizer:
As Screwmachine and others have pointed out, your first step is going to be to find out whether it's an epicyclic gear train or an involute or some hand carved weirdass bastard profile.
I'd try to find someone who has a 50:1 Shadowgraph (optical comparator) and set up my gears on that so I can see the profile at some sort of reasonable scale.

Each profile will have a characteristic shape, and you can take a picture with your smartphone of the shadowgraph screen and post it for all to see.
The gear guys on here can tell you what it likely is, based on the picture, what it's part of, and the history of it, so take pictures of everything you can and post them all.

Once you've done that, we can have a more useful discussion of how you might go about it.
From there you can tell your customer what this is all going to cost and he can make a decision about whether it is worth it to him.

Expect the bill to be breathtaking if this thing has to be accurate in any way.
If best effort with a dividing head and a hand ground flycutter is good enough, charge him half a day to grind the cutters under the microscope and a day to fuck around with making some gear shaped bits and see if he bites.
If not, politely invite him to piss off and stop wasting your time.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Whoops: I didn't read your post # 8 completely.
It sounds as though you actually do have a serious customer although what he wants with 65 copies of a 110 year old contraption I'm having a bit of trouble with; but whatever....
I'd spare myself the pain and farm this customer off to a proper gear maker if the requirements justify it and a hobby clockmaker if they do not, unless you have a strong personal desire to dive in and lose your ass.
Zahnrad Kopf springs to mind as a good resource, but so far as I know he's running like a one-armed paper hanger these days (correct me if I'm wrong ZK ).
 
Last edited:








 
Back
Top