Gear Cutting On Milling Machine

[Owain1602 0]

Hi, does anyone have any experience in gear cutting on a milling machine or lathe?

Me and another guy from work are starting a machine shop night class in a few weeks, he's got a steam locomotive to be doing and i need things to make really.

I know gear cutting is unbelievably complex so it would take ages to learn this but would it be possible to make my own gearbox for my 205? Choose the exact ratios i want, make the gears straight cut.

I have started reading about gear cutting and it very large field, Cyclodic curves, Hypocyclodic, PCDs.

I could sort of have this project in the back of my mind after years of practice i might begin to make it.

The lecturer said he can make absolutley anything without CNC machines even though they have them, i think he was just boasting. So if things are to complicated for me to make, he'll make them.

What do you guys recon? The machine shop is amazing, every machine you could ever thing of, plus they do heat treatment and tempering and things there.

So, I know it is possible cause anything is possible, but just how difficult and complex is it? and whats the difference between doing it in a lathe or a milling machine?

Thanks

[Beastie 1]

Well, I reckon that a) you are correct and b)you are correct: Gear cutting is incredibly complex and you can make just about anything without a CNC machine. However to cut all but the most basic tooth forms you neeed specialist gear cutting machinery. Manufacturing gearbox gears is an extra headache: Most constant mesh gearboxes use EN36 which is machined to an oversize before hardening. The teeth are then ground to size with a profile grinding wheel. You'll certainly need some sort of hobbing machine to cut gearbox gears and then you need the correct hob to fit the machine to cut the tooth form that you want. The gearcutters which I use carry huge stock of hobs but even they often can't match a tooth form and the cost of tooling is prohibiting. If the machine shop is that well equipped then I'd definitely take the opportunity to use it for this: It must be the chance of a lifetime

[Owain1602 0]

Yep, i guessed it wasn't going to be the easiest task in the world.

What do you recon the design phase will be like? I have what sound like a good book on order "Manual Gearbox Design" which hopefully will help a bit.

Is the gear material quite expensive to buy? Are there any better material than what is used for production boxes available since this will be a one off and cost isnt really a consideration.

I think it will be quite interesting really, i know its gonna take a very long time though. Any ideas what else I could make in the meantime for the car? Its gonna be a stage rally car. thanks.

[M3Evo 0]

Wowza! You'll have to take loads of piccies when you start!

 

Made a couple of ali gears years and years ago just using an involute form cutter and a dividing head but making an entire gearbox?!

[Beastie 1]

Another vote for the "loads of piccies" request please I cant afford / justify enough machinery to do much gearcutting so I usually turn and mill the blanks and supply them to a gear cutting specialist in the West Midlands. The design phase isn't too bad mechanically speaking: You are pretty much stuck with the shaft centres which the manufacturer desgined into the casing so you need to decide on a tooth form. This can be a little more tricky if you aren't just copying the original. It's probably easier to reach a decision with straight cut gears because you won't have to consider any thrust loads transferred to the bearings so you need to base your calculations on the desired strength, wearing qualities and noise. Deep toothed gears can be made quieter and their increased load bearing area can make them more durable. Profiles on deep tooth gears have to allow for greater tooth deflection under maximum load. Stub toothed gears can be stronger but less durable. It's important to distinguish between durability, stiffness, and strength! The amount of material you will need to make the blanks is modest so cost shouldn't be too much of an issue. EN36 has been regarded as a good all round material for a long while for production cars because it's hard wearing, quiet, and strong. Gearboxes for specialist applications used to use EN38 which has for some while been superseded by EN39 and this sounds like a worthwhile consideration for a project like yours. A couple of years ago I had some trouble with rapid gearbox wear on an old high performance car and I had a set of EN39 gears made. The material was easy to work when I turned the blanks but when hardened and ground it's very durable. The original gears were suffering from load induced chipping on the flanks and the EN39 gears cured the problem. That box is straight cut and I have to say the difference in material (with the original tooth form reproduced) made a terrific difference to noise: It went from a low pitched whine to a high pitched scream. General experience with straight cut boxes suggests that shaft stiffness has at least as big an influence on noise as does tooth form.

 

Choosing your ratios is a much bigger dilemna!! Suggest that you get your engine developed as near as possible to it's final spec and then measure power output and torque curves accurately. You'll then need to use a bit of science to calculate ratios which span the torque curve of the engine, and a bit of mystical magic to fine tune them to just how they satisfy what you want from them

Edited August 24, 2006 by Beastie

[Owain1602 0]

By the time I get the project underway, i think digital camera will be a thing of the past.

 

You sound like you have a bit of experience with this Beastie. Yes, a rolling road print out will show me where the usable torque is really and I can design the ratios around it. Also maybe a run with a BE3 gearbox then a run with the one i have "hopefully" made. See what difference in transmition losses.

 

There are endless things to consider really. I will let you know what i decide. Also, will i be able to keep the synchros as they are do you think of do these need changing, or maybe some sort of dog engagement possible? Thanks

[24seven 104]

I work in a machine shop (also with every type of CNC machine imaginable, plus castings, heat treatment, pressings, welding etcetc) and work with some very skilled people, all of which have told me that it's extremely difficult to machine your own gears, and it takes highly specialised equipment to do it.

 

I had the same idea when I started planning my track day car, and also wanted to make some mountainbike cassettes/chainrings.

Edited August 24, 2006 by 24Seven

[Owain1602 0]

i know its very difficult. Apparently most engineers avoid it because of its degree of difficulty.

But really, after all the planning and deciding on ratios and tooth design and all that, how dificult is the actual gear cutting process?

You need the cutter with the correct tooth shape, a dividing head and is there much more to it than that? I know the treatment after is inolved too.

[miamistu 1]

Could you not draw and spec the gears you require and then get a company like HPC gears to do the hard work?

[Owain1602 0]

i'd rather make them my self really, i dont learn much from getting someone else to make them.

[petert 587]

I think you might be picking a project a little beyond your abilities. What you're considering is more of a 4th trade project, rather than a night class project. Have a look at the price Quaife charges for a BE3 close ratio gear set and you'll appreciate why.

 

I'm not sure what they're going to try and teach you in such a short course. But if it's any help, the first thing I had to do as an apprentice was chip a 25mm mild steel round bar square, with cold chisel and hammer. Then file it flat, square and parallel with a 14" 2nd cut flat file, to 17mm +/- 0.05mm all over.

[Owain1602 0]

Obviously its beyond my abilities at the moment. But I will be going to the class every week for years. Im not gonna just run for the length of 1 term. The lecturer said that he doesnt teach any of the guys there anything because all of them ar engineers and sign up for the class just so they can use the college's machines so he'll have loads of time to teach me.

I dont know if you have read it but i have said that it will be a very long term project.

It cant hurt to give it a go can it? Its not gona be a project for long, ill have to make loads of things to start getting quite good.

What do you guys recon?

Edited August 26, 2006 by Owain1602

[Beastie 1]

Peter is casting doubts for good reasons: You don't often find the level of knowlege and experience(let alone the machinery and the tooling) for this sort of project amongst anyone - college lecturers included! If you are lucky enough to have found somewhere which is the exception to this then I'd wholeheartedly suggest giving it a go. You can always practise with mild steel stock which will cost little, and if you are succesful in your attempts you can go on to purchase suitable steel for the final project. Even if you fail with your attempts, you're going to come out of this a lot more knowledgeable than you went in! Best of luck!