EDM experiences

[Wildefalcon]

I'm hoping to buy a LSD for my Landrover differential. It's a rare set up, being a 101, so there is no off-the-shelf unit.

I've found a unit that should fit, except the internal diameter of the side gears is too small, which is ideal as it gives me material I can remove. I was thinking that EDM would be the ideal process to do this.

However, my supplier is concerned that the process might damage the hardening on the side gear, and might distort the gear. I'm also a bit concerned that the broaching might not be 100% in alignment, though I suspect that getting that sort of thing right is bread and butter to an EDM outfit.

Has anyone experience with this sort of thing? What are the things they'll ask me when I phone up a business? Or am I off in a strange direction again?

 

[awemawson]

By the Way EDM works micro hard zones are created. The electrode (be it a wire edm or sinker edm) creates minute explosive discharges to the work piece at a fairly high frequency resulting in a surface hardening in the heat affected zone and very small fissures that can propagate cracks. NB this in on a microscopic scale.

For really critical parts this layer can be etched off, but none of the work I've ever done with my wire or sinker EDMs have been critical to this extent.

 

[Nick DV]

Being the numb nuts that I am, I had to look EDM up Pretty clever stuff eh.

 

[Agroshield]

What shape are you wishing to EDM?

A simple circle could be cut undersize and then honed or ground to final dimension to remove any heat affected zone.

Clearly, if the shape is some complicated internal spline, the options are considerably more limited.

What reference surface(s) are available on the unmolested gear? If there is only one (i.e. the internal bore) and it will be removed as part of the EDM process, that complicates matters. You might then need an intermediate step to establish a new reference surface concentric with the existing one before you remove the existing one.

If the new surface you create has a different (lower) hardness to the old one that has been removed, the part will wear out a lot quicker. Most stuff is not through hardened, only surface hardened. If the depth of material removed is more than the hardening depth, that will be a problem. It is not easy to determine the hardness profile of an object.

 

[stuvy]

have you spoken to ashcroft transmissions in luton

Home

We are a family owned business and have been supplying quality products and excellent customer service worldwide since 1988. From initially supplying just remanufactured Transmissions we now supply a whole variety of additional products for the Land Rover Drive Train, both for Off Road...

ashcroft-transmissions.co.uk

 

[Wildefalcon]

That's all my concerns, hardness, and reference concentricity.

It's looking less and less likely to be a good idea.

@stuvy I've been in touch with Dave Ashcroft and he understands the problem. He's got a minimum order quantity of 100 units before he'd consider it.

 

[Wildefalcon]

Oh, and it's an internal spline profile.

So, the alternative is broaching and rehardening. I know nothing about who would do such a thing.

 

[MetalMonkey]

How much material do you need to remove?
Could hard turning or internal grinding be an option?

*EDIT* just seen it is splined. Ignore me.

 

[Wildefalcon]

Yes, I think the hardening and getting true after will be the challenge.

I'll call into a few engineering places next week. See what can be done.

 

[Agroshield]

Oh, and it's an internal spline profile.

Could you take something that has the correct (size, shape and hardness) internal spline profile and machine off the outside of that something to a plain cylinder?

Then machine the inside of the new part to be a little less in diameter than the part above. Drop the first part in liquid nitrogen and poke it in the hole quick.

You'd have to ensure the shrink fit could transmit the required torque. Also have a real good look at it to make sure the internal spline does not have to have any kind of clocked relationship to any outside feature (e.g. gear teeth).

 

[Morris]

I would be looking at custom half shafts rather than modifying the diff.

 

[Wildefalcon]

I am open to custom, but prefer standards parts whenever I can

 

[Morris]

I am open to custom, but prefer standards parts whenever I can

But
"I've found a unit that should fit, except the internal diameter of the side gears is too small, which is ideal as it gives me material I can remove. I was thinking that EDM would be the ideal process to do this." is not standard

 

[stuvy]

But
"I've found a unit that should fit, except the internal diameter of the side gears is too small, which is ideal as it gives me material I can remove. I was thinking that EDM would be the ideal process to do this." is not standard

A one off costs more “if” it breaks and needs replacing

 

[Wildefalcon]

A one off costs more “if” it breaks and needs replacing

This is it. The half shafts are the "weakest" part, most likely to fail. So, keep standard.

 

[sako243]

I've got a mate just up the road who cuts his own gears and splines fairly regularly from what I remember for heavy plant etc. All the stuff seems to come in blanks and you broach / machine to the appropriate size.

I've got to take a flywheel up to him to bore out (my lathe isn't big enough), his can just about handle it - being able to take 5ft diameter parts... I'll give him a call today hopefully and ask.

 

[Morris]

This is it. The half shafts are the "weakest" part, most likely to fail. So, keep standard.

It's the weakest point because it's standard.
The last custom shafts I had made were heat treated 4340 and good for 500hp and mucho torque.

 

[sako243]

But the halfshafts are nice and easy to replace and don't occupy much space if you're on a really long offroad trip. Easier that snaps than say a crankshaft which was what happened in my case (upgraded all the drive train as I put lockers in). Only thing I've broken since has been two crankshafts (unrelated to the lockers but rather ironic).

 

[Morris]

I think the issue here is a difference in mindset between a hotrodder and a Land Rover owner

 

[mike os]

Custom half shaft or custom gear seems like the same thing to me ...

So it's mess with a (assumed) perfectly useable diff, with the associated work and increased possibility of failure, or make a simple commonplace and relatively easy to replace spline shaft...

I know which I would sooner replace