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undercutting half shafts?


02GF74
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Probably been discussed before but came across this idea on another forum. :rolleyes:

The idea is to make a small groove near the drive flange so that this becomes the weakest point. Then should a half shaft snap, it will be here and not in the diff making it easier to remove. ;)

Obviously the undercutting must not be too much, perhaps making a deep score of not more than 0.5 mm depth would be enough?

Now discuss. ;)

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Doesn't sound a great idea, you'll be making the shaft weaker no matter what. Combine this reduction in the cross sectional area with the fact that you'll be monkeying about with the heat treatment and surface tempering which give the shaft it's strength, and it'll be significantly weaker.

I'd be inclined to keep the shafts standard and buy an X Eng broken bit remover thingy from SimonR.

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In terms of carrying the torque load through the shaft, the outermost material is the most important bit, so you are really going to harm the shaft's rating by cutting into the outside.

What's the point in making it weaker???

I know why people do it, but it doesn't make much sense to me - especially if they have splashed out of stronger shafts!

You could still get bits which have sheared off getting into the diff and knackering it, so I'm not sure you gain a lot in that respect either. plus as Tonk says - it can just knacker the outer end (stub axle etc) instead!

IMHO bad idea.

Spend you time thinking of ways to make them stronger, not weaker!

Al.

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It actually makes good sense to score up the shafts.. and no it hasn't broken anything like a diff of stub axle.. not sure how it can to be honest..

Just score the shafts to the same depth as the splines.. that way you don't weaken the shaft you just move the place of breakage. I have had this done for years and I have only broken two shafts in all that time.. and I have 35" simex and silverstone 117's and ARBs.

If you can not afford to buy hardened shafts then get the standards scored instead.. maybe not as good, but you only spend 5mins replaceing shafts instead of 2 hours... taking diff out etc etc..

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In terms of carrying the torque load through the shaft, the outermost material is the most important bit, so you are really going to harm the shaft's rating by cutting into the outside.

... is this going to degenerate to discussing tubes again?????? :lol::lol:

I guess you could look at the half shaft as a tube of hardened/treated steel with lesser steel instead of air on the inside :(

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:ph34r: Anorak On :ph34r:

Ok, I've borrowed a packet of fags off someone, just so I could scribble on the back. Here's what I came up with (as an example):

If you take a 1 inch shaft (2.54cm) and cut a groove 0.5mm deep in it (so the diameter at this point is now 2.44cm), the polar moment of inertia reduces by 15%!

Lets take the example a little further and bring it back into the real world.

The maximum shear stress seen in a shaft under torque loading (i.e. a halfshaft) occurs at the outermost point of the shaft (radially). In other words the material carrying most of the load is on the outside of the shaft.

My fag packet is telling me that the maximum shear stress in the non-grooved shaft is about 88% of that in the grooved shaft.

For the sake of a 0.5mm groove, that is one hell of a difference.

:ph34r: Anorak Off :ph34r:

Al.

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I dunno, I don't smoke - how do you work this damn thing?

But as far as the calculation goes, yes I'm afraid its right - thats the whole point. If you cut a small groove in the outside of your shaft, the maximum shear stress seen by the material increases by quite a bit, so it will FAIL EARLIER than a non-grooved shaft as the torque load increases.

Significantly so.

Does that explain it better? (probably not... :( )

Al.

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It actually makes good sense to score up the shafts.. and no it hasn't broken anything like a diff of stub axle.. not sure how it can to be honest..

I think the diff centres (even ARBs) can break due to the sudden shock loading when a shaft snaps. I don't understand it either but people say they do/have.

As for the stub axle, when a shaft breaks it usually seems to twist off rather than just snap (at least the ones I have seen have done that) and so the broken end becomes a slightly odd shape. I guess the problem here will be if the break is inside the stub axle where it is a fairly tight fit, if it is grinding round inside it will knacker the inside of the stub axle, probably weaken it, and may be very hard to get out?

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I still prefer my Lr to snap a shaft before anything else gives way....

I didn't know it was a bad thing for a diff to experience that sorta sudden impact (make sense when you think about it) However its even worse for the diff and other bits when a shaft breaks in the diff and the bits get flung about inside the axle, as I ahve seen several wholes put into an axle case because of it. So I would still prefer a easy break point (which really isn't that easy at all considering what it puts up with) and save a lot of hassle/time and possibly more breakage.

My shafts so fat have not damaged anything else apart from themselves so far, the type of break is as smooth as a babies bum , no burs no nothing just flat.

Having said that - as soon as I break a shaft I stop on a flat surface and change it straight away, instead of carrying on.

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Probably been discussed before but came across this idea on another forum. :rolleyes:

The idea is to make a small groove near the drive flange so that this becomes the weakest point. Then should a half shaft snap, it will be here and not in the diff making it easier to remove. ;)

Obviously the undercutting must not be too much, perhaps making a deep score of not more than 0.5 mm depth would be enough?

Now discuss. ;)

As others have said, DO NOT GROVE Halfshaft, 10 spline ar wek enough as they are !

Options ?

Buy the tool from Simon, and / or upgrade to std 24 spline (cheap and have a large core increase so much stronger) or even better upgrade to 24 spline HD either quaiffe, MaxiDrive, Ashcroft GKN, depends on the depth of you wallet

Theres no way around 10 spline std stuff breaking, groving was an old comp safari racers trick, soon stopped !..other was to braze a welding rod to the shaft both sides, and secure top end (wheel end) with self almalgam tape, then when shaft breaks pull on welding wires to remove end...it often worked !

nige

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