edmandsd Posted February 24, 2003 Share Posted February 24, 2003 I know this is an area that certain members are looking at...having done it myself with live axle shafts. Obviously numbers will bring the unit price down so I'm keen to know who's interested ? The shafts will be made by Elite (who manufactuer the new light weight five speed sequential in line gearbox) I appreciate that there are different types of shaft but presume it's the most up to date design people would want ? Home of BDR700 Link to comment Share on other sites More sharing options...
Blatman Posted February 24, 2003 Share Posted February 24, 2003 For those of us who may not know what exactly gundrilling is, or does, could you elaborate a little on what we should expect, and what the shafts will look like when finished 🤔 Ta........ Link to comment Share on other sites More sharing options...
Peter Carmichael Posted February 24, 2003 Share Posted February 24, 2003 The steel down the middle of the shaft does very little to transmit rotational force, but weighs just the same as all the other steel. Insert hole down length of shaft and you have a lighter shaft and same strength... unless the failure mode is buckling, which is unlikely. Link to comment Share on other sites More sharing options...
allen Posted February 24, 2003 Share Posted February 24, 2003 This is of course, something you can do to all the bolts on the vheicle, seem to recall being told there was a certain percentage of the diameter that could be removed without loosing any strength. Good winter project, eh? Link to comment Share on other sites More sharing options...
JAG Posted February 24, 2003 Share Posted February 24, 2003 Its not quite as simple as removing the steel, in the centre of the shaft, that's doing nothing. All of the steel in the shaft contributes to the rotational stiffness. As you near the centre of the shaft it's contribution gets less, down to an infinitesimal contribution at the molecular level in the centre. Therefore removing ANY material will actually reduce the strength of the shaft - the bigger the hole up the centre the greater the reduction in strength. How much can be calculated quite easily, whether it's enough to cause failure can only be decided once you know the loading experienced in real use etc... and that can be a complete bitch to figure out 😳 I guess the only way in real life is to use a bit of trial and error. Tried and tested designs and known operating circumstances can be used to give confidence. You pays your money and takes ya chances! Justin Link to comment Share on other sites More sharing options...
Chelspeed Posted February 24, 2003 Share Posted February 24, 2003 As far as I know there are two sorts of shafts, those used up until last year and a newer one introduced last year. The only difference appears to be 3 big notches in the metal sleeves over the CV joints in each end on the newer ones compared with a full cylindrical sleeve on the older ones. Miraz posted last year that the new shafts were much lighter, unless he had a third design of shaft then I disagree, the CV joint is a tripod type of thing, the rest of the inside of the metal sleeve is empty, they appear to have closed the metal sleeve in around the working bit of the joint. Weight saving, using the scientific "pick it up and juggle it from hand to hand" and "feels about as heavy as mine that I stripped down last year" approach, appears to be minimal. The problem with this is that I presume you'd need to strip the drive shaft into the three bits, stub axle into the diff, drive shaft, stub axle into the hub. To do this means stripping the metal sleeve off and refitting it afterwards. I've done this to replace a leaking rubber gaiter and it was not easy. You'd need to factor in 4 new sleeves (approx 30 quid a shout from Fords). Would you gun drill the two stub axles too? I'm interested subject to the normal: How much would it cost? What would the weight saving be? Why wouldn't the CV grease migrate into the diff and vice verse, ally plugs? With regard to the strength, we gundrill our turbine shafts (18 inch hole up a 3 foot diameter, 30m long shaft) and on average it increases the strength. The reason is that when yoiu first cast the shaft all the impurity nasties end up in the centre. So drilling out the middle leaves you with no nasty stress raisers loitering to start cracks. Not sure if the smae applies to our drive shafts or not. Link to comment Share on other sites More sharing options...
mr_ed Posted February 24, 2003 Share Posted February 24, 2003 At a guess, I'd say my driveshafts were 2.5cm in diameter. This makes their cross sectional area 4.9cmsq. If you were to drill a 1cm hole up the middle, that 1cm hole would have an area of 0.78cmsq. So the cross sectional area of the gundrilled shaft would be 4.1cmsq. In other words, it'll weigh 83% of the weight of the un-drilled one. On a full pair of driveshafts, I guess this'll be a saving of 2kgs or so, unsprung. Dunno if the hole is 1cm, or if its safe to go bigger just guessing. Interested to know whats typical. My driveshafts were designed to take the torque from a 2.5v6 in a Freelander, and I'm putting a weedy 70lbft from my fireblade through it... Wouldnt want to try it with my hand-drill ;) Cheers, Ed Edited by - mr_ed on 24 Feb 2003 17:00:44 Link to comment Share on other sites More sharing options...
Miraz Posted February 24, 2003 Share Posted February 24, 2003 Chelspeed - I did weigh both of the shafts - the new ones are definately lighter, don't remember by how much now but it was more than a kilo of difference between the two designs. I've not yet got round to putting the drive shafts back into the car...I'll weigh them again when I get a moment. Can't help but think that a lot of weight could be removed from the two hulking great joints on the drive shafts.... Edited by - Miraz on 24 Feb 2003 20:05:24 Link to comment Share on other sites More sharing options...
edmandsd Posted February 25, 2003 Author Share Posted February 25, 2003 A shaft with a diameter of 1.125 inches will actually be over 10% stronger with a 5/8th hole through it's centre - which will redue the shaft weight by over 30% - Ref Forbes Aird Automotive Math Handbook. Existing shafts cannot be used as they need to be hardened post gundrilling. I'll need to get my hands on a standard set up to see exactly what's required - I think Dave Kimberley's supplying some to Elite. My weight saving totalled circa 3.5 kgs incl circa 1kg from lightened flanges. Price shouldn't be prohibitive but will obviously drop with volume. I had my gundrilled shafts sealed at the diff end by HTR. I think you'll find that most 'proper' race cars run hollow shafts these days. Home of BDR700 Link to comment Share on other sites More sharing options...
Anthony Posted February 25, 2003 Share Posted February 25, 2003 Dave, if someone can confirm my new shafts will not self distruct, count me in. Would like to do this asap though as car going back together soon ...famous last words Link to comment Share on other sites More sharing options...
R2D2 Posted February 25, 2003 Share Posted February 25, 2003 I don't really agree that drilling a hole in a shaft can increase its strength. I would be interested in knowing how this can happen. I agree that material close to the neutral axis of a shaft doesn't contribute as much, proportionally, as the material at the outer diameter in terms of bending and torsional stiffness/strength but the presence of a hole must increase the working stress. If you do the calcs for a 1.125" dia. shaft, drilling a hole of 0.625" diameter will increase the nett stress by 10% for any given applied torque. This is probably insignificant in terms of mean torque realtive to the shear yield strength of the standard shaft. If you consider the transient torque that can be developed due to gearchanges etc. the situation could be much worse. The transient torque will be affected by the type of gearchange used, dog boxes generally introduce higher transients than synchro boxes and racing tyres with higher levels of grip will also generate higher transients. Clealry the more powerful the engine the higher the applied mean torque and the more sesitive the shaft will be to fatigue failures caused by transients. Interesting subject but quite tricky to analyse accurately. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted February 25, 2003 Share Posted February 25, 2003 So what you need is someone with 300bhp, big slicks and a sequential dog box to test everything for us... Dave, when you get the standard shafts I presume you can compare dimensions with the shafts in your live axle. Link to comment Share on other sites More sharing options...
dino ferrana Posted February 25, 2003 Share Posted February 25, 2003 Have to agree with Peter on this one (even though he told me to sod off) I think Dave has probably give the shafts in his car the most brutal testing possible with his extremem machine. I have seen a video of this car running an acceleration test and he was fighting to keep it in a straight line due to the massive torque/power/whatever. He hasn't broken them so I would assume that they work! FWIW I have heard from a very experienced and trusted source that hollowing out drive shafts does increase their strength and reduce failure. Link to comment Share on other sites More sharing options...
edmandsd Posted February 25, 2003 Author Share Posted February 25, 2003 I will do Peter - Elite were convinced I could get away with a bigger hole but I wanted to be cautious - I'd suggest a similar approach re the de dion shafts. The shafts I use are complete overkill really and would probably withstand twice the torque i'm putting through them. I ran standard English shafts in my Sylva when the BD was on carbs without problems - I'm sure the reduced inertia inherant with light cars contributes to the reliability of the shafts - I also strive to reduce the weight of tyres/wheels/discs etc which all helps. Home of BDR700 Link to comment Share on other sites More sharing options...
Blatman Posted February 25, 2003 Share Posted February 25, 2003 Cripes. Didn't mean to start this big a debate. Dave. I'm sorry that it appears to be diverting attention away from the original subject of you trying to arrange a bulk buy of drive shafts. Please accept my apologies. Link to comment Share on other sites More sharing options...
JAG Posted February 25, 2003 Share Posted February 25, 2003 I believe that Chris Flavell and I were trying to understand remarks made by some of the group such as, "A shaft with a diameter of 1.125 inches will actually be over 10% stronger with a 5/8th hole through it's centre" and, "Insert hole down length of shaft and you have a lighter shaft and same strength... " This is NOT TRUE. But as I said earlier the only way to be sure the shaft will be strong enough for your installation is to use a bit of trial and error. Tried and tested designs and known operating circumstances can be used to give confidence for other less stressed installations. I believe that with Dave Edmonds car (300bhp, big slicks and a sequential dog box and all....) you have such a mechanism in place and his results can indeed be used by the rest of the group to create confidence with regard to their own installations. The shafts should be fine - but don't believe they are stronger because that's just NOT TRUE. Justin Edited by - JAG on 25 Feb 2003 16:17:00 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted February 25, 2003 Share Posted February 25, 2003 Just because I attempted to write a brief response in the first instance... "Insert hole down length of shaft and you have a lighter shaft and same (near as sod it is to swearing ) strength... " What are you? An engineer or a physicist? How big a hole? As hole diameter tends towards zero, effect on strength tends to zero also. In a pure shear failure, which element will fail? The outside surface that suffers the greatest shear stress. What rule affects the relationship between total strength and that shear stress - second moment of area about the central axis. Second moment of area of a circle is: 1/2 x pi x r^4 Second moment of area of a thick walled anulus is: 1/2 x pi x (R^4 - r^4) Therefore if r is small in comparison to R, then r^4 will be insignificantly small in comparison to R^4. The effect on second moment of area will be negligible. Please note that I know I have been sailing reasonably close to the wind so I have edited in some smilies because the jibing is all well meant. Edited by - Peter Carmichael on 25 Feb 2003 19:26:38 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted February 25, 2003 Share Posted February 25, 2003 I reckon the comments about stronger shafts come from shafts designed from new to be gundrilled which can be both lighter and stronger but only by using a larger outer diameter. It all follows from the above. Link to comment Share on other sites More sharing options...
edmandsd Posted February 25, 2003 Author Share Posted February 25, 2003 You're correct guys and i'm wrong. The peak stress in the remaining material of a gundrilled shaft in the example I gave will actually increase by 10.5% over the peak stress in an equivalent solid shaft. However this is in reality a tiny price to pay for the benefits obtained from a 30% lighter shaft, and is very unlikely to result in failure of a gundrilled shaft where failure hasn't already been experienced with a solid shaft. As Peter rightly states a very small increase in the overall diameter, with an equivalent reduction in the weight saving will result in a gundrilled shaft with the same max shear stress as the slightly smaller diameter solid shaft. Home of BDR700 Edited by - edmandsd on 25 Feb 2003 21:19:25 Link to comment Share on other sites More sharing options...
JAG Posted February 25, 2003 Share Posted February 25, 2003 Peter and Dave, the truth is if you take an existing shaft and drill a hole through the centre it will be weaker. As you say how much weaker depends upon the size of the hole. If you have a solid shaft and a hollow shaft and both contain the same amount of the same material then the hollow shaft will be of greater external diameter and will be capable of carrying a greater torsional load. I wasn't directing any criticism at anyone. The truth is I was hoping to hear a good argument and did wonder if there may be some special set of circumstances involved - like Chelspeeds non-homogeneous cast shaft. I also have a terrible habit of not being able to tell when I am being too pedantic 😳 Justin Edited by - JAG on 25 Feb 2003 21:25:58 Edited by - JAG on 25 Feb 2003 21:27:21 Link to comment Share on other sites More sharing options...
dino ferrana Posted February 25, 2003 Share Posted February 25, 2003 It's OK I have a terrible habit of not being able to tell when I am too drunk! 😬 Link to comment Share on other sites More sharing options...
Chelspeed Posted February 26, 2003 Share Posted February 26, 2003 Too drunk, whats that then? Back to the plot. Yes Dave I am interested. Even with new shafts that sort of weight saving is tempting, particularly if the new shafts are lighter before you start as well. I'll even offer to be guineau pig and try and break the first set, I think that's what Peter was suggesting? Link to comment Share on other sites More sharing options...
Blackbirdman Posted February 26, 2003 Share Posted February 26, 2003 Getting away from the physics for a moment, is anyone aware of any actual failures of the standard shafts? They look and feel over specified (not very scientific) but the Autosport Blackbird car at the Nurburgring in 2000 (?) snapped one drive shaft during the race. The main center section of the shaft failed, not one of the joints. It looked like someone had heated a glass rod and twisted it! The car was not on slicks but was being driven hard with lots of curb usage! Any other examples? I would still be interested in a set depending on the price. Matt Is it a bike? Is it a car? No it's Blackbirdman Link to comment Share on other sites More sharing options...
edmandsd Posted February 26, 2003 Author Share Posted February 26, 2003 Elite will need a complete assembled pair of latest spec shafts to determine exactly what's required and so as to determine the cost - any suggestions ? Home of BDR700 Link to comment Share on other sites More sharing options...
Chelspeed Posted February 26, 2003 Share Posted February 26, 2003 At nearly £200 each side that means someone would need to invest £400 before we could even see if lightening is feasible, how much weight could come off and what it would cost? First thought is that's it's not worth the risk. Second thought is why do they need both? Aren't both sides the same? If 1 side is OK and there are 10 people interested we could each invest £20 in a feasibility study? Link to comment Share on other sites More sharing options...
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