Machined brake discs
Discussion
So as part of a college project a took some decent quality brake discs and machined some holes and grooves in them as I have access to a CNC Mill.
Everything came out okay all equal about and done properly, my only concern is ive gone a bit deep on the grooves.
The grooves are 3mm deep meaning instead of the discs having 9.5mm wall thickness between the outside and the start of the vents there is only 6.5mm. Just a little worried i may of gone to deep and weakened them to much as im not feeling cracked discs.
Any advice on if itl be okay to put on the car would be appreciated and if you got grooved discs or dimpled lemme know the depth of your grooves as i may be worried over nothing
They will be going on the fronts, 315mm outside diameter, 8mm vent thickness and still has 9.5mm wall thickness of disc meat on the most of it either side of the vents.
Everything came out okay all equal about and done properly, my only concern is ive gone a bit deep on the grooves.
The grooves are 3mm deep meaning instead of the discs having 9.5mm wall thickness between the outside and the start of the vents there is only 6.5mm. Just a little worried i may of gone to deep and weakened them to much as im not feeling cracked discs.
Any advice on if itl be okay to put on the car would be appreciated and if you got grooved discs or dimpled lemme know the depth of your grooves as i may be worried over nothing
They will be going on the fronts, 315mm outside diameter, 8mm vent thickness and still has 9.5mm wall thickness of disc meat on the most of it either side of the vents.
TooMany2cvs said:
What's the maximum allowable wear? I'd not want to go much deeper than that.
More to it than that as any groove at all will also introduce a weak area or 'stress concentration', worse still if the grooves have been milled with a square profile type milling tool. Grooves would typically have rounded seats to try to relieve stresses. Could be fine but I wouldn't fancy taking my chances.
bobalong135 said:
So as part of a college project a took some decent quality brake discs and machined some holes and grooves in them as I have access to a CNC Mill.
Throw them away.I'm astonished that you even consider the question needs asking, and equally astonished that your college allowed you to hack into brake parts for a roadgoing car without talking to you about the legal and safety implications of using them afterwards.
Were you planning to tell your insurers about this? Make sure you're sitting down if you do.
Edited by GreenV8S on Wednesday 25th April 17:37
GreenV8S said:
bobalong135 said:
So as part of a college project a took some decent quality brake discs and machined some holes and grooves in them as I have access to a CNC Mill.
Throw them away.You are now in possession of two paperweights.
If you really must have drilled & grooved discs buy some from one of the brake companies that make & sell such things.
There's an awful lot of non-engineering paranoia in the above replies. The normal manufacturer wear limit recommendation on discs is 1mm per face but it's perfectly common to give them a skim, fit another set of pads and go to twice that. 4mm total off the thickness is way more material than a few grooves 3mm deep. They won't make a scrap of difference to the serviceability or strength. However normally groove thickness would be about 1.5mm.
None of the vents had been damaged in the process as I was able to cad it up and avoid damaging them. Used a ballnose cutter so has a radius on the bottom of the groove. After machining them a chap at work brought a AMG, which has grooves 6mm wide on the discs, I ended up doing 5mm grooves.
I know discs you can pay to get them re skimmed, surely there’s a point we’re you run out of material to skim on your discs for safety reasons and at that point that would be the groove depth limit?
I know discs you can pay to get them re skimmed, surely there’s a point we’re you run out of material to skim on your discs for safety reasons and at that point that would be the groove depth limit?
Grooves are of very dubious benefit, and actually unknown function. Gas venting? Do tell!
But some race temas do use them. Perhaps because they get sponsored, but anyway.
If they do, the the disks are inspected before every race. Eventually, and quicker if they are grooved, cracks will appear, and when they do, the discs are scrapped, in pairs.
Unless you are willing to inspect and scrap as often, which for road use means daily, don't use them.
JOhn
But some race temas do use them. Perhaps because they get sponsored, but anyway.
If they do, the the disks are inspected before every race. Eventually, and quicker if they are grooved, cracks will appear, and when they do, the discs are scrapped, in pairs.
Unless you are willing to inspect and scrap as often, which for road use means daily, don't use them.
JOhn
bobalong135 said:
that would be the groove depth limit?
The grooves and especially the holes will form stress raisers and make this weaker and less durable than a plain disc of the equivalent thickness. Even standard un-hacked discs can suffer fatigue failure. The machining you've done on yours will have weakened them substantially. You have no idea whether they're safe. I think they aren't. What does your insurer say?
Mignon said:
There's an awful lot of non-engineering paranoia in the above replies. The normal manufacturer wear limit recommendation on discs is 1mm per face but it's perfectly common to give them a skim, fit another set of pads and go to twice that. 4mm total off the thickness is way more material than a few grooves 3mm deep. They won't make a scrap of difference to the serviceability or strength. However normally groove thickness would be about 1.5mm.
The comments about stress raisers sound more look good engineering judgement than non-engineering paranoia to me.
Mignon said:
There's an awful lot of non-engineering paranoia in the above replies. The normal manufacturer wear limit recommendation on discs is 1mm per face but it's perfectly common to give them a skim, fit another set of pads and go to twice that. 4mm total off the thickness is way more material than a few grooves 3mm deep. They won't make a scrap of difference to the serviceability or strength. However normally groove thickness would be about 1.5mm.
I'm pretty sure any good engineer is paranoid when you start modifying Safety Critical devices.
stevieturbo said:
Yet people are quite happy to buy cheap grooved/drilled discs regardless......hell...most replacement discs are probably made in China anyway and not a word said lol.
I suspect that you're observing two different groups of people here. i.e. those offering an informed opinion might not be the same people buying grooved discs on ebay for £9.99 a pair. Regarding Chinese manufacture, I'm afraid you're several years out of date if you automatically assume that Chinese made is a mark of low quality. Sure, you can buy junk from China if you want to but you can also buy engineered products of the highest quality and anything in between. The key there would be to ensure you're buying from reputable manufacturer and reputable supplier just like anything else in this world.
Edited by Gad-Westy on Tuesday 1st May 07:23
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