Can you fix a warped disc?

Cuprinol Man

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I know car disc's can be skimmed but bike ones are much thinner so not sure if you can or not.

A mate suggested finding where on the disc it was warped and heating it up then putting it in a vice to cool!
 
Cuprinol Man said:
I know car disc's can be skimmed but bike ones are much thinner so not sure if you can or not.

A mate suggested finding where on the disc it was warped and heating it up then putting it in a vice to cool!
Click to expand...

Tell your mate to get down to the local pharmacy for a high dosage of reality pills, about 500mgs should suffice.

Replace the disc, it isn't worth messing about with.

Out of curiosity how much warpage are we talking about?
 
I believe that there is an engineering tool called a 'blanchard grinder' that can skim discs of this nature.
However given the time and money involved, if you can find someone willing to do it that is, its not worth it and it is therefore false economy.
Steptoe sells them for £75, Grimeca I believe.
 
Cuprinol Man said:
I know car disc's can be skimmed but bike ones are much thinner so not sure if you can or not.

A mate suggested finding where on the disc it was warped and heating it up then putting it in a vice to cool!
Click to expand...

Your friend obviously wants to kill you. If it's a stainless grade you would totally change the structure, have a very rusty disc in no time and quite possibly it would decide to crack. £75 is not a lot for piece of mind imho
 
Your friend is a grade 1 nutter!

Given these discs have a reputation of warping don't even bother skimming and making it even thinner - replace it.

Andres
 
Cuprinol Man said:
I know car disc's can be skimmed but bike ones are much thinner so not sure if you can or not.

A mate suggested finding where on the disc it was warped and heating it up then putting it in a vice to cool!
Click to expand...

Most car discs are only skimmed by people wearing ten gallon hats and spurs on their boots There is not enough thickness, especially with vented disc to allow for skimming without taking the discs close to the minimum thickness.

And I agree with the others, your mate need the treatment he has suggested for the disc!

John
 
Many years ago I used to work in the car world and it wasn't uncommon to skim brake drums and fit over-sized linings, but I have not heard of discs being skimmed.

You sure?
 
Used to skim discs for cars all the time but i have never done one for a bike. I would have thought they were too thin to be put in a lathe as they would probably chatter whilst being cut. We used to do aircraft discs on a surface grinder but that was a long old job and they were a lot thicker.
So in answer to the OPs question I would say go and see St Eptoe as I did and get a new one.
 
Rusty Bolts said:
Used to skim discs for cars all the time but i have never done one for a bike. I would have thought they were too thin to be put in a lathe as they would probably chatter whilst being cut. We used to do aircraft discs on a surface grinder but that was a long old job and they were a lot thicker.
So in answer to the OPs question I would say go and see St Eptoe as I did and get a new one.
Click to expand...

You are partly correct, the old style discs (70's/80's) would 'sing' in the lathe because theycan't sit far enough back in the jaws of the chuck, and so needed to be supported with either pressure pads at the back or to be put into a fixture before machining. I skimmed my discs many years back on my old stroker , GT500, but in those days they had some material thickness to them!

A modern disc wouldn't sing, or chatter because it can be separated from its carrier and held flat in the chuck jaws, though it would have to be machined at very low rpm to prevent the chatter, thereby making it very time consuming. That aside, they have a very small serviceable tolerance range and once warped it would be quite impractical, non-beneficial and quite simply wasted money.

As there is no call for such a service today then by the time somebody had machined up a fixture, whether for Turning or Grinding, the cost would have exceeded that of a new replacement disc.
 
Fugu said:
I believe that there is an engineering tool called a 'blanchard grinder' that can skim discs of this nature.
However given the time and money involved, if you can find someone willing to do it that is, its not worth it and it is therefore false economy.
Steptoe sells them for £75, Grimeca I believe.
Click to expand...

I found a link to Steptoes and it took be to www.gsshop.biz.


Is this Steptoes?
 
I had a pair of cast iron discs reground years back, one disc was better for the regrind because it was ground perfect, the other was no better really because it was ground with I suspect a bit of swarf under one side (magnetic faceplate on lath) so not flat ( or at least the two surfaces wern't parallel ) anyway, I wouldn't bother again, they were both scrapped and new S/steel discs fitted soon after, waste of time...
 
If the disk is mounted against an alloy face, remove the disk and check there is no bubbling or corrosion of the alloy behind the disk which could cause the warping.

If you have a DTI and a marker pen, clock the disk runout and then undo the disk and rotate it so that the highest point is fitted to the previously measured low point and vice-versa and see if that improves the runout.

If not improved, replace the disk.
 
I know someone that took their discs off,slapped them on a surface grinder,touched them up,put them back on, and they were just as bad.So he takes them off again and takes a bit more off,puts them back on,same again.

Fourth visit to the surface grinder,one of the other blokes pointed out that it was a magnetic table,and every time he put the disc on it,the magnet pulled it flat,so he was grinding a flat disc anyway.Turn the table off,and disc has warp again:blast

May I point out that the poor sod didn't suffer at all for this,and no one took the pish out of him afterwards:rolleyes:
 
Which is why it should be done in a fixture, if it is to be done at all.
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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