Skimming Brake drums

[The Other Mike]

You don't need a 4 jaw it's far quicker and more accurate to align off the bearing recesses, there is no need to even clock the drums with this method.

Chuck a lump of round bar of say half inch bigger diameter than the lead in to the drum bearing and maybe eight inches long

face and centre

Find the midpoint of the bar

Undercut say half an inch wide down to half inch diameter at this midpoint

Turn a 45 ish degree taper getting bigger towards the headstock from the midpoint

Turn a 45 ish degree taper getting bigger towards the tailstock from the midpoint

The angle is not critical nor does it need to be identical on the two halves

Do not remove the bar from the chuck until all drums are skimmed

Part off or cut at the midpoint with a hacksaw

Mount the drum between the two cones with a live or dead centre in the tailstock keeping lots of pressure on the tailstock and ensuring it is locked.

Machine the drums

If you need to machine a drum later just mount the bar in the chuck and remachine the taper, the other bar for the tailstock will not require any further machining..

If you had a four jaw chuck then a parallel turned section clocked in would be the quickest way to get the mandrel running true again.

[harry]

If it's just the lip, grind or file it off. No big deal.

[harry]

Simple. Put the centre hole on the OUTSIDE of the chuck jaws and tighten by moving the jaws outwards. Check concenricity before machining the metal. Doesn't your neighbour know this?

[DerbyBorn]

harry wrote in news:fdfe190f-3d17-4aab-8325- [e-mail]:

+1.

I could have done it by now. A decent half round file is all that is needed. Used to to it routinely before disc brakes.

[DerbyBorn]

Sorry - just realised you mean the lip at the back face end.

[stvlcnc43]

It can't be a very wide lip, so why not remove some of the brake shoe? Even if you make the shoe 6mm narrower the braking won't be noticeably affected.

[Rick Hughes]

... On comments about using a grinder - just not easy when lip is at back edge.

I am not worried about skimming the 'contact face' though would be a 'nice to have' Just that if I fit 4 sets of shoes .... brakes will fit this lip before the braking face.

Check concenricity before machining the metal. Doesn't your neighbour know this?

The jaws won't fit in the bore - it is too small.

Can't just reverse jaws and tighten on outside of drum as it would not be concentric with the bore- hence far better to do in 4-jaw chuck. You could shim it ... but could take a long time, and even then may not be accurate.

Done it myself in past with 4 jaw chuck in a large DSG lathe- but no longer have access to that.

My neighbour (fitter machinist - so knows his stuff) is going to try tonight, to see if he can make up a jig to hold it, using a pipe centre.

The option on turning up a mandrel is valid - just he only has limited time each night to spend on this in his meal break.

[Rick Hughes]

Thanks ... I'll pass this on

[Fredxxx]

My chuck couldn't cope with the small internal diameter, perhaps the neighbour's chuck can't either?

[harry]

n by moving the jaws outwards.

Must be a very small hole in the centre. Three jaw chucks are stepped on the outside for this purpose.

[dennis]

You can usually take them out and reverse them too. Maybe someone has and that's why they are too big?

[harry]

No. Three jaw chucks are usually self centring and work with a scroll plate. You need a different set of jaws to reverse them.

Four jaw chucks usually have independent jaws on separate screw threads, they can be reversed.

[rick]

OK was lucky .. neighbour was able to turn up a mandrel and has skimmed the first 2 .... 2 more to go.