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MG Midget and Sprite Technical - Shrinking Disk

Anyone used a metal shrinking disk? Are they as easy to use as online videos imply, or is there lots of hard-won experience needed?

http://www.youtube.com/watch?v=X8cruauERmI

Also, anyone know where one might buy one in the UK. The Ebay ones are all supplied from the USA with high postage costs. Anyway, there's a rumour going round that USA don't want to trade with other countries any more.
GuyW

Yes. I use one. It is not a miracle tool, but it does have its place. It is most useful on bonnets and doors. However, it is VERY loud.
Trevor Jessie

Thanks Guy and Trevor. That was interesting and relevant as I'm going to be reskinning Don's GT6 doors sometime soon. I think this will help.

Any practical tips gratefully received.
Greybeard

Guy,

I'm pretty sure the disc is just used to generate a local hot spot by friction which is then quenched to shrink it. There are a number of shrinking videos on youtube where a flame is used to heat the area being shrunk such as http://www.youtube.com/watch?v=vZcA2yUdPQw so no need for a fancy grinder shrinker disc. Should be easy to get or make a dinged panel to try the procedure on with a torch.
David Billington

Hi David,
Yes I have done it before with a gas flame. Fairly effective but takes more skill to heat only the right areas than I have yet acquired.

As far as I could see from the shrinking disk, the point is that it touches and creates heat specifically just at the high spots. So when then quenched these are the areas that shrink back. In theory this should be more controlled than use of a flame.
GuyW

Agree Guy. That's why I was interested. The gas-axe method does work but I've never found it very controllable.
Greybeard

Ive done this but im notba fan of this method as all your doing is removing metal which weakens the metal

The ideal better way is to use a Oxy act welding torch and heat to (cherry red) then bump the metal backdown and use a wet rag to recool and shrink the metal back down...you can also drill a 1/8th inch hole in the center of the high spot and heat shrink it to make the task eaier and faster

Prop
1 Paper

Prop, these disks Don't remove metal, they heat it by friction. There are some sparks but it's not a grinding disk. And as they rub on the high spots the heat is restricted to where it's needed. At least that's the theory.

Can't work out why no one in the UK is selling them. H & S regulation maybe ?
GuyW

Guy,

Stakesys list a 9" version and mention a 4.5" so maybe they're out of stock of the 4.5", why not ask them, see http://www.stakesys.co.uk/dagger-tools-shrinking-disc , made in the USA. I can't imagine why more people don't sell them unless not much demand, as for HSE regs I can't see them being dangerous compared to the angle grinder wood carving discs which are sold such as http://www.axminster.co.uk/arbortech-mini-carver-blades-600491 .
David Billington

I would be more convinced that the process was metal shrinkage from a heat/cool cycle if there wasn't a stream of sparks from the work surface. Metal grinding!
J Thomson

The stakesys link doesn't seem to pull up the product page but if you search for the shrinking disc it's there. The mini carver blades aren't to fit an angle grinder but I've seen the same type of thing to fit a 4.5" grinder and another type with chainsaw chain around the periphery which looked scary.
David Billington

J Thomas, - you would expect some sparks off a steel disc to steel contact. But its nothing like the quantity of sparks you get from a grinding disc!

David, thanks for the contact. I might give it a go just to learn something new. And I know what you mean about those chainsaw/angle grinder hybrid blades! Horrendous! From when I did my tree surgery ticket I know just how a chain can bite and kick back. A mini grinder has no equivalent chain brake or anti=kick mechanism and continues to run for ages after switched off. All near lethal attributes!
GuyW

For what it's worth I will continue to buy from your side of the pond.
J Bubela

Like I said they have their place. I would not try to use it on heavy gauge sheet metal. For that you need to break out the oxy-actylene torch. The also still require you to be able to "read" the metal, so they are not magic. And I suppose you could rub a hole in the metal it you stayed at it too long.

Be prepared for the loudest and most obnoxious sound to ever come from a bodyshop tool ... which may be why they are not very popular.
Trevor Jessie

Forgot to say ... the larger disc can run at a slower rotational speed since the concern is the surface speed.
Trevor Jessie

Actually thinking more abut this I won't bother. At the better part of £50 delivered it would be too expensive an experiment for me. I have some slight ridges and high spots in my recently fitted rear deck. they are not bad and will either planish down with the help of some carefully directed heat. Or failing that a thin skim of filler will sort it. And the £50 will go on something else!
GuyW

This thread was discussed between 21/01/2017 and 23/01/2017

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