MG MGB and MGB GT Tech Talk
I posted this in the MGA section, but I figure there is as much need for the info here. I bough one of these shrinking disc and can attest to how useful they are when it comes to getting rid of a peski high spot in the metalwork. Plus the thing is cheap.
If you are cheap like me, you can make one out of an old pot lid to give it a try. The one I bought works better though.
http://metalshapers.org/videos/Kelly_Shrinking_Disk.wmv
Pete
I bought one when I redid my B last year. All I can say is, "I loves me a shrinkin' disk!" Did you get one of Wray Schlein's?
I don't know a thing about body work, so what was I supposed to be seeing here? Looks like it makes noise, and makes the metal a little shiny. I like it for those reasons, noise and makes metal shiney, but what is the main function of this?
I've used one of Wray Schelin's shrinking discs in the process of rebuilding my B. It works great! I got mine from eBay.
http://cgi.ebay.com/ebaymotors/Shrinking-Disc-36-Ford-49-Packard-55-Chevy-40-Willys_W0QQcmdZViewItemQQcategoryZ43998QQihZ002QQitemZ120160639801
He also offers metal shaping classes. A friend of mine took a 3 day class and still raves about it.
Phil
Guess how it works:
My guess is that the metal to metal rubbing makes the work piece get hot, and then hitting it with cold water makes it shrink. We used to do something like this using a torch, in which we'd warm the metal where we wanted it to shrink, and then, once it was warm (less tha turn blue) quench it with a cold wet towel . This item is especially neat because it only heats the highest spot ('cause that's what touches the rubbing surface).
Cute tool. Any of many material should work quite well. Sheet metal (steel) is a good choice.
There seems to be some debate about the science of it all. The best visual I can conjusre is like this:
Take a bowl of water and sprinkle some black peper evenly on the surface. Now take a bit of dish soap and put it on the tip of your finger. Pretend that the peper is metal molecues and your finger is the shrinking disk. Observe what happens when you put the tip of your finger into the bowl.
When the disc heats the metal, it forces it to expand away from the source of heat. However, the metal is trapped by the unheated metal surrounding it (the bowl sides). The result is that there is a concentration of metal in a ring shape around the heat source.
When you quench, the metal cools faster than the molecues can re-shift and hence the center is going to try and be of a smaller diameter when it returns to the original temperature. Result is less metal in center= no high spot.
Of course I could be wrong. Still the best 50 bucks I spent.
Pete
looks like the guy in the video is chasing the high spots all over to me
I learned to do this with a torch many years ago in tech school. The idea was to heat the raised area, causeing it to raise further, then work it back down with a hammer & dolly and quench with a wet rag. One guy said his method was beat the high spots into low ones and fill em with mud. lol
Same sort of principle with this disc but useing less heat which would be good. This is sort of a lost art these days. I know we get some flak in our bussiness for being parts replacers but the metal in todays cars is far different from what an MG is made of. Thinner and what they call HSS (High Strength Steel) Has a different temper to it makeing it stronger while lighter. Plus it all has a galvanized coating for corrosion protection. When it gets to the point of damage that shrinking is required, it's time for a new panel.