Projects Need some help with metal shrinking

Hey,
A shrinking disc isn't some big mysterious tool, contrary to what some who sell them want you to beleve! It's a metal disc that creates friction, and friction = heat. When you heat sheetmetal it expands, quench it with water, and it contracts, rapidly. A shrinking disc is much easier (for some) to control vs. a torch ,hammer & dolly.

If you're having trouble getting good shrinks without heating the metal to a red heat, perhaps what you're trying to shrink isn't really stretched metal, but misplaced metal a.k.a. a false stretch. Always be sure that you've straightened all the metal you can move, and returned it to its' correct shape, before desiding what the panel needs is to be shrunk.

I've used several shrinking discs, including the one pioneered by Scott Knight, and now being sold for obsceen amounts of money by someone in Pasadena California, but my favroite is a homemaid one. Depending on what sized grinder pad you have, cut a 10''-12'' disc from 18 gague steel, and drill a hole in the center the size of your arbor on your grinder. Now, take a 3/8'' bolt & nut and a lug nut and with the tapered end of the lug nut facing towards the disc, tighten the 3/8'' nut and bolt until a depression is created in the center of the disc. This depression should match the backing pad on your grinder when you're done. You can put ridges into your disc if you like, but the ones I've used that are just flush-faced work fine. Be sure to check the fit up on your backing pad to the disc and adjust for a good tight fit, much as you would if you were installing a grinding disc. ALWAYS ware a faceshield when using one of these, and ear plugs ain't a bad idea.
Ya don't need to spend big bucks to repair/shape sheetmetal.

" Life ain't no Disney movie "

 

Or if you are too poor for that, try putting a worn out sanding disk on a grinder backwards and use it as you would a shrinking disk. The fibre backing creates plenty of heat for shrinking, just takes a little longer to happen

They do smell pretty rotten though

 

I use a shrinking hammer but for small dimples, the teeth grab the metal to help hold the metal so it will gather and thicken. I have a shrinking disc or two, the generate heat in the high spots "not the low spots" they work well too. blue heat is plenty.
Now there are times you want to go red heat in spots, repeat damage, dang metal is work hardened and does not want to go back. One problem I see with the pump is that it probably had a slight crown, just part of the way they were made. It's how you learn to use your tools that will help you become a good metalshaper! And it helped being an old guy, just at the end of the autobody craftsman, turned into a part swapper / bondo slingers. Someday I may learn to spread bondo halfway descent, it's pretty embarrassing to spread it worse than concrete..... hmmm never thought of using a bull float on bondo???? hey there maybe hope for me after all.....

 

You can torch shrink using no color change in the metal It swells slightly, you quench (should see steam) then do it again if it needs it. Slow and controllable with just a torch. Not quite as nice as a disc, but it works great and you can do it multiple times without hardening the metal. I show one way to make a shrinking disc in this album:

http://allshops.org/cgi-bin/community/communityalbums.cgi?action=openalbum&albumid=9980121727059

If you don't have an edge shrinker to make a disc, you can tuck shrink the stainless. Or you can make a hammer form and make a flanged safety disc. You do not even need stainless. You can use cold rolled steel. With any disc, make sure you check it for cracks before each use. I have some stainless blanks left over from when I made shrinking discs if you want to try making one.

Wray Schelin makes a nice shrinking disc. His email: wesparts@charter.net

Once you use one, you may never torch shrink again.

John