Shrinking Disc Protocol

J

jvo

Well-Known Member
Supporting Member
I'm doing this thread for the folks that haven't been initiated to a shrinking disc yet. There is still a lot of doubt as to their usage and effectiveness.

I'll start with the discs themselves and mounting them. You can use any grinder that is big enough to handle the job, as long as its rated for the size of the disc. You will probably need to buy a thin mounting nut. I use a Milwaukee nut, available at most tool stores. The thick nuts that come with your grinder will protrude beyond the surface of the disc, so that you cannot place the whole disc on a flat surface without the mounting stud or nut protruding past that surface. I've tried about everything I could think of, and I have found that old worn out flap disc pads are good for spacing and mounting the discs. And don't ask what the sharpie lines on the small disc are for either. I can't remember.
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The small disc, as pictured, works great on convex areas where the big disc will not fit. The rolled edge on the small disc makes this possible. I'll add here also, that the only reason for the rolled edge on either disc is for safety. The round disc on the meat slicer at your butcher shop would work just as well, because it is stainless steel also, but mounting that on a 9 inch grinder is pretty dangerous, eh?

I'll also add here that the discs are made out of stainless steel, as stainless against mild steel is slightly abrasive, which creates heat, which enables the shrinking to happen. You only need to be able to make steam to shrink metal. It does NOT have to get extremely hot, or glow red, like with a torch.

IF, the disc doesn't seem to be working well, take a piece of sandpaper, fairly coarse, like 80 grit, and hold it against the disc while it is spinning. This is quite dangerous, and is best done by two people, one to hold the grinder so it doesn't take off when you pull the trigger, and the other to swipe the sandpaper across it to clean it and take off any burnishing or paint and crud that may be adhering to the surface of the disc after a lot of usage. I do this to a brand new disc as well to get it to "bite" better. You only have to do that once in a blue moon, or when it appears cruddy.

I hold the grinder with one hand, and use my sanding disc to do 2 or 3 passes over the disc, and its clean and good to go again.

When I first started using one, I would go over and over the panel, and I've seen others do it as well. You only need to run the disc on the surface of the metal for several seconds. If you work it too long in one spot, all the metal will get hot and you might just over shrink the area. You only want the disc to touch the high spots on the panel. It only takes about 3 seconds for this to get the high spots hot, before the heat starts to travel into the low spots as well. Once I figured that out, and didn't run the disc for 20 seconds or so, it started working like magic. Work a small area, perhaps the size of the disc, with a hammer and dolly and get it as smooth as you can. Remember, you are trying to restore the crown in the panel again. Remove all the highs and lows.

When you can't get it any better with a hammer and dolly, you will have a panel that has that "mottled" look, tiny highs and lows everywhere. Those tiny highs and lows can be removed with a slapper and dolly, but any areas that are over stretched now need to be shrunk down.

Run the shrinking disc over the area that you are working on. When you pull the trigger, count one tho
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usand and one, one thousand and two, one thousand and three, and let the trigger go. Place the grinder on the floor beside you, (if the grinder falls and the disc gets bent, good luck trying to get it to run true again) and grab your wet rag. I like to use an old cotton T shirt. Do NOT use a rag with a lot of plastic fibres in it, poly whatever it is, as it will melt on a really hot surface.

Cool the panel down till it is the same temp as the rest of the panel, then go to work again, either with hammer and dolly or more shrinking, whatever you need.
 
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That’s very interesting. Wonder how someone ever figured out to do that......
 
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I had a lot more going here, but froze up yesterday and couldn't log back onto the site till now. I restarted my iMac, that might have been the problem.

I think James has the history pretty much down on the shrinking disc. And he has an original. I think it had something to do with a guy at California Metal Shaping using a worn out sanding pad, and finding out by accident or something like that. I "think" it was James that told me, might have been Wray. I'll get my shit together again, and try to post the rest of this.
 
On second thought, I think I'll wait till I encounter a nasty oil can somewhere in the future. I might just do up a video on how to repair it. I was taught basics, but I've worked on more than my share the past few years. When I do that I'll emphasize that there isn't necessarily anything wrong with the oil can itself. It is often caused by damage adjacent to it, and a ding the size of a dime can make a very large oil can dent. Fix the tiny dent, oil can goes away without touching the area at all that appeared to be damaged.
I would do the shrinking disc demo on that also.
 
I have always been scared to try a shrinking disk. For some reason I have a fear that it will crack and fly apart. I do shrinks with my stinger or a torch. Perhaps I should get over my fear and try this
 
Hotflint said:
I have always been scared to try a shrinking disk. For some reason I have a fear that it will crack and fly apart. I do shrinks with my stinger or a torch. Perhaps I should get over my fear and try this
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I know a guy who had a flat ones come apart. He checked it every time he used it but must have missed a hairline crack. Thankfully he was not hurt. John Kelly stopped making and selling the flat ones because he had one come apart on him and didn't want it happening to anyone else. I stopped using mine. I have never heard of the ones with the upturned lip coming apart so I am waiting on a new one of those coming up from Calgary as we speak.
 
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