What are Shrinking Discs?
When using a Shrinking Disc, you are able to shrink overstretched areas and repair damaged sheet metal panels to a like new condition, making for a better quality, longer lasting finish with little or no body filler at all! The secret to them, is they create the heat that is needed to shrink through friction. They produce better results and are much more controllable than shrinking with a torch or a solid tipped stud gun. When using a torch, you are directly controlling how much heat is being inserted, and were it is going. This is easily and many times overdone, resulting in warping and further damaging the panel. With the shrinking disc and its large surface area, it eliminates some of the guess work, especially when smoothing a lumpy panel by only touching the higher overstretched areas! The heat is also more concentrated on the higher peaks of the damage and tapers off to the lower areas, which results in a much greater accuracy of heat placement, in turn ending with a much smoother nicely blended panel.
Once you have started using the shrinking disc and get a little practice under your belt, it will make you feel more confident in your metalworking skills when you can finish a panel with no body filler at all! The more you use it, and the better you get, the less filler you have to spread and sand! It saves lots of time on sanding, keeps the shop cleaner from having less putty dust, and makes for a better quality, longer lasting finish with little or no body filler at all!
How is it used?
In normal conditions, you would roughly straighten the panel, tap the dents and low areas up with a hammer and dolly and then make a couple of passes with the shrinking disc, heating and cooling. Look over the panel to determine were more work is needed, and using a hammer and dolly, rearrange or tap up any remaining low spots followed by a few more passes with the disc. After completing several loops of this process, your panel will be smooth, and back to normal surface tension.
When using the shrinking disc after welding in a patch panel to arrive at an almost invisible seam, you should start by carefully grinding the bulk of the weld. While doing this, you want to minimizing excessive heat buildup and prevent thinning of the panel itself. Then the HAZ (Heat Affected Zone, the area that was discolored while welding) needs to be stretched by using a hammer and dolly (with slightly more contour than your panel), striking the hammer "On Dolly". This is required, because the welding process heat causes shrinking just like the shrinking disc does, although it happens in an unwanted and uncontrolled manner. After stretching the HAZ, it will be closer to the original profile, but still lumpy, uneven and possibly over stretched from the various hammer blows. Now is when the shrinking disc works its magic. By using the shrinking disc over this area, and blending around the edges if needed, it will only touch the higher overstretched areas as mentioned before, and shrink them down so the entire weld area is smooth, and has the same surface level. More details on using the discs included in the Instruction Manual.
How does Heat Shrinking work?
Shrinking occurs after heating (causing expansion) and cooling metal (resulting in contraction). This happens because while a panel or sheet of metal is being heated, the heated area is trying to expand. The surrounding cold metal is containing the majority of the expansion and holding it in, preventing the expansion from happening. When cooling the panel, the heated metal contracts (which the surrounding metal cannot prevent, in turn shrinking the heated area. Important aspects of this method are heating and cooling fairly quickly. Slow heating is usually more of a problem than slow cooling, as it will let the heat disperse into the entire panel before any expansion containment has taken place, reducing the shrinking discs effectiveness greatly. If heating happens quick enough, some shrinking can occur with only room temperature cooling, but is greatly accelerated and multiplied by cooling with either compressed air or water (squirt bottle or rag), but water generally tends to provide quicker cooling.
These shrinking discs work well on steel, stainless, aluminum, brass and may on some other metals. (it is recommended to use separate discs to prevent cross contamination) Also it only touches the higher overstretched spots that need to be shrunk. So you are able to shrink an area on a panel without worrying about making the problem even worse like you can with a torch. The shrinking disc also works excellent on removing those "oil can" dents that were caused by overworking and stretching the metal too much!
Which size disc should I get, 3", 4 1/2" or 9"?
The small 4 1/2" disc has a low initial investment (almost everyone has a 4 1/2" grinder), and works great on small parts (for example, stainless trim, grille shells, motorcycle tanks, etc), light damage, tight spaces, or after primer and block sanding, it works great for catching any high spots that were overlooked, instead of beating them in and covering them with filler, without disturbing much of the surrounding primer (as it is more difficult with the large disc).
The large 9" disc excels when working large, low to medium contour panels such as, hoods, roof, door, trunk or heavily damaged panels, because of its greater working surface area. Compare it to block sanding, were on a large panel, a longer sanding block makes it straighter and works more area at one time, but the small ones still work and are needed for some situations as well.
The 3" Disc and Kit are designed to compliment the larger shrinking discs for extreme fine tuning and to get into hard to reach areas. If there is room for a larger disc, using the larger disc is recommended, as you will have much better and faster results. After personally using the larger shrinking discs for many years and talking to customers, I found that a smaller shrinking disc would be a great compliment to the shrinking tool arsenal. The SD3 disc would not be a good option to try to repair an entire 1/4 panel or heavily damaged area, it would take too long and/or just not work very well. However, it is very handy, especially when repairing sandblasting damage from the outer skin being stretched when it is blasted from the backside between the bracing. This creates a “Hard Edge” of stretching from the blasting process because of the bracing blocking some of the panel. The small lipless discs allow you to get into the open areas between the bracing and even slightly under to finish blending the repair as far as the blasting process was able to stretch the sheetmetal.
(1) 4.5" Metal Shrinking Disc
(1) Backing Pad
(1) Washer and Arbor Nut
Made using a Special High Grade Stainless Alloy & Manufacturing Process, that creates a long lasting, low galling, crack resistant, safer and higher performance disc compared to older designs.
• Works on steel, stainless, aluminum, brass
• Creates Heat through Friction to allow shrinking of the sheetmetal
• Works with compressed air or water cooling (spray bottle or rag)
• Is good for shrinking, smoothing, blending and relieving surface tension created from damage
• Have sizes and Kits to fit standard 4 1/2" & 7" or 9" electric sander/grinder/polishers and right angle air die grinders (3" disc)
• 3" Discs, Recommended RPM 20,000 - 22,000, Max RPM 22,000
• 4 1/2" Discs, Recommended RPM 10,000 - 13,000, Max RPM 13,300
• 9" Discs, Recommended RPM 3,000 - 6,000, Max RPM 6,500
Always wear proper safety equipment when using this type of power tool. Ear, eye, hand and breathing safety equipment is recommended.
1 Year Manufacturers Warranty
Eastwood Offers Free Lifetime Technical Support
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