Looking for a set of LS1 calipers. When I get em I wanna polish em, anyone got any tips on polishing? A step by step would help alot. . .
Posted by 2002Z4CSS (Member # 1393) on :
You can get the calipers from any GM dealer or autoparts store.May get a set cheap at a junkyard.A die grinder with a sanding disc will knock off the rough edges and a dremmel tool may get in those hard to reach spots.Then sand smooth using different grits of sandpaper.Follow up with a polishing compound.
[ 07. August 2003, 06:48 AM: Message edited by: 2002Z4CSS ]
Posted by William J. Finch (Member # 1507) on :
they don't polish good because they are anodized (shot-peened) metal!
Posted by RareSS (Member # 1818) on :
Mine did not polish that nice so I powder coated mine red. I also chromed the pad brackets. I have the vert and coupe SS/LE's and they look nice on them. Jim, Julie, and Jenny
[ 14. August 2003, 11:11 PM: Message edited by: RareSS ]
Posted by FireChicken (Member # 2067) on :
quote:Originally posted by William J. Finch: they don't polish good because they are anodized (shot-peened) metal!
The shot-peened finish can be polished out, but it will take a lot of work. You have to understand a few things before you can decide how to approach a polishing problem.
1. Any specific grit of sandpaper produces a surface finish by cutting grooves in the direction in which the sandpaper moves. Low grit numbers have large grains, and therefore, fewer grains, in a square inch. These will cut a small number of deep grooves when the sandpaper cuts into a metal surface. Inversely, fine grain sandpaper (a higher number), has a larger number of grains per square inch, and therefore the grains are smaller. As such, fine sandpaper cuts a much larger number of grooves, and they are also much shallower, when compared to the more coarse grades of sandpaper.
2. This characteristic of polishing is the fundamental thing. You will always start with rougher paper, and move to finer. Where you start depends on the existing finish. If you have smooth metal, but it just has some light scratching, say for example... the aluminium fittings on AC lines. Those you can start polishing with around a 240 grit or so, and then move up progressively to 320, 400, 600, etc. Rougher surfaces, however, like the cast finish on most valve covers, brake calipers, etc, require more work. Your best bet will be to start with 60 or 40 grit sandpaper. Polish in the same direction everytime (either up and down, OR side to side, but not both, and remember to let the paper follow the contours of the metal). Over time, you will see the rough, shot-peened finish be replaced with a lined finish created by the sandpaper. What is essentially happening is that you are sanding away the high spots on the shotpeened finish, until all surfaces are relatively level with one another. You are then sanding them all at the same rate, which makes a uniform surface finish.
3. Now lets talk about buffing wheels and polishing compounds. These fit into the same scale as sandpaper, however, a cloth buffing wheel has a super fine grit, much finer than that of any sandpaper. The actual scale is something like this, from finest to coarsest.
Clean cotton buffing wheel. Buffing wheel with compounds on it. 1000 grit sandpaper. 600 grit sandpaper. 400 grit sandpaper. 320 grit sandpaper. 240 grit sandpaper. 60 grit sandpaper... and so on.
Now, what about grinding wheels? Well, grinders come in all kinds of grits too, but since they are powered by a motor or air, we put them in the category of being rougher than sandpaper. Even the finest grit grinders are still usually far more coarse than the sandpapers that carry the same grit numbers as the wheel. For example, a wheel marked with a 150 grit will usually be a bit rougher than sandpaper marked 150 grit, simply because its a power tool. In all honesty, you really only need power tools for things like smoothing out seams, casting lines, and removing burrs (sharp edges that can cut you).
4. I would not reccomend really using a power tool to smooth down a shot peened or cast finish, mostly because you dont have the element of control you have with sandpaper. Grinders will also make trouble in small corners and dips too, and sandpaper is a much more accurate, albeit time-consuming tool to use. I would use a grinder where you have rough corners that need to be rounded over, and sharp edges, and then move to sandpaper.
5. Now lets talk about buffing. You really only buff if the last sandpaper you use is 600 or higher grit, AND you are looking for a better finish than the sandpaper provides. Typically this is something that has a mirror quality. The type of buffing compound that you use has a lot to do on what you are trying to accomplish. There are four main types of buffing compound.
I will post their specifics tomorrow, since im too tired to go get my chart out of the car. Suffice to say, buffing compounds also fit in the grouping like sandpaper, based on their abrasiveness. You will probably not need buffing compounds for your calipers, but up to about 400 grit sandpaper should be the most. If you want to go higher, perhaps to a mirror shine, I would leave it as bare metal, and not paint or powdercoat them.
Posted by mikerc (Member # 2021) on :
Quick question. Should you be polishing a part that was shot-peened to begin with? Doesn't the shot-peening have something to do with the strength of the finished part? What effect would polishing have on that? None? I can't remember enough details from my intro materials class I took in college 13 years ago... Posted by pg318 (Member # 1810) on :
quote:Originally posted by mikerc: Quick question. Should you be polishing a part that was shot-peened to begin with? Doesn't the shot-peening have something to do with the strength of the finished part? What effect would polishing have on that? None? I can't remember enough details from my intro materials class I took in college 13 years ago...
Shot peening is used to increase the fatigue performance of materials by inducing a residual compressive stress on the surface, so that the microcracks are subject to less tensile stress as the part is flexed. It's also used on aluminum castings to remove casting flash, to provide a uniform appearance, and to some extent to enhance corrosion performance, since the surface porosity of the material is closed up. It should be safe to polish the outside of the calipers, since the tensile stresses are only present on the inside, particularly around the corners at the outside of the pads. In any case, you're only going to remove enough to take the high points off, and not remove a substantial layer.
Posted by FireChicken (Member # 2067) on :
quote:Originally posted by pg318:
quote:Originally posted by mikerc: Quick question. Should you be polishing a part that was shot-peened to begin with? Doesn't the shot-peening have something to do with the strength of the finished part? What effect would polishing have on that? None? I can't remember enough details from my intro materials class I took in college 13 years ago...
Shot peening is used to increase the fatigue performance of materials by inducing a residual compressive stress on the surface, so that the microcracks are subject to less tensile stress as the part is flexed. It's also used on aluminum castings to remove casting flash, to provide a uniform appearance, and to some extent to enhance corrosion performance, since the surface porosity of the material is closed up. It should be safe to polish the outside of the calipers, since the tensile stresses are only present on the inside, particularly around the corners at the outside of the pads. In any case, you're only going to remove enough to take the high points off, and not remove a substantial layer.
True, and the effect of the shot peening will penetrate further than just the surface of the calipers. Its not like an anodized coating, where the alteration occurs soley on the surface of the part, but its more like a nitriding or carburizing process, where there is penetration into the material (although nitriding is a very low penetrant hardening process). So polishing it should not alter the material strength in any way that is important.
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