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| Removing scratches from UHMW sheet http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=9799 |
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| Author: | Todd Rose [ Tue Dec 12, 2006 1:31 pm ] |
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I just got a sheet of UHMW for making jigs and things out of. I've never really worked with the stuff. The sheet arrived with many parallel scratches across its surface, on both sides. Not terribly deep scratches, but certainly obvious, significant scratches. First question: For those who've bought UHMW, is this unusual? In other words, should I consider this a sub-standard product and return it, or is this typical of a new sheet of UHMW? Second question: Can I just go at the surface of this stuff with my ROS and some stearated paper to remove the scratches, or do you have any other suggestions? |
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| Author: | JJ Donohue [ Tue Dec 12, 2006 2:36 pm ] |
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Todd...These are probably extrusion marks that are quite common. It's so soft that it will acquire scratches over time anyway. It'not like Lexn which is much harder. The advantage of UHMW is that it's an excelent bearing surface with a low coefficient of friction that allows things to slide smoothly. You could probably use a cabinet scraper to smooth it out. |
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| Author: | Rod True [ Tue Dec 12, 2006 3:28 pm ] |
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I'll have to disagree with my bud JJ. When I worked at the fab shop we used a lot of UHMW in all different thickness'. When new, it should be as smooth as a baby's bottom. There shouldn't be any scratches of any sort on it. I would say take it back if it's not a hassle or to inconvenient for you, check with who ever you got it from to see if they have any that doesn't have scratches. I can see surface scratches, kind of like rubbing your finger nails against a lacquer finish which is only a week or so old, but nothing with any real depth at all. My guess is that it was dragged across some surface somewhere along the transit route. It is rather soft as far as materials go. Does make great bearing surfaces, as long as it's not for high speed use. "going at the surface with the ROS" wouldn't solve the problem, I think. This would just cause more scratches. What are you planning on using it for? Are the scratches hindering its use, or is it just something that looks "used" and not new? |
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| Author: | Keith M [ Tue Dec 12, 2006 10:53 pm ] |
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I double face taped UHMW to a carrier board and ran it through my thickness planer. I also had longer sacrifical wood strips on each side to minimize snipe. The stuff doesn't sand but it machines fairly well. |
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| Author: | Todd Rose [ Wed Dec 13, 2006 1:12 pm ] |
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Thanks for the responses, JJ, Rod, and Keith. You know, taking another look at the "scratches", they do look like extrusion marks. Interesting. From Rod's experience, though, there are clearly sources of this material without the marks... maybe they machine it smooth somehow after it's extruded and hardened?? In the future, I'll check out some other sources, but this sheet should work fine for the fret-slotting sled runners I'm planning to use it for, and I'm sure I'll find uses for the rest of it. Thanks for saving me the trouble of attempting to sand out the marks. It sounds like that would have been a waste of time. Here's what I'm thinking for making the runners: 1. The sheet is 1/4" thick, which should work well in the 3/8" depth of my table saw's miter slots, so I'm good for thickness. 2. To get the width I need, I'll cut strips a bit wide on the band saw (or table saw), then carefully take off a little at a time by running them in between the fence and a straight bit on my router table, until the fit is just right in the table saw's slots. Another thought - If Keith has had good success with this material in a planer, I should be able to use my jointer to get a straight, smooth edge on the sheet before cutting each strip on the band saw. Then I'd have one true edge on the strip to run along the fence on the router table. Sound good? Other ideas? Am I at risk of melting this stuff during cutting/machining and making a mess on my blades/bits? Thanks again! |
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| Author: | Rod True [ Wed Dec 13, 2006 3:16 pm ] |
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You won't melt it by cutting or machining it like wood Todd. I cut the stuff all the time on the table saw, you should have just as smooth of an edge as you do with plywood when cutting on the table saw. This stuff works great for mitre slot runners. You can cut it spot-on on the table saw, or just a hair big and than sand the edge to final fit. You really can machine UHMW just like you would wood. It's great for jigs and for sliding surfaces and glue regular wood glue won't stick to it so that's also good for jigs. Have fun. |
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| Author: | Todd Rose [ Thu Dec 14, 2006 1:34 am ] |
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Thanks, Rod. Okay, so it will sand well enough to sand the edge to final fit. Maybe I'll do it that way, then, instead of on the router table. Or maybe I can get a spot-on fit right off the table saw. Cool. |
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| Author: | Brad Goodman [ Thu Dec 14, 2006 1:57 am ] |
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Todd, I would be very carefull when machining a soft plastic like that on the jointer. I had a scary experience routing polycarbonate(lexan). The router "grabbed" the material-I finally had to take very small"bites" in order to machine it. I have never heard of it happening to anyone else-but it was my experience with that material. |
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| Author: | Todd Rose [ Thu Dec 14, 2006 8:40 am ] |
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Thanks for the warning, Brad. |
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