Replies

1. 
   Scrit | Feb 01, 2004 03:04pm | #1

   We machine UHMW (HDPE) plastics on our CNC for a couple of customers and it is a real swine to secure to anything. The material is totally impervious which means that in general it can only be secured by drilling, countersinking and screwing into place, especially if you are going to subject it to any shearing forces. It drills just fine with woodworking drills and sharp edges can be knocked off with a standard block plane (well sharpened blade). Do watch out for the edges as the 1000 grade (the hardest) in particular can cut you if you haven't taken the arrisses off.  

   I've experimented with double-sided tapes but even the best suffer from the tendency to creep over time unless the application is a very low shear load one (and let's face it the reason for using UHMW is for its ability to handle shear loads....), although I've had limited success with UHMW surfaced using a spoil board cutter at high revs/high feed rate on our CNC. This produces a coarse surface rather like that left from a scrub plane but more uniform and gives the DS tape a friction surface to adhere to. In time, however, even this can creep unless some mechanical method of attachment (i.e. screws) is used as well.

   Scrit

1. 
   Novy | Feb 03, 2004 11:14pm | #14

   Scrit,

    Just a thought and not particularily applicable in Chucks scenario but have you any experience with methelyne chloride and UHMW ?On a hill by the harbour

1. 
   Scrit | Feb 04, 2004 11:21am | #15

   Sorry, no.

   Scrit

2. 
   WayneL5 | Feb 01, 2004 10:28pm | #2

   There's a lot of thermal expansion with plastics, so if the area is going to be experiencing temperature variations, you'll have a tough time with any fastening system.

1. 
   Scrit | Feb 02, 2004 12:50am | #3

   That's why we tend to drill round holes for the middle of pieces and rout slots for the outsides, although the stuff is flexible enough to accomodate a degree of expansion - depends on what the plastics are going onto, though

   Scrit

1. 
   10fingers | Feb 02, 2004 01:37am | #4

   Thanks everybody for the replies.  The top of my workbench is made from the back of the piano.   The main portion is 11 1/2" X 6 1/2" X 58".   There are 5 beams mortised into the main portion.   They are 5" X 2 1/2" X 24 1/2".There is a 1/8" difference between the main portion and the beams.   I want to put the slick stuff on the top of the beams to level off the surface.   I figured the slick stuff would help slide material along and the gaps wouldn't matter.  The main portion is a great place to pound on things when needed.   I have had this bench in 2 forms over the last 8 years.   It isn't pretty, the legs are 2 X 6 screwed together, but it works.

1. 
   Scrit | Feb 02, 2004 02:04am | #5

   I use strips like this in the shop on top of a mobile run-in/run-off trolley we have parked by the panel saw. Because the trolley is always in the shop and the temperature is fairly constant the strips are just countrsunk and screwed. the trolley strips are 12mm (1/2in) thick and have heavily chamfered edges (router).

   The slotted jobs are for customers who use stuff out of doors. For the same reason we drill bolt holes oversize (e.g. 10mm bolt - 12mm hole). Any idea where you are getting your UHMW from?

   Scrit

   Edited 2/1/2004 6:08:32 PM ET by Scrit

1. 
   10fingers | Feb 02, 2004 05:13am | #6

   I had planned on getting my UHMW from a mail order WW source.   Do you have a better source of supply?

2. 
   Dan019 | Feb 03, 2004 09:28pm | #12

   Yes. MSC Industrial Supply Co. 800-645-7270. http://www.mscdirect.com Ask for their free catalog, it's over 4,000 pgs. They got all kinds of stuff you can use in w/w.

   Dan019

3. 
   craigmoe | Feb 03, 2004 10:37pm | #13

   I found a few companies when I was searching for a UHMW supplier for a potential future project.  I have not purchased from any of these sites, but they have an extensive selection:

   http://www.usplastic.com/catalog/category.asp?catalog%5Fname=USPlastic&category%5Fname=UHMW&Page=1

   http://www.polymerplastics.com/mechanical_uhmw.shtml

   http://k-mac-plastics.net/uhmw-sheet-general-purpose.htm

   Craig

3. 
   Telemike | Feb 02, 2004 08:05am | #7

   Polyethylenes are among the hardest materials to bond. Virtually nothing sticks to them. Industrially, they are prepared by oxidizing the surface to give some carboxylic acid groups to bond to. Flame can be used and nitric/sulfuric acid mixtures are used (don't try this at home - it's very dangerous and doesn't work very well anyway!) I also vaguely remember (the best I can do these days) a formulation with metallic sodium in tetrahydrofuran used to prepare poly for bonding - also, very dangerous (an understatement).

   None of these treatments give more than mediocre adhesion at best. Mechanical bonds work best like screws.

   There are high molecular weight polyethylene tapes out there with adhesive on one side (to reduce friction for jigs). Ever since I first saw them in a catalog, I've wondered what the adhesive is and whether it holds very well. Anyone use this stuff?

1. 
   wrudiger | Feb 02, 2004 08:11am | #8

   I've used the UHMW tape for table saw jigs.  Cut a few tenons so far and everything seems to be staying put.  Like you I wonder about how long it will last.  In the jigs the stresses are such that I doubt there will be much shifting, and when I first applied it it sure didn't want to move!

2. 
   Scrit | Feb 02, 2004 11:54am | #9

   It works, but only on very thin strips and it just doesn't last in industrial applications - light duty stuff. Hence my advice to use screws

   Scrit

3. 
   mlbfreestyle | Feb 02, 2004 04:16pm | #10

   I have used the tapes under drawers to reduce friction.  I've had very good results.  It does the job it is supposed to and I have not had any failures of the adhesive.

1. 
   mitch | Feb 03, 2004 05:24pm | #11

   the eternal puzzler:  what makes the teflon stick to the pan?

   maybe sandblasting* one side and then using some sort of industrial psa (pressure sensitive adhesive)-which is basically kickbutt 2-sided tape in sheet form?  they make some amazing strong stuff these days both with and without a liner film.  my company used to use it for a sporting goods application to bond closed cell cross-linked pe foam to shiny smooth hdpe.  it stuck like death to a dead horse- after a day or two, you couldn't peel it off without wrecking the foam.  uhmw is a slightly different animal, but you should be able to find something suitable if your application is not too critical (high shear- which is hard to get on something as slick as uhmw anyway).  thin sections should have less thermal expansion/contraction problems on incompatible substrates- this should be minimized by applying it and using it at a fairly constant temperature, ie, a heated/temp controlled shop as opposed to putting it on in a cold garage then using it out on the driveway on a sunny day.

   m

   *just thought of something- depending on what sort of sticky substance you use, roughening (roughing?) the surface of the plastic may actually hinder adhesion.  while sandblasting or etching increases the total surface area, it only helps if the adhesive is capable of oozing down into those nooks and crannies.  some types of psa would have better adhesion on a smooth polished surface.  i learned this the hard way many years ago when trying to use screen tone film (zip-a-tone, letra-tone) on clear acetate or mylar film instead of matte drafting mylar for a graphic design application.  the tone film stuck like crazy to the slick surface -which was a big problem- but had a nice, workable tack on the etched surface of the drafting mylar (which i should have used in the first place, but was new to the materials and the process at the time)

   Edited 2/3/2004 11:28:56 AM ET by mitch