Posts Tagged ‘uhmw’

Ultra-High-Molecular-Weight Polyethylene (or “UHMW” as it’s commonly known) is one of the most popular industrial plastics. Unfortunately, due to its well-known reputation, people overestimate the properties of the material and their expectations of it are, frankly, too high. The plastic hold poor tolerances due to thermal expansion. This means that the tolerances of a part when machined may be much different then when the part is actually installed.

In addition, the part’s geometry will change due to thermal expansion once installed. This has created an odd paradox – customers try to impress on us that somehow due to wishful thinking these poor tolerance holding properties of UHMW will somehow ‘not exist’ if we just hope they won’t. That statement may not make sense but it’s actually what we often encounter at Redwood Plastics and Rubber with customers. They dislike the wide tolerances of UHMW and ask us if there are ways to account for the thermal expansion issues in machining. We can mitigate some effects but expecting UHMW to hold good tolerances simply doesn’t work.

This short YouTube video highlights some issues with UHMW and serves as a good primer of the challenges you will face with the material.

 

Redwood Plastics and Rubber, the sponsor of this blog, offers many resources on their website to help their customers work with plastic. Some of these charts and information are ‘overkill’ for what the DIY community really needs, however. In this case, more basic information is best. The good news is their website actually has a page that links to several sub-pages that give general information on fabrication and care for plastics. These guides include some of the most common plastics used by the DIY community: UHMW, acrylic, polycarbonate, and acetal.

You can find the guide and the link to the sub-pages here: https://www.redwoodplastics.com/tools-data/fabrication-machining-guidlines/

 

 

There are a lot of outdoor enthusiasts who are interested in food-grade plastic cutting boards. But it for an outdoor kitchen to something exotic like a fish cleaning station on a boat. The applications might seem different; however, the same family of plastic, polyethylene, is almost always used. But which plastic to use? What concerns are there?

Both UHMW (ultra high molecular weight) polyethylene and HDPE (high density polyethylene) in their “white” or more correctly, “natural” grades are FDA and CFIA approved for direct contact with food. HDPE, even though it’s less expensive, is preferable because unlike UHMW, it will not dull knives over time. If you have UHMW lying around it’s certainly a good option though and is probably worth the trade-off vs. buying a whole new sheet of HDPE. UHMW is commonly available in 4′ x 10′ sheets but many plastic companies will send you a partial piece of that sheet (with a nominal cutting fee included). HDPE is commonly available in 4′ x 8′ sheets though many companies also stock it in 4′ x 10’s.

Cutting the plastic to size is easy: household power tools such as drills and saws will easily cut it. Having a 40 grit sandpaper on hand would be good to deburr the cut edges. The plastics glue very poorly so if you’re installing a blacksplash, for example, attached to the cleaning station or cutting board you will need to screw it in. 3/16″ or 1/4″ self-tapping screws 6-12″ apart should be fine. The plastics are soft enough that your drill will countersink the heads slightly.

The problem with these natural grade plastics is that they are not UV-stable. You should expect some cracking of your cleaning station if exposed to the sun in about two years depending on exposure. The board surface should be seen as a “sacrificial” surface which will need replacement every few years – just part of the gig. The surface will become brittle and crack which isn’t good because it allows bacteria to hide in the crevices but otherwise this degradation does NOT make the plastic toxic.

If you need assistance or a quote on either of these food-safe plastics, please contact Redwood Plastics and Rubber.

 

One of the most common questions the DIY community has is trying to figure out what type of plastic they have or need. Maybe you have an old part or sample and you forget what it is? Perhaps the two plastics people most want to differentiate between are acetal and UHMW (or other polyethylene). But they both come in white and black and they kind of look similar, so what to do? Well, if you’re familiar with the two plastics UHMW or HDPE will feel different: more waxy and lighter than the acetal which almost feels like more of a metal than anything.

There’s another way to identify polyethylene though as long as you can disfigure the sample. Take a sharp knife, such as a steak knife, and start scraping the plastic, give it some gusto with long strokes. If the plastic shaves off in curls then you have polyethylene. Acetal and other plastics will not do this, an example of polyethylene with this type of shaving is pictured here:

 

BRAXX Anti-Slip Sheeting

Posted: December 20, 2018 in Uncategorized
Tags: , , ,

Ever worked on a home project where you need a rugged anti-slip surface? Could be stair treads, maybe the side of a pool, a deck or anywhere slippery. One option is BRAXX anti-slip sheeting for an application that does not require load bearing material, IE. you are going to simply screw, nail, or bolt the anti-slip surface into a substrate. BRAXX comes in a standard 3′ x 9′ sheet that is 0.30″ thick and this is the only size available. There are two options, a blue UHMW plastic with sand surface anti-slip buttons or the more popular safety yellow UHMW with LUNS (clean coal slag) anti-slip buttons. See picture below for detail of each. This product is very strong as UHMW cannot break and it was originally developed for military applications such as the floor surface of naval tank carriers.

The product cannot be ‘glued’ using a liquid adhesive. Mechanical fixation is required but there is no special hardware for this…Nails, bolts, screws, whatever you have lying around will work. UHMW is easily fabricated with power tools found at home. This is a premium product, you can expect a cost of approximately $600.00/sheet US funds before freight is factored in. However, for a premium anti-slip surface from the demanding DIY individual, it’s the best there is.

This product is available from Redwood Plastics and Rubber: http://www.redwoodplastics.com

For those not very familiar with plastics, it is sometimes difficult to tell the plastics apart. A plastic rod feels like, well, just plastic and we don’t consider sometimes the nuances of each material. One major consideration for those of us in the DIY community is how a material is fabricated or machined. Acetal is a very hard plastic and machines very well and can be held to tight tolerances (+/- 0.005″) whereas realistically (+/- 0.05″) is the best you can get out of UHMW in a DIY setting. UHMW is much softer and less dimensionally stable; however, it is slicker and more economical.

A short video on YouTube we found shows both plastics being machined and offers a comparison, take a look below:

Sick of cracked, rotten, and unstable wooden jack pads for your RV? Want to do a little project that will make you feel accomplished and provide a long-lasting solution? The good news is making your own plastic jack pads is an incredibly easy project that virtually any member of the “DIY” community can do! Fabrication of a couple pads for your RV should take 15 minutes or less.

What you will need to start:

-(1) 12″ x 24″ x 0.75″ (thick) piece of UHMW black-reprocessed plastic.

-(2) pieces of rope 1/2″ in diameter 12″ long.

-Table saw

-Power drill with 3/4″ bit. The bit should be at least 1.25″ long.

Instructions:

  1. Measure with a colored marker or tape the halfway point on the UHMW plastic. You want to simply cut it in half to obtain two 12″ x 12″ pieces. One of the pieces may be undersized but that is not important for this application.
  2. Cut the UHMW in half.
  3. Find the midpoint on each pad again. Mark it.
  4. On either side of your mid-mark, 1″ in, make two points 2.5″ on either side of that line.
  5. Drill thru-holes with your 3/4″ bit in those two marks.
  6. stick a piece of rope through the holes. Tie knights on each end wide enough that the rope cannot get pulled back through the drilled holes.
  7. *Optionally you can then cut the corners off the pads.

There you go, you have two jack pads that should last as long as you have your RV! Estimated cost per pad would be $35.00 including materials but they would likely retail around $70.00+ for an equivalent pad were you to buy them.