My slab of UHMW-PE has too much warp.

I purchased a .75x24x36 slab of, TIVAR 1000 Natural Plate, UHMW-PE to make a FDA compliant cutting board for a customer. Unfortunately, it has over 1/2" of warp; more curl than I can take out when screwing to it's support frame. I made a similar table for the same customer about 15 years ago and it was nice and flat. I don't remember what material I used back then but it isn't UHMW-PE. The old one is white but not the same white as the new UHMWPE sheet.

I've my plastic supplier for recommendations, but they said all slabs of that size have 1/2" of warp tolerance. I find this hard to believe. Does Cast Nylon run flat?

Can you suggest a different material?

Thanks,

John

Just clamp it to where you want it to be, put it in the sunlight and a day later it will be what you want. UHMW is not a stable material. I have machined parts as in long bars left them over night and found them warped the next day. Nature of the beast.

Depending on the size and thickness, nylon or any of thermoplastics will warp to a degree. Nylon 6/6 and acetyls are much better. These are also harder on knife edges.

Tom

Try boiling it to soften it up, then lay it between two heavy pieces of steel and allow it to cool for a few hours.

Yeah, you might not find a 2 foot by 3 foot cauldron to boil it in, but mild heat (softening temperature for UHMW PE is 180F) applied uniformly together with restraint will help. Keep in mind that UHMW PE has a large coefficient of thermal expansion. It's going to shrink as it cools.

Do you have any idea How much water UHMW can hold? It's about like wood! (not really, but compared to glass or metal, plastics are sponges!

And you know, water takes up space!

Hey Guys,

Thanks for the suggestions. Right now, I'm looking for a more stable material vs trying to straighten what I have. In the long run, I believe this is the better course of action.

JohnnyJohnsoninWI said:

Hey Guys,

Thanks for the suggestions. Right now, I'm looking for a more stable material vs trying to straighten what I have. In the long run, I believe this is the better course of action.

Click to expand...

Don't be looking at plastics if you are looking for stability

CalG said:

Do you have any idea How much water UHMW can hold? It's about like wood! (not really, but compared to glass or metal, plastics are sponges!

And you know, water takes up space!

Click to expand...

Actually, UHMW is extremely low in water absorption. Less than 0.01% typically, which is much lower than many other plastics.

specfab said:

Actually, UHMW is extremely low in water absorption. Less than 0.01% typically, which is much lower than many other plastics.

Click to expand...

The warping is testimony to just how badly plastics play with water.

As I stated. If stability is the goal, do not be looking at plastics.

JohnnyJohnsoninWI said:

Hey Guys,

Thanks for the suggestions. Right now, I'm looking for a more stable material vs trying to straighten what I have. In the long run, I believe this is the better course of action.

Click to expand...

End-grain WOOD has come back into fashion. Look it up. Educate your customer to do their own due-diligence as well, you can "machine" exotic woods for them just as easily as plastics.

One source of MANY, out there, these days:

Cutting Boards of Plastic and Wood Contaminated Experimentally with Bacteria

Fast Facts About Cutting Boards and Food Safety in Your Kitchen | NC State News | NC State University

Turns out certain woods have enduring natural biocides action built-in to them that put-paid to bacteria right quickly where the plastics either don't give a toss, or even HARBOUR some of the tinier of critters and can cross-contaminate for looong periods of time.

What is the Best Cutting Board? (for Meat to avoid cross contamination) - The Kitchen Professor

Chinese, Vietnamese, and Thai have known this for a few thousand years, if only by "observation", underlying cause "don't-care, so long as it has always JF WORKED".

They still prefer as-had shaped end-grain "slices" out of a single tree to re-glued end-grain

Annnnd... consider Gweilo DAFT for using plastics instead of just lemon, lime, Thymol, Eucalyptol, or ginger & salt or soda for scrubbing their wooden cutting timber-slice boards and hang them up to air-dry between meal-prep times.

Result? ALL of my "portable ONLY" poly boards now get one-use, a quick scrub, into the dishwasher.

NB: That ain't so easy if they are even SEMI "built-in", 'coz folks just WONT go to the bother.

Only the revived Asian woods (Acacia, Tamarind, Teak, bamboo-which-isn't-a-"wood") get a citrus or "Listerine" and salt-wipe and move on immediately to the next cutting task, stay on the counter for the duration.

Mind - separate workspace and double-barrel sinks for the vegetarian M'In Law and the omnivorous wife doing meat or seafoods, so cross-contamination has a dual barrier to begin with - nothing shared.

There's an "original" Listerine pump at each sink as well as a Listerine/detergent cut-back, plenty of vinegar, lemon, lime, ginger, and peroxide right to-hand.

No need of "complicated" nor carcinogenic man-made chemicals. Salt, soda, vinegar, and "stuff that trees make", JFW.

In regard to stability of plastics generally, and UHMW specifically, water absorption (or drying out) is not that much a factor in any observed warping or shape change, compared to other factors. The manufacturer's specs are as loose as they are, such as 1/2" warpage tolerance over 3 or 4 ft, because the manufacturing process is full of various inputs, e.g., extrusion temp variation, non-uniform cooling, non-optimum storage conditions, etc., that end up as residual and built-in stresses in the material, in exactly the same way that many metals exhibit. The major difference is that the plastics generally don't have the stiffness or tensile strength to resist self-deformation, in the way metals do. Machining metals will often release stresses that are built-in, as will machining plastics, so you end up with the pretzel or banana you always wanted, regardless of material used.

I agree with the point that plastics are not going to be as stable as glass or metals in general; you need to perform some type of stress relief process for most materials to "be all they can be". Some plastics do absorb more water than others, and you need to be careful in material selection if dimensional tolerances are important, such as in bearing fits, but the OP's dilemma with UHMW is not a water absorption issue, just one of typical manufacturing stresses in the stock.

For the OP: Cast nylon plate MIGHT be flatter, but it WILL absorb much more water than UHMW (or any other polyethylene grade). Might be the possibly worst choice for the intended application. My recommendation would be to get a flatter piece, or anneal/reshape the piece you have. I would bet that laying it on a piece (or between two pcs) of decently-weighty aluminum tooling plate in the sun for a few hours would help some. Get it up to about 150F for a few hours and let it cool off slowly, this may help. If you want a real annealing process instruction, check out websites for some of the mfrs of the material, like Garland Mfg.

I have found HDPE to be alot more stable than Uhmwpe and machines better too. Slabs typically come in much less tapered in thickness.

thermite said:

End-grain WOOD has come back into fashion. Look it up. Educate your customer to do their own due-diligence as well, you can "machine" exotic woods for them just as easily as plastics.

One source of MANY, out there, these days:

Cutting Boards of Plastic and Wood Contaminated Experimentally with Bacteria

Fast Facts About Cutting Boards and Food Safety in Your Kitchen | NC State News | NC State University

Turns out certain woods have enduring natural biocides action built-in to them that put-paid to bacteria right quickly where the plastics either don't give a toss, or even HARBOUR some of the tinier of critters and can cross-contaminate for looong periods of time.

What is the Best Cutting Board? (for Meat to avoid cross contamination) - The Kitchen Professor

Chinese, Vietnamese, and Thai have known this for a few thousand years, if only by "observation", underlying cause "don't-care, so long as it has always JF WORKED".

They still prefer as-had shaped end-grain "slices" out of a single tree to re-glued end-grain

Annnnd... consider Gweilo DAFT for using plastics instead of just lemon, lime, Thymol, Eucalyptol, or ginger & salt or soda for scrubbing their wooden cutting timber-slice boards and hang them up to air-dry between meal-prep times.

Result? ALL of my "portable ONLY" poly boards now get one-use, a quick scrub, into the dishwasher.

NB: That ain't so easy if they are even SEMI "built-in", 'coz folks just WONT go to the bother.

Only the revived Asian woods (Acacia, Tamarind, Teak, bamboo-which-isn't-a-"wood") get a citrus or "Listerine" and salt-wipe and move on immediately to the next cutting task, stay on the counter for the duration.

Mind - separate workspace and double-barrel sinks for the vegetarian M'In Law and the omnivorous wife doing meat or seafoods, so cross-contamination has a dual barrier to begin with - nothing shared.

There's an "original" Listerine pump at each sink as well as a Listerine/detergent cut-back, plenty of vinegar, lemon, lime, ginger, and peroxide right to-hand.

No need of "complicated" nor carcinogenic man-made chemicals. Salt, soda, vinegar, and "stuff that trees make", JFW.

Click to expand...

Someone didn't tell FDA that.
Black walnut, housewives go mad over it and bacteria don't survive on it. Hot water and a scrub only, 3rd year Food Microbiology class was unable to isolate any pathogens from it an hour after 24 h inoculation and the hot water rinse.

specfab said:

Actually, UHMW is extremely low in water absorption. Less than 0.01% typically, which is much lower than many other plastics.

Click to expand...

.
i agree, its nylon thats famous for absorbing water and warping like as piece of wood and it changes dimension as it dries out

Greenwud said:

Someone didn't tell FDA that.
Black walnut, housewives go mad over it and bacteria don't survive on it. Hot water and a scrub only, 3rd year Food Microbiology class was unable to isolate any pathogens from it an hour after 24 h inoculation and the hot water rinse.

Click to expand...

.
some wood have hazardous compounds in it. cedar, redwood and many tropical woods are actually not good to breath the dust as it actually not good for humans.
.
poison ivy is natural and obviously also not good for humans. many plants are natural and naturally hazardous for humans. some mushrooms are extremely hazardous and they are naturally hazardous

JohnnyJohnsoninWI said:

I've my plastic supplier for recommendations, but they said all slabs of that size have 1/2" of warp tolerance. I find this hard to believe. Does Cast Nylon run flat?

Can you suggest a different material?

Click to expand...

Guess who bought a couple of warped sheets of Tivar 1000? I tried to do the un-warp with weights. Didn't work

If your original was really white compared to UHMW( which seems to have a yellow tint as it ages) it might have been Delrin (acetyl resin). It's not nearly as bad as UHMW as far as warpage is concerned. Nylon is between the two as far as warpage.