# Problems cutting HDPE



## Northerner (Nov 9, 2010)

I'm having grief cutting a new piece of white HDPE. I picked up the 1' x 2 'x 3/4" piece from a specialty shop and was told it's HDPE. My jigsaw struggles to cut this stuff with a Bosch 20TPI blade. It does cut but it's noticeably harder than other poly that I have used. The cutting line actually welds back together leaving a bead down each side of the board. It welds solidly and can't be broken apart with a heavy hit from a hammer. I tried cutting through the beading but it welds back again. I was finally able to separate the throat cut after going over it many times and hitting it many times with a hammer. I tried to gave the throat a quick filing with my rotary file but didn't have much luck.

After giving up on the bad poly, I proceeded to cut a frame from some 1/2" HDPE Seaboard. The same jigsaw blade and rotary file were used and I had no problems at all. The HDPE Seaboard cut smoothly and filed easily.

Any thoughts or suggestions?

I have successfully made 10 frames from 4 other poly boards. I have 5/8" and a 1/2" polypropylene (recycle #5) cutting boards that cut well and make fine frames. I also have 1/2" HDPE board and 1/2" HDPE Seaboard and both cut and file without problems. These HDPE boards are from the same dealer as the problematic HDPE board. Sometimes I get a little bit of melting when cutting these materials but the board doesn't glue itself back together again. They all file up nice.

Thanks


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## Notsofast71 (Jun 7, 2015)

Melting and welding back together is due to excessive heat. Try a blade with fewer teeth. A wider kerf would help too. (wider cutting channel from teeth that lean left and right of center) And try cutting slower. With plastics like this, you only want the blade going as fast as necessary to cut through the material. And a band saw would also probably help instead of a jigsaw.


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## Alexander Holman (Jun 8, 2015)

Rather than that, try increasing your feed rate too. Basically what's happening is your blade is going up and down in the same place for too long without moving forward.

-Xander


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## you'llshootyereyeout (Apr 5, 2014)

HDPE is pretty easy to cut, try using a copping saw. They are cheap and easy to find. I have never had the whole remelt thing happen.


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## Northerner (Nov 9, 2010)

I wonder if there is different kinds of HDPE. The same blade that caused melt on the problem piece of HDPE was then used to successfully cut a different piece of HDPE. I have 5 different pieces of poly. Only this one piece seems to be a problem.

I have 2 sqft of this odd HDPE so I'm not giving up yet. Maybe tomorrow I'll try more speed, less speed, and different blades.


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## Arnisador78 (Apr 10, 2013)

I had that same problem with plexi. Band saw works really well. Scroll saw too. Maybe its just because it's harder to cut thicker material so it doesn't move as fast through cuts and the plastic is exposed to the friction of the very rapid up and down movements of the jig saw.


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## Samurai Samoht (Apr 6, 2013)

I had the same problem where even the slowest setting on the scroll saw was producing too much heat and it just melted back together. I went to the store and bought a $10 Coping saw and it works like a charm.

Tom


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## Wingshooter (Dec 24, 2009)

I have run into this a couple of times. It sounds like you are cutting nylon instead of HDPE. There are a lot of different formulas for this plastic. I found that UHMW is the best to work with regular tools. It acts like wood.


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## pgandy (Aug 15, 2011)

I've had troubles working plastics with power tools. By reducing the speed, which reduces heat, often helps. Breaking out a hand tool always helps.


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## treefork (Feb 1, 2010)

The reciprocating blade when used on the one inch stock is not completely expelling the waste chips cause friction and thus enormous heat thereby melting and fusing .


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## stej (Jan 16, 2013)

As mentioned by Wingshooter, I would also guess that you work with nylon (PA6, or polyamid). It melts very easily and slow speed helps only partially - I couldn't do it by machine. I was succesful only when I used my own hands, no machine.


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## Dayhiker (Mar 13, 2010)

There can be huge differences in HDPE. I usually use a coping saw, but its blade gets real hot very quickly. I stop often and rub a candle on the blade for lubrication and this seems to work well. However, I once melted down a construction worker's hardhat that was made of HDPE and it was so hard, I couldn't make the saw turn in the tight curves.


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## Kalevala (Jul 20, 2014)

I had melting and welding back problems when cutting my plastic slingshots with blade 2301.

After changing to blade 2300, that is made for thick wood, I had no troubles at all.

I don't think there is a big difference between the looks of these two blades.


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## Northerner (Nov 9, 2010)

I use a Bosch T101AO blade. I actually cut out 2 good frames after giving up on the problem piece of HDPE. I'm not good with a handsaw so I prefer the jigsaw and a rotary file.

http://www.boschtools.com/Products/Accessories/Pages/BoschAccessoryDetail.aspx?pid=T101AO#specs


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## Viper010 (Apr 21, 2012)

you'llshootyereyeout said:


> HDPE is pretty easy to cut, try using a copping saw. They are cheap and easy to find. I have never had the whole remelt thing happen.


I have, even with a hand powered coping saw. I'd recommend courser teeth and slower blade speed. Also, regular application of a little candle wax or silicone spray or even a drop of dish soap will help. 
Less friction, less heat, no more melting back together.


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## Northerner (Nov 9, 2010)

Well, I found out why I was having so much grief with the HDPE. I visited the outlet where I bought it last year and chatted with the employee. I described how it melted and how hard it was compared to the other HDPE that I bought. We looked at some of his inventory and we figured out that they I have UHMW. The surface is quite shiny compared to HDPE and it's not translucent like regular poly. Now I have to find out how to shape this stuff.


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## TheNewSlingshotGuy (Oct 11, 2014)

The problem with the melting is caused by a few things:

-A 20TPI blade has shallow gullets in between each tooth, which cannot clear the HDPE shavings out of the cut fast enough. The gullets get clogged with HDPE material. This causes excess friction, which in turn causes the melting problem.

-Melting/burning is also a result of a feed rate that is too slow. Meaning, the saw blade is in one spot for too long, and the rubbing of the blade against the side walls of the cut causes too much friction and melts.

These two things alone or in combination will cause problems. You must have the correct blade for the type/thickness of material, and a feed rate to match. I use Flying Dutchman "Heavy Duty" blades, which are 5TPI I think. They cut 3/4 inch HDPE without a problem, even at high speed.

These rules apply to any material you may cut, not just HDPE.


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## Northerner (Nov 9, 2010)

The 20TPI jigsaw blade worked great for 1/2" HDPE and 5/8" polypropylene. The cut is very smooth and melting was not a problem. Slow cuts on sharp curves worked fine. After the cutting, I always shape the contours and bevel edges with a rotary file going full speed in my power drill. No problems. I now have some 3/4" HDPE and plan to try this same 20TPI blade and rotary file. I'll report the results.

The UHMW seems quite different than HDPE. It's a much harder material. I'll see if I can find a 4-6TPI blade to cut it.

Thanks


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