Can you plane plastic?

[AndrewLee]

Hey guys,

Someone came up with the brilliant idea of using cut up strips of chopping board to make runners for tablesaw jigs.

Is it safe to plane down a little bit of plastic or will it seriously dull the blades on a thicknesser?

[Hatchcanyon]

Andrew,

plastics is a variable material, what are we talking about?

Acrylic plastics will be probably destroyed - broken -, Polycarbonate (PC) may damage the planer. PC is ductile, there is not much chip breaking.

One can cut these materials with a saw but don't use a jigsaw. A bandsaw will work, a circular one too if you know what to do. Drilling these materials with normal spiral drills can break Acrylic and PC may wander up the drill bit. There are special drill bits for such materials that work fine:


Left: masonry bit; middle: acrylic or PC bit; right: spiral bit

The bit in the middle will not damage the materials. If you are desperate you can drill a hole into PC by using a masonry bit. It scrapes away PC not cutting it like the spiral bit.

PC edges may be cut with a razor sharp handplane. This is good for removings saw marks.

Never use acrylic plastics with any power machine. The material is brittle may burst on impact throwing around lots of sharp edged debris. Always use PC!

Rolf

[Ken S]

Nicholson (and probably other makers) makes files called Magicut which are designed for cutting plastics.

I have used strips of wood 3/8" x 3/4" as runners for tablesaw jigs. They also work well for ripping pieces of wood or plywood which are irregular. Just tack the strip to the piece with two or three eitghteen gage finishing nails, either by hand or with an air gun.

Ken

[mark1]

Hey Andrew -

Most plastic cutting boards are polyethelyne (PE) or high-density polyethylene (HDPE). I've cut plenty of HDPE with wood working tools and never damaged any edges. The only issue I've ever run into is that if the blade heats up (like long rip cuts on the tablesaw) the plastic can get a bit gummy. One thing I wouldn't do is use the bandsaw - the chips are too soft to clear from a fine blade and you just end up clogging it.

Good luck and let me know how the runners work out - I would like to do that same if it works.

[AndrewLee]

Sure Mark, I'll have to try it out once I get hold of some chopping boards. As luck would have it, someone chucked out the only thick chopping board I have in the house.

I'll have to source some somewhere. Quick check for hdpe plastic boards will end up setting me back £16 for the smallest ones including delivery. At that point I'd be better off treating myself to come baltic Birch plywood instead for runners.

[AndrewLee]

Another problem just popped into my head. Does anyone know if wood glue would adhere to hdpe plastic?

I'm not familiar with plastic as a material but I'm sure that I read somewhere that pp plastic is notorious for not working with glue. If so I would be able to glue plastic runners to the board for a tablesaw jig..  I don't think screws alone would suffice

[Hatchcanyon]

Andrew,

HDPE is not easy on glueing. A citation from Wikipedia:

"Adhesives and solvents are rarely used because polyethylene is nonpolar and has a high resistance to solvents. Pressure-sensitive adhesives (PSA) are feasible if the surface is flame treated or corona treated."

One can find more or less similar explanations in technical papers from glue manufacturers.

Rolf

[Ken S]

Why wouldn't you use wooden runners? Wood is readily available; inexpensive (probably free from your shop); easily cut, planed and sanded; glues well with everyday glue; and is easily sealed and/or rubbed with parafin.

Ken

[AndrewLee]

I got caught up in the whole wood expanding discussion and didn't want to deal with building a jig, and having to deal with the sliders not working right due to seasonal humidity changes.

Anyone know if all wood expand due to moisture or does it depend on the type of wood?

I bought a heavily discounted Birch chopping board for this very reason and I hear it's one of the hardest hardwoods around

[Hatchcanyon]

Andrew,

all kind of wood inevitably expands or shrinks with changes in moisture. That is the bad news.

The good news is that it depends on the type of wood how much it moves.  Fir or pine has relatively low changes, European Beech has considerably more.

The next good news is, that the changes are minimal in direction with the fiber (the direction a tree grows). Usually these changes are less than one-tenth of a percent for a percent of moisture change in the wood.

Rolf