Types of hard plastic?

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Coaster

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I intend to fit three cheek blocks to one side of our boat's boom. As each block has a flat back I'd like to cut and shape plastic plates or spacers, using sheet material about 10mm thick.

Metal types and timber species are familiar to most of us. On the other hand I have very little knowledge of the plastics that are available, or where to get them from. Is there someone who could explain a bit about the subject?

Otherwise I may have to resort to teak backing plates.
 
http://www.directplasticsonline.co.uk/
Have you got a milling machine? Shaping blocks by hand to fit the contour of your boom will be a bit tricky if not, just about possible by hand but not a job I'd want to do.
One option might be to heat a sheet up in an oven until it's flexible ( depends on the type of plastic, but maybe in the region of 120-180 C), then bend it round the boom to give you the shape, while it cools. Then attack the other side of it with an angle grinder to make it flat, after which you can cut the blocks out from the sheet. (You can't use Tufnol to do this as it's a thermoset plastic, you need a thermoplastic like nylon or polypropylene).
 
I have an idea that you might be able to buy these from the makers of your cheek blocks but, if not, the simplest way would be to mould some in situ using thickened epoxy resin.

The technique is well described in the WEST product guide.

http://www.westsystem.com/ss/bonding-hardware/

See the section entitled "Casting a base".
 
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I've previously made mounting plates and spacers from old kitchen chopping board - the white plastic type. Easy to shape with blade,file, or abrasive. I'm not sure it will suit your purpose though.
 
Second the link to directplasticsonline.

Quicky method would be to cut the shape then do the curved shape with a flap disk on a small angle grinder. Works fine for me with Tufnol, but be careful of the dust, not good for you.
DW
 
srp said:
http://www.directplasticsonline.co.uk/
Have you got a milling machine? Shaping blocks by hand to fit the contour of your boom will be a bit tricky if not, just about possible by hand but not a job I'd want to do.
One option might be to heat a sheet up in an oven until it's flexible ( depends on the type of plastic, but maybe in the region of 120-180 C), then bend it round the boom to give you the shape, while it cools. Then attack the other side of it with an angle grinder to make it flat, after which you can cut the blocks out from the sheet. (You can't use Tufnol to do this as it's a thermoset plastic, you need a thermoplastic like nylon or polypropylene).
Click to expand...

I would agree with heating and forming around the shape of the mast then form a flat on it.Tufnol is very easy to work with but in this application it would be more difficult as you would need to use machinery cannot be softened wear dust mask. Most thermo-plastics can be shaped using basic wood workers tools or belt/disc sanders, be careful not to overheat the plastic as it will load up the belt.
 
Plastic filler blocks

I have used the plastic cutting boards for filler in my swing rudder with much success replacing the old plywood. It may be possible to shape by heating. Certainly easy to cut and shape.
I have also made a big wedge shaped block of polyester resin and chopped strand mat that has the mast base pivot box sitting on. It is easy to make the shape you want by grading the sizes of CSM so that final shaping does not involve wasting much material.
I have of recent times got rid of my side cheek blocks for reefing because I felt these were dangerous in the case of the boom hitting someone's head. The sharp hard protrusion I felt would certainly kill someone compared to a flat boom side. I went for carbon fibre boom to reduce weight and inertia also hopefully a little softer than Al.
Anyway I made block that screwed inside the boom but on the top of the boom where reefing line emerges at the right place. The reefing line itself being inside the boom. I have only one reefing point roped up but the boom is also quite small about 55mm diameter. It works and looks good. I have posted photos in the past. (about 9months ago) olewill
 
For any body with a bench circular saw, running the plastic at an angle across the blade can get the result. With the blade projecting to the depth of the cut and the block held on some ply (to keep ones fingers away!!) successive cut at increasing angles (by clamping a fence to the table) until it matches. Bit of practice on scrap wood. The curve is actually an elipse but the boom may not be round either.
 
DownWest said:
For any body with a bench circular saw, running the plastic at an angle across the blade can get the result. With the blade projecting to the depth of the cut and the block held on some ply (to keep ones fingers away!!) successive cut at increasing angles (by clamping a fence to the table) until it matches. Bit of practice on scrap wood. The curve is actually an elipse but the boom may not be round either.
Click to expand...

I'm not, by any means, a H & S freak, but I can think of at least four reasons why that is dangerous.
 
A useful method of shaping the plastic is to tape a sheet of sandpaper over the profile you want and sand the block in situ.
Many sorts of plastic will do. A couple of layers of GRP sail batten epoxied together can be good. Plastics that are too soft may distort under load, this may throw all the load onto one fastener etc. Not usually a problems except in thick blocks.
 
srp said:
I'm not, by any means, a H & S freak, but I can think of at least four reasons why that is dangerous.
Click to expand...

It all depends on how one approaches the job. FWIW it was discussed in a US magazine and they are usually pretty careful.

If one sunk the plastic into a routed out recess in some thicker wood and used the usual precautions, I can't see if it is any more risky than many other tasks on bench saws. (and I use one a lot)
 
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