A friend of mine took on a job installing plastic wall covering in a local restaruant. He went to the hardware store and asked for a blade to cut plastic with his skil saw. When he got home he saw an arrow on the blade that was backwards in relation to the teeth..I'm wondering if this a manufacturing goofup or if makes use of some sort of friction sawing process? Engineman1
If he specified a blade for plastic, and it's a relatively fine toothed blade, no, it's not marked backwards. The recommended procedure for cutting some plastics, including materials like vinyl siding, is to run your blade backwards. That prevents the positive rake of the typical blade from picking up the material and shattering it. The negative rake seems to make no difference in how the blade cuts. Give it a go and see the results. Works super good!
Harold
When I was repairing the vinyl siding on my house I just took a normal roughcut blade and put it in my circular say backwards. It works great and is a normal practice.
Relz
If this is a steel sawblade it is Not a screwup, just a way to get a negative hook angle. If it is carbide tipped it could be a screw up as the cutting direction should push the tooth against the saw plate not try to rip it free. In the field carpenters run a plywood blade in reverse to achieve the same result on plastic or aluminum for trim. Feel the chips , if they are hard and a bit melted you are feeding too slow. Soft and fluffy is what you want.
Backwards teeth is the classic way to cut plywood. However, I once experimented with all my blades, forward and backward, and the nicest cut was with an _abrasive_ blade! I know, I thought that it would just melt it, but it didn't. I suppose the trick is to not cur too slowly. The cut was beautiful - very smooth. Smoother than the backwards tooth cut, which tends to leave micro cracks. This was on vinyl siding, BTW, so YMMV with other plastics. A trial cut would be advised.
Bob
My friend reversed his sawblade and began cutting the wall covering. The cutting went slowly and he noticed he was getting sparks. He discovered that it was fiberglas filled plastic and ended up cutting it with a handsaw. What type of skilsaw blade should be used for this? Engineman1
Diamond or Carbide. Fiberglass is relatively easy to cut but very abrasive and will kill many - if not all cutting surfaces. Plan on rep[acing blades often.
Regards, Joe Agro, Jr.
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