cutting plywood

Just finished cutting my plywood for my wooducky 8.  Noticed that when cutting the plywood, one side of the blade chips out chunks of wood while the otherside of the blade gives you a clean cut (using a Porter Cable saw with brand new blade also metal cutting blade for a cleaner cut).  Is there side "a" and "b" to a blade, or is it in relation to the direction you are cutting the plywood?  Maybe some oldtimers who still work from plans could speak to this phenomena.


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RE: cutting plywood

I think this chipping is the result of the different layers of the plywood grain running in different directions. Certainly sounds like you're using the right blade. If there's a speed setting on your saw you might try setting it to run at the slowest speed, which can help.

RE: cutting plywood

Chipping will occur if the blade is dull, if you are pushing it too fast, or if you have it set too low. It should be set so only the depth of the teeth protrude through the cut. I have also found that fine-tooth saws, even those designated as plywood saws, tend to chip more than a carbide toothed saw with fewer teeth. I recently cut through 1-1/2" thick birch plywood with a 7-1/4" 40-tooth carbide blade, and had no chipping or burning. For kayak building I use a 4" 24-tooth carbide blade. -Wes

RE: cutting plywood

First, the large majority of jig saw blade have the teeth facing up towards the tool. I'm assuming this is the blade you are using and the chipping is on the top of the board (closest to you). There are other blades with the teeth facing down and I'm assuming you aren't using that one.

Put blue painter's tape along the line you want, then draw the line on the tape and cut with the tape on. It will prevent "tear out" as its called. Its much more likely to tear out when cross cutting across the grain than when ripping with the grain. 

Also, if your jig saw has the ability to adjust the agressiveness of the cut, turn it off. The agressive mode pushed the blade out then pulls it up and likely to tear the grain. In non agressive mode, the blade moves up and down only. 

Hope that helps. Try practicing a bit with these techniques.

There is a more extreme approach using a router and template but I don't think you will need it. 

Michael

RE: cutting plywood

Btw, I don't think the metal cutting blade not helping since the sides are not straight and it is likely rubbing against the side or the wood and pulling up the top grain on the up cut. 

Michal

RE: cutting plywood

It didn't even occur to me that you were using a jig saw. No wonder you were tearing the wood. Michael's suggestions are good, but you really need to be using a circular saw for plywood unless you are cutting tight curves.

-Wes

RE: cutting plywood

I was using the slow speed--the plywood was 3mm.  I don't feel anyone addressed the question of chipping on one side of cut.  Circular skil saw is used for straight cuts, not curves, you are looking for trouble using it for curves.

RE: cutting plywood

Cut slightly outside the lines. True the panels up with a sharp plane. Adds about an hour to cutting out the panels, but saves three or four when wiring them up. Also eliminates the worry with slightly chipped edges.

RE: cutting plywood

I have cut panels for two kayaks and a sailing skiff using a 4" blade in a Porter-Cable worm-drive trim saw. It will easily cut the long curves of S&G panels. It is as easy to guide within 1/16" of a line as a jig saw and many times faster. John Harris uses one of these saws to cut the panels of the Shearwater Sport illustrated in the current issue of Sea Kayaker magazine. -Wes

RE: cutting plywood

I would use the same tape "trick" for the circular saw if u use that. It's the blade coming up through the material that is causing the chipping. cutting curves with a circular saw, even wide curves can cause chopping. Also, i

Like the weight of a jigsaw better than a circular saw. 

Lastly, jnjclarks suggestion of using the plane is excellent as well. Make sure the

Plane blade is sharp. 

Michael

RE: cutting plywood

I cut 3mm with a Japanese pullsaw AKA Dozuki saw. A hand saw. With little effort it travels about 2'/minute - quietly, and no tearout.  Goes around sweeping curves very well. Also cuts 4mm and 6mm rather quickly and quietly as well.l

RE: cutting plywood

Hokey also has an excellent suggestion. I also use Japanese saws in my woodworking but have never used it for ply, only hardwoods for furniture building or other small tasks, e.g. cross cutting 4x4, dove tails, miters, etc. I typically use a ryoba vs a dozuki. A ryobi is a double sided saw that rips wood on one side and cross cuts on th other. Like all Japanese saws, it's a pull saw but cry thin so cuts quickly. Michael

RE: cutting plywood

Get a thin blade for you jigsaw that cuts on the down stroke.  Then you can make all of your cuts on the good side of your stock then if it chips on the other side that will be the inside of your kayak, then it will get covered when you fillit and glass the inside.

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