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Arnie Eaton

Cutting thin plywood

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I have plans for a Birder kayak. I also have many types of cutting tools. What is the best tool for cutting thin (3,4 MM) plywood? I have tried some saw types but they seem to be rough cutters. A demel type of tool with a saw blade is very slow. Anyway, give me some hints as to the best way to do the cutting.

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I use a Bosch jig saw with either a fine cut blade or a metal cutting blade for thin plywood.  Some prefer a skilsaw type but that seems a bit crude for a lot of the work, at least to me.  Any of the better name orbital jig saws will probably work just as good.  The key is to have the orbital feature which makes the jig saw a real tool instead of a toy.

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This is one of the most useful tools for a boatbuilding shop.  I even built a lot of my house with it.

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I too swear by the Bosch. Be sure to get the anti splinter insert - a little plastic dodah sold by the company that virtually eliminates tear out in the thin veneers. PeterP

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I used a small craftsman circular saw on big curves and straight lines.  Jig saw on sharp corners.  I don't have a Bosch (wish I did) but I got it done with an old cheap craftsman.

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I agree with you Ray.

My Mikita cordless skill saw is wonderful for cutting plywood. It easily makes the long sweeping curves and doesn't make all the little wiggly curves that I make with a jigsaw. Of course, someone with even a bit of skill doesn't have this problem, but I need all the help I can get.

I learned this after I built my boat.....

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;D

I use my old 6 1/2 inch Porter Cable circular saw with it's aluminum housing. By chance it happens to be the exact model beloved by Dynamite Payson  ;) Maybe it's just a function of getting old but that old saw just keeps on cranking, so I'll keep on using it. It's so old it has grease cups for the bearings ;D

One point- when cutting across the grain, I lay a steel straight edge down and score the line with a razor knife. Then saw slightly OUTSIDE the line- keeps the top veneer from splintering. If I'm cutting many pieces from the same piece of ply I sometimes score BOTH sides, then saw between- no splinters either side.

But then I ALWAYS saw outside the line and block plane back to the line- that's the ONLY way you'll get a precise cut.

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Thanks Guys; I think I will try to find some fine blades for one of my jigsaws (I have three). I can't find the right blade for my small cir. saw, all I have are not very fine and make a mess. So much for imports.  Arnie

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If a really clean edge is needed, then as said above cut large and dress down with a block plane.  Another option that can help is a saber saw blade that cuts on the down stroke.  Bosch makes a very nice one.  You will still get some splintering on the bottom, but it works well for finish work where only the one side is going to be visible.  And it takes some getting used to, your saw now wants to jump off the wood.

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I have a variety of blades for my Bosch jigsaw. Standard "get it done" blades are 10 tpi. But a much smoother cut (surface) comes from blades with 20 tpi, but those are also skinny and that makes it easier to wander back and forth off your line. It it's a straight cut that matters, I put down a straight edge to act as a guide to prevent wandering around. And that little plastic insert does help. The only problem I've had with jigsaws is cutting thicker solid stock (like for breast hooks, etc.). You would think with such a rapid up and down motion they would make a straight 90 degree cut, but at times, my finished cut is angled. That may be due to the curve and uneven pressure or perhaps one side was dulled? Whatever the case, it's frustrating to deal with. First noticed it with my old dime store Black and Decker but the Bosch does it too. BTW, the blades I have are filed with a rake and fleam angle, like you would find on a crosscut hand saw. I used to think they were filed straight, like with a rip saw. Speaking of handsaws, I recently tried cutting doorskins with a 10 tpi handsaw and it was a disaster. The entire bottom ply blew out.

And to further cloud the issue, they make fine toothed plywood/laminate blades for circular saws. They make a very fine cut. The problem I've had with those is if the plywood is thicker like 3/4 inch. Those are thicker, solid blades and when they heat up, they start cutting crooked. But set to make a very shallow cut with thin plywood should not be a problem.

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I have a variety of blades for my Bosch jigsaw. Standard "get it done" blades are 10 tpi. But a much smoother cut (surface) comes from blades with 20 tpi, but those are also skinny and that makes it easier to wander back and forth off your line. Howard, metal cutting blades are made in much finer pitch such as 24 and 32 TPI.  We use these for fine cutting, especially when cutting out a section of deck that will be reused as a hatch.  The Bosch T101 (I think) series cuts very clean but will not do curves as the teeth have no set. It it's a straight cut that matters, I put down a straight edge to act as a guide to prevent wandering around. And that little plastic insert does help. The only problem I've had with jigsaws is cutting thicker solid stock (like for breast hooks, etc.). You would think with such a rapid up and down motion they would make a straight 90 degree cut, but at times, my finished cut is angled. That may be due to the curve and uneven pressure or perhaps one side was dulled? Whatever the case, it's frustrating to deal with. First noticed it with my old dime store Black and Decker but the Bosch does it too. When cutting curves, there is a tendency to help the saw around the curve by pushing it sideways.  This will always cause the cut to be off 90 degrees.  It's the same problem some have on a bandsaw.  You must rotate the machine or workpiece, not push to the side.  I have cut curves on 6"X12" timber with my Bosch.  That requires a blind pocket cut from both sides and the longest blade.  You need a lot of set, go slow and never guide the saw sideways but only rotate it to the line with full orbital action. .  BTW, the blades I have are filed with a rake and fleam angle, like you would find on a crosscut hand saw. I used to think they were filed straight, like with a rip saw. Speaking of handsaws, I recently tried cutting doorskins with a 10 tpi handsaw and it was a disaster. The entire bottom ply blew out.

And to further cloud the issue, they make fine toothed plywood/laminate blades for circular saws. They make a very fine cut. The problem I've had with those is if the plywood is thicker like 3/4 inch. Those are thicker, solid blades and when they heat up, they start cutting crooked. But set to make a very shallow cut with thin plywood should not be a problem.  Hollow ground plywood and planer blades are available for the circular saw.  The teeth, even the blades with no set, are thicker than the blade stock and they have much less tendency to heat from friction in a curve.

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Arnie, good to see you posting as I had not noticed any for a while.

I use a Ryobi 18V 5 inch circular saw set to just cut through the panel and the scoring technique that Charlie mentioned, sometimes.  What really works well for me is to place masking tape down on the panel where the cut lines will be, then make the lines, then cut with the saw.  I learned this trick when cutting hollow core doors.  It works well most of the time and since that blue painters tape has come around, it is my tape of choice.  I almost forgot, also use a blade made for panel cutting.

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Truth be told I just don't bother with scoring the panels, using tape or using a plywood blade to cut BS 1088 ply panels.

The panels have always been of high enough quality I just don't have any problem with fiber tear out as long as I use a fresh blade and only have it a wee bit lower than the panel is thick.

In truth I would think using a plywood cutting blade would make lofting out curves rather difficult.

Good points Ray, except Arnie did not say he was using BS1088, but maybe that was implied?  The plywood cutting blade works very well cutting curves in the 5 inch diameter blade, and as I said earlier, I only set it deep enough to go through the panel, and only up to the 10mm thicknesses.  Perhaps you should try it?  I do not do the tape thing for stitch & glue boat building, but for any veneer work, such as doors, or fine finishing work for paneling.  I find it surprising that you do not have any tear out problems. ;)

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Ray, how many panels do you order at a time to get $33/panel?  Of course, the next question is.....from whom?  Does that include the shipping cost?  I am paying about $50 to $55 per panel of Okume (6mm), which I pickup in South Bend.  For only a 20% increase in weight I would be wise to shift to merianti (20LBS vs. 24 LBS per panel) and save $22 per panel.  On a spindrift this might be too much of an increase but I doubt (just guessing now) the overall weight would change by more than 10 lbs?  :)

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