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What to use for cutting a 1" foamboard+ 1/2 inch plywood sandwich?

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What to use for cutting a 1" foamboard+ 1/2 inch plywood sandwich?
Posted by IDRick on Saturday, November 27, 2021 5:58 PM

I need to cut several 3" long x 1" wide x 1-1/2" deep sections out of my finished benchtop (construction = 1" foamboard + 1/2" plywood).  Does not need to be a finish surface as these cut-out sections will be hidden.  Any suggestions?

My thought is to use a jigsaw but different blades are needed to cut plywood versus extruded foam.  Came across an interesting video showing jigsaw blades for foam that give a finish cut with minimum dust but these blades would not work for cutting plywood. 

https://www.youtube.com/watch?v=U8Po8NoM7g4

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Posted by doctorwayne on Saturday, November 27, 2021 7:35 PM

Extruded foam can be cut with just about anything (I've been cuttting some of it today, using a keyhole saw).  Your jigsaw, with a wood- or metal-cutting blade will cut the plywood and the foam, too.

You did mention...

IDRick
Does not need to be a finish surface as these cut-out sections will be hidden.

Wayne

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Posted by IDRick on Saturday, November 27, 2021 8:29 PM

Okay, thanks, Wayne!  Think I'll search for a longer jigsaw blade and try cutting all in one fell swoop (drilling guide holes first).  Probably want to try some different blades as I'm thinking an aggressive blade might make more mess...

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Posted by doctorwayne on Saturday, November 27, 2021 10:39 PM

IDRick
..Probably want to try some different blades as I'm thinking an aggressive blade might make more mess...

That's why I suggested the blade for metal, as many of them have finer teeth...they won't cut as fast, but should make a neater cut.

Wayne

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Posted by Doughless on Sunday, November 28, 2021 11:02 AM

My response falls into the category of "thinking out loud", so it may not be very good.

When cutting plywood, many will run masking tape along the cut line to keep the top layer of veneer from sharring off into little chunks, making a nice clean edge.  Taping the top cut line and underneath if neatness matters on both sides.

I would assume that since your foam is securely sandwiched, that it would tend to cut neater than if it was exposed and allowed to flex around. 

I think that I would worry about cutting the wood and not so much the effect on the foam, but a finer blade would be better than coarser.

- Douglas

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Posted by FlattenedQuarter on Sunday, November 28, 2021 2:05 PM

Get a jig saw with dust extraction port and use a coarse blade

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Posted by BigDaddy on Sunday, November 28, 2021 2:55 PM

Have a friend aim the shop vac at the jig saw.  Wear masks.  It going to be messy.

Henry

COB Potomac & Northern

Shenandoah Valley

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Posted by MisterBeasley on Sunday, November 28, 2021 3:02 PM

Can you first cut the foam with regular once or hot knife, and thengo back and cut the plywood with the saw?  Using power tools to cut foam is messy.

It takes an iron man to play with a toy iron horse. 

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Posted by IDRick on Sunday, November 28, 2021 7:32 PM

MisterBeasley

Can you first cut the foam with regular once or hot knife, and thengo back and cut the plywood with the saw?  Using power tools to cut foam is messy.

 

 
Good point Mr B, easier cleanup with big foam chunks cut out with a utility knife and then using a jigsaw to cut out the plywood bottom.
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Posted by gregc on Monday, November 29, 2021 4:46 AM

you can put copper wire (e.g. 12g) of any shape into a soldering gun to cut a grove using some thin wood strips on top of the foam as a guide and to limit the depth.

bend the contour you want, 1"x 1/2".  at the top of the 1/2" edges, bend the wire wider than 1".  after that, bend the wires to fit into the soldering iron.

with the wire hot, plunge it into your foam up to the wood guides at one end.  slide it to the opposite end and pull is straight out.

greg - Philadelphia & Reading / Reading

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