Problem cutting epoxy laminated part

I've got 2 small bolt down deck pieces here, Airex foam core. System III Silvertip. Piece shown, from inside out is 1800, 10 ounce cloth 2x. Hand layup. I do it one layer at a time, allow to cure, then next. Product has a 72 hour no sand bonding window, I never go over 24. It's cool here, 40 F at night 60 F day, cures slow.

First part, my first epoxy part in a long time, no problems. I'm cutting this 2nd part via jigsaw and I see I'm disturbing the top layer of cloth somehow. Strangely only on the top side which I completed days ago - bottom side I finished yesterday doesn't seem to mind being cut.

Saw this issue, stopped, played around with other 14 to 20 tooth blades (on scrap areas), good blades as I don't run junk blades, similar trouble. So I'm stuck here..

Other part, I did allow to sit for awhile before I cut it, was busy doing other stuff. Is that likely the issue - cure time? Or is there some trick to cutting this stuff I should know? Thanks!

This is the part:



Here's what happened when I tried to cut it top and bottom:

 

Incomplete cure, delamination.

The jigsaw is a terrible tool for this work as the shear force is nearly perfect.

 

Thanks! What do you cut this sorta thing with if not a jigsaw? A lot of cutting over time, that's really become my go to for fiberglass anything.

Below similar almost finished product from opposite side of boat, edges decored but gotta finish running a DA around and topcoat of course.

 

Well, I only use two things anymore for trimming, but the main issue is the temp. You need that thing to cure at 72F for a good 12 hours, any lower temp and it'll do that easy.

I use a 4" circular saw, but that will delam the part not cured.

The only way to cut that light stuff, undercured is with an oscillating tool with a carbide head and down or across the part, no up force.

 

Thanks! Alright, so sounds like - last part, that 2 weeks with it sitting around was the difference, just got lucky. That all makes sense.

I'm gonna have 3 parts to cut coming up real quick (this one and 2 others that are like 3x6 ft). What I'll do is hold off on cutting, do other stuff, and I will give them all together a good 24 hour bake at 80 degrees or so via electric heat on the layup table.

Then hopefully the jigsaw is no problem and I'll just spend a night flinging foam and filling edges.

 

I never use a jig saw for the very reason every up stroke is a direct shear force on the laminate. Even a 4" skilsaw imparts its force on an angle. Stop the cut and look sometime...might be 45 degrees, but the direction is down, not up. Also, for most of my work, the jigsaw blades failed too fast versus carbide.

But, if you cure overnite with 80F; it should be okay. Most epoxy fails to cure or is retarded at temps below about 60F. So, your part cured until sunset; then did nothing; then started to cure again maybe day 10am next day.

 

Fallguy has pointed out the root of the problem and a solution.There is a more common tool for the job and if you have any amount of composite trimming to do it is much faster to use a diamond blade in an angle grinder.The blades last for a very long time,unless you stand on them and because they don't operate perpendicular to the surface,they have a greatly reduced tendency to delaminate.In fact you can use them with a totally cured laminate and they really excel.The only thing they can't do is trim a neat radius and for that you really need a diamond bit in a die grinder.

 

The ultimate tool to use is a tile wet saw. Except for leaving a very clean cut, there is no itchy and harmful dust. I bought a low budget saw for about $50 and it works great.



To fine shape the pieces, I use a combined desk standing belt & disc sander.


I cut and sand from 0,5mm up 10mm G10 with these small machines.

 

This stuff cures to 35 degrees F on the fast cure hardener but that doesn't mean it will full cure in a couple days averaging 45. Which I guess is what I'm seeing.

They make carbide tooth jigsaw blades, good for about 50 feet of 1/4 inch solid glass before you note the cut speed is slowing down. You pay for them - $15/each. Not talking the tile versions, also carbide, those are out there too. But for this stuff, and decent blades last fine, not a lot of glass involved.

I have a dewalt atomic, 5 inch circular saw - with carbide plywood blades. That's probably the ticket here. I'm gonna finish all the parts first, bake them, then maybe try that.

As you said I believe the entire problem is resin curing. I've done tons of this with VE and PE parts and basically if you can handle them, you can cut them, epoxy ought to be more tolerant even. It has gotta be, those other resins come so close to full cure in short time, epoxy just takes awhile (everything about the stuff requires patience so this included I suppose).

 

Specifically what confused me is the epoxy. I've cut a whole lot of foam+glass parts via jigsaw, honestly never was an issue until this epoxy part. Has gotta be curing schedule.

I could definitely try one of those in a circular saw, I've done that with abrasive wheels before. But man, I'd be hard pressed to cutout entire parts with a wiz wheel, sounds insane. Basically with light foam I make a panel a little bigger than the part, so that edges of the layup can be disregarded, then cut it out 360 degrees based on some pattern. Thanks for the input just can't see using an angle grinder as a cutting tool for something like this - I'd at least put it in an actual saw with a face and guard on it .

 

Those diamond blades (and others very similar) are the standard method of cutting laminates of all types.I have never,ever seen a circular saw used for the job.It does get dusty and good extraction is necessary but you will get the job done very quickly and for professionals time is money.The guard of the angle grinder needs to be in place.The wet wheel for tiles would serve for straight cuts on flat panels and be cleaner in use,but it would take many times as long.

 

You are absolutely correct about it being slow, still the one I showed above is very easy to use freehand for short straight cuts if removing the guide situated on the far left.

 

I deflanged 300 dock boxes and lids, plus about 5o trashcans and lids for Marina Del Mar that way. I worked 20 hours a day at it till I was done, then started hanging hinges and hasps. I cleaned the cuts up with an 8" sander running 140 psi. Had about 3 cubic yards of dust swept up in the corner when I was done. Standard pneumatic angle grinder running 4 inch diamond wheels.

 

If you have air, you could go smaller for smaller parts with a right angle die grinder with small diamond wheel.

 

Indeed you could and you would be at it longer than the fellow using an angle grinder.Post #13 explains the way it is when work needs to be done.Then there is the difficulty of achieving a vaguely square edge if the cutting disc is appreciably smaller than the body of the die grinder,but if a die grinder is the only tool in the cupboard,you may have to do it that way.