How to cut Masonite-like stuff without fraying

I have a partial sheet of some sort of synthetic board, brown, smooth on one side, and comparatively rough and unfinished on the other side with many tiny parallel vertical and horizontal "grooves" there. Is this what is meant by fibreboard? Is it like Masonite? Maybe mine is more bendable (though my piece is only 10" wide so of course it's bendable). If it *were* Masonite, wouldn't it say so?
My piece is over 4 feet long, 10" wide, and 1/8" thick and i want to cut a hole in it without making it thicker where the cut is. IIRC cutting this stuff with a saw makes it like a rope frayed at the end, thicker and softer. . At least right at the cut edge and within 1/8 or 1/4" of the edge.
Any suggestions on how to cut it?
Or I could cut it and leave some material, that 1/8th or 1/4". Any suggestions how to take off the last 1/4" without making the remainder just as thick?
I think a sharp knife would not make it thicker but it would take for ever. I have a toothless blade for my saber saw, and it's sort of like a knife, but I think that's meant for something else (though I forget what)
A band saw would be better than a sabre saw, because it' only goes in one direction, but it's an internal hole. No way to get the band saw blade in there.
Does it matter if the smooth side is on the bottom versus the rough side, if I'm using a saw?
Thanks
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micky wrote:

Masonite is a brand of fiberboard.
The rough side is rough because that side was on the screen when they made it.
Yes, it matters which side is up if you cut with a saber saw. Saber saws cut on the down stroke so you want your "show side" up. More TPI = smoother cut.
You will make the smoothest cut with a router and template. Any fuzz - with either router or saber saw - can just be cut/sanded/filed off.
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Noting Bob's correction, which I hope I would have noticed on my own, I can do that. I've got blades with lots of teeth and I can buy a better one.

I'd forgotten that I have a router somewhere!! It would be nice to use it for a change. . Making the template will be harder than just drawing a line.

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wrote:

Clamp it to a table or sheet of plywood with a board on top to act as a straight edge guide for the router. Align it so the router just clears the table, or actually eats a little of it if this is a sacrificial piece of plywood.
I usually cut sheet goods like this on my table saw with the blade barely sticking through the cut. Again you want a board stabilizing the edge of the cut. A scrap of plywood or OSB that you can "kerf" a little will make these cuts factory fresh.
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On Sun, 21 Jun 2015 16:34:13 -0400, snipped-for-privacy@aol.com wrote:

Okay. Thanks.
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No, but maybe this would be a good reason to buy one. You think it would do even better than what we've talked about?
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Sounds good.

Darn, you ruined it. No excuse to buy another tool. Just kidding. I can still use this as an excuse, even after I've done this project with the sabre saw. I often buy tools that I might use and this just proves that I really might use it. But I won't make a special trip and I'm wail until it's on sale (like it is 1/3 of the time.)
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dadiOH wrote:

Yeah, I know, I said the exact opposite of what it actually is. I know better, don't know where my head was, I'm really not senile.
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That sounds great. I knew there must be a way to do this right. Thanks a lot.

I get it. I've got plenty of scrap wood and plenty of clamps.

I have a nested set of hole saws, but despite that, probably not the right diamter. Plus they're cheap and probably not sharp. The sabre saw will do well.
Backgrond, A friend lent me his portable AC. He told me last year that he had it and he actually found it pretty quickly this year. But he doesn't have the flat piece that goes in the window**, so I have to make a flat piece of something, wood or masonite to mount the hose to. The end of the hose is like a circle that's been squished, so it's shaped like (_____) with a line across the top also.
Actually only 4 parts of the circumference have to be done well where there are built-in clips to hold it in place, so if cutting nicely is too slow, I can switch blades for most of it. The clips are meant for a 1/8" thick piece of plastic, the exact same thickness as the fiberboard I have already.
I know I could have done a crappy job of cutting and then trimmed away whatever made it too thick where the clips were, but I like to at least plan to do things right.
I know all about the inefficiencies of a "portable" AC, but I only need it for 12 days a year, for one room, and probably only 8 hours each night, to sleep. (The basement and first floor are cool enough without AC) So for 96 hours a year, it can't be as expensive as running central AC. I'll fix that when my mood has changed.
**He did include a round plastic part for mounting the hose through the wall, but I don't think I'll ever be willing to do that. ;-)
He also can't find the remote control, but since it has a thermostat, I probalby don't need that. They still sell replacements for $30.
The drain hose is the remaining issue. The outlet is 1 foot off the ground, so I think I could run a 1/2" I.D. hose 25 feet to the shower, and it would drain????? Or I coudl run a hose 6 feet to the closet where it overhangs the first floor, and drill a hole through the floor to the outside (like the cable guy did to install the cable, when I had cable) From there it's only a foot to the downspout, and where the downspout runs at an angle (because of the overhang) I was going to make a hole in the top of it and put the drain hose in the downspout.. (Well, after I watch the water dribble out for a few days. I'm curious about that.)
And I was going to seal the hole in the house around the hose with brown vinyl caulk, unless there is something better.
But before making a hole, I'm going to run it with the built-in removeable bucket and see if it works. It probably does.
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wrote:

Just use masking tape on the cut line. Use a fine blade.
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