exploding MDF

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So Im out in the garage today working on a new router table. A few days ago I took two pieces of 1/2 MDF, glued them together, clamped them tightly and let them sit. Today I need to rip those pieces down into a slimmer shape. I started to slide the mdf into the blade, got about 14 inchs into the cut when the wood seemed to explode! I have no idea what happened, but explode is about as close of a description as I can get. Pieces went flying everywhere, into my gut (lots of blood and bruises from that one, but no trip to the hospital), my wifes truck (that one is gonna cost me a pretty penny) and all over the garage! I was being safe around the saw, push sticks and hold downs and all. Has anyone ever had any trouble with perhaps weak spots in your wood reacting poorly to a blade?
Jason
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I'm just guessing, but I would bet on it having some residual tensions from the glue up that caused it to warp and bind up against the blade. If it had been a more solid peice of wood things might have been worse.
Jason wrote:

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Solid wood tends to kickback and tosses it at you, but I never heard of it exploding. The fact that the fibers run in one direction and are fairly long would help there. MDF has no fibers like that.
You mention tensions from gluing. I wonder if it absorbed the water from the glue and swelled it making that tension?
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I'm only guessing, but: Yes, similar to case hardening in solid woods. The glue up resulted in some form of internal stresses, and when it was sawn, the peice twisted, and bound up on the blade. If it was a peice of solid wood there would have been a nasty case of kick back.
Another possibility is that the glue wasn't all the way dry, and bound up on the front of the blade, resulting in the peice being driven down into the table, and things did the "rapid spontaneous disassembly" thing.
Edwin Pawlowski wrote:

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On Sun, 10 Apr 2005 03:07:15 +0000, Jason wrote:

While we wait for answers from people who actually know what they're talking about, I'll wave my hands and say "steam explosion." Water in your glue couldn't get out and saturated nearby areas of mdf, then the sawblade superheated that area.
--
"Keep your ass behind you"
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On Sat, 09 Apr 2005 22:55:03 -0500, Australopithecus scobis

If he'd have grounded it first, that wouldn't have happened. Unless he cleaned it with acetone.
--
LRod

Master Woodbutcher and seasoned termite
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LRod wrote:

How many times does it have to be said? The circuit breaker protects the wiring NOT the MDF?
Any damage to the saw blade? I'm wondering about a "freak" occurrence where you might have had a piece of metal in the MDF mix.
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Yeah, I wonder about that too. Seems more likely than anything resulting from residual moisture: the OP said he glued it up "a few days ago" which should be plenty of time for moisture to disperse and dissipate. I've cut MDF glue-ups within a couple hours of gluing, and never experienced anything similar.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Doug Miller wrote:

crosscutting it on an RAS. Tore up my right hand a bit and a chunk large enough to matter hit me in the groin so hard it was 10 minutes before I realized my hand was pumping blood all over the place. What happen? My guess: lack of glue at the point I was cutting allow wood chips to catch, ride the blade and catch again in the kerf, ripping the kerf apart, and flinging wood all over the place. I don't know if MDF fibers can do the same, but I'd guess it's possible. Even a small chunk of metal that rides a tooth instead of getting flung would something similar, I'd guess. A larger metal piece might just tear the hell out of things more immediately (as if 1/1000th of a second is going to make a lot of difference).
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Charlie Self says...

Ouch. I feel your pain. I could see that happening more easily if there was a ripping blade in the RAS where a crosscut or laminate blade would have been much better. The manager of one of the Indy BORG said that OSHA is so strict on RAS's that there's is caged to the extent that it is almost worthless.
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Hax Planks wrote:

Combination blade, IIRC. No matter how bizarre an accident is, there is always that chance for error, or for simple chance crappy luck, that creates the hassle.
Though it wasn't the saw's fault, I got rid of it the next week, and have seldom used an RAS since. Kind of silly, because it was almost certainly a combination of operator error--did I have the wood all the way against the back fence--or poor wood storage. Or both.
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Charlie Self says...

I've never had a problem using a RAS, though I never used one frequently enough to lose the required healthy fear of it. They seem to be increasingly rare these days. One would have to fall into my lap for cheap before I would think about buying one, since the table saw can be made to do the same tricks with some fixtures.
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And it wouldn't have happened with hand tools, right? When was the last time the dozuki kicked back?
Patriarch, also in smartass mode...
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On Sun, 10 Apr 2005 02:24:02 -0500, the inscrutable Patriarch

The little red button on the end of my ryoba puts it in automatic kickback-free mode. I leave it engaged.
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wrote:

dunno.. ask Steve Knight..
mac
Please remove splinters before emailing
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Jason wrote:

I have had some interesting things happen with *wood*, but MDF ain't wood and is remarkably well-behaved, cutting wise. This is a very bizaare story.
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I checked out the saw and the remaining mdf pieces that I could find today. The blade and saw are in great shape, no signs of any mishap at all. I found a couple of pieces of shrapnel mdf, it does look like I may have had a small, eraser head size dry spot between the two boards where glue didn't make it. It's possible though that the glue just absorbed into that section. Or the glue could have been an additional projectile. As of this morning, my stomach looks like I got into a sumo wrestle with one of the blue man group. The cuts look like they may leave a cool scar, which I guess is a bonus since I will be able to make up cool knife fighting stories instead of telling ones about lame compressed wood bombs. I have a nice leather aparon on order, so hopefully I'll be back in the shop this weekend.

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Jason wrote:

Since you raise the safety apparel issue, I'll ask: Were you wearing eye protection? If not, will you be doing so in the future?
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Eye protection, hell! I've said it before, many times, and I'll say it again: there are *other* things on your face that are worth protecting *too*, not just your eyes. I wouldn't fancy catching one of these MDF bombs in the teeth.
Face shield, face shield, face shield!
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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wrote:

I concur.
I have seen enough accidents to make sure I got a good one., I went to an industrial safety supply house. I got the kind that fits onto a hard hat. And I got the toughest, thickest polycarbonate face shields they have. A bunch of them. Just to make sure I have plenty around.
I have had several smacks in the face shield with various objects. It makes a big noise, but I was well protected. Best investment in safety equipment I ever made. And I am, by nature, quite cautious and safety conscious. I even wear additional eye protection under the face shield if I think it warrants it.
My face ain't pretty, but it can get considerably uglier. Gotta protect it!!
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