My MDF Questions: #2 Can you Joint it?

[Tom Overthere]

Q2: Is it possible to clean up the edge of 3/4" MDF by running it over the jointer?

Is that a particularly good idea?
Is that a particularly bad idea?

My understanding is that MDF dulls blades more quickly than most hardwoods will (apparently due to the glue). Is that true?

Will MDF dull a jointer blade so quickly that you would advise me against jointing MDF edges on a regular basis?

Thanks

[keith ouellette]

I saw norm build some wall panels out of mdf and he said the same thing. The glue is very hard on steel knives. If your blades are carbide it doesn't present as much of a problem.

[Karlan Talkington]

I've heard the same about MDF on the jointer (or planer for that matter)

Typically the faces of MDF should be pretty straight, so if you are wanting to joint the edges, I would run through the tablesaw and save the blades of your jointer the effort.

my 2 pence

[David Christopher]

Tom, I cut mine with the table saw and then belt sanded and it turned out just fine

[Lee Schierer]

Q2: Is it possible to clean up the edge of 3/4" MDF by running it over the jointer? Yes

Is that a particularly good idea? Not really a good idea, the glue is hard on the blades
Is that a particularly bad idea?Depends on how much yoou like to buy and change blades

My understanding is that MDF dulls blades more quickly than most hardwoods will (apparently due to the glue). Is that true? Yes

Will MDF dull a jointer blade so quickly that you would advise me against jointing MDF edges on a regular basis? How deep are your pockets?

Thanks
Carbide blades may change all of the answers above.

[Chris Padilla]

With a well tuned-up table saw and a sharp blade (almost doesn't matter what kind of blade but I'd say 40 tooth+ are probably what you want) and good technique, you should get very clean edges that shouldn't need a jointer.

Also, you'll find that MDF produces really really REALLY nasty flour like dust. Use dust collection...I wouldn't saw MDF without it.

[Scott Mann]

You could also use a straightedge and router with a flush trim bit. I would not use a jointer.

[Abe Hachmann]

I have jointed MDF with great results. I only do it sparingly on pieces that must be exact. It definitely wears the knives faster than hardwood. Check the edge to make sure there aren't any steel pieces embedded in it that would nick the knife. I save the very back 1" of my knives for edge jointing mdf and plywood.

[Tony Bilello]

I keep hearing that MDF dulls blades. I have cut acres of the stuff and never noticed any dulling more than hardwood. MDF texture is like powder and more like cutting cardboard. If you really want to dull blades quickly cut construction grade pine. Between the pinching of the blade and constantly hitting knots your blades will dull or chip prematurely.
One soft wood in particular that will dull blades quickly is Cypres. Lots of really fine sand in the grain,
I think the legend of MDF wearing out blades comes from particle board. Particle board cuts with hard chips and hard pieces of glue. This is entirely different than MDF. As someone said earlier, MDF dust is like flour.

Getting back to the original point, MDF machines exceptionally well, whether it be cutting, routing or sanding.

[Russ Boyd]

Finally! Reality hits. Thank you Tony. I'm not alone.

[Peter Quinn]

MDF chews up HSS jointer knives like a hungry monkey eats bananas. Not maybe, but really. So if you want to joint it, use your own jointer and leave mine alone. It is not a myth, I have been silly enough to do it and seen the results. Pass a piece of hard maple over your jointer, as wide as it will go. Then try passing a piece of MDF several times with the fence set to joint in the middle of your knives, then pass another piece of hard maple as wide as your jointer will take and take a good look at the results in a glancing light. Like what you see?

Is it a silly idea to joint MDF? Generally speaking IMO yes. Not really necessary in most cases either. But by all means try it at least once. Just be sure to order a back up set of knives first.

[Brian Jarnell]

I use the jointer,would prefer not but don't have TC knives.

[Bruce Page]

I agree with Chris. If your tablesaw is set up right and you use a good blade, then there shouldn't be a need to use the jointer on 3/4" or 1" stock.

[Ken Whitney]

In one of Alan Lacer's turning videos, he likens turning MDF to turning a "dirt clod". I imagine jointing would be similar!

Ken

[Tom Overthere]

"...like turning a DIRT CLOD"! !!!:DLOL:D!!!

I was laughing out loud, literally, upon reading that :D

Thanks for all the opinions. Seems to me, MDF takes/holds a good profile, as when running a raised panel edge on a router table. So I was hoping for a concensus saying, "Sure, you can do anything to it that you'd do to a normal piece of mahogany, ONLY MDF IS BETTER!!!"

Yeah, somehow things never work out that way... ;)

[Chris Tsutsui]

I thought about this too (regarding A-grade mdf)

Wood is made up of cellulose fibers in a hollow structure.

MDF is those same cellulose fibers fluffled and mixed with urea formaldehyde thermosetting resin and compressed...

The main difference here is this "resin" has high tensile strenth, flexible, high surface hardness, and elongation at break.

I'm thinking that these differences causes MDF to put more wear on steel blades (like HSS). Like others have mentioned, carbide can take the abuse better.

I'm not sure if some of you have ever experienced this but I've found what looked like thin metal splinters embedded in MDF before. I doubt this would rarely be found with non-engineered lumber.

[Chris Padilla]

I'm not sure if some of you have ever experienced this but I've found what looked like thin metal splinters embedded in MDF before. I doubt this would rarely be found with non-engineered lumber.

Weird! I was just noticing this the other day in some MDF I was working. I tried to flick it off with my fingernail but it wouldn't budge and strange (I thought at the time), it appeared that wasn't embedded by me setting it on a table that may have had metal shavings on it. It appeared "extremely well embedded" and I really couldn't feel an edge to it.

[Tom Overthere]

I thought about this too (regarding A-grade mdf)...Wood is made up of cellulose fibers in a hollow structure...cellulose fibers fluffled and mixed with urea formaldehyde thermosetting resin and compressed...

The main difference here is this "resin" has high tensile strenth, flexible, high surface hardness, and elongation at break.Chris ==

What do you know about off-gasing and other "hazard" considerations? Are there special MDF products that are "non-off-gasing" perhaps without the formaldehyde...?

a) I'm thinking in terms of MY health in working with MDF.

b) I'm also thinking in terms of health concerns/objections on the part of clients. They could conceivably say, "I won't buy your product because I fear the MDF will off gas carcinogens in my super-insulated 'green' home."

Access to more and more information is turning more and more into a prison... :(

[Rich Engelhardt]

Hello,
Google everything in quotes:

"edge jointing table saw"

There's several hits that will come up.
I tossed together the one from woodworkingtips (dot) com.

I bought a 3 pack of Irwin 10" blades for ~ $20.00 that I've devoted to use for this.
They work perfectly on both MDF and plywood - both reputed to be "knife killers".

[Tom Overthere]

Rich ==

THANKS for the search string, and for the good news re MDF and plywood.

If I ever learn how to type, I might just take to searching Google first - instead of asking obtuse questions here :confused::D:confused: