# Routing MDF



## jpratte (Aug 4, 2009)

Hello,

I am trying to route (dado) MDF to support other MDF shelfs. The MDF seems to measure 3/4 inch and the router bit is 3/4 inch, but the pieces don't seem to fit.

What's up with that?

Thanks, Jefa


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## bobj3 (Jan 17, 2006)

HI jpratte

The new MDF is the same size as the 3/4 " plywood, ,under size  like the new candy bars ,all getting smaller for the same price..

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jpratte said:


> Hello,
> 
> I am trying to route (dado) MDF to support other MDF shelfs. The MDF seems to measure 3/4 inch and the router bit is 3/4 inch, but the pieces don't seem to fit.
> 
> ...


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## Dr.Zook (Sep 10, 2004)

Welcome to the RouterForums Jefa.


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## kp91 (Sep 10, 2004)

Jefa,

Sometimes the MDF is actually 'bigger' than 3/4 inches on the edges if it has had a chance to absorb moisture, or has been manhandled. I have learned real quick not to force it into the dado, you can end up making scrap real fast.

Try using a sanding block to chamfer the edges of your shelves just a bit and see if that doesn't help get it started into the dado. 

The other culprit could be your 3/4 inch bit is not exactly 3/4 inch. In that case, you can either offset your guide by the tiniest fraction and widen the groove just a bit, or make a rabbet on your shelves so that they fit into your dados.

Like I mentioned earlier, If you force a shelf that is too tight into a dado in MDF, you'll probably cause the side to split, or to curve outward.


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## xplorx4 (Dec 1, 2008)

Greetings Jafa and welcome to the router forum, pleased that you have joined us,


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## Shutterbiz (Aug 22, 2008)

Get yourself a Digital Vernier Caliper and you'll be able to see exactly where your problem is. Get them on Ebay quite cheaply.

Mike


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## Mike Wingate (Apr 26, 2009)

Undersized bits and oversized material. Check your measurements.


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## skypilot2 (Jul 30, 2009)

Hey Jefa - That is so weird that you wrote about the mdf and the dado. That is exactly what I was doing yesterday afternoon and mine didn't fit either. Plus, mdf is really messy. Tons of dust. It cuts easily, but don't know if it is worth it with all the dust. I decided that by the time you clamp everything and line it up perfect, it would be much easier to do the dados on the table saw using the "dubby" crosscut sled. I'm on my way now to replace the mdf with birch plywood. Have a great day and happy woodworking.

Demi


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## Billat908 (Jun 25, 2009)

*MDF Safety Rant.*

Warning: Safety rant follows.



skypilot2 said:


> MDF is really messy. Tons of dust. It cuts easily, but don't know if it is worth it with all the dust.



Yes. And the dust can be toxic. So can the gas produced when it is cut with a power tool, particularly when there is a little heat buildup. To add to that, in recent years, MDF has been supplied from countries with lax or nonexistent safety laws regarding toxic ingredients. Even a standard dust mask is not enough protection. I would not cut, sand or rout MDF in a basement, for fear of the safety of the occupants, no matter how good the DC system. The outgassing of formaldehyde and who knows what else is just too risky for my family. 



> I'm on my way now to replace the MDF with birch plywood.
> Demi


 Yes. Way more satisfying to work with, stronger, takes a good finish and does not swell with moisture. 

However, the glues in it can also be toxic, with large amounts of formaldehyde and who knows what else. There is a big stink (literally) with Chinese plywood in trailers right now. Again, countries with lax or nonexistent laws are poisoning us. 

Even our own country needs to be watched. A coupla years ago, the EPA attempted to exempt US plywood producers from toxic air pollution limits. They ere overruled by the courts, but that ruling only addressed plywood production, not the inherent toxicity of the product itself. 

You can Google MDF toxic or Plywood toxic for a lot of info on this. 

End of rant.


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## Mike Gager (Jan 14, 2009)

jpratte said:


> Hello,
> 
> I am trying to route (dado) MDF to support other MDF shelfs. The MDF seems to measure 3/4 inch and the router bit is 3/4 inch, but the pieces don't seem to fit.
> 
> ...



you dont clarify if the dado is to small or to big.

either way id just do some sanding on the opposite piece til it fits


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## Bogydave (Nov 14, 2008)

Hi Jefa
I'm in the same situation, when I measured the thickness (calipers) , I got various readings on the same sheet from pieces I've cut. MDF is not a stable wood (moisture speaking). 
I'm building a "changing table" for my daughter (expecting 1st child).
She wants it painted so I'm not going to use good wood. This is my first time building a whole project with MDF. (Tried some pocket screws & well, don't snug them very tight . (learning curve here)
I'm tempted to drill out where the screws go, glue in a 1/2" plug & hope that holds better.
The tip about sanding the edges is what I used to get the dados to fit. 
Plan to take care & use lots of glue & clamps. 
Routs good but I here it's tough on bits.

Here's a question?? At Lowes, 1/2 MDF is $4 more per sheet than 3/4. What gives?

Is particle board any better?


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## skypilot2 (Jul 30, 2009)

Billat908 said:


> Warning: Safety rant follows.
> 
> 
> 
> ...


Hi Bill - I am very concerned about toxins in the wood and the outgasing, etc. I have a Jet AS1000 air filtration, a dust collection system, and wear a mask. I won't be cutting any more MDF, but I have a lot of built-ins to make and if plywood isn't safe either, what the heck can I use that IS safe?? Please advise. I'm new to wood working.
Demi


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## AxlMyk (Jun 13, 2006)

Bogydave said:


> I'm tempted to drill out where the screws go, glue in a 1/2" plug & hope that holds better.


Probably your best bet.


> The tip about sanding the edges is what I used to get the dados to fit.
> Plan to take care & use lots of glue & clamps.
> Routs good but I here it's tough on bits.


Yep, yep, and yep.


> Here's a question?? At Lowes, 1/2 MDF is $4 more per sheet than 3/4. What gives?


Interesting.



> Is particle board any better?


Nope.


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## Billat908 (Jun 25, 2009)

skypilot2 said:


> Hi Bill - I am very concerned about toxins in the wood and the outgasing, etc. I have a Jet AS1000 air filtration, a dust collection system, and wear a mask. I won't be cutting any more MDF, but I have a lot of built-ins to make and if plywood isn't safe either, what the heck can I use that IS safe?? Please advise. I'm new to wood working.
> Demi


I think it would take a chemist or toxicologist to really give a decent answer. I think some back issues of the woodworking mags have some articles, too. Try a google search on plywood toxic or MDF toxic For starters, use the best mask you can get, ventilate the he** out of your work area and avoid chinese glued products. Be double careful if there is a fetus or infant around. My son is expecting, and his reading has made him do all his work outdoors except on plain wood. 

A mask needs to be more than a dust mask. It needs activated charcoal or similar to protect you from formaldehyde, which is in a lot of wood composites and plywood. I think 3M would be a good place to look. 

Perhaps someone more current can make a rec. ....Mine is an antique made by Mine Safety Appliances. I also try to cut mdf and plywood outdoors, at least most of the time.


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