# MDF and Routers



## Grootser (Oct 27, 2013)

I'm in need of some advice.
Normally I stay away from MDF but my wife wanted a custom cabinet for her laundry room. She planned in painting the unit so using solid wood would be a bit of a waste of money. I decide to use 3/4" thick MDF and cut dado's so I can slide the shelves into them and make the unit nice and strong.
I also thought this would be the perfect excuse to purchase a new router I've had my eye on (Dewalt DW618B3).
I cut up my boards to the dimensions I needed and got everything ready to route in the dado's. I had decided to cut the dado 3/8's deep into the MDF and thought 2 passes would be enough to get the job done per dado.
The boards clamped side by side were rought 3-1/2 feet for the left side and the left back of the cabinet. I made the first pass on the bottom dado and was happy with the result. I continued to cut and finished 3 complete dado's. As I was cutting the first of my two passes on the 4th dado. I noticed some sparking coming from the router. I quickly turned off the router and inspected the unit. I didn't see anything or smell anything. I thought maybe the brushes needed to cut themselves in. I started again working on the 4th dado and at one point smoke started to come from the unit and it failed after that.
So my real question here is as follows.
1. Was I taking too much of material in one pass?
2. Should I have been using a spiral up cutting bit, instead of the straight bit i was using?
3. Or was this router not powerful enough for what I was trying to do.

Any advice is greatly appreciated.

Robert...


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## Cherryville Chuck (Sep 28, 2010)

What you were doing shouldn't have had an effect on that router or even one a 1/4 its size. Take it back. You got a lemon.


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## vindaloo (May 30, 2009)

I have a Ryobi 1.3Hp router and they recommend max depth of 3.2mm. However I have made 6mm depth cuts per pass in the past. The DW you have is stated at 2 1/4Hp, so is more powerful, but I'd think 6mm (1/4") is probably the deepest per pass. You mentioned you wanted 3/8 depth of dado, and made 2 passes per dado, so I'd assume you didn't exceed 1/4" on either pass, so I'd say there's summat wrong wit the router. Not sure sparks should fly in any case at all.

My tuppence.


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## jw2170 (Jan 24, 2008)

Take it back......


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## Semipro (Mar 22, 2013)

Hello and welcome to the forum Robert
You did nothing wrong take it back ,only thing I have against MDF is it hard on router bits, you differently should use carbide bits. But I use it and router it all the time I do not waste hardwood on the sides and backs of cabinets nobody ever going to see


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## Mike (Nov 22, 2004)

A spiral upcut bit would of given you more tear out on the edge. Just a defective router to be returned. I do not care for DeWalt tools but many members are happy with them. If you get another lemon you might consider switching brands.


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## malb (Sep 15, 2008)

Just a comment and a couple of questions.

MDF is a stressed skin sandwich product, i.e all of the strength is in the two outer skins, the meat in the sandwich is just fill to keep the two skins at the appropriate separation. Once you cut a dado through a cabinet side, you are weakening the side and giving it cause to bend under load. OK, you will position and glue a shelf in the dado to fill it, but unless the dado and shelf thickness are exactly matched, you will either have a gap between the internal skin of the side and the shelf or the shelf will be too thick and tend to open the dado, bending the side outward. To my eyes it is probably better to screw and glue rather than dado the walls for the shelves. Yes the back and face frame (if used) will help to keep the sides straight, but I suspect that it's a battle thats easier to avoid than win.

With the dados you have cut, I assume because you have only mentioned 3/4 material, that your shelves are 3/4 MDF, the dados are 3/4 nominal and you are using a 3/4 bit. If the first couple of dados went OK, and the unit started to have problems on the forth, how is the bit fairing? MDF can be very abrasive, and if the bit was a well used one from your collection, or a poor quality new one, making the three dados might have blunted it to the point where it could not cut efficiently, increasing the load on the motor substantially. This can be more of an issue if you don't have some form of dust extraction to prevent the dust packing into the dado and causing accelerated wear to the bit edges. 

Also you did not indicate what bit speed you were using. If you had the bit speed dialed down to a slow speed, you also reduce the cooling airflow available to the motor, with increased possibility of causing the motor to overheat, particularly if the bit lost its edge along the way. All of the bit diameter/ motor speed charts I have come accross suggest around 24000RPM for a 3/4 bit.

Just some thoughts to toss into the pot from 5years cutting Melamine and MDF cabinets and panels with a commercial large sheet CNC.


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## Grootser (Oct 27, 2013)

Thanks everyone for the replies. Mal, thanks for the info on MDF as I mentioned I don't use it a lot. The bit was new and still seemed sharp after I took it out. As for the quality I think it was a decent one. I had the speed setting between 5 and 6 on the router which translates into 21,000 for setting 5 and 24,000 for setting 6. I did get to speak with Dewalt and bringing in the unit to the local service center to have them take a look. Will update how that goes.


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## TangoDown3727 (Oct 13, 2013)

Cherryville Chuck said:


> What you were doing shouldn't have had an effect on that router or even one a 1/4 its size. Take it back. You got a lemon.


^^^THIS^^^ I'd definitely take it back. And buy a Porter Cable!


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## CharleyL (Feb 28, 2009)

You should take the router back, as others have said. It should not give off sparks or smoke when you use it, especially when working on your first project. I have 2 of the DW618B3 router kits that are about 5 years old now. They are my "Go To" routers over the other 8 routers in my shop for most of the router work that I do and they are holding up very well.

I have a concern with your choice of material. MDF is NOT a material to be used in moist areas. It fails quickly when water gets in it. A laundry room is not a good location for it's use.

Charley


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## malb (Sep 15, 2008)

CharleyL said:


> I have a concern with your choice of material. MDF is NOT a material to be used in moist areas. It fails quickly when water gets in it. A laundry room is not a good location for it's use.
> 
> Charley


Good point Charley, but in Australia MDF is available in a Highly Moisture Resistant variety which is quite suitable for wet area use, and is frequently used for kitchen, laundry and bathroom panels and doors etc. No reason why HMR could not also be used for carcasses etc except that we tend to use HMR chipboard melamine because it is cheaper.

But Grootser didn't specifically mention HMR MDF so quite likely is using standard bix box store style material.

If the bit was fresh and still appears to be in good condition, I think I would be joining the queue of people suggesting early failure of the tool, generally about 1 in 1000 machines will fail very early in life.


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## MAFoElffen (Jun 8, 2012)

*Mdf...*



malb said:


> Just a comment and a couple of questions.
> 
> MDF is a stressed skin sandwich product, i.e all of the strength is in the two outer skins, the meat in the sandwich is just fill to keep the two skins at the appropriate separation. Once you cut a dado through a cabinet side, you are weakening the side and giving it cause to bend under load. OK, you will position and glue a shelf in the dado to fill it, but unless the dado and shelf thickness are exactly matched, you will either have a gap between the internal skin of the side and the shelf or the shelf will be too thick and tend to open the dado, bending the side outward. To my eyes it is probably better to screw and glue rather than dado the walls for the shelves. Yes the back and face frame (if used) will help to keep the sides straight, but I suspect that it's a battle thats easier to avoid than win.
> 
> ...


Mal-
I'm getting too old. You made me feel old. Not trying to start anything with you... Just saying. (LOL) But since we both have had some experience with plywood, melamine and mdf...

I just felt I needed to comment on your description of mdf. I thought some clarification on MDF would compliment your description of it. Having had to work with those materials as a finish carpenter, master carpenter, cabinet maker, etc. since the 70's... Unlike you, I do not have any CNC experience (yet), just hands-on. I thought I'd share this and get it out before I'm too old to...

MDF is made from wood fiber & adhesives, then pressed together. The way it is made, the outside surface will be relatively harder, but there is no actually separate skin or veneer (except for special veneered MDF's). Because there is no actual skin in normal MDF grades, you will not see any layer transition when tooled below it's surface. 

The outside surface is "harder" because of how it is made. Think of squeezing a sponge (made from wood fibers soaked with glue)... As you squeeze, the fluid (glue) goes to the surface. Dried, there is more glue at the surface. That is why the un-tooled surface of MDF is harder. But visually, as you tool into the surface (to below), you would need a microscope to see any transitional change in density (no actual layers). But as it fails, it will separate into layers that are somewhat parallel to the original surfaces. Somewhat like grain, but more like sheets of paper.

MDF will machine very well as it is very fine particles throughout. Because of that, it will take very fine detail work. But under the surface, it is relatively softer. So it will wear somewhat quickly and is not durable on it's own. A lot of that depends on what you use for paint/finish. If before painting you prime it with thinned glue and you can slow down that wear by more than double. (re-hardening the exposed surface of your millwork). If not careful, that fine detail work will tear off along those paper-like grains if handled too rough before "finishing." If finished right, there is no visible end grain, as there is with wood.

Tooling MDF by hand, you will experience/feel a slight harder density as you plunge through that surface, then it will plunge and tool easier through the softer subsurface. Tooling from there on will be consistent. Keeping that in mind, if you make your first pass shallow to get through that surface, you will end up with less tear-out at the surface and the rest of the tooling below the surface will be easier.

The dust created from the tooling will be a lot and very fine. Remember that it is made from fine wood fibers. The dust particles are paper dust like, 1-5 microns. (This is where the description starts to vary from the previous post.) Paper is "very" abrasive. More than "wood" (from which it is made from). That, along with the adhesive it is made with, is why it wears down bit's faster. It is also more consistently dense than wood, so you need to slow down your rate of feed, compared to wood.

On the dust, some people are irritated and/or affected by the fine particles and the adhesives used in it. Most of these affects are respiratory. Please use DC, goggles and a dust mask.

As Mal mentioned, the adhesives and the fine abrasive particles need DC to extract the particles from your tooling to slow down the tooling wear. This is also true for woods with resins. If insufficient DC, the adhesives will try to bond the abrasive particles to the tooling, prematurely dulling that tooling and also cause over-heating failure from those bonded materials. (Will keep in the heat.) Keep your tooling clean.

Because of those fine particles, tooling came be detailed and that detail will show. Along with that, if your tooling is dull, any defect in your tooling will show. It sands very easy, but too much sanding and you will lose your detail and sharp edges. Also because of the way it is made, there is no x-y endgrain, so no with-grain, end-grain like with wood. It is bi-directional in that... so is the main material choice for woodworking CNC work.

Strength wise, how it is created (by pressing the 2 surfaces together), it creates paper-like layers (although it is not actual separate layers) than has strength linearly along it's length and width, along the surfaces, but not laterally between the surfaces. (Think of a phone book.) If you have ever tried to screw into an edge of mdf with a screw without pre-drilling a pilot hole first... it will split and separate those into paper-like layers. So (again) the strength is x and y (length and width) but not in Z (it's thickness). It doesn't take screwing into the edge well... But any fasteners are more to hold it together while an adhesive cures... The strength will be in the adhesive bond, not in the fastener itself. 

Strength wise in cabinets, the outside carcass is strong if the weight is along the surface of the MDF. Shelves that are going to bear a lot of weight across the mdf thickness should be braced with stringers. If not, they will warp over time.

You can screw into the surface... which I think being as more work than in wood... I pre-drill a pilot hole... screw in a screw... take the screw out... knock down the pulled out "hill" caused by the screw compressing the wood fibers-> with a wood chisel to get the surface flat again... a drop of glue in the screw hole... re-screw the screw into it's prepared home... The drop of glue helps bind all those fibers together and makes a stronger joint.

If you have ever seen a piece of this that has had moisture damage or break a piece by folding it in half, those paper-like layers will be very apparent.

With all the things I just mentioned, you might ask why someone would want to use it. It has it's structural strengths if you understand them and work with them. It is very inexpensive. It is easy to machine and easy to get quality detailed results. It's surface is very smooth, can be sanded to be very smooth... and it's surface very consistently parellel in it's thickness and is consistently flat. There are no change of knots or voids!!!

Those paper-like layers and the exposed layers in it's edges are also part of it's strengths. It takes glue very well. Because it is paper-like fibers, it will suck up any glue and it is easy to get a bond as strong as the material itself. On a properly glued joint, a joint failure is usually outside the adhesion, not the adhesion itself. 

Because it is paperlike (like a phone book) it is strong, but can warp if not braced underneath it. Because it has paper-like fibers, it needs to be primed to seal the surface. If not sealed, or if you add too much moisture at one time it will swell!!! It is definitely not resistant to moisture on it's own (except for special "high moisture resistant" grades of MDF).

Because of it's linear layered strength, glued spline joints end up very well and are very strong.

As an aside, because it will "bend", we often use thin mdf stock to laminate together to create rounded custom mouldings and millworks.

Some consider it a material where there is lower quality, yet it is a material of choice in 1-3 and 3-6 million dollar homes or high-end commercial work... where very fine, quality finish or detail work is being displayed.

It is a wonderful interior building material if you understand it and work "with it." It has it's own purpose, place and time.

As there are different grades and types of Plywood, there are the same for MDF. There are moisture resistant grades of MDF. IMHO, the trade off on moisture resistant MDF is higher cost and that the added moisture resistance effects it's ability to soak in glue... So the result is not as strong of glue joints with the same types of glues. (RF Gluing works good for that.) Some grades of MDF are lighter in density and weight than others. I feel the trade off there is that the lighter weight is a tradeoff in strength. There is veneered MDF. Then there is MDO, that has MDF surfaces with a plywood core.... It is "stronger" and lighter, but it limits your tooling depth and then you have to hide/cover any exposed edges, because of those layers (like plywood). 

Melamine is more like you described. It has finish quality veneered skins than add strength, but the inside core (between the veneers) is like the "meat filler" between the skins that you described. It's filler (alone) is as strong (or weak) directionally x, y and z (length, width and thickness)... It has it's own strengths and weaknesses... purpose, time and place. But a more detailed description of melamine would be for another post or thread.

EDIT-- I know this seems like a long post. To some it's going to seem like a novel, with much too much detail (an engineer's reference)... But I feel if you understand the materials you are working with and how to work "with it," then the easier it is to be a success with it. That "logic" had set up my past apprentices for success...

You know this info should be posted in that "lost" and supposedly "sometime in the future" re-constructed forum "woodworking glossary" section... (yes?) LOL (I know the story on that...) Hopefully some of the jewels that people like "Mal" shares will be used to recreate that section.


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