A contractor would like us to build a 32"x80" mdf interior door that will hang from rolling barn door type hardware. It will have a traditional stile and rail look with a chevron looking feild. These details will be machined into mdf on our cnc with a v-groove bit and have a painted finish.What is the best way to build up the mdf to maintain flatness? 2 layers of 3/4" or 3 layers of 1/2" and machined to a final thickness of 1 3/8" or ??? The panel area is also 1 3/8" thick.

Never done it but any balanced option, and machined both sides, should be fine. We have had some major issues with thick MDF that is heavily machined on only one face potato chipping. Having your glue lines telegraphing through the edge would be the only real concern which you could always v notch the edges and glue in a face piece on the edges if that was a concern.

P.S. if its a rolling door I'd talk him into just leaving it 1 1/2". No need to meet the 1 3/8" residential standard. That way you can leave the much more easily painted face of the MDF intact as opposed to machining that face off and having to deal with the raw core.

Any time you remove material from a face of MDF, you have a mess. The material will bow and finishing is a difficult task. The surface will be so fuzzy, that it will take some real skills so it doesn't end up looking like a corn cob.

Agreed Rich but shops by the boat load are running gobs of deeply machined simulated raised panel doors. I agree with you about dealing with the core. Running double refined is much easier to finish than straight MDF but its still nice when you can leave as much of the face intact as possible.

The issues we had with potato chip were 5x9 sheets of 1 1/8 that were 3D machined across their entire face (one entire face completely removed) and deeply carved.

OP states what sounds like the panel face and the rail/stile face will be flush so if 1 1/2" is acceptable the bulk of the door faces would not be machined.

Crazy as it sounds If 1 3/8" is a must and 3/8" MDF isnt available I'd plow down a sheet of 1/2" knocking .0625 off each face and sandwich it between two sheets of 1/2" just to keep the outer faces easier to finish.

Tell him that you will only make it out of a solid piece of 1.5 sheet. Laminating mdf is a fool’s errand. Laminating & milling mdf is not rational.

We have made over 1000 simulated flat and raised panel cabinet doors from double refined mdf and have never had an issue. I understand why we should have issues but we don't. I assumed laminating 2 or 3 layers to achieve the final thickness would be more desirable than using a single 1.5" thick piece of mdf. I suppose if a single piece of 1.5" is straight to start with my chances might be good that it will stay that way?

Making a definitive wood door out of anything other than wood is like building a kite out of MDF. Yes, it can be done, and be done so it works. But why? Wood is what you are copying, and readily available. The technology to make that door out of wood is established very well by over a century of making.

You are contemplating making a simulacrum - a simulation of an otherwise unremarkable object. How about some pants made of insect screen?

My observation is that MDF is a great material for a very limited list of uses. My opinion is that it is not appropriate to use it as you propose. Wood is plentiful. Respect the craft.

If you or your customer have fallen under the marketing spell (warp, rot, split, twist, crack, cup, bend) of those that compete against wood doors, please wake up. Wood is superior to plastic, steel, and even MDF. Use the proven methods to work with wood.

As you can see there are no proven methods with MDF.

Price is the main issue. We can build that paint grade door out of mdf for one third the cost of solid wood. The contractor is a knowledgeable guy and he specified mdf so mdf it is. As I stated, we have made many mdf cabinet doors with no issue so I don't have a problem using it on this door if it is done correctly.

Hi Gary,

I am with David on this, MDF has its place
and we use it sometimes for door panels.
We never use it for stiles or rails.
Just out of curiosity how do you address the hinge screw holding problem on the door edges? I seems to me the weight of the MDF doors and the poor screw holding
habit of the MDF edges are a problem.

Good point but to be clear I did mention this door will hang from rolling barn door hardware so there are no hinges. Also it is not typical stile and rail construction. It is just a thick mdf slab that is machined on the cnc to give it a stile and rail look. If this were a hinged door I would agree with you and David and would have turned it down. I suppose for a paint grade door one could glue solid wood on the edge of the hinge side stile for the hinge screws to bite into I wouldn't want to trust it. Also as mentioned a glue line would probably show up. Our cabinet doors are hinged with doweled cup hinges so screw holding is not an issue.

We build 1000’s of MDF interior doors, machine what ever design you want on the cnc using 1/2 mdf, then glue up with a 3/8 or 1/2 piece of mdf in the middle, dado the 2 edges for a piece of solid wood for fastening hinges and handles.
The home builders loved them because it was easy to make doors whatever height you wanted.
Like someone else mentioned , there is a few people on this site who think they are the door experts and anything not done the way they think it should be done is stupid. Just because you did that in the 60’s doesn’t mean you need to do that now. There are tons of new products and materials available these days, maybe try something different. Live on the edge.

You should be able to find 1 3/8 mdf it just might not be double refined. Laminating two peices of mdf is just asking for trouble (not to mention the extra work involved) Anytime you can remove a joint will remove any chance of separation (ie a failure in your product) in the future. I would use 1 1/2 and run it through wide belt if needed to get it down to 1 3/8 if needed, just remove equal parts from both sides. The problem with the screws holding can be easily taken a care of by thru bolting which will never fail and is very common on doors. As far as using mdf it is a very stable product , and is quite acceptable in a number of applications. It is specified by many Arch. firms. Exterior grade MDF comes in many different thicknesses and will not swell, and routes profiles very well, it is just a bit pricey.

David; I heard that the Navy is considering building submarines out of MDF. Should we be concerned ? I sure it would be MUCH CHEAPER and isn't that the only standard worth considering ? When you are holding a hammer ( CNC) everything looks like a nail
( MDF doors).

Most of the cabinetmakers on Woodweb are Custom guys, working the premium residential or commercial markets. Also they should be getting direction from designers/contractors/owners what is needed. It would be rare to have 'cheapest' as the spec for cabinet doors.

As such, the cabinetmaker does not specify, unless it is just a cheap project. Building a cabinet door out of MDF is irresponsible cabinetmaking. It is driving the price so low that the door can't compete with wood.

Auto Insurance commercials are all over my TV. They are all screaming they can beat what you are paying now. And they can save you 15% or more. By giving you less protection. That is the key - they don't do the same thing for less - they all know what the other guy is charging. They do it by giving you less. You play the dumb consumer and give them a call. They will take you to State Minimum faster than a jackrabbit.

Building MDF doors is the bottom side of cabinetmaking. The part that will sell out the craft for a few pennies, never to go up-market again.

Work the top of the market! Show off your skills, give them more than they bargained for.

David,
I would agree with everything you said, but what happens if one of your high end builders has a client with a lower budget?
There is no way they can afford your fancier not expensive work, do you tell the builder your not interested because you don’t work with MDF?
I can never do that, I always try to accommodate the clients, if they want MDF, they can have MDF. To me any work is better than no work.
Just my 2 cents.

I have turned down many an MDF job. I simply will not work with the stuff beyond using it for veneer substrate. I tried to make my peace with the stuff, and have to some extent. But I won't use it for millwork of any kind.

If you walk into a Ferrari dealership, but find out you can't afford anything they have on the floor, are they going to come up with a lesser car just so they get the sale? No. But they will hold the door for you as you walk out.

Like good stand-up, you want to leave them wanting more. Several of the folks that wanted MDF said they hoped to be able to afford us in the future.

We did make the door I originally asked about out of thick mdf. Turned out great. Price was an issue on that door but for our cabinet doors it usually is not. We give the customer options for mdf or five piece doors and they almost always pick mdf. We don't care what they choose we just present the options. They love the clean look of painted mdf shaker/mission style doors. It's not for everyone but it works for us.