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substituting MDF for plywood in shop furniture

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Forum topic by leftcoaster posted 05-05-2017 03:46 PM 1533 views 0 times favorited 14 replies Add to Favorites Watch
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leftcoaster

258 posts in 1296 days


05-05-2017 03:46 PM

Hi all,

I am building various pieces of shop furniture—some carts for cutoffs and some tool stands.

Most of the plans I have call for 3/4” ply. I happen to have some 3/4” MDF lying around. Aesthetics aside, am I going to be sorry I used this instead?

I know I need some kind of different screw for MDF joints and I can throw in some biscuits if you all think that will help.

I basically just want to use this stuff up. If there’s a better application for MDF in the shop, I’d be glad for suggestions. I’m in a new space, so building everything from scratch.

Thanks for your insights and suggestions.


14 replies so far

View nkawtg's profile

nkawtg

288 posts in 1671 days


#1 posted 05-05-2017 03:56 PM

As long as your MDF isn’t required to take loads or stresses I’d say go for it.
What’s the worst that could happen?

MDF makes great jigs too.

View papadan's profile

papadan

3584 posts in 3788 days


#2 posted 05-05-2017 04:09 PM

Yeah, what he said! LOL Non structural is OK for MDF, otherwise it makes nice bases for jigs and sleds.

View leftcoaster's profile

leftcoaster

258 posts in 1296 days


#3 posted 05-05-2017 04:56 PM

So the “load” here is a small parts cut off bin. I guess I could just rebuild it if disaster strikes. Something tells me that I will never move it despite the casters.

View Desert_Woodworker's profile

Desert_Woodworker

1833 posts in 1634 days


#4 posted 05-05-2017 05:11 PM

Pre drill and countersink the screw head (1.5 -2” screws)

-- Desert_Woodworker

View Rich's profile

Rich

4564 posts in 1009 days


#5 posted 05-05-2017 05:25 PM

I find MDF to be structurally sound. I built shelving units for my (huge) laundry room to expand pantry space. It’s all MDF, and the shelves are loaded with hundreds of pounds of canned goods, etc. It’s rock solid.

A couple of MDF tips I learned along the way, some are true for plywood too:

- It can’t get wet. You can paint, poly, whatever, and it’ll protect the surface from spills, but if the core gets wet, it’s toast.

- Screws hold great when screwed into the surface, but screws will not hold going into the edge. You can try using adhesive or something to lock them in tight, but it’s not worth the hassle. Even though pocket screws go into the surface of the board being joined, the core of the board that has the pocket hole won’t be strong enough, and they’ll rip through. Only use nails to tack something to keep it from sliding, and use a nail gun, or pre-drill.

- It will sag. Watch the width of boards that will have a load applied. You can reinforce it though.

Pretty much all of these issues are avoided with careful planning. The main downside is that it creates a mess when you mill it. Picture a sack of brown flour exploding in your shop.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

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leftcoaster

258 posts in 1296 days


#6 posted 05-05-2017 06:22 PM

@Rich, so the guidance is glue + nailgun brads for butt joints? Biscuits would help too, no?

BTW Rich, I like that cabinet. Desert_woodworker, yours too!

View Desert_Woodworker's profile

Desert_Woodworker

1833 posts in 1634 days


#7 posted 05-05-2017 07:01 PM

This method also applies to melamine….
no glue, no nails, no biscuits needed

-- Desert_Woodworker

View Loren's profile

Loren

10477 posts in 4067 days


#8 posted 05-05-2017 07:22 PM

Confirmat screws are the best for MDF but they
require special drills for the pilot holes.

Here’s another option: https://www.mcfeelys.com/spax-mdf-hardwood-clear-zinc-trim-head-screws-6-x-1-1-2-in-qty-315.html?gclid=CKqu44G82dMCFUlXDQodyWYHTQ

I like biscuits in MDF but obviously clamping is
required. Dowels are good too. With screws
there’s a pretty delicate tolerance range with
the shank size. Deep threads are required to
bite and hole in MDF edge but if the hole is
too small the edge will split.

View Rich's profile

Rich

4564 posts in 1009 days


#9 posted 05-05-2017 07:27 PM


@Rich, so the guidance is glue + nailgun brads for butt joints? Biscuits would help too, no?

BTW Rich, I like that cabinet. Desert_woodworker, yours too!

- leftcoaster

It’s difficult to say exactly without seeing the plans for what you’re building. If you zoom in on the shelving in the photo, you can see that the shelves are supported on each side. Those support boards are glued and screwed to the vertical pieces and the shelf just rests on them. I countersunk the screws and used plugs to hide the hole. I used 18 ga brads to tack the shelves down so they don’t move around. If you tried to do that with biscuits without any other support, the joint will likely fail under load because the MDF core is weak and the shelf will split.

On some shop items, like the mortiser stand below (I needed to turn the head around to get the extra height to mortise 5 to 6 inch door stiles), you can see that I used poplar for the sides of the platform, since it’s screwed into the edge, and I needed real wood grain for the screw to hold. It mattered here too, since the base isn’t just supporting the vertical load of the mortiser, but with the head turned around it is keeping it from falling forward. The clamps weren’t necessary, just playing it safe when I first built it. The stacks of MDF allow a large piece to fit there when removed. Kind of a hack, but it works.

Plywood has many of these weaknesses, maybe just not as bad. I wouldn’t have trusted using plywood instead of poplar for that stand if I had built it with plywood. I’d still have used the poplar.

Like nkawtg said, what’s to lose? Worst case is you wind up with a bunch of ruined MDF you were trying to use up anyway. Just don’t trust any valuable tools on it until you test it out.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View 000's profile

000

2859 posts in 1319 days


#10 posted 05-05-2017 07:28 PM

I’m not a fan of edge screwing mdf. Glue and nails, and use a dado whenever possible.
Make bottoms run through so the bottom will carry any weight.

Whenever I cut 45 deg bevels on the edge of hardwood,
I save the little drop off to use to reinforce corners on mdf, whenever I can.

If there are going to be hinges (piano type) I add a wood strip to the edge for screws.

View CharlesA's profile

CharlesA

3383 posts in 2217 days


#11 posted 05-05-2017 08:03 PM

I find pocket holes work dang well with MDF because if avoids the issues named with butt joints. I spend as little time as possible making shop furniture—things that get the job done but nothing more. I use both plywood and MDF. I don’t particularly using MDF, but I do for some things.

-- "Man is the only animal which devours his own, for I can apply no milder term to the general prey of the rich on the poor." ~Thomas Jefferson

View Desert_Woodworker's profile

Desert_Woodworker

1833 posts in 1634 days


#12 posted 05-05-2017 09:07 PM



Confirmat screws are the best for MDF but they
require special drills for the pilot holes.

Here s another option: https://www.mcfeelys.com/spax-mdf-hardwood-clear-zinc-trim-head-screws-6-x-1-1-2-in-qty-315.html?gclid=CKqu44G82dMCFUlXDQodyWYHTQ

I like biscuits in MDF but obviously clamping is
required. Dowels are good too. With screws
there s a pretty delicate tolerance range with
the shank size. Deep threads are required to
bite and hole in MDF edge but if the hole is
too small the edge will split.

- Loren


Thse are the type of screws that I use- works great

-- Desert_Woodworker

View Rich's profile

Rich

4564 posts in 1009 days


#13 posted 05-05-2017 09:27 PM

I find that screws with a type 17 point self-tap into MDF beautifully. I drill a full pilot hole and countersink the surface board, and the screws go right into the board I’m screwing the piece to.

-- Knowledge is not skill. Knowledge plus ten thousand times is skill. -- Shinichi Suzuki

View Desert_Woodworker's profile

Desert_Woodworker

1833 posts in 1634 days


#14 posted 05-05-2017 10:09 PM



I find that screws with a type 17 point self-tap into MDF beautifully. I drill a full pilot hole and countersink the surface board, and the screws go right into the board I m screwing the piece to.

- RichTaylor


Yes these are what I get from my supplier.

-- Desert_Woodworker

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