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MDF workbench top warping a bit

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Forum topic by Luke posted 04-29-2011 10:57 PM 2587 views 0 times favorited 9 replies Add to Favorites Watch
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Luke

289 posts in 2151 days


04-29-2011 10:57 PM

Topic tags/keywords: question

Hello All,
I am in the process of building my workbench, a few days ago. I built the bench around a 1 1/2” Solid core door and dropped a 3/4” MDF sacrificial top over it. When I cut it, It fit great, flush and flat, but now a few days later I am finding that the MDF is warping a bit causing it to stand proud of the bench apron.

I don’t really want to use screws to lay it down, hoping for a pure wooden surface incase of planes and bits.

Any suggestions on how to get the MDF to sit flush again?


9 replies so far

View Sarit's profile

Sarit

514 posts in 2604 days


#1 posted 04-29-2011 11:17 PM

You can use a 2” screw to secure the mdf from the bottom up. You’ll want the holes in the door to be just big enough so the screw threads don’t catch on it and allows you to pull the MDF down to the top. You can also counter sink the hole on the top side of the door, since screwing into MDF causes a little volcano to form around the screw.

MDF is usually fairly stable, are you sure its not the door shrinking?

I don’t know what your bench design is, but if you want to make the apron and top flush for clamping purposes, then it might be easier to build up a frame on top of the door, flush with the edges, and then cut the MDF to fit inside it (maybe with a small gap for expansion/contraction). The frame will protect the edges of the MDF and since its attached to the door, not the mdf, will stay flush with humidity changes.

View DrDirt's profile

DrDirt

4169 posts in 3207 days


#2 posted 04-29-2011 11:19 PM

I’ve never seen MDF move – Could it be that there was some out of level floor and now with the weight of the Door + MDF on it…the bench has shifted.
Have you laid a level/straight enge over it? – I’m wondering if the door is what changed…But see if you are just “pulling the MDF” down to a warped surface.

However – I have seen where people have screwed down the surface using countersunk brass screws. So if you hit one it would certainly dull a blade but shouldn’t cause much damage.

-- 'Political correctness is fascism pretending to be manners' ~George Carlin

View JasonWagner's profile

JasonWagner

527 posts in 2644 days


#3 posted 04-29-2011 11:20 PM

Is the bench in your garage or somewhere that is affected by moisture? I have never had MDF warp. I agree with Sarit that your door may be warping.

-- some day I hope to have enough clamps to need a clamp cart!

View Luke's profile

Luke

289 posts in 2151 days


#4 posted 04-29-2011 11:28 PM

my thoughts are that there were some tight fits in certain areas, and perhaps the bench was expanding and contracting causing the mdf to sit proud. In so cal, it was raining on easter and 50degrees, now it is almost 90

Warp may not be the best term to describe it, more so, it was flush a few days ago, now the edges in a few places are proud by maybe a 1/34” or so, just enough to notice its not flush.

View crank49's profile

crank49

3981 posts in 2435 days


#5 posted 04-30-2011 12:41 AM

My top is 3/16” hardboard over 1/2” MDF on top of 4 layers of 3/4” plywood. The plywood is all glued and screwed and the top two layers were held down by gravity and contained by the apron. It all adds up to 3 1/2” thick. My top sheet had a tendancy to get proud depending on weather or dust getting between layers. I coated the MDF with BLO and after it dried I used a little spray adhesive to hold the hardboard down and keep dust from getting between the layers. Now it seems to be much more stable.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View Luke's profile

Luke

289 posts in 2151 days


#6 posted 05-06-2011 01:32 AM

I pulled the 3/4” MDF off the top to see if the table had bowed. To my surprise the MDF top has a clear bow from end to end running the length of my bench, I’m not sure if it was the drastic temperature change we experienced going from Winter right into summer. I took the advice of Sarit, and screwed from the bottom up in order to pull the top down. Perhaps I didn’t notice it, but the bow is the length of a 4×8, and maybe it was bowed from leaning against the wall causing the middle to sag (Like Plywood does)

Oh well, I’ll beat it up, and someday replace it taking care to not stand the MDF on its side for a week.

View Tim Dahn's profile

Tim Dahn

1511 posts in 3029 days


#7 posted 05-06-2011 01:37 AM

Can you flip the mdf top over?

-- Good judgement comes from experience and experience comes from poor judgement.

View ajosephg's profile

ajosephg

1878 posts in 3025 days


#8 posted 05-06-2011 01:50 AM

Did you varnish one side and not the other?

-- Joe

View Luke's profile

Luke

289 posts in 2151 days


#9 posted 05-06-2011 01:59 AM

Tim – I cant flip it over because I have a integrated tail vice making the cut not a perfect rectangle.

Joe, no finish as of yet.

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