Please note that I tried to break this question up into three relevant sections, separated by the large headers

Here's what happened to the cabinet

I was moving an empty wood file cabinet down some stairs; I goofed, which caused the back casters to get ripped out of the bottom of the wood part of the cabinet. As a result, on the bottom face, and part of the back edge on the cabinet were damaged. I'll need some wood filler.

Here's how the cabinet & casters look.

Here's my plan

The Resources I have

I'm able to clamp a board along the edge to keep it straight. I also have all kinds of glue, I was able to recover some parts of the MDF that came loose (I have sawdust, I have access to scrap paper (for paper pulp), I have similar veneer, I have similar stain, and I have a few other relevant tools for the job.

Planned Approach

  • Fixing the MDF: I'm planning on mixing a glue/sawdust/wood-filler/mdf/sawdust mixture up, clamping the board in place, applying the glue, letting the glue dry, removing the clamps and board, and then sanding it down.

  • Fixing the edge: If it looks good; I won't veneer it over. However, if it's bad, I'll sand it all down, and then apply new veneer. After the veneer's applied, I'll finish it.

  • Reapplying the casters: For this step, I'll just put them further towards the front slightly, maybe an inch or two depending on what I need. This will be done to ensure the casters are secured.

Clarification on the question & Answers I'd like

Clarification My main question is with regards in the wood filler used. The bottom panel of the cabinet is maybe 3/4" thick, and of that 3/4" maybe 1/8" or 1/16" is affected by the missing mdf. I want it to be smooth when I remove the clamped board, so that minimal wood filler sticks to it. I.E., when I remove the board I don't want to take any MDF with it.

Answers I'd like

Is there a specific kind of filler that would set well? If so, how much sawdust do I use?

Thank you friends!

up vote 3 down vote accepted

Fixing the MDF: I'm planning on mixing a glue/sawdust/wood-filler/mdf/sawdust mixture up, clamping the board in place, applying the glue, letting the glue dry, removing the clamps and board, and then sanding it down.

This will likely work fine as far as making a cohesive fill that's strong enough. I've repaired small defects in MDF and hardboard in much this way myself.

For MDF I would generally use a mix of PVA glue and MDF sawing dust (I keep a small amount in a jar for precisely this purpose). As a rule this filler tends to be perfectly adequate, in fact what often happens is the fill ends up harder and denser than the surrounding material :-)

I think there are two important tips here that will help ensure a good result:

  • Lightly dampen the surfaces of the MDF prior to the fill going on.
  • Protect the face of the clamped-on board from the filler.

You can dampen with just water, but dilute glue is better. Depending on the thickness of your glue you might dilute it 25-50%, aiming for a consistency a bit thinner than single cream (but you don't have to be too accurate about this). Paint or dab on just enough to dampen the surface before applying the filler.

For the board that will be clamped in place, it must be protected from the glue or the filler will stick to it just as well as, if not better, than it does to the MDF! Two good ways to do this are to wax it well or to apply some sticky tape. Packing tape is great for this type of thing if you have any.

Now after filling...... if this were not veneered there's a decent chance that the fill will look good enough after a light sanding that you'd be happy to leave it as-is (using white PVA at least, the yellow form will make the fill noticeably darker). Because it's veneered though I expect it will stand out like a sore thumb so I think you're going to want to veneer, if a good aesthetically pleasing result is important. But note that if you'll be veneering the fill must be flush with the original surface of the MDF, not flush with the veneered surface.

Alternative approach
This would be to avoid having to fill. Without a picture of the damage it's hard to know if this would be appropriate but I just thought of it so wanted to throw it out there.

You could forget about filling and just chamfer the bottom edge of the MDF panel, removing material until the bottom edge is uniformly straight. From normal viewing angles you won't be able to see the chamfer (probably wouldn't matter anyway) and you can be sure it'll give a neat, clean edge where there's some uncertainty with the filler approach.

If you go this route it would be worth doing the same to the opposite side's bottom edge. In addition to having them match visually a chamfered edge on MDF is less prone to damage so you'll help it stand up to future use.

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