Bondo over MDF?

[mac]

I have some milling imperfections that need smoothing but don't want to lose the crisp cabinet edges. Anyone have any sanding/finishing tips to share?

[mac]

[jleaman]

If you use bondo then you will see the bondo if you put a clear finnish over top of that nice wood how about a clear varathane or something that maybe build it up to make it level..

[BillFitzmaurice]

Bondo is fine. If you want to spend 3 times as much you can get some high-performance wood filler that is actually bondo anyway. However, I'd lose those crisp edges. They look nice to the eye but they're hard on the ears as sharp boundaries accentuate edge diffraction, while rounded edges help alleviate it. It's also easier to veneer over soft edges that you can wrap around.

[RHosch]

IIRC, large chamfers alleviate edge diffraction more effectively than small radius round-overs. Though in this case, it looks like only the sides are chamfered so perhaps the argument can still be made for radiusing corners (of course, with a tweeter of limited vertical dispersion, the side edge diffraction will probably dominate the far-field response).

However, I've never seen published measurements of large chamfers with small radius round-overs on the 135-deg corners. Perhaps that combination yields better results than either alone?

[mac]

Alternate view that better shows top bevel.

[johnkramer]

if you want to keep the wood grain, then you're gonna have to just bear down and sand by hand.

Use a large wood sanding block and start from the course grains up through to finish grains. I'm sure you know the drill on sanding, go with the grain, the lighter the sand paper grain, the lighter the touch... careful to stay flat on the edges.

I'd recommend a belt sander if you know what you are doing, but those can also really take a gouge out of things if you're not careful.

The varathane idea also can work, but while the surface will be flat, you will still see the machine marks throught the clear coat.

[jewilson]

From your picture your cabinet looks to MDF. Besides using bondo you can mix up some yellow glue with fine particles of either the wood or MDF, then apply with putty knife. Of course what ever method you use will require a bund of sanding.

As Bill stated, you should round off the sharp edges since they will just cause diffraction. A belt sander can eat up material very fast, a random orbital sander is the way with a flat block with sand paper rapped around it is the to go.

[BillFitzmaurice]

In this case the lack of rounded edges wouldn't be critical at all with the shape of the cab being what it is. But they wouldn't hurt either, and it's easier to get a good looking cab with rounded edges than squared, as squared will show every imperfection.

[Jimmy154]

If it was me I would want to keep the sharp edges, but maybe mac doesn't. Looks better that's why you don't see cabinets like this with rounded edges.

I have limited experience, maybe these people know better. But I use wood putty for wood cause bondo is for metal, I think. Bondo has come unstuck when sanded very thin in a unique tapered application (you might not have the same application), maybe I did something wrong though (ie not cleam the surface well enough or it was starting to set). I stick with wood putty now. It's far easier, if you remember that it shrinks when it dries and bonds better to wood.

If you wanted to cover you whole speaker or a large surface, like a whole side or more, bondo is probalby better than wood putty.