Quick practical question. Curved MDF.

[MatthewRedStars]

Hi all,

I'm making some curved moulds for an artist... about 2000 mm long, 1000 mm wide, 250 mm thick and with around a 300 mm curve on the width (like a humpback bridge with the road surface as plaster). Doesn' really matter

One concave, one convex.

I'm going to screw 3mm MDF onto a framework to form the curve, pretty much a full sheet. It has to be removable.

How can I stiffen this without doing any curved work (the curves are being CNCd elsewhere and I'm assembling on site)? The client wants minimal sag.

I thought: smear some PU on some MDF strips and stick them down with tape, until cured. Stupid idea? Any better

Ta, Matthew

Edited for gramatical violence.

 

[Wildman]

fibreglass?

 

[MatthewRedStars]

I don't know anything about fibreglass and it needs to be done first week January. Is it an easy process?

 

[lurker]

I think you can buy sheet "pre-kerfed" to do exactly this.

The pros will be along on a moment

 

[MatthewRedStars]

Yeah, it's not the bending I'm worried about.... more that it may be a little drum like.

I'll do some tests!

 

[petermillard]

Presumably the curves form the sides of the structure; apologies if I have the wrong end of the stick bit I don't think I'd fancy gluing strips of MDF to the skin *then* bending them onto the curves. Is it too late to get them CNC'd with slots in for MDF 'ribs'? Alternatively, a central curve section (or two) between the sides (bolted onto M12 studding with spacers, maybe??) would support the skin(s).

Curious re the reason the skin needs to be removable, though.

Cheers, Pete

 

[MatthewRedStars]

I'll bend before gluing for sure. Just wanted to make the bended (and screwed down) sheet of 3mm a bit stiffer.

Its not so much that the curve needs to be removable. The convex one isn't an issue (the opening will be bigger than the finished piece), but on the concave one the finished piece in poured plaster will need to come out of a smaller hole that it went into (so to speak). So it all needs to be collapse-able.

edit - Id love to get a groove for the curved sheet but its a bit late. I'm late to this project.

 

[petertheeater]

Hi. Not sure if I totally understand but if you want the curved form to remain once removed from the frame structure I would suggest using 2 skins of the 3mm MDF glued between them. Once the glue is set you can unscrew from structure.

 

[MatthewRedStars]

Hi. Not sure if I totally understand but if you want the curved form to remain once removed from the frame structure I would suggest using 2 skins of the 3mm MDF glued between them. Once the glue is set you can unscrew from structure.

Cool, it doesnt have to be pretty so this might work well. I was just trying to save material but an extra sheet is only £10 ish I guess.

 

[andersonec]

If I have understood correctly then maybe you could laminate a few bits before gluing then they would not straighten and would be fairly strong.

Andy

 

[Dan j]

As you've only got two to do, laminating another sheet will probably be the quickest and cheapest option.
Or as you said gluing some reinforcing strips on.

Fibreglassing would do the job but unless you've already got the stuff, or are willing to buy more than you need to get a price saving, will surely be more expensive.
Also it can be messy and if you haven't used it before it'll be time consuming.

 

[MusicMan]

I made part of a film set from the pre-kerfed MDF once. Overall thickness about 10 mm, kerfs to about 7 mm. Worked very well and was strong. As suggested, you can glue thin MDF or ply onto it when curved to retain the shape.

B&Q supplied it then but I don't think they do now, but it can be ordered online from sheet timber suppliers.