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Bending MDF


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#1 R-P

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Posted 02 May 2018 - 15:48

Lazy, so didn't search...

 

What's the best way to bend MDF?

 

For a (non-audio-related) project* I finally wanted to try this and have read about it many times (years ago before having a plunge- and circlesaw). If it works well, I will start using it for subwoofer enclosures as well ;)

 

I made cuts with my plunge saw every centimeter and ~6mm deep in ~8mm MDF.

 

I feel like 2mm MDF left is still hard to bend and probably breaks before getting to the desired angle.

So should I cut deeper so only 1mm MDF is left?

Or make more cuts? I tried two cuts per cm but then the remaining MDF between the cuts disintegrates (right most cut second pic). The blade is probably 2.5 to 3mm wide.

 

And for the next step: what do I use once it DOES bend? Regular white woodglue? Will impregnating it with woodglue make it bendier? Or use water? (I think this is the biggest no-no as far as MDF is concerned, but no clue if it might actually be benificial here...)

 

 

 

* It is the roof (alkove) of a 50cm long camper that I am making for a wedding to throw the envelopes with money in so the bride and groom can e.g. go to Australia (with their daughter and a camper, hence the 'theme')

I was planning to make an internal light barrier (is "lightslot" the correct term?) that will activate e.g. the headlights when interrupted (by someone dropping in an envelope). Any other ideas welcomed.

 

J78oXacl.jpg3Ek3zGIl.jpg


Edited by R-P, 02 May 2018 - 16:06.

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#2 Karl MCC

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Posted 02 May 2018 - 17:55

What radius are you trying to achieve?

Cascamite works well with mdf, particularly for curves. Hard as a nail once set and no bounce back.
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#3 R-P

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Posted 02 May 2018 - 18:45

The model is 46cm long. The quarter circle on top of the campervan (front side of alcove if that's the word used in English) has a diameter radius of about 5cm. The rear (top and bottom of camper) should be an even sharper corner, but doesn't necessarily have to be rounded MDF. I could do that with two straight boards and just round it a little with sandpaper.

 

The side-view of the camper is actually two boards screwed together for the cutting of the shape. The loose board with the cuts goes inbetween to become the curved roof of the camper. Here's the cartboard mock-up with the MDF on top that should eventually be curved like the cartboard roof.

 

p9LPoAjl.jpg


Edited by R-P, 02 May 2018 - 18:53.

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#4 Rug Doctor

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Posted 02 May 2018 - 19:05

Can you not buy pre slotted bendy MDF over there?? 

 

You don’t really want the edges of the MDF visible either,  so a good idea to put a lip 6mm on the inside of either side and then fix the mdf to that.. I’d even put some pieces the right width in place in a few strong areas and clamp it up to get the shape you want,  then insert the MDF with a friction fit and then nip it all up a touch more. No exposed MDF edges and if your precise with the lining up should make for a seamless join from side to top. 



#5 Karl MCC

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Posted 02 May 2018 - 19:14

50mm radius might be too tight for bendy mdf (which is what you're making, and the stuff which Rug Doctor is referring too). The saw kerfs won't allow it to curve before the ridges hit each other. Even moreso in 8mm material. I would remove the ridges in the section being radiused, essentially leaving 2mm thickness, and see how you get on. Or try it in 6mm material - that would probably work. I've got some in the workshop so can look tomorrow.

Ps - is it the front curve which you're struggling with?
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#6 Karl MCC

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Posted 02 May 2018 - 19:24

Also, 10mm between kerfs is too much.
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#7 Mannparry

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Posted 02 May 2018 - 20:09

When Lee made the boxes for my van he cut strips of mdf in a wedge shape joined them together to form a tight curve and used filler to fill the gaps.


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#8 mx0range

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Posted 03 May 2018 - 06:59

would it not be a whole lot easier to just make that bit from a solid bit of wood?


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#9 R-P

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Posted 03 May 2018 - 07:20

I only learned there is such a thing as bendy MDF when googling "bending MDF" yesterday :raz:

 

As usual, I want to make it from stuff lying around (=zero cost). I started with the idea of using coated MDF (that gets thrown away at Ikea and I have several 8mm thick ~60x100cm boards from), but I figured the plastic coating would be too stiff and bend even less.

 

I did read about speakerbuilding projects where they DID put the MDF on wet grass to get it to soak up moisture and then bend it in shape and let it dry with e.g. rubber bands in the desired shape.

 

I think I will try this on the strip that I already made, and if it doesn't work, try one cut per 7.5mm instead of one cut per 10mm and also go for the 1mm remaining thickness. This was just a quick try and my accuracy left a lot to be desired.

 

And yes, it is the front curve that seemed like the biggest challenge, so that's what I started with. Many older campers have a V shape, so I can always resort to that if all else fails. But I love the learning process!

 

@ Rug: I am not completely sure what you mean with the edges of the MDF (not) being visible, but the plan was to sand the whole thing down once assembled and glued together to get a seamless finish all over before painting it.

The friction fit is what I planned to do, but I hadn't thought about it in too much detail. The idea of clamping the sides with distance-holders to the correcct width is a good one!


Edited by R-P, 03 May 2018 - 09:55.

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#10 Bass_Junkie83

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Posted 03 May 2018 - 07:45

What you are doing looks right, as you have seen you can buy bendy mdf pre-cut.  But from your image it looks to me like the radius you are trying to bend to is too tight.  

 

For what you are doing I would use 2mm flexibly plywood. Cut out two panels, and glue and panel pin it to the side pieces to get the shape .  Then cover the whole surface in a layer of wood glue and add the second layer on top and pin it in the same way.  Us some ccamps/weights to keep the two pieces together until the glue dries.  The two sheets bonded together will form a laminate and if you were to cut through the panel pins and remove it from the sides it will keep its shape.  


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#11 markwalker84

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Posted 03 May 2018 - 07:48

Similar to suggested above, could you glue a few chunks of mdf into a block and shape it with band saw / jigsaw / sander etc.

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#12 R-P

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Posted 15 May 2018 - 12:20

Endproduct. Not perfect, but fun to try something new. May try it again for a sub but will use a less sharp radius.

The roof is the piece I already posted a pic from earlier. The headlights and hood is also one piece of MDF that I cut every 7mm.

Do note the detail of th door being on the 'wrong' side for us, but the correct side for Australia (or GB if they don't get enough envelopes)

 

giphy.gif


Edited by R-P, 15 May 2018 - 13:49.

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