LS50 like front baffle from mdf ?

[00940]

I'm wondering how to best emulate the curved baffle of the KEF LS50 (read: in the easiest way) with mdf.

My current plan is the following: use an horizontal sander and suspend the baffle a bit above it, with 4 wires about 50cm long attached from the baffle's corners to a frame centered above the sander. Then pushing down on the baffle slowly round it. It might be a good idea to start a bit high, then lower the baffle down if needed.

Any better idea ?

 

[DPH]

Do as much of the work as you can on the table saw/band saw to get the curve close. 5-10 degree tilt will get you very far, especially if you make a 45 degree sled (thin v block to lay the speaker on)

I half wonder if you glued sandpaper to a very flat (large diameter) bowl and essentially lap the baffle might not give you a good profile.

But I'm spitballing.

 

[daanve]

By sanding away much of the MDF top layer you remove the harder part and the inner part of today's MDF is very soft.
A better idea I think is to give the vertical sides of the enclosure the right profile, and glew multiple layers of the thinnest available MDF (3 mm) which you can easily bend in the profile of the enclosure.
Repeat this procedure until you reach the right baffle thickness.
Another advantage is that a multiple thin layer MDF will have a higher density (around 800 instead of some 600 of single sheet MDF of comparable thickness).

 

[00940]

It's quite true for "common" mdf. I plan on using Valchromat, which is colored mdf. In my experience, it is much more consistent (almost no difference between the outside and the inside) and quite a bit stronger than common mdf. Its density is about 800 on its own.

 

[DPH]

You can also readily harden the cut surface with thinned out glue (50:50 or so), or shellac/sanding sealer before starting your workup for paint.

 

[00940]

If the whole face is sanded a bit, no need for paint. Just some mineral oil (as suggested by Troels Gravesen who uses the stuff a lot).

edit: of course for common mdf, yes a primer would be mandatory.

 

[mediumroast]

For quickly removing material, I would suggest a hand planer/block plane/bench plane or even electric hand planer.

 

[00940]

Good point on the planer. I'd be afraid of taking away too much too fast with an electric one though.

@DPH: I thought more about the bowl solution but I'd really need a bowl almost 1m wide to have a reasonable slope. Not that common. :/

 

[DPH]

Planing MDF would be a trip! Definitely going to dull blades quickly with all the glue.

If you're going to leave the MDF au naturel, then 50:50 polyurethane and mineral spirits will deeply penetrate and lock the surface without leaving a hugely plasticky film (works better than shellac). I was assuming you meant to paint it black like the KEF.

It was a hair-brained idea on the bowl (more like a rounded plate, but anyhow, not practical).

 

[nigelwright7557]

I always use 18mm plywood for my builds.
I have used chip board in the past but it tends to crumble a bit if your not careful.
Also I tend to use my speakers on a mobile disco so they can get wet sometimes going into and out of gigs. Chip board swells if it gets wet.

 

[00940]

@DPH: actually Troels' advice on his website for faceting mdf is chisel then planer then sanding. Valchromat makes big claim on their resin being less hard on tools than the glue commonly used for mdf. I guess I'll see if that's true (I've only worked on it with power tools until now). Anyway, the most difficult part is a nice smooth finish curve.

I also considered building a gig to use a router on a moving axis but that seems more work than needed (similar to this: YouTube ).

@Nigel: we're speaking very small 5 to 6l (internal) speakers here, with a 240*190mm front baffle. They will stay safely at home on a desk.

 

[sippy]

I wont put my chisels or hand planes anywhere near MDF.
I'd use a hand held belt sander and blast the bulk off (take your time) with 40grit, then go down to 250 for a finish ready for sealing.
Wear a mask.