'LGT' Construction Diary

[ShinOBIWAN]

Originally posted by Vikash
Put it this way, a sheet of birch ply is a fraction of the cost of the products in that link. I did their website about five years ago, and remember inquiring about it then, so you're better off discussing it with them to get an idea of cost.

I rang them up Vik and the price of that stuff is immense. They also said that regular tooling isn't effective and heavy duty machinery is needed for best results. They said to think of it more as a metal and treat the machinery needed to work it as such

Its really only made for smaller pieces rather than large baffles but after roughly explaining what I wanted they estimated that something could be fabricated for a cost of £400-500 and thats for each baffle including all machining done by them (which they strongly recommended). So between £1600-2000 for 4 finished mid/bass baffles!

Forget that!

[richie00boy]

£62 is actually not bad for 4 inch thick. When you consider the time, hassle and risk saved having to glue several sheets together, against the cost of the sheets as well, the saving is not worth worrying about IMO. 4 inch 8x4 must be one heavy beast though! Will they cut it to size?

[ShinOBIWAN]

Originally posted by richie00boy
£62 is actually not bad for 4 inch thick. When you consider the time, hassle and risk saved having to glue several sheets together, against the cost of the sheets as well, the saving is not worth worrying about IMO. 4 inch 8x4 must be one heavy beast though! Will they cut it to size?

That sixty two quid was for a 4ft x 2ft sheet(the largest they do in 4") so the equivalent 8ft x 4ft is £250.

They do cutting too and I had those two sheets done to size and these will eventually become the plinths for the speakers.

[ShinOBIWAN]

Tweaked the cabinet a little more without causing a major rework. MTM spacing now 5cm closer plus the mids and tweeter are time aligned on tweeter axis at 2.75m.

[MadMutt]

Firstly let me say, your projects are awe inspiring.

Now, regarding the finishing, I'm just wondering if maybe giving the baffles a coat of fibreglass resin might help seal and lock everything in place ?
Or even just a single coat of fibreglass.
Would basicly give a single solid surface to work with and any joint creep would be behind a 'wall' so to speak.

I've no idea if this would work, just throwing it out there....

Maybe marine grade paint could help.
Isn't that some sort of epoxy resin ?????
Maybe even the stuff they use for 'refurbished' kitchens.
Granit speakers, now thats a different look..

[Bob Barkto]

Wow, good find.
Nothing like that thick around here.
1-1/2" is special order and also the thickest stocked from any of the distributors.

Originally posted by ShinOBIWAN
Managed to find some 2" MDF from a local timber merchant called "Allen and Ore". It was interesting to learn that they can also special order upto 4" thick MDF in 2ft x 4ft sheets although they are expensive at just over £62 a sheet for the 4".
...

[Bob Barkto]

Shin,

The veneer won't eliminate it. I've tried it several times using various application methods.

It will slow the appearance somewhat. But moisture will get through eventually and cause the telegraphing.

The best results I've had were using 2-3 coats of clear epoxy as a primer. It is formulated for coating wood. It's much thinner and has better wetting/penetrating properties than automotive epoxy primers and is inherently much better at blocking moisture than the 2K automotive primers.

It can be topcoated without any sanding required with automotive primers/colors if done within the recoat window, usualy 12-24 hours.
After that you'll need to scuff sand for adhesion.

If you can get aluminum powder pigmented epoxy that is even better than the clear. It approaches 100% effectiveness at blocking moisture vapor.

Originally posted by ShinOBIWAN


If you look at the mid/tweeter baffle and closely at the angular sections you can make out the joints. Not a problem from say more than 1m and you had to move around to let the light catch it in a particular way otherwise you couldn't make it out.

I think taking the same approach as before but with the veneer will eliminate it.

[agent.5]

Originally posted by Bob Barkto
1-1/2" is special order and also the thickest stocked from any of the distributors.

[/B]

I found a local shop that have something like these in stock.

I was told that they are grey in color, lighter than regular mdf, but with same strength as regular mdf. $96 for a 8x4 sheet of 1-1/2" thickness

Is this price OK, almost 2x the price of two 3/4" sheet?

What is this grey, lighter mdf that the guy is selling me?

[Bob Barkto]

Probably LDF (Low Density Fiberboard).

It's lighter because it is less dense and there is a lessening of the physical properties compared to MDF. But probably not much of a concern for a speaker cabinet.

Color is not a good guide and can be practically discounted. Any variable in the production of a panel can account for changes in color. It does not inherently indicate the material properties of the panel, unless the manufacturer claims so.

[ShinOBIWAN]

Thanks for the suggestions chaps.

Bob, I do agree with you but also thought it prudent to point out that the expansion is really only a problem where the MDF has been put together on differing planes such as a joint where you've got the face of the MDF meeting up with the thickness - they expand at different rates.

The baffles have slices where all the joints roughly expand at the same rate because they're in the same plane and the only problem is the glue in the seam doesn't follow suit. The veneer will mostly eliminate that along with other treatments such as the high build primer.

Its good that you also mention the resins etc. because I treat most parts of the MDF with this:

http://www.decoratingdirect.co.uk/viewprod/b/BONWH/

Which I said this about sometime ago:

Its actually used for stabilising rotting wood and uses the moisture within the wood to actually form a chemical bond that locks the fibres in a resin cast that penetrates deep into the MDF. Once set its water proof and very tough, much tougher than untreated MDF, which also means I'd suggest you do all you sanding and detail work before applying this as it will cause you some extra work. Its excellent for applying spray finishes onto though as its almost like steel in its substrate toughness.