Woodworking advice for A75 case

[nmackie]

in first position maple or alternative pear tree

You made a very valid point in your last post Till. The amplifier will get very hot. I have already ruined one set of mains transformers during testing when they overheated.

I did not show it on my earlier diagram of the case, but the top of the case will be open, covered in something like a speaker grille. This opening is above the heatsinks which are like large square tubes with the fins on the inside. At the bottom of the tubes are fans blowing air up through them to keep the 96 output devices cool. The front and rear aluminium panels have an array of holes in them to let the air in.

So I am convinced, and if you suggest Maple I will take your suggestion.

you can´t use a piece of wood like it comes. You need to cut it into rods and glue them together.

Could you explain this a bit more please? I can understand how a large width of wood could warp of not completely dry. However what effect does cutting the wood into narrower strips and gluing it together again have. I do not see how it can help reduce the tendency to warp. I appeciate the effort involved in your posts and I would very much appreciate an explanation of this point.

You will see I have been able to use quotes (I hope). Is there a print option to print the thread out in a compact format?

Regards,
Neil (J Mackie).

[pinkmouse]

Originally posted by nmackie
You will see I have been able to use quotes (I hope). Is there a print option to print the thread out in a compact form?

Yup, just look at the bottom of the thread and you will see a button marked "printer friendly" or somesuch

I think what till means is that you should make the boards for the sides out of planks with alternating grain curvature, (see pic below), this will reduce the amount of cupping as the wood dries out.

I didn't realise how hot this amp would run- I thought the A75 was a class AB amp! Wrong again

I am veering back to the idea of man made boards, they will be much more stable under those conditions - did you check out the website, and spot the edging veneer I was talking about?

[pinkmouse]

Oops, forgot the pic

[faustian bargin]

Originally posted by nmackie


....Could you explain this a bit more please? I can understand how a large width of wood could warp of not completely dry. However what effect does cutting the wood into narrower strips and gluing it together again have. I do not see how it can help reduce the tendency to warp. I appeciate the effort involved in your posts and I would very much appreciate an explanation of this point.

....

if i'm not mistaken, the warp resistance in this instance will mostly come from the glue. it adds internal structural reinforcement to the panel of wood. all those glue joints will tend to prevent the strips of wood from either bending or shearing. BTW this is the principle behind Glu-Lam beams, and is the reason a glulam outperforms a solid wood beam of the same dimensional profile.

**edit: just to clarify, it's not *exactly* the same as a glulam, because the beam is resisting bending in a different direction than the panel. but it's the same sort of principle.

[faustian bargin]

pinkmouse: structurally that works very well, but aesthetically you end up with something a bit different than a solid-looking panel of wood...which may or may not be what is desired.

another strategy to employ, in terms of grain appearance, is bookmatching, but that's probably a little out of the realm of feasibility unless you've got the right tools.

[till]

What i meant is exactly what pinkmouse´s picture illustrates. If you do the glueing very good (high pressure, good tools neccessary....) it is possible to match the visible struckture of the rods so that its not so easy to see were the one part ends and the other begins.

example for (mecanicaly) very stressed high quality part of wood: neck of bass guitar, made of 5,7,9 pieces of wood.
http://www.marleaux-bass.de/bilder/bild1.jpg

this one shoud be maple, padouk, wenge

browse the site http://www.marleaux-bass.de/

for examples of good woodwork!
(i worked with gerald more than ten years ago)

[faustian bargin]

man i just love all the wood samples on this page! so nice.

[icceman]

You can use quarter-sawn wood to reduce warping and twisting.
http://www.frankmiller.com/Quartered_Rift.htm
http://www.stuarts.net/Stuwritup/qua...uartersawn.htm
http://online.sfsu.edu/~janets/wood.htm

You can also try to add some insulation between the wood and the amp.

I'm using PTFE foam tape to insulate the wooden faceplate from the amp's chassis (which is about 39C).

[nmackie]

As it has been some days since the last post I thought I'd just wrap-up the thread.

Thanks to everyone for their posts. It has been most informative for me and it has helped develop my ideas about what I want. My aluminium end panels have been made and so I'm ready to start specifying the cases.

I'm a member of the London DIY HiFi Circle which has monthly meetings in a London pub. At the last one I meet another member who has a kitchen and furniture making business and all the relevant power tools. Hopefully I will be able to get him to make the cases to my specification which I will produce using all the information and advice given above.

Thanks to all
Neil (J Mackie).