Woodworking advice for A75 case

[nmackie]

I have been building a pair of Pass/Thagard A75 amps for quite a while now. The project has progresssed to the point to where I am considering the construction of wooden cases for the amps. However I am a beginner at woodwork and I'd like to find a buddie or two with woodworking experience who can provide advice.

The amps (two monoblocks) are build on to two L shaped pieces of MFD which will be slid into wooden jackets and the cases completed with aluminium front and rear panels (in the process of being ordered). These pannels are 630mm high and 230mm wide and so the cases will be (roughly) high (630), narrow (230) and deep (830mm). I want to build in solid oak, to match the room the amps will be in.

My knowledge of woodworking is limited to reading the speaker building articles in audioXpress. I think/realise I will have to join two or more pieces of wood to get pieces wide enough for the panels but do not know how to go about it.

And beyond that I'm at a bit of a loss. I do not know what type of joints to use, or which types are within my capability. I realise that I should try to hide the end grain but do not know how to go about doing it. Even if I cannot build it myself and I find someone to build the cases for me I'd still like to know what to ask for and design the joints first.

If you have wookworking skills as well as audio ones I would welcome your suggestions as to how to build cases for my A75's, to a standard so that the cases on the outside match the quality of what is inside.

Regards,
Neil J Mackie.

[pinkmouse]

Hi Neil

Whereabouts are you? I have far too many woodworking tools and am just in Sarf Laahndahn, near Crystal Palace. If you can work out what you want, a rough drawing will do, I can advise and maybe come over sometime and give you a hand

[till]

I build everything with wood:

http://www.diyaudio.com/forums/showt...4640#post74640
http://www.diyaudio.com/forums/showt...952#post155952
http://www.diyaudio.com/forums/showt...593#post160593

The simple connection bewteen 2 parts of wood i made in case of the two amps shown is as following. All you need for this is a circular table saw.

[nmackie]

Thank to the above for their replies and pictures.

Till, those horns looks lovely. Thank you for your diagram showing how to join using a slot in both pieces with a wooden peg glued into the gap to join them (is my description correct?). This seems similar to the 'biscuit' method described in a number of audioXpress articles, for example 'Building the Thors' in the September 002 issue. However that article lists one of the tools as 'biscuit cutter' and from the illustration it looks like a hand held power tool which cuts a slot from above. Conversely a circular saw (if table mounted) cuts from below and cuts only the width of the saw.

Is your peg the width of your saw cut and if so, is that not rather thin?

Can you advise me on hiding the end grain? For the base I do not mind the end grain showing, it will be on the floor and will be less obvious. However at the top I would prefer to minimise the visual effect of any end grain. Can the edges of the sides and top be cut at 45 degrees and held together with a biscuit? Does such a joint require more experience and skill than I have (to get the edges straight and mating perfectly without any end grain showing)?

Does anyone know the availability of 'biscuits' in the UK, they might just be a US thing that have not reached European shores yet?

I'll try sketching out what I'm considering and post the result. Till then you can see the extent of my woodworking skills at
http://www.n.mackie.btinternet.co.uk...l#introduction

The wooden parts there were professionally cut, dead straight and so fitted well. I doubt if I'd be able to make cuts as good. The joints are also supported internally, being glued to a small piece of wood at each corner. For the A75 cases I want the insides of the case to be as clean as the outside, so no braces or metal brackets and screws, which is why I'm asking/thinking about biscuits or pegs to support the joints.

Regards,
Neil (J Mackie).

[till]

nmackie,

as i´m no native speaker i tried to describe as good as possible. I don´t know all the words. The little piece of wood is called in german "Feder" whats same as a spring, the slot is called "Nut". So this kind of connection is called "Verbindung mit Nut und eingelegter Feder". This piece is same size as the circular saws blade. The saw blade (300mm Diameter) is usualy 3.2 mm thick (carbide). So its perfect too use a piece of 3mm plywood. I use this connection often because its quick to build and easy to make in good quality. For this 45° solution "auf Gehrung" : its not so easy because pieces dont want to stay in position when you press it together. Whatever they write on the pot with glue: if you want a good and good looking connection you have to press pieces together, long time, very firmly. It is important to use good big fastening clamp with large pieces of wood between clamp and workpiece. I would use the solution with end grain (?) looking to left and right side.
example cd box:

[till]

example CD player

[Peter Daniel]

Very original idea with a CD player. How does it sound? And is the remote working from far?

[till]

How does it sound?

I have not much experience and no real good other CDPs to compare. I would say good.

And is the remote working from far?

Very far. No problem from the other room and 2 walls reflecting the signals.

Very original idea with a CD player.

Thanks!

[nmackie]

I sketeched an idea for a case - it should appear below.

It is what I consider the 'ideal' in terms of hiding the end grain, but while drawing it I think there are some drawbacks which I will describe.

The end grain of the base is on the left and right. To get the required dimension a number of short planks have to be joined edge to edge. The disadvantage of this is that, because of the joins, the base is weaker. The amp is heavy, I'm not sure if I can lift it off the bench, and the base will have to support all the weight and therefore is should be strong. So while it would be nice to have the end grain on the left and right of the base, so it gets hidden by the sides, I think the base will have to be one piece of wood with the end grain at the front and back in order to provide maximum strength.

The sides are made of three (or 4 depending on what width I can get) pieces, end grain top and bottom.

The top is shown with the end grain to the right and left, like the base. However, depending on the quality of the joins, it may be better to have a single piece with the end grain front and back. I'd also like to have the option of putting speakers on top of the amp case, so a certain amount of strength is needed, which again favours a single piece of wood.

The case is finished off front and back with aluminium panels which are fitted to the frame of the amp which slides into the case from the front or back.

I would welcome any comments and suggestions.

Regards,
Neil (J Mackie).

[pinkmouse]

Hi Neil

If you have no end grain visible your life gets a lot simpler

You can use veneer ply or mdf, which is much cheaper and stronger than oak, and is relatively easy to get, (Shadwells, down in Barking, comes to mind as a supplier). If the ends need finishing, because your metal front and back don't cover the woodwork, you can get matching iron on veneer in strips for just that purpose.

If you decide to go the solid wood method, making panels with biscuit joints is very straightforward, you just need to make sure you have loads of sash cramps for the glue up. Prepping the wood is not so straight forward tho, you need to make sure each piece has smooth, true, parallel sides, so you will need a good plane for that, and lots of time and practice if you have never planed hardwood before. Or an electric tabletop jointing planer!

You also need to make sure you have no crossgrain situations in your glue up, as the wood expands at differing rates along and across the grain, causing splits and shakes over time.

Another option for the top is to use a mitre lock joint, cut with a special router bit. This gives more glue area than just a biscuited mitre, and has the useful facility of being self aligning, and less likely to slip when clamped. see attached pic