Greenie512

NOTE: if you have followed a link from another site to my “work in progress”, that wip may have been transfered to my other projects list as an old job - have a look thorough this page

Poor Mans Strads

See Troels Gravensens excellent site at http://www.troelsgravesen.dk for full details ....

NOTE: I did nave pics of the crossover here but I’ve removed them as I’m reconsidering whether to mount them internal or external. If I go internal I’ll break them down to 3 boards for easier placement in the restricted volume, local to each driver (if possible.). This will also necessitate some form of bracket to fix to the curved back!

Well how about this ... we found some seconds “soundboard” at my local plywood factory seconds outlet. This was some left overs from a Yacht builders order for 12 mm acoustic dampened ply, kerfed one side to assist bending in the hull.

So, the idea is 2 layers as per picture below. The kerfed side will be internal and I’ll fix the first skin to the skeleton and bond the second skin with a heavy layer of liquid nails. the idea being to fill the internal kerf voids with liquid nail “fill”.

This is my initial take on TG’s design, curves are based on 0.5m radius curves. Now all I have to do is manufacture a template?

First test looking good [TG’s original shaped rib] ..............

Trammel set up to cut the initial ellipses ...

Bottom is the base shape for all internal ribs, top one is the template for the top and bottoms which is large enough to take a rebate for the inner skin and make the box air tight. Then it’ll be flush routed absolutely flush with the inner skin. The outer skin will hide this rib.

Now this is a good Christmas day for me - a few hours in the shed before a blow-out lunch. So this is how I’m duplicating the ribs - routing to the pattern/template.

Can not annoy the neighbours for too long the router + dust extractor generate quite a volume. Not bad work though - hive got six out of ten internal ribs done.

Dry fit of first skeleton, a few joints need loosening. With a bit of trail and error I’ve found that 9° was the best angle to cut the verticals to match the rib curves. 

It may be way to hot in the shed to work but there’s no reason I can’t do a dry “strap-up” in the A/C’d lounge

The above show’s I’ll need to fix the front “flat” section first as it wants to bow out as shown above. The back panel is perfect.

Above - the panels are currently about 100 mm taller than they need to be, remember this unit has ports firing down so will be raised (somehow?) off the floor by 60-70 mm.

Japanese saws are the best, razor sharp ideal for deepening the joints.

Skeleton almost finished - just need to do top and bottom ribs

And finally! - tops and bottoms rebated for verticals. Side fillets just lightly clamped at top to get final effect. All we need to do now is align every bit and glue?