DIY rack for line mixer / pt. 1, design and construction

Test fitting. Looks okay to go!

Test fitting. Looks okay to go!

I got my mitts on this old 4 channel Monacor mixer, that was presumably broken. It is rack mounted and inputs, outputs and power connector stick out straight from the back side. I take it’s not been used in a rack, because power plug was broken and there was quite a bit of wear in the back panel. I opened it up, and sure enough, the 3-pin power supply input was fixed many times, and finally ruined with a soldering iron. Connector was stuck to the pins, but I managed to pry it off without breaking anything. Mixer  uses dual-rail power supply and inputs were labeled -12, 0 and +12 V DC. Luckily I found the original power supply in a random pile of fax machines, telephones and other debris. After checking the power lines with multimeter and verifying the voltages, I soldered three short heavy gauge  wires directly to mixer’s input pins (in lack of proper connector). Then I connected them to a plastic screw terminal (we call them ‘sugar cubes’ in Finland, dunno if there’s a better word in english :P ). It worked perfectly! I got signal in all channels and even the retro-cool VU meters were flawless. With electronics side of things in order, it’s time to begin this project!

Design

I won’t be using this anywhere but in my home studio, so I decided to use hardwood, make intarsia decorations with veneer and finally buff it up with shellac and a french polishing. If I was to design a rack for live use and/or transportation, it would be totally different. Think plywood, metal reinforcements and a lid! But this works for me, besides I need to practice intarsia and polishing. So I began designing the layout in 1:1 scale with pen and paper. Dotted line in the drawing is a power supply, which I’ll screw on the other end piece

Layout in 1:1 scale, measures in millimeters

Layout in 1:1 scale, measures in millimeters

Making end boards

I had a nice board of walnut, just the right size for the two end pieces. First I straightened the board with hand plane, and then marked pieces with sharp pencil. Sawing gave me bit of a headache, because my electric saw is a piece of crap, and its blade just doesn’t want to travel straight. I have a decent back-saw, but the ‘backbone’ of it is attached permanently to blade, thus preventing sawing cuts that are deeper than blade’s depth. I had to use coarse-tooth builder’s saw, that’s hardly ideal for precise cuts. It also caused some splintering, but luckily on hidden edges. Next week I’ll get a fancy laser guided circular saw though, so no more this sort of crap :D

After sawing the end pieces, I clamped them together and used rasp, hand plane and sander to iron out coarse edges and to make the pieces identical. Here is the mixer screwed on to the pieces.

Checking the alignment of end pieces

Checking the alignment of end pieces

Intarsia and top board

When the end pieces were of the correct size, I moved on to designing and making the top board and intarsia. This was mainly inside-the-house job, which was a delight, because there were over 9000 flies in my workshop. I really need a fly-zapper.

Designing the intarsia pattern with my helpful cat Lemmy.

Designing the intarsia pattern with my helpful cat Lemmy.

I didn’t want to waste my precious hardwood onto something that I’ll cover with veneer anyway, so I cut the top board from 12 mm MDF. Good thing to remember if using MDF is, that it doesn’t like moisture at all! It will swell and get all clumpy very easily. Well, I bet mixers don’t like water either.

I’ve got small stock of different veneers on hand, and I used quite a few in my design: Mahogany, walnut, birch, cherry and beech. Generally it’s not so great idea to mix so many different varieties in one design, but what the heck, I think they looked nice together. I sketched few patterns in my notebook and then drew the final design onto the MDF board with an angle ruler. I used only straight cuts, because I think i’m not quite up to making curvy lines just yet. Then I measured and marked the shapes onto veneer sheets, and clamped them firmly in between a scrap board and a straight MDF board. I used cheap hobby knife for cutting the veneer. I got very straight cuts by supporting the knife’s edge to the MDF board and cutting the veneer in multiple light passes. The veneer will surely rip and splinter if you try to cut it with single stroke.

I clamped veneer in between MDF boards and cut it with sharp hobby knife, using top board as a ruler

I clamped veneer in between MDF boards and cut it with sharp hobby knife, using top board as a ruler

When I had all the necessary pieces of veneer cut out, I test-fitted them, and then assembled the final sheet with low-adhesive masking tape:

I used masking tape to assemble the veneer sheet

I used masking tape to assemble the veneer sheet. This will be the top side.

Next I applied PVCa adhesive glue (just a fancy name for your regular wood glue) to the seams in other side of the sheet with my finger. Just a hint is needed, don’t soak your veneers in glue! Then I left it to dry for half an hour, and removed the masking tape. This step is needed, because you can’t leave the masking tape on when you glue the sheet to the board, or the glue in the tape will seep into the veneer, most likely ruining the surface. The thin film of glue will hold the pieces together, while pressing veneer sheet to the board with clamps. I applied same glue to MDF board and aligned it with veneer. Then I compressed the whole sandwich in between plywood and a board with my DIY vise (made out of plywood,2 by 4′s and an old car jack).

Applying glue to the seams

Applying glue to the seams

Glueing the veneer to the MDF board. DIY all the way, even the vise :D

Glueing the veneer to the MDF board. DIY all the way, even the vise :D

Straight from the press

Straight from the press

Damn! Too much glue again. Well, it's better than too little, right?

Damn! Too much glue again. Well, it’s better than too little, right?

As seen in previous photo, I used way too much glue. It’s dripping from every crevice and even through the walnut ply on one spot! It wasn’t such a disaster I thought it would be, I got it pretty clean when sanding.

Sanding with my ultra high tech 14,90 € sander

Sanding with my ultra high tech 14,90 € sander

This little sander isn’t so bad.. Actually it has awesome price/quality ratio, and dust removal pipe even fits my vacuum cleaner! I sanded the finished board with 120 and then 240 grit Mirka sanding mesh. It’s far superior to sanding paper, because it doesn’t clog and lasts longer.

Construction

Here i’m test-fitting all the parts without a glue. It’s together with 5mm countersink torx-screws. I try to use only torxes, they are the best! Far better than philips, or gods have mercy for me even saying it, slot-headed screws. Remember to widen the screw holes with countersink drillbit, or you’ll get in trouble. Oh, and remember to drill those screw holes, or you’ll get in even bigger trouble! Boards tend to split easily, if you try to screw a screw (:D) without proper pilot hole. It should be of slightly smaller radius than the screw.

Test fitting. Looks okay to go!

Test fitting. Looks okay to go!

There’s also a bottom rim, that i’ve told nothing about. It’s just a simple MDF board with birch veneer on top. Rather than being a straight board, there’s a 45 degree angle on the top edge hidden inside, so the mixer fits in there. On the afterthought, I should have recessed the top board between end pieces as well. Now it looks somewhat detached. Two reasons why I didn’t:  A) There’s some splintering on top of another end piece that would look ugly, and B) all the extra work that’s involved in recessing. Damn, why didn’t I do it anyway? I should have, now it bugs me for the rest eternity. Well, it’s still doable, but with even more work now that it’s glued and all.

The pieces fit nicely, so I added glue in between and let dry. Then I removed the overlapping part of top board with rasp and sander.

Rasp is a very nice tool, although a little brutal.

Rasp is a very nice tool, although a little brutal.

The boards are now sanded flush

The boards are now sanded flush

I’ve written this all morning day. Now I have some things to build, so I’ll get to finishing, polishing and all that in separate post!

 

 

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