I’m building a 19-inch rack for our music room…
In the first part of this story, I put together a design, and bought and prepared some lovely Oak that would be used to build a frame to hold the rack. Now it’s time to begin the assembly.
First of all, a quick recap. A 19-inch rack is basically a hollow cabinet that has rails running up the sides at the front and back, into which electronic equipment can be mounted. My design involves a wooden frame of upright pieces connected front-to-back and side-to-side by cross-pieces.
The front and back of the frame had to be open so that equipment can be inserted. I had the choice of leaving the sides open or covering them. I decided in the end to cover them using an oak hardboard recessed into the inside of the frame, so that the uprights and cross pieces are prominent. This is the same technique as I used for an earlier project, the Laundry Basket.
The technique will require some routing to cut a recess into the pieces into which the hardboard can be fixed. The recess needs to go around the inside of the frame but not be visible at the frames’ outside edges. This means that I can cut recesses right down the lengths of the cross pieces…
…but I must finish the routing the recesses before reaching the ends of the upright pieces.
Router bits are generally round, and so can’t cut nice square corners. I now need to finish these off with a chisel.
While I’m working with the chisel, I notice that I’ve been a bit careless with the router in one section. All it took was a slight jump or wobble and I’ve accidentally dug holes into the wood that I wanted to keep. I could probably get away with this, since the recess will be filled with hardboard, covering up the marks I’ve made, but there is a possibility that I’ll see the edges of these holes against the edge of the hardboard. It won’t take too long to patch up.
I decided to fill the holes using some of the wood shavings I had produced when I planed these pieces smooth. Wood shavings come off as long, flat sheets, like an ultra-thin veneer. So, I glued layers of shavings into the holes to fill them up. I used a small spring clamp to pack them tight as I build up the layers.
When the holes were full and the glue fully dry, I used a chisel to get rid of the excess.
I ended up with a fairly convincing repair. As mentioned, the recessed area made by the router will be filled with hardboard. What’s important for me is the repair gives a nice straight edge along the top of the recess, and the top surface of the wood (which will be visible) looks very good.
The critical dimensions for the 19-inch rack unit are set by the lengths of the rack rails and their distance apart. I knew it would be worth putting the effort into making sure all pieces are the right lengths and that my frame would end up nice and square. So, I planned to do some end-planing to square-off each strip of wood and to make sure they all pieces were equal.
For example, here is a cross-piece up close. The Try Square shows how the saw cut has created a slightly curved end. This end will butt up to the side of one of the upright pieces. If I attempt to make this joint with the cross piece like this, I will either have a gap, or a slight angle to the frame which will mess up the shape.
Planing the end of a piece of wood is very tricky. Firstly, because the end grain is tough and prone to splitting, and secondly because ends are typically quite small and hard to line up with a plane. The solution is to create a Jig that can secure the wood against a fixed right-angle, then make use of a long straight edge to keep the plane perpendicular to the end of that wood.
(I learned this following technique from a video, to which I have unfortunately lost the link! If you were the creator of that video then thank you very much!)
First, find a smooth, flat board with a straight edge. (Here I’ve chosen a piece of veneered board, and positioned it with the straight edge at the bottom of the picture.) Then find a piece of scrap hardwood that is thicker than the piece you want to plane, and lay this at 90 degrees to the straight edge. (Here I’ve got a piece of Ash that I had previously used to practice with when making my TV Table.)
Clamp the scrap hardwood block tightly down onto the board and then onto the workbench so that neither the board nor the scrap block will move while you’re working. You will be planing towards the end of this scrap wood and you want it to be exactly flush with the straight edge. I usually achieve this by making it initially overlap by a fraction of a millimetre, then using the plane to knock off the end of the scrap until it is flush.
You can see by these pictures I now have a flat edge with a block that sits flush and perpendicular to it. I can now place the wood I want to plane up against this scrap block, and scrape away at its end until it is nice and square.
The scrap block serves two purposes here; first to keep the worked wood square so that its end is planed at 90 degrees to its side, and second to provide support to the edge-corner of the wood to stop it from splintering or fraying. If you plane the end of a piece of wood on its own, the blade will most likely catch the last bit of grain at the corner and split it rather than cutting it off neatly. This will give a ragged corner and could damage all down the length of the wood you want to keep. The scrap block stops the wood from being able to split and helps give a good clean cut all the way across the end.
Here’s that close-up of the cross piece again, this time with a picture showing the result of the end-planing.
End-planing can also correct measurement errors. I’m pretty good at measuring and sawing wood – I reckon I can saw wood to the nearest millimetre. However, there are times when that doesn’t look good enough. For example, here are four cross-pieces that all should be the same lengths.
With a bit of end-planing I can get them much closer.
Now I can use biscuit joints and sash clamps to create the frame. I have decided to assemble the frame by making the large rectangles for each side first. These will then be joined together by the front and back pieces. So, one by one, the sides get clamped and weighted down to ensure they are assembled as flat and square as possible.
With the sides assembled it’s time for a little more planing. I knew when preparing the wood that, I would want these side rectangles to be flat and smooth on both sides. This would mean getting all the pieces to have exactly the same thickness. Being this exact before assembly would be difficult. An easier approach, I realised, would be to line up the joints so they’re nice and flush on one side and then use the plane after assembly to smooth out differences on the other side.
To my advantage, the exact thickness of these side frames would not be important – they could be 19, 20, 21mm thick without affecting the rack itself – what would matter here is that they look good and equal, and the joints look smooth. So a quick run over with the plane gives me nice even wood, and smooth and flush joints.
One last detail I put in into the sides was to round off the outside edges. Planing wood tends to leave very sharp corners that don’t actually feel very nice to touch. I first found this when making the Book Stand; I got a better result there when I took off the sharp edges.
I could round off the edges by sanding or chiselling, but that would take a while and it risked an uneven finish over such long sections. Instead I used the router with a Chamfer Bit, set to take just a slight strip off the edge.
I used some scrap to test this and set up the bit, then ran it around the inside of the frame and down the outsides of the upright pieces.
A quick run round with various grades of sandpaper then turned the flat chamfer into a curve and left a lovely smooth finish to the edges.
That’s enough for this post. Next time I shall complete the frame’s assembly then maybe think about adding some wheels.