OM 01 Project - Back Bracing

 

The back has 4 braces glued to give it strength and also a slightly curved profile. The braces have been cut from quarter sawn spruce, so that the grain runs vertically in cross section, to give the greatest resistance against bending.

The glue face of each brace is cambered to between 1.8 and 3mm, using a plane. I used a couple of panel pins and a flexible batten to mark out the curve. A chamfer is cut into each end of each brace - this will be refined later, but helps to make sure you glue it in the right way up at this stage!

The back is marked out to show the position of each brace, being careful to make sure they are at right angles to the centreline.

And then the centre reinforcing strip is scored down each side of each brace, with a sharp craft knife, and the surplus removed with a chisel, being careful to get a nice tight fit between the reinfoircing strip and each brace.

Then the braces are glued in. I did it in two phases as I didn't have enough clamps to do it all at once. That also meant I had a bit more space to work in. It's hard to get in to clean up the squeezed out glue but worth persevering, as it's a much neater finish if you can get it all off!

I left all of that to cure for a few hours and then repeated for the remaining two braces.

That all feels a bit stronger now. But looks a bit ugly.

I protected the back with some card and then planed the braces down to size and with an arched profile. Then I used the belt sander to add in a nicer chamfer at the end of each brace.....

... before hand sanding down to the final shape. I protected the reinforcing strip with tape so I didn't change the profile of that at all.

I'm really pleased with the end result and it's great to have the first "component" finished.

OM 01 Project - Every Cloud has a Silver Lining - the new Back and Sides

If you have been following this sorry tale, you'll recall that I spectacularly trashed the original American Black Walnut back wood in the planer/thicknesser. When I came to order some more wood to start again, a) the walnut was out of stock and b) it was somewhat expensive!

So I started looking at alternative woods. Mahogany is the "go to" wood for beginners as it is relatively cheap and easy to work. It just looked a bit ordinary for my liking.

I came across a wood called Zebrano, which is really distinctive (it's not also known as Zebra Wood for nothing!); apparenty fairly good to work and also was about half the price of the walnut. When I looked around, high end makes like Lowden use it so I figured it must be OK.

I decided to take up the service that was offered to machine sand the back and sides down to the required thicknesses. It was £20, which didn't seem unreasonable to avoid any chance of repeating my previous thicknessing disaster!

Anyway, I ordered some of that and it arrived yesterday. As you can see from the photo, it is definitely more distinctive than mahogany! I'm really pleased with it. As described in a previous blog entry, I planed matching straight edges using the shooting board and then glued up using the set up below. 

The moment of truth and the joint is good!

I sanded the joint flush and then cut the body blank out using the bandsaw again.

I now have 2 guitar shaped objects!

To make the centre reinforcing strip, I cut a 16mm wide cedar strip from the top board offcuts. It's oriented so that the grain will run across the back joint and strengthen it. Then glued on and, after it dried, sanded it to a pleasing shape 😀.

Back to work tomorrow, so some thinking time now before starting on the bracing.

OM 01 Project - Soundhole and Rosette

I was going to do a fairly basic ornamentation, with a couple of black/white stripy bits around the soundhole, but then came across some nice real wood rosettes on the Touchstone Tonewoods website, which I thought would look a bit more special with the cedar top. 

While I was ordering that, I bought a selection of purfling strips as well, to see which one would look nicest for the back joint. I'm amazed how relatively cheap these are for the detail in them (this lot came to less than £25, including the rosette). I guess it's a bit like making a stick of rock - once you've got it all set up, you can cut thousands of lengths in one go.

The two halves of the soundboard were unclamped and then both sides sanded to get rid of glue marking etc; also to select the best side for the outside. Then I marked the centerline along the joint and used the half template to mark the outline. 

Following a tip off the internet, I coated the surface in shellac to protect it and also to help prevent "tear-out" of fibres when I rout out for the rosette and soundhole. Then marked the position of the centre of the soundhole and also the various points where the channel and the soundhole needs to be cut.

I had a couple of abortive attempts now to prepare for circle cutting. First I made an adaptor to mount a craft knife in the Dremel circle guide; the idea being to cut the fibres before routing and end up with a cleaner cut. 

There were two problems with that. Firstly, the craft knife blade was flexing too much, so not giving an accurate cut, and secondly, the adjuster on the circle guide is so coarse that I was struggling to get an accurate diameter set. Fortunately, both sides of the wood were equally good, so I could start again on the other side! (That is also why there are 2 centre holes in the later photos, as the template was drawn in a very slightly different location.)

After much deep thought, I resisted buying the precision circle cutting jig for £150 and came up with this solution instead - a piece of scrap polycarbonate shaped and fitted to the bottom of the Dremel attachment, that I could drill the various different centre holes in. Cost - £0 Accuracy - not as good as a proper precision  jig but almost there. I think any inaccuracy was more about my lack of precision in setting it up than anything else.

It was easy as pie to use - I drilled a 3mm hole in the soundboard and building board and matching 3mm holes in the jig and then just took it nice and slowly, taking shallow passes. I routed the inner and outer channels first, then took the middle parts out in 2 passes.

The inner cut should have been about 0.5mm bigger diameter. Doesn't sound like much, and isn't TOO noticeable, but it's a discernible gap. I'll have a go at filling that with sanding dust and glue or superglue. All part of the learning curve!

I glued in the rosette; and weighted it down well. Once dried, I added a bit of glue / sanding dust mix, then sanded it flush. There is still a little work to do on that gap but I think it will be OK.

Cutting out for the soundhole was easier; just one location to set up and then gradually increase the depth of cut by about 1mm each time.

The final task for the soundboard plate was to cut it to about 5mm oversize using a fine blade on the bandsaw and, Wow!, I have a vaguely guitar shaped piece of wood.

OM 01 Project - Let's start again - Preparing and Glueing the Soundboard

After the disastrous attempt at thicknessing the back, I took a much more careful approach with the soundboard. This is made from Western Red Cedar and comes rough sawn as photo below. The markings are as delivered - just to show it is guitar sized! Again, this was delivered at about 5mm thick and needs to be taken down to about 3mm.

The soundboard comes in 2 "book matched" pieces (i.e. mirror images) and needs to be glued together down the centreline.

Using the thicknesser, taking nice small amounts off each half to keep them the same thickness, this really shows the lovely cedar grain. I was careful not to go too thin!!

Using the half template I could find the ideal line for the centre joint and marked it out so that the joint line was parallel as possible to the grain direction. Then I carefully cut it out on the bandsaw.

The joint now needs to be planed absolutely perpendicular and straight on both boards. To do this you use a "shooting board", which is a posh name for 2 flat pieces of timber. I used some scrap contiboard and ply that I had and set it out as below and clamped to the WorkMate.

Using a freshly sharpened plane, you can then run it along it's flat side so that it remains accurately perpendicular. Taking nice thin shavings off each time, the joint was soon straight, as can be seen in the picture below. The "acid test" is to hold the joint together against a window and see if any light comes through the joint anywhere. I had to go back two or three times before it was flat enough to pass this test.

When glueing the joint, you need to keep a horizontal pressure on. The following method worked well. 

You put a thin batten (I used about 6mm) below the centre joint and then a row of nails down each side to restrain the board edges. The idea is that, when the batten is removed and the joint clamped flat against the board, the distance between the nails is fractionally too small, so applies a constant pressure to hold the joint together.

Having set it up, I put some cling film each side of the joint to prevent it sticking, then applied the glue; rubbed the 2 edges together to spread evenly; put the boards in the jig on the batten; withdrew the batten and then clamped up using some scrap ply to spread the load and a slightly curved clamping beam, so it can be clamped at each end but applies pressure along the whole joint.

I left it overnight to set and was really pleased with the result. When It's sanded back, I think the joint will be barely visible.

To procrastinate for a while before I have to start cutting into my lovely new top for the decorative inlays around the soundhole etc, I cut the various braces for the backs of the soundboard and back from a piece of quarter sawn spruce.