Build an accoustic guitar: Day 10

Day 10 the mould is sanded down and what I have to do is drill the holes for the stop blocks and attach the two sides of the guitar mould together.

Sanded guitar mould

What I need to do is form the holes for the stop blocks. The stop blocks will be used later to raise the body of the guitar so the edges can be worked on because the bottom of the guitar has a taper which has to be formed with the sides above the mould. There will be another set of stop blocks but these cant be set until the base of the guitar has been shaped. The stop blocks themselves are 18 mm x 18 mm softwood blocks 28 mm long with a 12 mm dowel glued into them which will be used to anchor it into the mould. It is very important to have all the stop blocks at the same level (and square) because they will be supporting the whole of the underside of the body and all need to be in contact with the guitar. I managed to get hold of some 12 mm dowel but couldnt get a 12 mm drill bit. the closest I could get was a 13 mm drill bit but even with a deep hole the difference in diameter between the dowel and the hole meant that it would not sit in the hole at right angles to the material with the hole in.

12 mm dowel in 13 mm hole

Whilst I couldnt find a 12 mm wood drill bit I did have an old 13 mm drill bit which was incredibly blunt, dont know why I kept it but Iam glad I did now. I sharpened the drill bit at the shoulder with a round file and re filed the point so it was sharp also. I filed the edges of the drill bit to reduce it from 13 mm to 12 mm. Both sides had to be filed / reduced by the same ammount.

Filing the drill bit

The result was that the 13 mm drill bit on the left was reduced to 12 mm. The bit is shown alongside a virgin 13 mm drill bit to show how much it has been reduced by.

Comparrison of filed and unfiled drill bit

The result was a tight hole that the 12 mm drill bit fitted snuggly into.

12 mm dowel in 12 mm hole

I now have to make sure that any hole I drill in the mould is at right angles to the surface of the timber being drilled. To do this I have decided to make a jig. A hole drilled at 90 degrees will guide the drill bit into anything being drilled into ensuring the hole is at 90 degrees. I tried a number of ways to drill the hole in the jig itself guiding it in with a square beside the drill bit guiding it in with a square behind the drill bit but nothing seemed to work. In desperation I drilled a number of holes in a piece of timber checked each 1 for square and actually had one hole which was square. I marked this with marker pen and made sure the hole went all the way through.

90 degree angle freehand hole drilling jig

Close up of hole drilling jig

Next task was to mark a line around the softwood timbers 25 mm from the edge of the mould. Initially I tried to mark it using a tape but I was actually getting 24 mm 25 mm and 26 mm - not good enough. I drilled a 6 mm hole through a piece of softwood timber, pushed a pencil through it and then screwed another piece of softwood to it at right angles in a position which ment when it was placed against the bottom edge a line was marked 25 mm in from the edge of the mould. I think the pictures explain it better.

25mm marking jig

Marking jig being used

Now I can use my 90 degree drilling rig to drill the 12 mm holes.

90 degree freehand drilling jig in use

PROBLEM !!!!!!!!!! the drill bit would only go into the timber by 10 mm and then it hit the nails placed to anchor the softwood spacers.

hole drilling aborted because we have hit a nail.

There was only one thing for it the nails had to be removed in the locations where the holes were being drilled.

Nails being lifted with a chisel

Nails lifted with a hammer

The holes were drilled to a depth of 28 mm at each location (6 equally spaced on each half) then all I had to do was join the two halves together. I mentioned in earlier posts that the two halves were not flush so I decided to use wood filler to fill the gap between the two halves. I ended up using Cuprinol ultimate wood filler wich is sandable 45 minutes after application. It is a two part material (base and hardener) which are mixed together at a ratio of 1:1.

Cuprinol Ultimate wood filler

The filler was placed on the two ends.

Filler on two ends

The two ends were placed alongside each other screwed together and the filler allowed to harden. Again as detailed earlier there is a slight peak where the two halves meet this had to be sanded back to give good symmetry and a flush face to fix the internal blocks of the guitar against.