Tuesday, 24 February 2015

Scroll saw box part 6

Hi all,
This project is taking longer than expected; I thought it would be done in three posts but I'm up to six and it might even take a couple more. The thing is, I don't want to rush it and miss out any vital information for those who might want to have a go at making a scroll saw box.

In this post I'm going to be concentrating on the inlay, for me, this is the most challenging part. It is easy to make a mistake when cutting an inlay and I'll show you one of mine later in this post.

The essential thing to do before cutting out the inlay for the project is to cut out some test pieces. I have already explained that if you just put one piece of wood on top of another and cut the design, the top piece will just drop straight through the bottom one because of the material taken out by the saw blade. That is the gap that is left by a saw blade, which is known as a kerf.

The way to get around this is to make the saw cut at and angle. In the rough drawing below you can see two pieces of wood from a side view. Imagine that the blade is cutting out a circle and you can see how, that when the circle is cut, the piece of walnut at the bottom can be removed and the piece of BB ply at the drop will drop down into the void cut in the walnut.
It's a bit like a stopper going into a wine bottle, but to be successful you need to get the angle spot on. If you cut it too shallow, the BB ply will drop too far into the hole in the walnut and, if you cut it with too sharp an angle, the BB ply will fail to go right into the walnut so that it finishes up flush.

Here is a photo of some test pieces that I cut to show how different cutting angles can make a difference.
It took four attempts to get it exactly right.
I started at 2.75 degrees but the BB ply only went a third of the way into the walnut, so I reduced the angle and tried again and then again. Eventually, with a setting of 2 degrees the ply wood fitted tightly into the walnut and that is exactly what I was after.

Now you may be asking how the angle is changed. Well, luckily for us, most scroll saws come with a table that will tilt all the way to 45 degrees, which makes the job quite easy. The tilting function was important when I purchased my scroll saw so I went a step further and bought an Excalibur, which allows the saw to be tilted instead of the table.

Above is a photo of the tilting mechanism on my Excalibur saw and the saw bent over to 45 degrees. I certainly wouldn't want to cut at that angle, but for 2 or 3 degrees it works great and I'm sure it gives me more control than would be the case if I was using a saw with a tilting table.

Okay, I hope that's explained how cutting at an angle allows us to saw a tightly fitting inlay. It is important to take ones time when cutting the inlay to avoid breaking a blade. Breaking a blade doesn't matter on normal scroll saw cuts, but when cutting at an angle it is almost impossible to change the blade and successfully get back to the cutting face without making the kerf wider, which will lead to a loose fitting inlay.

You also need to be aware that the thickness of the wood you are using and the thickness of the blade will alter the angle at which you need to cut. I made this mistake myself when doing the current box. I had a number 7 blade in the saw when I did the test pieces shown above, but then I changed it to the finest blade possible before I cut the rose inlay. The result was that the inlay only went three quarters of the way into the walnut.

At this point I was quite upset, I had put a bit of work into the lid and if I had to sling it in the bin it would be a waste of a nice piece of wood. So being the twit that I sometimes am, I decided  to rescue it by giving the inlay a light sanding all the way around so that it would fit. I really should have know better, because after five minutes vigorous work it still wouldn't fit. However, I'm British so I was about to give up and I kept on giving it a good thrashing with the sand paper until it jolly well did fit.

below is a photo of the inlay after spending about an hour sanding the hell out of it.
I've made it larger so that you can see the gaps. What a mess, I should have whacked it in the wheelie straight away. Ah well, we all learn by our mistakes. In my next post I will show you the replacement inlay that hopefully won't have any gaps big enough to drive a ski-doo through.
Meanwhile, don't forget, if you want to see some of my scroll saw or pyrography work you can visit the gallery on my webs site by clicking here.

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