Friday, March 5, 2010

More Shawms - reaming and turning

When I show these shawms to people, one question many ask is how the internal tapered hole was made. I tell them that I push in a tapered steel bar and turn it by hand round and round and round until it is done. This often leads to a short blank silence as though I am being deliberately obtuse, but here is my proof.

 I used the same two sizes of reamers from the first shawm making. Here is the larger one with a handle clamped on.  As I mentioned the first time around, the handle allows a lot more control and torque to be applied.

 And here it is in action, getting on toward the end of reaming.  When the reaming is complete, virtually the whole length of the reamer will have entered the hole, so there is still some work to do.

This thicker reamer is easier to use since it is stiffer and does not flex much.  The thinner reamer used to shape the narrow end of the bore tends to twist if I force it too much.  This time, I did the wide end shaping first, and then put in the narrow reamer on the end of an extension (sorry, no photos for this).

Here's the extended smaller reamer, and you can see the twist on the working part.  I just straighten it out in the vice and carry on - more carefully, for a while.

The essence of all this is that it is all pretty low tech.  The reamer material is just mild steel; no hardening is necessary.  I have honed the big one once, but the narrow one is still on its original sharpen from when I made it.

This particular shawn had the curved bore, and it was obvious from turning the narrow reamer that something unusual was happening inside.  In the best of worlds, there should be a seamless transition between the part reamed by the wide reamer and the narrow reamed part.  Because of the curved bore, this one had a bit of a step.  Again, nothing much to be done about it, but carry on and hope.

 Looking down the throat with the reaming complete. I used several grades of rasp to extend the bell's flare down the throat to produce a smooth transition.

You can see that it is a bit off-centre from the curved bore, and not quite circular, since getting an even rotation was a little difficult.

 After the reaming, the composite body workpiece went back on the lathe.

Here is a view looking into the bell, showing a circular packing piece held in place by friction with the inside of the bell, as a transition between the driven centre (not quite visible on the nut in the foreground).  This simple arrangement worked remarkably well and did not slip significantly while I was doing the finishing turning.

 Here is the workpiece with final depth cuts made all along the body.  This was actually quite an exciting part of the work, since the transition from a roughly shaped piece to a slinky, silky smooth result all happened in the space of less than an hour.  All of a sudden, the chrysalis was transformed into a butterfly.

 The "butterfly" stands on the right here with the original shawm in the centre, and with the workpiece for the second shawm on the left, which has been bored but no more.

To bore the second body, I just clamped it on the bench, put the long 6mm auger in an electric drill and just bored it by sighting along the length.  Whether by luck or skill, this produced a much straighter and centred bore than the first one.  Reaming was straightforward, and I was able to get a pretty good smooth taper all the way along the bore.

 Here is the second shawm glued up and back on the lathe, well advanced in final turning.

Just 30 minutes later, it looked like this.

I have to say, at this point, I was pretty well pleased with the look and feel of these.  So, here are a couple more gratuitous images of the turned bodies.

You can see some filler on the right hand one, dressing a spot where I had cut a little too vigorously during the rough shaping.

Since the timber was recovered building framing, there are several nail holes in both pieces, so there are actually spots of wood filler all over both of them. No-one has noticed or commented on this at all.

A worm's eye view of the first shawm, showing the internal shaping of the bell.

Next stage: doing the staples and reeds at the other end. Not so easy!

Thursday, March 4, 2010

More Shawms - long boring

Since I was making these shawms to be joined up as a single unit, the body pieces of wood were longer than in the first one, which had a midsection joint (see this old post).  The lathe bed was long enough, but I wanted to make some improvements to the long 6mm drill.

I had made a drill for lengthwise boring the first shawm by extending a 300mm auger with some steel rod.

This is the joint formed with some copper shim wrapped around the rod and soldered together.  It was strong enough, but required an oversized hole to enter the bore, which defeated quite a bit of the point of being able to make long bores.

This new joint was made by lapping the shafts for about 15mm and brazing them together (reclaimed my gas plant, ha ha), giving a substantially uniform joint (after grinding off the high spots).

 Here is the blank for one of the shawms, mounted in the lathe with the hollow centre.  The bed is long enough, but not too long. Notice that the drill guide and the workpiece are not far apart, and this probably contributed to the drilling problem to be described.

With my son Francis working the lathe's treadle again, I lead the drill into the end.  The boring started well enough, and the first 300mm was easy enough.  After that, things went a bit sour, with the drill seeming to present lots of friction and the shaft getting very warm.  I greased it with some candle wax, which made a bit of difference, but by no means not a complete solution.

Also, the drill became more difficult to withdraw to clean out dust, which rather suggested that there was a curve or kink in the bore, somehow.

Since parts of the bore needed opening up anyway, I ran in a 10mm reamer to widen the hole.  This reduced the drag on the 6mm rod for a while, but there was still this feeling of a curve or kink.  The bore should have been 560mm in length, but I gave up at about 450mm.

At this point, I wasn't sure that the workpiece was actually going to be usable, or how off-centre the bore had become.  I took a length of 3mm brazing rod, filed a flat on the end, and used it in an electric drill to extend the bore all the way through.  As you can see in the picture, the brazing rod has come through well off centre, but not so much to be unusable, so I carried on.

I finished the boring with an electric drill and some brute force. Sighting through the bore, there was a definite curve, deviating nearly 6mm from true.  Acoustically, I guessed/hoped that this would be tolerable, but the reaming would be interesting.

 Jumping ahead, here is the body and the bell being joined.  The body piece has been shaved down approximately with sideaxe and drawknife, centred on the eventual path of the bore.  I turned a tenon in the wide end to mate with a 30mm socket drilled in the end of the bell with a spade bit.

I tried holding these pieces together in a furniture cramp for gluing, but could not get the two pieces to sit squarely together reliably.  I could have made some supporting blocks or something, but this arrangement in the photo was easier to do, mostly. It  has the clamping force applied centrally, via the nylon cord running down through the bore to the weight. The force is only about 3kg-wt,  but it was enough.

I used a modern polyurethane glue (Gorilla Glue), which is plenty strong enough, with some space filling ability as well.

Let's leave it alone to set and come back in the morning...