Building Tips and Modifications

by Don Johnson

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Feed Spool
Instead of using a slot in the end of home-made spools with a mating aluminium blade in the rewind handle, I found an easy way to replicate the commercial hex drive hole. Before turning down the ends, I drilled one end and glued in a 6M hex cap head screw - one with about 20mm of thread, which had the same Allen key size as the commercial spool. After the glue was set, I turned down the ends to 10mm - which was the diameter of the screw cap head. Only one key is now needed for both types of spools. The screw was inserted before turning, as drilling and fitting afterwards could otherwise split the spigot.

Connecting Rod Ends
I found that appropriate sized rubber grommets were easy replacements for leather 'buffers'.

Tracker Bar Fixing
As I had used MDF for the support, I found that the woodscrews which permitted adjustment of the tracker bar position soon started to work loose. I decided to glue two M3 nuts to the underside of the support and use M3 screws to clamp the tracker bar instead. M3 captive nuts are better than ordinary nuts, as there is less chance of getting glue in the screw hole, although Vaseline on the screw used to hold the nut in position during gluing could prevent this.

Crankshaft Suggestions
Noel Maw has suggested using roll pins and Loctite to construct the crankshaft in place of silver-soldering or welding. If this approach is taken it opens up the option of using alternatives to the hardwood versions of the connecting rods, as it is possible to fit them to the crankshaft before assembly without their becoming damaged by heat. I used Rod End Bearings, usually used on air cylinders, on the crankshaft - which I kept at 6mm dia. I used the female type (RS Components Part No: 198-8951), which enabled me to use 6M screwed studding for the connecting rods (RS 530-321). The crankshaft ends were fixed with Loctite, and two nuts (and grommets) at the bellows ends enabled easy and fine adjustment of the bellows movement.

Using the alternative crankshaft construction also meant that I could use ball-race bearings on the crankshaft. I actually fitted four to the shaft, adding an extra support on the handle side of the first crank to reduce the load on the shaft fixings. These were shouldered bearings, as I like the idea that the shoulders keep them square (RS 540-283)*, and I screwed the two inner supports into position whilst a plain 6mm dia rod was threaded through the bearings to get the alignment correct. I used a turned brass drive bush to mate with the idler wheel -as suggested by Gordon Scorpio and I left the two roll pins from the middle web out until this and the bearings, rod ends and crank had been put into position.  (* I found these bearings to be much too flimsy, having very tiny rollers.  I would recommend RS 619-0014 they are much stronger, and a quarter of the price! - MW.)

I actually used tapered dowel pins for the middle web fixings, so that I could assemble and dis-assemble the crankshaft until everything was tested, but a couple of small split pins could probably serve the same function. Also, I chose the support positions with some care, so that - with the supports in position - the handle end of the crankshaft could be inserted through the bearing holes without fouling on the other support. The bearings were only pushed into their holes and glued into position at the very last moment. Inserting roll pins with the crankshaft in position may be tricky, but my tapered pins could just be tapped in and fixed with Loctite.

I appreciate that the use of bearings and rod ends may be 'over the top' compared with John's original, and perfectly functional, design, but as I currently have access to some of the components, and I figured that their cost is really irrelevant anyway in terms of the hours spent on the project, I felt that I could indulge myself with a bit of 'over-engineering'.

B flat and F Pipes
John's diagrams on page 15 show that both these pipes are mitred to have middle sections 8 inches long. If the B flat pipe 8 inch dimension is reduced to around 6.25 inches, the two pipe ends are no longer in line, and adjustment of the stoppers for tuning becomes easier.

One last point regarding these two pipes; I managed to make the tracker bar honeycomb the wrong way round so that the sets of pipes on the front panel had to be swapped from left to right, and vice-versa. This was so that the air tubes did not have to cross over (twit!).  If you do this, do not forget to reverse the two largest pipes as well - swapping the mitring measurements - or, like me, you will have an even more fiddly job getting the air tubes on!

Pressure Box Seal
In place of a leather seal on the inside of the box, an oil seal (RS 211-8721) can be used to stop air leaking around the take-up spool shaft. This has to be fitted on the outside of the box, into the box wall, so an extra bearing plate needs to be fixed to the inside of the box for the shaft to run in - removing any load from the seal itself. I actually used two more of the 6mm stepped bearings mentioned above, fitted into the plate mentioned, and another on the other side of the box. The plates were glued into position after checking alignment of the spool.

Idler Wheel
I again used 6mm steel rod for the idler wheel shaft - tapping the handle end for a 3M screw. Another grommet was fitted in a hole in a small metal plate attached to the outside of the organ, and a screw and washer used to stop it passing through the grommet, but leaving it able to move slightly. A washer and collar at the other side of the organ held the shaft in position on that side. Would you believe it? I then fitted yet another bearing into the Idler wheel, and used Loctite to hold it in the correct position relative to the take up spool reel.

The picture shows some details of the items mentioned in the above text.

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