Final stages

So today I finished fine tuning all the keys to within 1 Hertz of their fundamental frequencies.  As for the harmonics, I got lucky with one or two of the seventeen which show strong resonance at four times the fundamental but for most these harmonics were not correct.  Most were flatter than they should be so the keys don't sound so creamy sweet as they might have done had I got this right.  Next time I make a test key I will try different cuts with the router.  I will still take 6mm of wood out between the 25% lines, but my second cut will be inside the 40% lines in the first instance, and probably a little deeper than 12mm to get the fundamental down.  Hopefully by leaving wider shelfves from the first cut the harmonic frequencies will be more in play.... Watch this space!

Today I also fitted the catch on the mouth of the 'crocadile' so the rails don't raise by accident in transport.  Then I sanded down any rough corners and brushed the whole instrument over with a first coat of clear varnish.

I also made plugs to the tubes which I cut this morning from a plastic kitchen cutting board using a circle cutter fitted to my drill.  The plugs each had a small washer and bolt system fitted through them so I can move them up and down inside the tubes to find the best resonant air column length.  I fitted these into the pipes but will adjust their depths when the varnish is dry and I have refitted all the keys. Photos to follow!

The last job I did was make some new and harder beaters for use on the higher keys of my soprano marimba. Again these were made from thin dowell salvaged from wooden coat hangers, but this time I stuck onto the ends some wooden 'wheels' cut from a drawing pin.  Finally I wrapped these with woolen yarn.  They feel and look good but I have yet to try them out on the marimba...but that's a job for Wednesday...

Comments

Post a Comment

Popular posts from this blog

My first key

Here is the first key I tried to make.  At this stage I had used salt to find the nodes of the bar and had taken out wood from the underside using a small bladed saw.  However, I had cut too deeply into the wood and made the note too thin, such that it lost integrity and sounded too low to be of use on my two octave soprano. I tried a second time and got a little closer but impatience got the better of me and again I went in too deep.  I saved these early notes for experiments on staining with shoe polish (as it appears wood stain is not readily available in Shymkent either). You may notice under the table there is a mitre saw too.  I bought this so that I could cut the 50cm length bars to the correct lengths to match my stencils.  I would also have rails and legs to cut, so it seemed like a necessary thing to get.  I also bought a drill to drill holes for cords, and a router with which to tune the keys.  I mounted this under my workbench (a con...
Read more

First notes completed

So, when I wish to tune a new bar I mark on one side of the bar the centre line, and the points that correspond to the distances that are 25%, 30%, 35% and 40% from the end of the bar. I open Audacity and do a test recording of the bar before removing any material.  This is usually way above the frequency I am looking to reach, but it is nice to have a record of where I started. Then using a round tipped 20mm router bit which gives a nice smooth curve to my first cut, and using the 30% line as my guide, I move the bar over the router (which is mounted upwards from under the workbench).  I say that I use the 30% line as a guide, but in actual fact the edge of the router curve just touches the 25% line on the higher tone bars. Once I have my limits defined, I remove the remaining 6mm from between these two cuts. Next I raise the router to about 11mm.  I now make two more cuts using with the same router bit, making sure that the edge of the router does not cross the ...
Read more