Marimba bar nodes

[goldnhands]

Hi, seems very little posting on this forum, but here goes with my contribution anyway.
If you take a look at the  Marimba One website, http://www.marimba1.com/marimbas/sound
They say that they start off by drilling the suspension holes at the nodes, and then go on to tune the bars.
This is quite different to the method employed and described in my building guide (Makeamarimba.com) and I would like to know if Marimba One do in fact drill first, and if so what is the effect on the final product?  I know that the nodes do move quite a lot during tuning, and Jim Mc Carthy's method does seem more sensible to me.
I just laid out my first set of bars for the 5 octave model, the nodal lines are all over the place and at different angles, some quite acute.  I think that my "average" line for drilling is going to be a serious compromise and I am wondering what will be the effect on the finished instrument?
Any help or comment will be welcomed.
Barry

[Jim McCarthy]

Hi Barry
Yes what you are looking at is really the difference between a custom job and a more commercial mass production approach. Most commercial maufacturers don't want to adjust their frame dimensions to suit a particular set of bars - so they average even further. The suspension system used on marimbas is actually quite forgiving so you will find it sounds good even with this seeming innacuracy for some of the bars. What I try to achieve though if you are individually customizing each instrument... is the BEST result you can. so make the frame dimensions... ie strut positions match as close as possible to the particular set of bars. Also of course the issue of the preliminary salt testing. I am not sure if this is normally done - I suspect not. I never heard of it before I had the idea to do it myself.... The idea is to determine the tendency for angle of the nodes on a bar before tuning to make that angle more accurately match the angle the strings will need to take anyway depending on whether they are black notes or white notes. You do the initial test then arch the bar on the appropriate side. All this process is just refinement designed to get the strings as close to actually on the nodes as possible for as many bars as possible.

[goldnhands]

I have arrived at what I think is the absolute best average for most of my bars, unfortunately my C2 bar is way off and my "average" node line results in the string holes for that bar being too close to the arch and would leave very thin wood if I drilled them there.  I guess I will have to remake that particular bar and try to keep the arch a little shorter.
I purchased 5mm cotton sashcord for my instrument's suspension, is this the same as you used Jim?  How much clearance would you leave in the holes?
I really feel that I am getting somewhere now, picked up a couple of boards of Mahogany for the frame today and looking forward to starting it next week.
Barry

[Jim McCarthy]

mmmm.. that is a little strange, but I guess not unheard of. Sometimes that C2 - especially if it is the first bar we tune - can be a little off in the shape. In general though the bars are close enough that none of them should fall too far outside the "average".

I can't remember the exact cord - and sometimes there is more than one option as discussed in the guide - it is a matter sometimes of trying a few things... 4.8mm cord is a common one I use or 4mm "starter cord". The trick is to find a cord/hole combination that gives room for the bar to vibrate freely - but not so much room that you get a rattle sound - sometimes a bigger diameter cord or smaller diameter hole will help here - or a softer cord exterior - like in the cotton sash cord.

I usually start with something like  4MM HOLE AND A 3 OR 3.8MM cord.
Jim