Sunday, June 30, 2013

Esraj final

One portion of the rim epoxy came loose after gluing; the job was salvaged by heating and molding the shape of the mylar over the rim, and gluing it completely around the edge with a 3M adhesive, Super 77. The stuff was very gooey and gross to work with, but did the trick- strong tack and fast, durable bond.

Here we are tuning and setting the bridge position:

And it was just in time! Here is a photo from a few days later, in concert with Arijit Mahalanabis, Samir Chatterjee, in the very able hands of Kishan Patel

Monday, June 24, 2013

Esraj head gluing

Here she is stretched on a frame:

and now with epoxy and clamps and weights (I eat heavy peanuts):

Thursday, June 20, 2013

Fiberskyn esraj head replacement

I do work on North Indian instruments quite often; sitar, sarod, tabla, etc. People have asked about replacing the traditional sheep or goat skin with a synthetic material, and now I have the opportunity to test it out.
This esraj had a large chip missing from the bottom rim of the bowl. I removed it, squared the edges, and prepared a piece of cedrela oderata which is an excellent match visually and for strength/weight ratio to patch it.
I shaped the new piece to match the rim, and scraped the excess sheep hide and glue from the gluing area of the rim. The patch ties in to a vertical support beam- one that is VERY sturdy- which will carry the string tension through to the neck. I am very confident this repair will hold, even with the very many strings putting tension on the assembly.

The next step is to test adhesives on the Fiberskyn head. Remo makes this excellent synthetic imitation skin. I chose the ambassador weight which is 10 mil thick. This matched a few samples I measured of the sheepskin from the instrument.

The material is mylar, and I opted to test three adhesives: cyanoacrylate (super glue), E 6000 (an industrial adhesive for exterior gluing on cars- recommended by 'the glue guy' at the hardware store) and long-cure epoxy.

I made a scrap assembly resembling the bowl. First I only glue the pieces to the top side of the rim (not wrapping around the edge for extra strength).

I applied some finger pressure, and both the epoxy and super glue broke wood away before giving up the bond. The E6000 bond broke quite easily; I would say I was only applying ca. 20 pound of finger pressue.

Next, I reglued the samples OVER the edge, to add strength. This mimcs the traditional attachment, and will really test the adhesives. Here is the result:
As you can see, I was able to clamp the mylar clear to the bottom of the channel; I would estimate forces in excess of 250 pounds and both the superglue and epoxy held fast. The mylar stretched to accomodate the pressure, and the glue bond held.

However, the E6000 let go after only a few turns of the clamp. Clearly, E6000 adhesive is not formulated to bond mylar.

I will feel very confident using superglue or epoxy. The epoxy was easier to bond the top of the rim with, so I will probably use it for that purpose. The superglue was much easier to use pulling the extra over the edge: the result also looked cleaner, and since that is the most visible part of the repair, I will probably use superglue for that.