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#1 2006-05-31 14:05:11

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Epoxy bore casting, filler density, etc.

Without infringing on any patents, I might be attempting a cast bore shakuhachi at some point. I already have West Systems resin. A couple concerns that someone who's tried this may be able to comment on:

- epoxy obviously generates heat as it cures. How do you mitigate this so it doesn't cause problems? Use a very slow curing type?

- any tips on shaping the bore positive form? shape, materials, etc.

- what's the barrier layer in between the bore form and the epoxy itself so you can still remove the form? If you use a reverse taper on the end, do you have to make the form in two connecting parts that meet at the choke point?

- are any thickening/filling agents used in the epoxy? On the one hand, it would be easier to 'pour' and ensure good filling if it was relatively thin. On the other hand, it would be lighter and cheaper to use colloidal silica or microballoons to make a lighter/thicker mixture.

What is the subjective 'density' of actual ji? Is it something like plaster, or heavier/lighter?

Also, drill finger holes before or after casting the bore?

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#2 2006-05-31 16:31:06

kyoreiflutes
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From: Seattle, WA
Registered: 2005-10-27
Posts: 364
Website

Re: Epoxy bore casting, filler density, etc.

Your best bet is just to try it on lesser pieces of Bamboo. No ne can really say for sure what will happen with your equipment, pieces, resin, etc, so I'd think that experimentation's your best bet.

You'd want to fill the flute with resin before you drill. Otherwise, you're going to not only have a horrible mess, but you always start with the bore shape before drilling anyway, right? Finish you bore and it will tell you what to do next. I wouldn't drill any holes, just put the resin in your piece and move it around so that it gets a nice, even coat. I'd do it by hand and keep watch down the tube, making sure to keep a drop cloth under you at all times.

I would also make sure your pieces have extra length at both ends, just in case. Better to have too much room to play with than not enough.

You can't do ANYthing about the heat caused by curing. Your best bet is actually to use a fast-curing resin, so that it doesn't sit there and have even more time to heat the oils and break the boo apart.

There shouldn't be a "barrier layer" with something like this: you can't take the resin "form" out, and it wouldn't fit into anything else, anyway. Once it's in, it's in. The bore shape you create with resin will very much mirror the existing bore shape. I'd think that with the right amount of resin, angle, and patience you could craft a pretty nice taper at the end, even out of a non-root piece.  I've even thought of doing all the resin bore work, then blocking the bottom part (with plastic, and the flute would have a little extra material at the end) and filling the bottom with resin; I'd let it cure a tad, then start moving it around so that it follows the taper better. When it's done curing, I'd take the block off the end and saw the end down to where it's supposed to be. I'd have a lot of extra resing to do some carving to, but I'd get better control over my end result. You could possibly even do some basic molds, some parts to slide down into the bore while it's almost done curing, but getting them to fit just right would be difficult.

And Monty's methods are far different than yours, using lasers and all that. I doubt there's any "copyright" concerns. You're not the first one to fill a flute with resin, and you won't be the last. I'd even like to do it with my next Hocchiku, and I'm kind of a resin nut, anyway.

I hope some of that made sense.

-E


"The Universe does not play favorites, and is not fair by its very Nature; Humans, however, are uniquely capable of making the world they live in fair to all."    - D.E. Lloyd

"Any man's death diminishes me, because I am involved in mankind, and therefore never send to know for whom the bells tolls; it tolls for thee."    -John Donne

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#3 2006-05-31 18:03:01

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Re: Epoxy bore casting, filler density, etc.

I think you misunderstand. The barrier would not be to remove the cast bore, but to get the *form* out of the bore. Casting a bore in epoxy is not like making it from ji - you can't just apply it to the inner surface and let it cure, there has to be some sort of form to define the empty space in the finished bore.

"Your best bet is actually to use a fast-curing resin, so that it doesn't sit there and have even more time to heat the oils and break the boo apart."

I doubt it. The heat generated from curing epoxy is a fixed quantity based on volume and configuration, and with a 24 hour cure catalyst that heat would be dispersed over a much longer period.

Fast curing epoxy obviously gets much warmer than slow cure. The type I have now is medium IIRC, but I can get a different catalyst from West.

"The bore shape you create with resin will very much mirror the existing bore shape."

Hence the bore positive, which I believe is what Monty uses. That ensures that the cast bore does *not* simply mirror the existing bore but gives a consistent, repeatable shape that can be carefully controlled.

It sounds like you're considering simply coating the existing bore with a thin layer of resin. That would probably brighten the sound and increase projection somewhat, but it's not really what I'm after.

I want to avoid 'carving' or sanding the epoxy as much as possible. As anyone who has spent some time working with the stuff knows, epoxy without filling agents is very difficult to work by hand.

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#4 2006-05-31 18:57:18

Mujitsu
Administrator/Flutemaker
From: San Francisco
Registered: 2005-10-05
Posts: 885
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Re: Epoxy bore casting, filler density, etc.

evan kubota wrote:

- epoxy obviously generates heat as it cures. How do you mitigate this so it doesn't cause problems? Use a very slow curing type?

I've had the best luck with polyurethane resin. It cures fast, it's lightweight, and even though it does cure with heat, I've never had a heat related problem.

evan kubota wrote:

- any tips on shaping the bore positive form? shape, materials, etc.

A lathe is a handy tool for making bore positives from wood dowels or plastic. You can make a few different sizes that way. A flexible bore negative (good for curved rootends) can be made from two part urethane. There are a number of bore profiles available on the internet.

evan kubota wrote:

- what's the barrier layer in between the bore form and the epoxy itself so you can still remove the form? If you use a reverse taper on the end, do you have to make the form in two connecting parts that meet at the choke point?

After losing a few bore positive inside flutes using spray on release agents, I settled on vaseline. A thin layer works well.

Exactly... if there is a reverse taper in the end, it needs to be made in two parts in order to remove. A simple dowel plug should work. (make sure to lubricate it well!)

evan kubota wrote:

- are any thickening/filling agents used in the epoxy? On the one hand, it would be easier to 'pour' and ensure good filling if it was relatively thin. On the other hand, it would be lighter and cheaper to use colloidal silica or microballoons to make a lighter/thicker mixture.

Thin polyurethane resin has worked best for me. It's easy to pour, and is also lightweight.

evan kubota wrote:

What is the subjective 'density' of actual ji? Is it something like plaster, or heavier/lighter?

Also, drill finger holes before or after casting the bore?

It is 'plasterlike' so I'd say it's similar in density.

For me, it's much easier to drill holes after casting.


Good luck Evan!

Ken

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#5 2006-05-31 19:39:03

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Re: Epoxy bore casting, filler density, etc.

"After losing a few bore positive inside flutes using spray on release agents, I settled on vaseline. A thin layer works well."

Yep... I usually go with petroleum jelly. There's also a thin plastic 'barrier film' that works OK but it depends on the application. Most of my experience is with vacuum bagging lightweight aircraft composite parts and the thin plastic film works OK there, but since the bore wraps around the entire form any seam or joining of the film would be visible on the interior.

I've never used polyurethane resin before. I was under the impression that it was prone to cracking easily... what brand do you use, and any sources?

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#6 2006-05-31 20:21:47

dstone
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From: Vancouver, Canada
Registered: 2006-01-11
Posts: 552
Website

Re: Epoxy bore casting, filler density, etc.

I have a naive question...  Does one bore profile tie you to one particular thickness of wall and/or outer diameter, one angle and depth of utaguchi, and one set of hole sizes and placements?  Otherwise, is significant tuning of hole placement, size, undercutting, etc. still involved if a flute with a cast bore didn't match the outer diameter of its "master"?

-Darren.


When it is rainy, I am in the rain. When it is windy, I am in the wind.  - Mitsuo Aida

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#7 2006-06-01 00:08:17

edosan
Edomologist
From: Salt Lake City
Registered: 2005-10-09
Posts: 2185

Re: Epoxy bore casting, filler density, etc.

dstone wrote:

I have a naive question...  Does one bore profile tie you to one particular thickness of wall and/or outer diameter, one angle and depth of utaguchi, and one set of hole sizes and placements?  Otherwise, is significant tuning of hole placement, size, undercutting, etc. still involved if a flute with a cast bore didn't match the outer diameter of its "master"?

-Darren.

Yes.


Zen is not easy.
It takes effort to attain nothingness.
And then what do you have?
Bupkes.

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#8 2006-06-01 00:42:20

jumbuk
Member
From: South-eastern Australia
Registered: 2005-12-15
Posts: 85

Re: Epoxy bore casting, filler density, etc.

I am not a maker, and I don't know anything about the process - but I used to make boats using the West System resins.  One of the techniques was to mix resin with a "microsphere blend" to make a thicker, gap filling material.  The spheres are very light, and the resulting filler is much lighter than solid epoxy.  Would this have any use in making a cast bore shakuhachi?


... as if nothing is happening.  And it is!

Paul Mitchell, Jumbuktu 2006

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#9 2006-06-01 00:58:02

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Re: Epoxy bore casting, filler density, etc.

That's what I referred to in my initial post... either microballoons or colloidal silica. Either one thickens and lightens the epoxy. I'm not sure if the reduced density would hinder resonance.

I'm now considering making a very 'soft' blend with plenty of silica/microballoons and applying that with a chopstick to the bore, then working it with files like you'd use in the traditional manner...

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#10 2006-06-01 12:09:59

kyoreiflutes
Member
From: Seattle, WA
Registered: 2005-10-27
Posts: 364
Website

Re: Epoxy bore casting, filler density, etc.

Well, I guess I didn't understand the question at all.

Suffice it to say, there's a new resin that is sculptable. I haven't tried it yet, but they were telling me about it at TAP plastics recently. I guess you can use it to sculpt for like an hour before it really starts curing. I'm going to try it out for something else, and I'll let you know how it goes. Could be a good alternative to Ji.

So, what we're talking about here is taking a flute you like, casting (copying) the bore shape, and then replicating that same shape for use in other pieces of bamboo? Is that what Montys doing?

-E

Last edited by kyoreiflutes (2006-06-01 12:29:39)


"The Universe does not play favorites, and is not fair by its very Nature; Humans, however, are uniquely capable of making the world they live in fair to all."    - D.E. Lloyd

"Any man's death diminishes me, because I am involved in mankind, and therefore never send to know for whom the bells tolls; it tolls for thee."    -John Donne

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#11 2006-06-01 14:44:16

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Re: Epoxy bore casting, filler density, etc.

Well, I was going to use bore profiles found on the internet and shape it closely to those. The West hardener I use gives at least 15-20 minutes of work time. Probably more if you spread it in a thin layer or keep it in the fridge.

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#12 2006-06-01 15:46:31

Mujitsu
Administrator/Flutemaker
From: San Francisco
Registered: 2005-10-05
Posts: 885
Website

Re: Epoxy bore casting, filler density, etc.

evan kubota wrote:

I've never used polyurethane resin before. I was under the impression that it was prone to cracking easily... what brand do you use, and any sources?

Evan,

It's been awhile, but I believe it was called 'Quick Cast' resin from Tap Plastics.

Ken

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#13 2006-06-01 16:01:47

Karmajampa
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From: Aotearoa (NZ)
Registered: 2006-02-12
Posts: 574
Website

Re: Epoxy bore casting, filler density, etc.

Can you give me the link to the bore profiles you found on the net.
I am considering making slip-cast ceramic flutes

Kel


Kia Kaha !

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#14 2006-06-01 16:37:00

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Re: Epoxy bore casting, filler density, etc.

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#15 2006-06-01 19:59:21

dstone
Member
From: Vancouver, Canada
Registered: 2006-01-11
Posts: 552
Website

Re: Epoxy bore casting, filler density, etc.

evan kubota wrote:

http://www.shaku8.com/makeshaku8/data/naikei.html

Nice to see some publicly shared bore data.  I'm really curious to hear how this works out for you.  But with all that bore accuracy, won't you still need chimney volume measurements to do that bore justice?  It seems making an assumption about that might negate the usefulness of such an accurate bore plot.

-Darren.


When it is rainy, I am in the rain. When it is windy, I am in the wind.  - Mitsuo Aida

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#16 2006-06-02 11:21:00

Mujitsu
Administrator/Flutemaker
From: San Francisco
Registered: 2005-10-05
Posts: 885
Website

Re: Epoxy bore casting, filler density, etc.

dstone wrote:

But with all that bore accuracy, won't you still need chimney volume measurements to do that bore justice?  It seems making an assumption about that might negate the usefulness of such an accurate bore plot.

-Darren.

Darren,

Exactly. Bore measurements alone might get a foot in the door. A complete recipe would be more helpful within this 'ultra' jiari approach. What I find interesting (and one of the many reasons I love shakuhachi) is my hunch that the same complete recipe, followed by a number of flutemakers, will result in many different flutes. Mysterious stuff, eh?

Ken

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#17 2006-06-02 14:02:23

Derek Van Choice
Member
From: Lake San Marcos, CA
Registered: 2005-10-21
Posts: 99
Website

Re: Epoxy bore casting, filler density, etc.

Hi, all...

It took ages of searching for the right company, and 7 months / $1,000 to have done, but I had a one-piece brass mandril made, with 10cm extensions on each end, using that same bore profile (to within .005).  I made subsequent fiberglass molds of the brass & pulled various parts from that, using both silicone and polyurethane.  The mandril, with that profile, worked exceptionally, as a foundation, casting epoxy (and other plaster-esque mixtures, i.e. plaster+aliphatic resin) around it.  I worked the bore subtly in a quite few places, added a couple thin layers of cashew lacquer, worked it again, and it really turned out to be a fabulous instrument (still my primary). 

Ironically, after all of that work, I have gone back to traditional ji, diameter gauges, and urushi, which, all in all, is a bit simpler in some ways, just not as immediate (and more tedious for us who are sensitive to it).  I won't open up the sonic material difference debate, but I will say that, after a bit of playing, my primary quadruples in warmth and resonance (which could just be ME warming up?).

That profile is really a good start, though...

smile

Derek

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#18 2006-06-02 16:46:38

dstone
Member
From: Vancouver, Canada
Registered: 2006-01-11
Posts: 552
Website

Re: Epoxy bore casting, filler density, etc.

Mujitsu wrote:

A complete recipe would be more helpful within this 'ultra' jiari approach. What I find interesting (and one of the many reasons I love shakuhachi) is my hunch that the same complete recipe, followed by a number of flutemakers, will result in many different flutes. Mysterious stuff, eh?

Yup.  Magical indeed.  Rocket science refinements on a medieval instrument.  And we're all musing about it in near-real-time from all corners of the planet.  Dig it.  I weep.

-Darren.


When it is rainy, I am in the rain. When it is windy, I am in the wind.  - Mitsuo Aida

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#19 2006-06-02 16:49:20

edosan
Edomologist
From: Salt Lake City
Registered: 2005-10-09
Posts: 2185

Re: Epoxy bore casting, filler density, etc.

'One flute's story':

Obtained a nice piece of Chinese madake from Monty Levenson suitable for making a 2.1 (this was ca. 1994).

Sliced up a pool cue, glued narrow dowels of various appropriate lengths into them, and measured the daimeters with a micrometer.

Used this set of bore gauges to measure a good 2.1.

Laid out a chart of these measurements along an axis and 'connected the dots' to interpolate between actual measured points.

Obtained a Delrin rod to make the bore mandril. Delrin is a hard, flexible, machineable plastic available in many rod diameters.

Machined the mandril on a lathe by feeding it gradually out of a hollow chuck to a rest, so only about 2 inches was exposed at a time.

The finished mandril is JUST flexible enough to work in the curve of the root end of this:

http://img450.imageshack.us/img450/6203/edo218hj.jpg

The sterling silver nakatsuge is a fake, used only for length adjustment.

Used catalysed casting resin (polyester, colored black) to do the bore--biggest problem was the releasing agent. Made an O-ring seal for the blowing end, and poured the resin down the bell end (no tone holes at this point).

Pretty decent flute. Also made a 1.6 this way, but that one's only a qualified success, and I don't crave the 1.6 length enough to put any more work into it; sure looks good, though yikes)


PS: Regarding the exothermic properties of casting resin mentioned above: Besides the activity of the catalyst (fast cure, slow cure, whatever...) a primary factor in the heat generated is the thickness of the resin to be cured (Even touched on this). In casting a bore, the resin thickness is merely millimeters, so little to no appreciable heat is generated, especially with slow cure resin.

Last edited by edosan (2006-06-02 17:03:29)


Zen is not easy.
It takes effort to attain nothingness.
And then what do you have?
Bupkes.

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#20 2006-06-02 22:31:35

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Re: Epoxy bore casting, filler density, etc.

Very cool.  What was the average bore diameter of the bamboo before you cast? I think the pieces I've been working with are a little large to start with - approx. 24 mm at the utaguchi and going to around 19 mm near the root. This would require a reasonable amount of resin or ji to reach the required diameter.

I've been thinking about alternative approaches. One thing I've considered is a 'pressure bag' setup that would use a sealed flexible plastic tube placed in the bore with a small hand pump to keep some pressure on the resin as it cured. This would give a smooth finish and result in less effort after the casting.

Has anyone used an alternative material for making the bore, but without casting?

I assume the traditional application method in Japan is applying it little by little with a wooden tool. Can anyone clarify the application?

I've obtained some joint compound which apparently uses water as the solvent and doesn't reek of chemicals. I've applied a coating of this to the bore of a scrap piece. It's advertised as easily sandable and when dry seems to be similar to plaster, but harder and lighter.

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#21 2006-06-02 23:43:50

evan kubota
Member
Registered: 2006-04-10
Posts: 136

Re: Epoxy bore casting, filler density, etc.

Ed - how did you ensure that the mandrel was "centered" in the bore? I guess because it had to curve it was possibly touching bamboo at some point anyway.

How was the polyester resin to work with? I've never used the stuff but it seems pretty cheap and if it's durable enough for this sort of thing I may go that route.

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#22 2006-06-03 11:23:16

Derek Van Choice
Member
From: Lake San Marcos, CA
Registered: 2005-10-21
Posts: 99
Website

Re: Epoxy bore casting, filler density, etc.

Hi, Evan...

Attempting to find an alternative to urushi, a couple of the ji's I played with were:  tonoko + water then aliphatic; tonoko + aliphatic only; the latter was quite good, as long as the tonoko was very finely sifted, as should be anyway--very creamy, applied well, sanded beautifully, good adhesion, and with appropriate density.  The tool I use for ji is similar to a long torpedo on a stick (+/- 4" x 1/2" diameter, made from ji).  You want to slowly rotate the bamboo, and the applicator, in opposite directions, with the applicator moving fore/aft a few inches or so, when applying the ji.  I have much, much to learn, but have had some good successes, as well.

Must be a great sounding flute, Ed... looks well played!  smile

A Q for the urushi veterans: Switching over from cashew, I am approaching my first full application of thin urushi lacquer to begin the fine-tining stages on a current.  As I am sensitive to it, but use gloves/caution/clean-up for the ji process, is it a crap shoot relating to urushi in the utaguchi & lip area, as to safety?  I know even 6 months after curing is not uncommon for some to be affected, yet the flute must be worked,and especially in that area, being near a balance point.  Maybe a temporary synthetic buffer between the lips/bamboo?  Of course, breathing it isn't all that great either--I tend to take a breath from the side, turn, blow, adjust, lather rinse, repeat.  Curious?

Last edited by Derek Van Choice (2006-06-03 11:23:48)

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#23 2006-06-04 23:03:32

edosan
Edomologist
From: Salt Lake City
Registered: 2005-10-09
Posts: 2185

Re: Epoxy bore casting, filler density, etc.

evan kubota wrote:

Ed - how did you ensure that the mandrel was "centered" in the bore? I guess because it had to curve it was possibly touching bamboo at some point anyway.

How was the polyester resin to work with? I've never used the stuff but it seems pretty cheap and if it's durable enough for this sort of thing I may go that route.

I saw no particular reason to center the mandril within the bore; after all, these are shakuhachi...

The polyester resin was 'OK'...it does smell like raw fiberglass compound (ie, Bondo, etc), although the odor dissipates pretty quickly after the resin is completely cured. It is cheap, and sold by most retailers of plastics. It may be heavier than some like, especially when using it to cast the bore of a culm with a larger inside diameter. I recommend using this method (or any cast bore method) with culms having bores in the ji-ari 'ballpark--in the neighborhood of 20mm and a bit.

It's VERY durable, and therefore somewhat hard to work in fine tuning the bore. I think Monty uses a similar resin (when I last spoke face-to-face with Monty--1988--he was painting the interior of the finished bore with epoxy paint. This put a nice gloss on the surface, and allowed him to vary the color to suit. I just used a dye in the resin). I like the idea of using 'fillers' (mentioned here previously) to reduce the desity of the resin. It'd be lighter and probably easier to work. Haven't tried this, though; I reckon my shakuhachi output will be nil in the coming decades...

eB


Zen is not easy.
It takes effort to attain nothingness.
And then what do you have?
Bupkes.

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