Bachi Casting

What follows is a description of my attempts at jiuta bachi casting and customization using RTV silicone in a two-part mold with clear epoxy resin as the casting material.

This is not intended to be a step-by-step mold making and casting outline. It is a general overview of the process. To see step-by-step procedures on single-part and two-part mold making and casting, please reference the many YouTube videos on this subject. Search under the following terms: mold making, rtv molds, silicone molds, epoxy casting, or casting. There are many excellent instructional videos on YouTube that will give you the confidence to cast your bachi for customization.

The casting procedures listed here are for a jiuta bachi. Because of the design of my particular bachi, a two-part RTV mold was required. If you have a standard wood bachi that does not have the characteristics as seen the in the photos here, than you can do a single-part mold. A single-part mold IS MUCH EASIER to complete than the following two-part mold process. The likelihood of errors is cut in half and chances for success are doubled. Something to consider.

Materials Needed

RTV silicone mold making material

Epoxy resin casting material

Coloring for resin material

Mold box

Modeling clay

Paper towels

Wood craft or Popsicle sticks

Plastic cups

Cardboard or plastic sheeting

Rubber bands

Razor blade or Exacto knife

General Procedures

Create a mold box or buy one. You can create a mold box out of a wide variety of materials. I was lazy. I decided to buy an acrylic mold box called Adjust-A-Mold Box from Makeyourownmolds.com.

Using cardboard as a base platform or plastic sheeting (as I did—available at Home Depot or Lowes), shape the mold box to surround your bachi with the following allowances: 1) A minimum of ¼ inch on each side between the bachi and the sides of the box; and 2) a space large enough on the butt end of the bachi as it approaches the side of the box to fit a cut line tube between the bachi and the butt wall.

A cut line tube is a small, round object that is placed between the butt end of the bachi and the adjoining wall of the mold box. It acts as a place holder where the RTV will not fill in so you have an entrance for the epoxy to enter the RTV two-part mold after it has cured.

Although I thought I would use a cut line tube at first, after watching one YouTube casting video on two-part mold making, I decided against it. I just placed the butt end of the bachi against one end of the mold box and hoped that no RTV would slide between the mold box wall and the butt end of the bachi. Big mistake. I could not keep the RTV from flowing in the small space between the bachi butt end and the wall. This made the complete mold more difficult to cast (the butt end of the mold was misshaped creating additional filing and sanding of the epoxy cast) and I had to do additional trimming of the RTV mold itself with an Exacto knife.

Seal the inner floor and sides of the mold box using modeling clay (standard oil-based clay available at Walmart or Michael's).

Clay "snakes" to seal bottom and edges

Create a clay base inside the mold box to take the impression of the bachi (critical in a two-part mold). The clay base must be thick enough so that about half of the bachi is imprinted into the clay. I first tried modeling clay from Walmart. Although modeling clay was fun to play with as a child, my old hands found it difficult to create a smooth, even, thick base for the bachi impression. Several attempts failed.

Walmart clay base that failed

I then decided to go with Monster Clay (available at Amazon.com). This is an oil-based clay often used for very detailed oriented model making and castings. It can be melted in the oven or microwave, poured into the mold box, and reused again and again. Although expensive, it was well worth it since I was able to pour a smooth clay base for the bachi impression without any difficulty. If using Monster Clay, there is an additional time factor as you will need to wait for the clay to cool sufficiently such that your bachi won't sink beneath the surface.

Monster Clay base

Whatever clay you use, make sure it is as even and smooth as possible. Place the bachi inside the box and press it down such that about half of the bachi is inside the clay and half out. This is your cut line. Be sure to press in a cut line tube at the butt of the bachi at this time. This item does not have to be a “tube” per se (hollow). I use the term “tube” here to indicate that this is a rounded object that you place at the butt end of the bachi to the mold box wall (at the cut line) to allow a convenient place to pour your casting material once the two-part RTV mold has cured.

You will now need to place anchoring or alignment marks inside the clay, around the bachi. These are to align the two parts of the mold once both parts have cured. Without these anchoring or alignment marks, getting the two parts of the RTV mold together so that the cast is correctly aligned will prove problematical.

Alignment points pressed into the clay surrounding the bachi

For these alignment marks, I used the eraser end of a pencil and placed several holes (about six or so) in the clay surrounding the bachi. I made two mistakes here. The use of the eraser end of the pencil made too small of alignment marks such that when I removed the second part of the mold after it cured, one alignment mark was ripped off the RTV. The second mistake was not going deep enough into the clay for more solid alignment marks. I suggest you go almost to the depth of the mold box clay when placing the alignment marks AND use the end of a Sharpie pen or some other larger marker pen that has a bigger butt end than a pencil.

Mix your RTV materials together following instructions and pour into the mold box. I used AeroMarine 125 RTV Silicone because the company (AeroMarine) is located in the same area as I live, thus saving me shipping costs. Use any suitable RTV material you desire. Be forewarned, however, that this stuff is not cheap to buy.

Once the RTV has cured, flip the box over, remove the box sides, then remove the clay bed from the mold box. You hope that the bachi stays inside the RTV mold as you remove the clay. However, mine came out during this process. I stuck the bachi back into the RTV mold and the mold outline appeared to be okay.

Mold box removed; clay removal begins on first part of mold

Bachi stuck to clay instead of RTV

Bachi RTV impression; first part

You may have to do some trimming of the RTV mold to be sure you have the correct outline of the bachi. Reassemble the mold box around the first part of the RTV mold and reseal the box using modeling clay.

RTV silicone will not stick to anything EXCEPT other RTV, glass, and porous materials (such as unsealed wood). Thus, since you will be pouring more RTV over the bachi that is held in place in the first part of the mold, you will need a release agent to prevent the RTV from sticking to itself. Most release agents are some form of Vaseline, either spray or liquid. I used just regular Vaseline you get from almost any store.

Bachi in place, ready for second part RTV pouring

Using a brush or some other method, brush the Vaseline over the bachi and the RTV mold. The mistake I made here was not being generous in its use. When I attempted to release the second part of the mold, I had some difficulty. So, make sure you generously grease up the bachi and surrounding mold with Vaseline. After that, remix the proper amount of RTV and pour into the mold.

Once the second part of the mold has cured, separate the two parts carefully. It was here that one of my alignment protrusions ripped out. However, with some patience I was able to separate the two halves without further damage to the mold and bachi impression. After I removed the bachi from the mold, I had to trim some additional RTV from inside the bachi impression itself, most notably on the inside of the blade impression as some of the RTV had spilled over.

Two part RTV mold complete

It was now time to cast. Any casting resin can be used. I used Amazing Clear Cast, a clear epoxy resin manufactured by Alumilite Corp (available at their web site and on Amazon.com). I added some coloring to the cast material to make it easier to photograph and easier for me to see any changes I may make to the prototype. But before I could cast, I ran into some difficulties.

For the second part of the mold, I did not use enough RTV material. I miss-measured the volume required. This is a bozo no-no. Measure carefully and try to make both parts of the RTV mold as equal as possible. Thus, the second part of the RTV mold was a bit ragged and thin. Let's be honest—it was crappy. This crappiness manifested itself at this point when I tried to place the two mold pieces together in preparation for the actual epoxy resin casting. When testing the mold to see if it would hold water, it leaked like a sieve.

As you will see in the pictures, the only way to remedy this was to wrap many, many rubber-bands around the mold to secure it sufficiently so there were no leaks. Normally, you would need only a few rubber-bands to secure the two-part mold together. Because I did a Pi$$ Poor Job, it needed a lot!

However, all's well that ends well. With enough rubber-bands, the mold was secure and really ready to cast. Since RTV is flexible and bends easily, I secured two additional pieces of plastic sheeting on each side to give the mold some rigidity so it could stand up for the actual casting.

Casting resin to the right of the mold

Epoxy resin cast into the two-part RTV mold

Follow the directions on whatever casting material you use and pour slowly into the mold. Depending upon the casting material, cure times are anywhere from 20-30 minutes to 24 hours.

I mixed too much epoxy resin as I wanted to be sure I had enough to fill the mold completely. Because of that I erred on the generous side. With the epoxy resin left in the plastic cup, I added some pennies to the cranberry colored resin and made a simple paper weight so as to not waste the material.

And here are the results of the casting:

As you can see from the photos, the epoxy bachi as it comes out of the mold needs to be filed, sanded, and cleaned up before additional modification can be made. Once I have completed that operation, I will post additional pictures and further customization efforts on this blog page.

Too much material seeped into the surrounding mold instead of staying within the bachi cast impression. I'm guessing this was because the mold was uneven to begin with, one mold part having less material than the other (referenced earlier in this post).

This unevenness caused a "warping" effect of the mold itself that allowed the material to spill over. Not having stronger/larger alignment points may have also contributed to the seepage. Additionally, the bachi design is an odd one--extremely thick in most places and extremely thin at the blade end. This unusual shape surely contributed to the difficulty of getting a clean cast.

The thinness of the blade impression in the mold appears to have caused the ends to not fill with epoxy because when I removed the cast from the mold no breakage occurred. Thus, the cast bachi blade will be shorter in overall width than my original jiuta bachi as I will have to shape both ends to points. I believe the only remedy for this is to tilt the RTV mold back and forth several times when I first pour a small amount of epoxy into the mold. This might allow the material to go deeper into these very shallow ends. That remains to be seen.

Please note that I cannot vouch for the efficacy of using an epoxy resin bachi on your sangen. Use at your own risk. The resin bachi formed is much lighter in weight than the original plastic one used for casting. My original jiuta bachi weighs about 7.5 oz--call it 1/2 lb give or take. The epoxy bachi weighs 6 oz. I am using the epoxy bachi as a prototype for further customization—not to use on an actual sangen

Clean up of materials is simple if you used containers other than disposable plastic cups. In my case, because of the large amount of RTV mold material required to cover the bachi, I used a cheapo plastic pitcher. Since RTV doesn't stick to surfaces except as noted, I was able to strip off the RTV after it cured and then use soap and water for final clean up.

Things I Learned

As you can see in the initial de-molding of the bachi, it wasn't perfect in form. However, for a first-time effort at ANY kind of mold making or casting, I consider this a success.

I made several mistakes as noted earlier: Not enough RTV material in the second part of the mold; not enough Vaseline on both parts of the mold to make it release easier; the small alignment protrusions needed to be bigger; not tilting the RTV mold back and forth when initially pouring in the epoxy to make sure the material flowed to the very end of each bachi blade point; and finally the first attempt to use modeling clay for the base of the mold is to be considered at your own risk.

I hope to do some further casting and/or mold making as I customize the bachi to fit my hand better. This is ongoing experimentation and should be considered a work in progress. In addition, I may also cast a one-piece mold on a standard wooden bachi that may act as a prototype for some other sangen player. All of these efforts will be documented here in the future.

UPDATE JULY 6, 2013

I finished trimming and sanding the epoxy bachi. I'm pretty disappointed at the end result IF I was going to attempt to use this as an actual bachi direct from the casting process. The cut-line spill over into the mold caused a large ridge that ran almost the entire length of the bachi. I trimmed and sanded this as much as I could, but of course, additional finishing work would have been needed if this was a final cast, say in acrylic or some other heavier plastic material.

The cast bachi blade turned out too thick and this would have necessitated additional sanding and trimming as well. I was able to straighten the ends of the bachi to some degree (coming to a point), but it was still not up to quality standards.

I decided to go ahead and "notch" or trim a piece out of the epoxy bachi handle so that my little finger could rest a bit inside the handle. As mentioned in other posts, this is where my pinkie is pinched a bit in holding the bachi. However, please note that the longer you hold/handle the bachi, this pinching (at least for me) is slowly disappearing such that I hope it will be completely eliminated. I guess if you give anything enough time, you get used to it. Good or bad, it becomes the norm.

The notching was a success as the epoxy bachi handle does fit my hand better with that modification. But to proceed any further in the customization process or to conduct additional castings of the jiuta bachi in other materials would not be worth the time or effort it would entail. I will, however, cast a a more standard wood bachi I have in my possession since I have sufficient RTV material left over for this small job. Because of the shape of this smaller wood bachi, I will do a single-part mold, not a two-part mold. Will report back on this page when that has been accomplished.

Here are some pictures of the epoxy jiuta bachi trimmed and modified:

Epoxy bachi before trimming, sanding begins

Bachi sanded, trimmed. Blade and sides crappy

Bachi butt end. Not shaped correctly--handle thicker than original

Another look at the whole epoxy bachi after trimming, sanding

This is a better view of how crappy the sides of the bachi turned out even after sanding

A look at the notch that I put in on one side of the handle to hold my pinkie

Another view of the notch from a different angle

Yet another view of the notch to ease the pinching of my little finger