Epoxy saving fingers for DD coil casting

[Mullihaka]

Casting DD coils into epoxy takes quite a lot of expensive mass and makes the search head heavy.

When vacuum forming the coil shell, one can place 2 “fingers” in the middle of the D’s. When finished, they are cut off, glued to the bottom of the shell, in the middle of the overlapping section. The coils are then added, nulled, glued and finally cast in epoxy. This particular shell saved 30 cubic centimeters epoxy, which makes approximately 50 grams less weight.

[Jerry]

That is a twist that I had not thought of. I have been cutting light weight quarter inch thick paneling to fill the void spaces in the shell. Will have to give that a try.

Jerry

[dfbowers]

Casting DD coils into epoxy takes quite a lot of expensive mass and makes the search head heavy.

When vacuum forming the coil shell, one can place 2 “fingers” in the middle of the D’s. When finished, they are cut off, glued to the bottom of the shell, in the middle of the overlapping section. The coils are then added, nulled, glued and finally cast in epoxy. This particular shell saved 30 cubic centimeters epoxy, which makes approximately 50 grams less weight.

Great idea! I almost had a coil failure last night. I did a pour of epoxy for my Barracuda project and I added some foam blocks.. Well about 2 hours into the curing process one of the blocks (that I used for filler) broke free from the adhesive and floated to the top.. Yikes!! What a mess. I was able to salvage everything with just a few bubbles on the top. If you use a fillers make sure that they are secure!

[Jerry]

Glad to see you making coils again Don. How is the wrist?

Jerry

[dfbowers]

Glad to see you making coils again Don. How is the wrist?

Jerry

Hey Jerry..

Yea, first coil in a while. It will never be quite "right" but functional.

[Tinkerer]

Microballoons

http://www.eagerplastics.com/7962.htm

Microballons are chemically and electrically inert. Mixed with resin, Epoxy or Polyester, they reduce the weight of the final product considerably.

I find the Microballoons an excellent filler for coil casting. When using a low viscosity resin, the load can be very high and the resulting density very low.

Milled glass fiber can be added in the mix, when there are considerations of strength.

Tinkerer

[bernte_one]

has anyone tried to add some baking powder to the resin, epoxy or pu filler

[Krzysztof]

Hi Bernte_one.
The hydrogen carbonate (NaHCO3) decomposes (during heating) to CO2 and H2O. Water probably would not want to. Bubbles do the resin as the dough (such is the task of the powder). PU is inert but very thoroughly because it will exit to the surface (light).
Best regards Chris.

[Wiltran]

Casting DD coils into epoxy takes quite a lot of expensive mass and makes the search head heavy.

When vacuum forming the coil shell, one can place 2 “fingers” in the middle of the D’s. When finished, they are cut off, glued to the bottom of the shell, in the middle of the overlapping section. The coils are then added, nulled, glued and finally cast in epoxy. This particular shell saved 30 cubic centimeters epoxy, which makes approximately 50 grams less weight.

Good idea, how does it affect the rigidity of the finished coil?

[Mullihaka]

Not too much, I think. There's three wide connections left between the halves anyway. I'll report here when I broke mine in use.

[bernte_one]

Hi Bernte_one.
The hydrogen carbonate (NaHCO3) decomposes (during heating) to CO2 and H2O. Water probably would not want to. Bubbles do the resin as the dough (such is the task of the powder). PU is inert but very thoroughly because it will exit to the surface (light).
Best regards Chris.

thats right
but pu filler (like polyurethane foam) reacts with the water and hardening progress is speeded up i hope fast enough to hold some bubbles in but enough of theory i think i will try next days

[Krzysztof]

Hi!
PU foam does not react with water. After a very long time to gather water but does not react.
Best regards Chris.

[bernte_one]

oh i mean not direct liquid water more wet air conditions (humid environment)

[jwms]

One could use the textured paint "grit" with epoxy but it might not work with polyester resins due to the solvent. just mix it in or put it in "cots" (little condom like things that go over your fingers). They can be made to size placed where you need them to cut weight but not strength.