The Talking Machine Forum — For All Antique Phonographs & Recordings

donniej wrote:... The area on the bottom, under the needle bar has also been reinforced. The holes will have to be drilled, and depending on which resin I use, they may need to be tapped as well. Does anyone know what the size and thread pitch is by any chance?...

I don't believe that the front plate "holes" holding the lugs in place on either side of the needle bar are threaded. The lugs, themselves are, to accommodate the nut next to the needle bar, and the end cap, holding the lug in place.
FROM: https://www.nipperhead.com/old/vic4sb02.htm

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I'm wondering what the optimum weight of the sound box would be. There must be enough weight to hold it "steady" in it's upright position, enabling the needle to properly track the record groove, and move the diaphragm back and forth. . If it's substantially lighter than the original, I think that softer, more complaint gaskets would be required to minimize the chance that the whole sound box/tonearm would sway back and forth with the needle's movement in the groove, instead of the needle bar and diaphragm. (Hope that makes sense.)

OrthoFan

OrthoFan wrote:
I don't believe that the front plate "holes" holding the lugs in place on either side of the needle bar are threaded. The lugs, themselves are, to accommodate the nut next to the needle bar, and the end cap, holding the lug in place.

You are correct, the holes for the needle bar pivots are not threaded. The holes that hold the front half to the back half are. A polyurethane resin would probably be "self tapping" but an epoxy wold need to be drilled and tapped or it would likely break.

OrthoFan wrote:
I'm wondering what the optimum weight of the sound box would be. There must be enough weight to hold it "steady" in it's upright position, enabling the needle to properly track the record groove, and move the diaphragm back and forth. . If it's substantially lighter than the original, I think that softer, more complaint gaskets would be required to minimize the chance that the whole sound box/tonearm would sway back and forth with the needle's movement in the groove, instead of the needle bar and diaphragm. (Hope that makes sense.)

The difference in volume from 100g to 200g is "not substantial". Considering the weight of the tonearm, I don't think getting below 100g is likely, without trying really really hard anyway

Forgive my incorrect usage of the words epoxy and resin...

Curt A wrote:Forgive my incorrect usage of the words epoxy and resin...

I'm not sure there really is correct useage for the term "resin". It's kind of like using the word "plastic".

The first casting was demolded this morning. This one was made with a polyurethane resin, the same one I make Diamond Discs from. It's comparable to the material hard hats are made of. It's lighter than epoxy but not as stiff, whether or not that matters is yet to be determined.

The original part weighs 53 grams, this polyurethane one weighs 10 grams. (The back half weighs similar.)

Looks great! Hope it sounds nice too.

For the 4 tapped holes that hold the back plate on, I would suggest using a course thread. The original ones use a very fine thread which may be weak and strip easily in the plastic version. Consider maybe even using self tapping screws as you might see used in many plastic assemblies.