Thanks guy's
Alaneye, the points you've highlighted are very valid & do deserve an explanation.
I have put alot of thought into the design of Bob as a sculpture.
Regarding the weight distribution concern... at present Bob weigh's 36lbs or just over 16kg inc the base. Hes mostly made of a very fragile foam mostly held together with PVA glue & a few wooden sticks, all that weight is transmitted to the base via 2 lengths of ABS waste pipe slipped inside one another & filled with urethane plastic. The majority of the weight is in the clay & the polyester filler I've used.
The head on its own weighs 14lbs or 6.3kg, the weight of the head slightly biases rearward & with the jaw attached is pretty much bang on in the middle.
A little while ago I did a test to confirm my thoughts, I placed the whole thing complete on a wooden rod to find the balance point & the weight is tranfered right through the middle into the base like this:
Since then A bit more weight has been added towards the rear only.
By its design it does give the impression that if its going to go it'll go forward when in fact its more likely to go backwards.
At this point your probably thinking whats the point of this, its all going to change when he's cast
My current plan is to rotocast him in urethane I'll be aiming for 5-6mm or 1/4" wall thickness. Then I want to make a GRP tube with about the same wall thickness, insert it into the stand inside the casting & pour urethane around it to bond it in.
Where it inserts into the base, my plan is to cast the base a similar thickness as the rest, make a thick 6-8mm or 5/16" GRP plate with a hole in it to surround the location hole & then add more urethane to the inside of the base bonding the plate in place & thickening the base at the same time.
I've used some of this urethane on the jaw & on his face & it is alot lighter than I expected. I can guarantee he will weight a fair bit less as a casting than he does now.
I believe I can get the support from a GRP tube that I need for this. GRP in the thickness I've suggested is very strong & much lighter than mild steel even in tube form.
The moulding & casting is something I am concerned about. I have read quite a few threads on the subject, seen a few vids & asked alot questions via pm. I feel nearly confident enough to tackle this but I expect I will seek some more advise as I get to that stage. I'll be taking it a stage at a time ie I'll be focusing all my attention on the moulding stage first & once I have the moulds I'll then move onto the casting.
whilst making the jackets for the moulds I will be considering the casting as in how to mount them to the roto caster. The roto caster is something I'll also have to make, working with steel is something I'm familiar & confident with.
I hope this lot makes sense
& thanks for the kind words Alan