Custom rudder mock up

I need to make a mock up on this rudder so I can have one casted.



I need thoughts on materials and techniques to do it.

thanks in advance.

Doesn't seem to brite of an idea since they are pretty readily available to buy finished all ready.

How many are you making?

Pete it seems like starting from a forging would be the easier route, don't see where the casting is going to have enough strength in the shaft area or even overcasting it, doesn't leave much meat around it.

Pete, I think I was looking for your advice on this matter.

I'm yet to talk to the foundry guy to see how he wants the model to be made regarding the shaft, my idea is that he could cast it around a stainless steel shaft. Would that be overmolding it?
I expected around 3% shrinkage.

My plan is to cut 2 templates and fill them in between with some plaster like material, from there sand and grind as needed.
What do you think?


79: what if the shaft has a few holes or patterns inside the rudder to "grab" on the casting?

Behind the prop: One for starts, but if I get it right maybe I could sell some around here.

Kapla: if my costs are too high I will consider it. As I just told on the phone, I feel this rudder will fit better the boat I plan on putting it on.

thank you all for the input, keep it coming.

Luch,
Yes, the "overmold" is casting the blade over/around a stainless shaft. Talk to you foundry first because as mentioned, the process can be tricky with pour temps. If he does do it, it may take him a couple of tries/experimenting!!! The shaft may need some preheat.

The stainless shaft would have small "wings" welded onto the shaft in the blades bossed area. They don't need to be very big. They transmit the torque better the a hole which doesn't allow for much shear.

Talk to your foundry on how he wants the pattern made exactly. I've done some sand casting and on a short run it's easy to had cut the parting line so a split pattern isn't needed. If overmolding the shaft, you'd make the plus 5% pattern in the blade area but leave the shaft at the 1". He'd make the mold halves, open it up, drop the stainless shaft in and close up the mold. If you cast as one piece, then I'd give the shaft more than 5%. 10% extra will ensure there's plenty there to machine.

Chris,
I agree that a forginging sure would be stronger but they are all cast. The boss around the shaft to me looks like there's plenty of meat to do the job.

EDIT:
Luch,
Have you considered just having one fabricated? CC was doing it on the 176's when they wanted to "detune" the hull because per Jody, the 176 was outperforming the 196!! CC couldn't find a small off the shelf rudder.

Also, if cast in one piece, you'd better talk to your machine shop. There's going to be some fixturing needed to hold the rudder for machining the shaft.

Pete, phoned the foundry guy, he said to add or draw patterns into the shaft so it could grab better in the cast, he estimated shrinkcage by 1%!!!

The 2 issues holding me, we didnt discuss price yet, and, he told me something odd, that there's a need for a 3/8'' clearance on the thinnest part of the piece the cast can pour correctly.
So, I might be taking another rudder so he has a better idea of what I want and can quote me accordingly.

As 79 suggested looked for something already finished and found a U$D250 offer for a complete rudder assembly, which would end up costing U$D500 shipped home.

Also called a local shop, they wanted U$D1000 for a complete stainless steel rudder assembly.

Eric, I was wondering the same on the machining.

Tim, dont take time in the acount, I wish I had U$D500 laying around to toss on a new rudder and not that much free time. Right now that money is for other more specific parts on the project.

I think I can have it correctly done for much less, that's what I pretend to find out. Costs wise, what's your thought?

Luchog wrote: Pete, phoned the foundry guy, he said to add or draw patterns into the shaft so it could grab better in the cast, he estimated shrinkcage by 1%!!!

Luch,
Ok, he's (and yourself) talking casting in Stainless reflecting the 1%. The 5% is for copper/brass alloys!!

Machining flutes parallel to the length of the shaft would be another option for a "gripping" surface in the blades bossed area. Probably even better because I don't fell it would produce as much stress as the welded on tabs.

behindpropeller wrote: Hey.... Your drawing is missing a key dimension....shaft length(out of the rudder) or rudder height.

you need a lesson on reading prints

The shaft will be measured regarding the boat in question, which hopefully will be here to work on in 7-10 days. If going the all custom route, I have many options for the base and packing gland or not.

79, yes, those U$D500 are a big chance at this moment, but first I will ask around. That's still free.

Finally...