Questions for Machinists:

[Don Kurylko]

I’m going to be making up a pattern for a rudder head fitting that I will have cast in manganese bronze at a foundry. The fitting will require a 1.5” diameter hole and a key way where it fits over the 1.5” diameter bronze rudder shaft. In the interests of simplicity, I was going to have it cast as a solid piece and have it bored out later.

My questions are:

1. Is it difficult to bore a 1.5” diameter hole into manganese bronze? The hole will be dead-ended, not bored completely through.

2. Is it possible to cut a ¼” keyway into this hole? The depth of the hole would be about 2.5” to 3”.

The bottom image is what I have in mind. Spartan doesn't make a fitting large enough for my boat, otherwise I'd buy one from them.

Thanks in advance for any help or suggestions.
Don

http://www.spartanmarine.com/image/19.jpg

[John E Hardiman]

My answers are:

0) On a piece that large, don't cast, forge.

1) You could, but I wouldn't. Too much chance for casting flaws in the solid body. Better to have all the sections about the same thickness to prevent cooling stress, then bore it out. Talk to the foundry, they have a lot of experience in that (as well as draft and srinkage allowance).

2) Yes, and time(i.e. cost) will greatly depends on what tool you are going to use: i.e. single end broach or shaper. With one you pay of the tooling, the other the machine time; neither of which is commonly found in the local shop.

[Dave Fleming]

Any HSM's in BC Dan?
Ask Guy Lautard for some recommendations.

[Gary E]

1. Is it difficult to bore a 1.5” diameter hole into manganese bronze? The hole will be dead-ended, not bored completely through.

2. Is it possible to cut a ¼” keyway into this hole? The depth of the hole would be about 2.5” to 3”.
1..... Easy,,, and your smart to not core the hole, let him bore it from the solid...

2.... Not as easy as a through hole but still it is done.... but why only 1/4 key?... 1 1/2 dia shaft should have a 3/8 or even a 1/2 in wide key...

Others are talking about forging, yes they are stronger, but if you have to pay for Dies to make one or 2 parts, you beter own a big bank fulla $$$$$$$. Open forged parts are less costly, if the part geometry allows.

[ 06-15-2005, 06:04 PM: Message edited by: Gary E ]

[PeterSibley]

Personally I would place a 1 1/4" core print for your opening,take some care to have standard wall thicknesses ,it stops shrinkage problems.If you choose to have the hole bored ask your foundry how to add extra metal to compensate for shrinkage ...it could be quite severe with a solid boss.

Good and incussion free castings are not that difficult and far cheaper than a forging.Here in Australia there are 2 grades of manganese bronze available,one has a tensile strength of around 20,000psi, the other 70,000 psi.They are otherwise indistinguishable ,same colour,same machinablity.

[holzbt]

Check the EDSON INTERNATIONAL catalog. They list a 1 1/2" bore rudderhead fitting as a stock item. There is a link to Edson in the "sites to see" on the WB homepage.

[JimConlin]

Port Townsend Foundry has 'em, too.

[Ken Hutchins]

Unless you have the skills and equipment to make stuff like that yourself you really should buy stock items. If you go the custom cast and machine route you had better have really deep pockets. Almost any configuration can be machined, the cost will be largely dependant on how the particular machine shop is equipped and what their normal products are.

[Keith Wilson]

FWIW, if the hole went all the way through, broaching the keyway would be fairly simple. A keyway in a blind hole is a lot more complicated (= expensive).

[Torna]

Another argument for having the hole go all the way through is that you can use a puller on it. Might prove handy 25 years from now when things are a tad corroded & stuck.
2c
-leif

[George Roberts]

1) I would get the piece welded up rather than cast, but cast will work.

2) Bore the hole (not much more difficult from the solid than from a cored start), cut a recess in the bottom, and then cut the keyway. Standard work on milling machines.

[Canoeyawl]

I have made a several of these fittings. These operations will be expensive; I would avoid drilling and boring a blind hole, not to mention the problems of machining a blind keyway… One way to do this job would be to bore through, broach the keyway then weld or silver braze a plug in the end to make it "blind" This could be neatly done by making a counter bore for the plug when you are doing the work. Another step to consider is this, if you want the part to have zero play, (if it is a rudder, you do!) You should provide for a pinch bolt or a taper fit. (The pinch assembly will be easier to remove and machine, just add a boss for the bolt to the pattern then drill and split with a band saw after finish boring) You may also want to provide for the final height adjustment.

[Bob Smalser]

I prefer to buy salvaged hardware inexpensively and either modify it or build the boat around it.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=31281&item=4556927528&rd=1

http://i10.ebayimg.com/04/i/04/55/37/00_1.JPG