How to cut a 1/4" slot through a 1-1/4" rod?

Hi folks: I am trying to make a skeg-mount rudder for a lobsterboat. the rudder is made from a 1/4" thick piece of 316 stainless steel. The rudder stock (shaft) is 1-1/4" diameter 316 stainless steel rod, cut into two pieces and slotted to accept the rudder plate which is then welded in. The two pieces of rudderstock are arranged so that the lower one is held in a bearing (on the skeg for all you boat folks), and the upper one penetrates the bottom of the boat through a packing gland and has a keyway to attach the tiller.

My question is how do I cut the slots? they need to be through the round stock and maybe 6 inches along the long axis of the rod. (2 pieces, top and bottom)

I have access to a Bridgeport mill with unknown tooling, so I will have to buy a cutter for the job. My plan is using something similar to a keyway cutter and attacking the work from each side. Maybe leaving the very end "un-slotted" to remain rigid before hacksawing out the last bit?

Plan B may be an 1/4" endmill attacking from the top? although this seems like it would be too flexy for a 1-1/4" cut.

As you can probably tell, I am not a machinist. Although I do read RCM regularly. I also understand 316 stainless is not easy to work with.

I would love to hear what you folks think of my plan,including lubes, speeds, what the cutter is called at Enco or wherever.

Thanks, Andy Lynn, MA

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On Mon, 8 Dec 2008 15:25:43 -0800 (PST), andy

It'd be much easier to cut rectangular slots in the rudder to accept the ends of the stub shafts, and it seems to me would accomplish exactly the same thing. I wouldn't consider slotting the shafts unless it's absolutely necessary.

--
Ned Simmons

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Ned/Bruce: Wow! I'm glad I asked. I wouldn't have thought of that approach. I guess I was thinking (incorrectly) that you modify the less expensive piece of stock to accomodate the more expensive. Your way is certainly easier, and can be done with my own gear.

In my head, it would easier to line everything up using the slotted shaft approach. But if it is 5x the work then the slotted plate method is looking better and better.

Thanks for the help! Andy

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On Mon, 8 Dec 2008 15:25:43 -0800 (PST), andy

You could equally well cut a slot in the rudder blade to accept the rudder stock which can be done easily with a cutting torch, a plasma cutter or a 4 inch grinder. You will probably have to tack the upper and lower rudder stock to a piece of angle or pipe to hold them in alignment before you weld them to the blade, but you'd probably have to do that anyway.

As far as strength goes I can't see much difference in the two designs as if you put a nice fillet weld on both sides the welds will be as strong as the 1/4" plate.

As far as stainless being hard to work with, it work hardens easily. Use a slow cutting speed and fairly heavy feed and you can cut it almost as easily as carbon steel (not the "almost" :-)

Cheers,

Bruce (bruceinbangkokatgmaildotcom)

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I'd envision the job as a hybrid of the two: mill slots in the shaft only about 1/4" deep. Cut a matching slot in the rudder. Slide the two together (self-aligning), then weld.

LLoyd

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On Tue, 09 Dec 2008 06:41:25 -0600, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

You will still have to use some sort of strongback or do a lot of back and forth welding to prevent warping as you are essentially welding on the middle of a plate.

Cheers,

Bruce (bruceinbangkokatgmaildotcom)

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On Dec 9, 7:41am, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

Is your approach based on ease of allignment or strength issues? I evision corrosion problems where the weld does not completely penetrate the slot. Upon typing this It is no worse (void penetration wise) than my original approach with slotted shafts.

With regards to some of the other suggestions: I envision problems with my buddy (owner of the mill) and his wife with me vaporizing gallons of sulfurized cutting oil in his garage. So I am leaning towards no milling of the shafts at the moment.

Thanks again for all the responses. I will post a pic or two in the dropbox upon completion.

Andy

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On Tue, 9 Dec 2008 09:41:20 -0800 (PST), andy

It sounds like you're concerned about crevice corrosion, and rightly so. As long as your welds are sound and prevent water from entering and stagnating in small cavities you'l be OK.

I don't know what the current thinking is on plate rudders. I built a few large rudders about 25 years ago and I believe the design was based on research from the University of Maine. There was fairing added around the rudder post (it was the full length of the rudder), a flange at the top and bottom, and a wedge cross-section at the trailing edge. These modifications were supposed to decrease drag and increase effectiveness without making the fabrication overly complicated. If you're interested I can make a quick picture.

(Say hi to Rex for me if you see him. He doesn't answer my emails. <g>)

--
Ned Simmons

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I read an in-depth article in Professional Boatbuilder magazine about rudder design. They talk about different foil types and effeciency and all sorts of stuff. My original plan was to make a bronze armature over which a white cedar core would be epoxied and faired to a foil shape. Cover the whole lot with fiberglass, and you have a rudder.

I have since spoken with a very knowlegeable gentleman from a propeller shop in Portsmouth NH. He says that he works with a lot of the racing lobsterboats from Maine. He tells me that the fastest rudder is a flat plate and to not waste my time with the foil shape. I also note that most of the boats that I see out of the water have plate rudders. Now this is more Monkey-see-monkey-do than engineering, but I am going to go with the real world experience rather than the books this time.

Unless you can convice me otherwise. Thanks again, and I will pass on a Hello to Rex. -Andy

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On Thu, 11 Dec 2008 06:53:34 -0800 (PST), the infamous andy

That's pure BS. The fastest rudder is a steerable jet. <vbg>

But I can see smoothing the leading and trailing edges of the rudder to reduce drag and turbulence if you're racing. The magazines and boat building shops are prone to marketing hype. I'd trust the prop guy.

-- At current market valuations (GM is worth less than Mattel) the Chinese government can afford to buy GM with petty cash. --Bertel Shmitt on kencan7 blogspot

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On Thu, 11 Dec 2008 06:53:34 -0800 (PST), andy

I'm not going to try based on 25 year old information clouded by memory. It sounds like you're aware of the arguments and have made an informed decision.

Thanks. I suspect his email filters think I'm spam, and I'm not good about thinking to call.

--
Ned Simmons

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On Mon, 8 Dec 2008 15:25:43 -0800 (PST), andy

That should work just fine.

Nah... you'll be fine. I would drill, say, 7/32" holes all the way through the bar. Use a 2-flue end mill.

Plenty (and I mean PLENTY) of heavy duty synthetic (or old sulfurized oil) lube would be my pick. (problem is.... you're looking at about $30 for a 1 gallon bottle and about $110 for 5 gals, if the gal isn't available) Stainless steels conduct heat poorly, therefore the heat will be concentrated in the cutter. Lots of cutting fluid will counter this effect. Take light cuts, but never let the cutter just ride in the cut without cutting. (Work hardening will be the inevitable result.)

PS Make sure all of this assembly is 316.... and that includes the rudder and weld filler metal.

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Gene writes:

You can get a quart or so bottle of sulfurized cutting oil at Home Depot, where they thread galvanized steel plumbing pipe.

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snip

I've just been doing something similar, although with a different brand mill - seems to me that a slitting saw would make short work of this job, and a 1/4 inch saw is cheap (there are a bunch on ebay) - it will do it in one pass. and end mill will break before you are done

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