Cutting Keyway in Rudder Shaft for AP

[silverp40]

I am installing a belowdeck autopilot (our boat) and really feel I should cut a keyway in the bronze Edson tiller arm (that connects to the rudder stock) as well as the rudder stock itself rather than use set screws.

The tiller arm I can take to a machine shop to cut a 1/4" to 5/16" key but I really would prefer not to take the boat to drydock, pull the rudder and take it to a machine shop!

Cutting a accurate keyway is not easy on a round surface, on hard rudderstock (probably ruddershaft material) and in an tight space!!

Can anyone suggest (maybe from experience????) a method or any ideas? I thought the grinder with a cut-off wheel....

Any ideas would be really appreciated!

[stevensc]

Instead of a keyway would you consider drilling a hole through both pieces, assembled, and putting a bolt through. Imagine a shear pin, It would be easier but I am not sure if it will work for your case?
Steve W

[bobconnie]

Many machine shops have portable keyway cutters just for things of this sort. Suggest you do some phone calling to see if one is available in your area ! I am pretty good machinest, and I would never try to cut a keyway by hand with a grinder of any kind. If ya drill good semi deep dents in the shaft and double up the set screws it should hold forever !! Just my 2 cents

[Nicholson58]

I work in a machine shop. You are not likely to cut a good key without putting it in the shop. A key will be a lot stronger than set screws. It might depend on how balanced your rudder is. My rudder post is at the leading edge - lots of torque required. If you have an almost neutrally balanced spade rudder the torque is small.

[silverp40]

Thanks all for the input...after modifying the rudder it is much more balanced than before...

The previous autopilot I had here had a 1/4" and a 5/16" set screw on either side of the tiller that went about 1/4" deep and were tapped.

I agree with Nicholson that a key is stronger than even 2 screws...and as far as drilling all the way thru the shaft...well I think it will weaken it quite a bit.

I think I should look for a portable key cutter to rent?

[bobconnie]

Unless you are a OLD machinst, ya better hire one to do it ! this OLD type portable stuff is hard to set up and use ! Ive done stuff like this in the type of places your shaft is in and it's no fun! just my 2 cents after 50 yrs of doing stuff like this !

[charliehows]

what about a 'scotch key' - i've used these a lot and all you need is a hand drill and thread tap - you can use an allen key or a bolt for the key, i prefer the allen key cos it can screw in to the full extent of the thread available. For a rudder i'd be using the biggest one i think i can manage to fit.

[Celestialsailor]

Good luck using a portable keyway cutter in a confined space like that. I've been a Toolmaker/Machinist for 32 years. I can tell you from experience to do it right. There will be an incredible load on that keyway from the torque of the arm. Why not wait for the next haulout to do it?

[Cheechako]

Originally Posted by bobconnie

Many machine shops have portable keyway cutters just for things of this sort. Suggest you do some phone calling to see if one is available in your area ! I am pretty good machinest, and I would never try to cut a keyway by hand with a grinder of any kind. If ya drill good semi deep dents in the shaft and double up the set screws it should hold forever !! Just my 2 cents

If it has been fine the way it is, just drilling those divits should work to double your confidence.

[Cruisingoneday]

I was a Journeyman Machinist working in a job type shop with portable work for many years before I went back to Mech. Eng school..

Here's what I have used for additional strength when even a standard key is not enough to hold. You can use a Pin Key as shown on attached link,

Shaft Keys - Types and Their Design#

It's shown about 1/2 way down the page.

It's easy to do in-situ with just a couple of drill bits and a hand drill if there is room. A standard straight dowel can be used. It can be drilled as deep as you need for the shear strength required. It may even be tapped and a set screw or bolt installed for additional piece of mind.

The only caveat is that the hub must be flush or close to the end of the shaft and the hub should have some meat on the outside as it introduces different forces into the hub than a standard Woodruff or square key.

For a 1/4" Dowel use a 1/8" or 3/16" drill first and then drill with the 1/4" to depth, if you use a drill that's been sharpened correctly you will end up with a thous or so clearance on the dowel.

A 1/4" x 1" long dowel has tremendous shear strength.

I have seen bolts/shear pins cross drilled but in my experience unless a tapered dowel is used they always seem to get some slop in the hole with an oscillating loads.


And put your bucket under it to catch the drill chips!

Cruisingoneday

[perchance]

If drilling for a dowel best practice is to drill slightly udersized and ream to final dimension. If using a tapered dowel in a blind hole use the type with the threaded end for ease of removal.

[Blue Stocking]

Power or sail boat?

[colemj]

Have you purchased the Edson tiller arm yet? At time of purchase, you need to tell them whether you want it with a keyway or with a through bolt for connecting to the rudder shaft. If you already purchased it, it should have one or the other - which solves half of your problem and decides the other half for you. If you haven't purchased it yet, then you have a choice to make.

I don't see set screws on any of their arms in the Edson catalogue, nor do they mention them - only keyways and through bolts.

Mark

[silverp40]

THanks againto all for your generous advice. Here are some answers and the latest developments...

It is for a sailboat

I already checked with Edson and their tiller arm cost plus 20 degree square section offset milling angle is about $650!

The arm that is here is by Buck-Algonquin (not sure of the spelling). The two set bolts were ok but only for a little use - the windvane did most of the steering. Hence I would like use a better attachment method.

So I decided to use the upper section of square cut rudder shaft that is above the quadrant and install the tiller arm there. Will have to move the drive up and make a glass pedestral about 3"thick to attach the drive. The new tiller arm will be built by a local machinist from a rectangular piece of 304L flatbar ss and split around the square rudder shaft area, attached with 1/2" bolts (I know, it's way oversized). The square section will provide all the grip needed for the hi torque . Oh,and the cost of labor and materials is half !

[popeye2818]

You could have milled the keyway to half thickness and had a local welder tig weld it on with a full pen weld,depending where you are it probably would be 75 to 150 dollar welding job.Im not fond of set screws ,even with divits.They tend to losen at the worst time.