Quadrant

[Duncan Gibbs]

Re: Quadrant

What is the tiller and quadrant made of? I notice that the top of the tiller is darker.. Angelique?

Yes:

A tiller sitting on a barn door rudder continues the curved line of the rudder profile. To this end the top was trimmed and an additional lamination of Angelique glued on...to protect the Locust from damage, y'see.

See... I yam paying attention!

[Paul Pless]

Re: Quadrant

So Jim, since you're giving up on an 8 foot tiller to steer your catboat in favor of the less physically demanding wheel; will you be machining a pulley onto the pinion shaft for ease of installing an autohelm?

[Cogeniac]

Re: Quadrant

No I've got the basics, the next question is about the involute tooth profile. What I think I understand from Scott and Jakes' descriptions is that over the length of the tooth (both rack and pinion profiles) that the profile has to slightly change from the wheel end to the rudder end so that the bearing surfaces always roll over each other rather than roll at one end of the tooth and slide at the other end, as the pitch radius changes?

Almost....

For spur gears the involute profile assures that the pressure point "rolls" across the face of the meshed teeth. This is a bit like two wheels, where the surfaces are rolling past each other, but not sliding relative to each other (the contact point is in static friction). If you didn't have an involute profile the teeth would though and slide against each other, and the effective pitch would change around as different parts of the gear faces and edges made contact. You can see this in the animations a few posts above.

If one of the gears has an infinite radius, so it becomes a flat gear, or a rack, then the involute profile flattens out into a straight sided trapezoidal gear (smaller at the tip than the root, but flat sided. This will mesh properly with a pinion gear that has curved involute profile teeth. Basically as the diameter of the gear increases the curvature of the involute gear decreases.

In Jim's case there are three complicating issues that arise because the quadrant gear is curved. Since it is curved, the pitch on the inside (the "rudder side") is smaller than the pitch on the forward side. This means that the teeth (and grooves, or non-teetch spaces) on the quadrant are slightly tapered (fatter/wider at the forward side and thinner/narrower on the aft side and linearly changing in between. The second issue is that to engage this tapered gear, the pinion must also be tapered. And the third, and most complicated issue, is that, as shown in my diagram of Post 222 above, the quadrant gear teeth will initially engage the pinion gear teeth slightly inward from the forward end of the pinion (all the way across the pinion). So the pressure line not only moves along the tooth from root to tip on the driving gear (See animation at Post 91), it has to move forward from the first point of contact to the point where the tooth is right on the centerline of the pinion, and then back out to the point of last contact. If the tooth is properly shaped this point will also "roll" and not slide.

I am not certain, but I think this requires the teeth to have a slightly thinner base (note this is a change from previous posts, but since the pinion gear teeth engage the rack at their root, either the root needs to be smaller or the tips of the rack need to be smaller. According to Andev, this is called an Octoid tooth, as opposed to an involute. The thinner tip assures that the pinion can engage the rack at the slightly smaller diameter and smaller pitch, and then stay engaged as the pressure point moves toward the outer edge of the pinion. I have a suspicion that the true rolling tooth form is curved, and a narrower tooth straight gear will have some sliding action, and thus more wear, but this is the limit of mu knowledge on this topic (yes! it's true!!). For this application it is probably academic, since it is not a high wear, application. What Jim will find is a tad more gear friction than he might otherwise feel....

Hope this explains things more fully...

S

[Duncan Gibbs]

Re: Quadrant

It does, but it then begs the question why not angle the rack and pinion gears toward each other thereby reducing the taper, the effect of quadrant's radius and the difference between the initial point of engagement and where the teeth mesh at the centreline of the pinion? I would assume that this gearing is, in effect, nothing more that a quartered right angle gearbox, albeit with a reduction ratio, and that the same principles that apply to a right angle gearbox apply quite directly to Jim's quadrant. Am I getting closer?

[Jim Ledger]

Re: Quadrant

Or, a pair of nice cast bronze stays through bolted to the tiller and to the quadrant ends.

Nick, don't say things like this to me...please.

[Jim Ledger]

Re: Quadrant

What is the tiller and quadrant made of? I notice that the top of the tiller is darker.. Angelique?


S

Scott, the tiller is a laminated from half-inch thick BlacK Locust. The top profile was then cut and a lamination of Angelique applied. The Angelique lamination covered the sliced laminations beneath and protects their exposed end grain. The quadrant was laminated from eight-inch thick Black Locust.

[Jim Ledger]

Re: Quadrant

and I am watching Jim's progress with bated breath because he is a bloke who actually thinks before cutting !

Sometimes thinks too much, I'm thinking. One time I stopped a cut half way and didn't finish it until the following year.

Some kinds of building are akin to playing chess, you have to think as far ahead as you can and consider a lot of options...and then take a chance anyway.

[Jim Ledger]

Re: Quadrant

So Jim, since you're giving up on an 8 foot tiller to steer your catboat in favor of the less physically demanding wheel; will you be machining a pulley onto the pinion shaft for ease of installing an autohelm?

I hadn't considered it, Paul, I didn't know it was possible on a catboat.

But, if I was going to install something like that, I'd wait until I had the piece of hardware and instructions in hand before modifying anything.

The wheel shaft will be fairly easy to remove, a few bolts is all..

[PeterSibley]

Re: Quadrant

The other school of thought is to wait 30 seconds, max, before doing something , even if it ends up being wrong because momentum is your friend.

[Paul Pless]

Re: Quadrant

One time I stopped a cut half way and didn't finish it until the following year.

Hey! I've done that before. . .

[Paul Pless]

Re: Quadrant

I hadn't considered it, Paul, I didn't know it was possible on a catboat.

But, if I was going to install something like that, I'd wait until I had the piece of hardware and instructions in hand before modifying anything.

The wheel shaft will be fairly easy to remove, a few bolts is all..

I remember you and I sitting in an old giant catboat at Mystic a couple of years ago. Tracey and Mike Mckien were with us as well. The owner had installed a belt driven auto helm with remote control to the wheel, so that he could work at the mast and cabin top raising and lowering the sail and still have control of the helm. It seemed a bit of overkill in a catboat, where there's many options for leading the necessary lines back to the cockpit. Mostly I'm just poking at you.

Frikking great thread, reminds of Ken Hutchins a bit. Can't wait to see some casting going forward, will you have Tracey do some video for us?

[Jim Ledger]

Re: Quadrant

Scott...Duncan? You two all right? There's nothing I need add here, is there?

The only thing I need is a tooth pattern of the right size and shape...and I have that. After that it's just an interesting woodwork problem.

Carry on.

[Jim Ledger]

Re: Quadrant

I remember you and I sitting in an old giant catboat at Mystic a couple of years ago. Tracey and Mike Mckien were with us as well. The owner had installed a belt driven auto helm with remote control to the wheel, so that he could work at the mast and cabin top raising and lowering the sail and still have control of the helm. It seemed a bit of overkill in a catboat, where there's many options for leading the necessary lines back to the cockpit. Mostly I'm just poking at you.

I remember. Paul. That boat was just a bit too flash for my taste. Maybe it was the black granite counters, but I didn't come away with much I'd like to copy.

Here's the first of the two braces for the tiller. Sorry, Nick, not cast bronze, laminated Locust instead.

[Paul Pless]

Re: Quadrant

but I didn't come away with much I'd like to copy.

the standing headroom was nice

[Jim Ledger]

Re: Quadrant

the standing headroom was nice

If your boat gets large enough that's a given.