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  #1  
Old 05-05-2011
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Shaft has no hole for Cotter Pin?

I recently removed the old Martec folding prop and bought a fixed one. When I slid it up to the taper, it had A) not enough threads for two nuts and B) no hole for a cotter.
Before I go and do something rash like drilling a hole, can someone explain why this is?
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Old 05-05-2011
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Quote:
Originally Posted by rbrasi View Post
I recently removed the old Martec folding prop and bought a fixed one. When I slid it up to the taper, it had A) not enough threads for two nuts and B) no hole for a cotter.
Before I go and do something rash like drilling a hole, can someone explain why this is?
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No hole for a pin? That seems really strange to me. Are you sure that maybe the hole isn't clogged by a broken pin? Besides that, I can't speculate.
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Old 05-05-2011
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Could the shaft have been shortened a tad, cutting off the cotter-pin hole, to get the folding prop hub to fit?
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Could the shaft have been shortened a tad, cutting off the cotter-pin hole, to get the folding prop hub to fit?
I hadn't thought of that.
I added something called a "shaft saver" when I repowered and that moved my shaft back about three quarters of an inch. I suppose that if someone had a problem like that they might have shortened the shaft.
I would think that they would have re drilled the hole though.
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Quote:
Originally Posted by SlowButSteady View Post
Could the shaft have been shortened a tad, cutting off the cotter-pin hole, to get the folding prop hub to fit?
I suppose it's possible, but it looks like a factory cut. There are definitely no holes. The previous owner was a racer and very meticulous, so it wouldn't surprise me a bit if he did have a factory shortened shaft.
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The shaft taper, threads and cotter pin hole are identical for the Martec folder and a standard fixed blade prop. The nut on the Martec is different - internal to the hub - but the shaft is identical. Are you sure the new prop is the right size (shaft diameter). If too small it won't slide far enough along the taper.
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Quote:
Originally Posted by JimsCAL View Post
The shaft taper, threads and cotter pin hole are identical for the Martec folder and a standard fixed blade prop. The nut on the Martec is different - internal to the hub - but the shaft is identical. Are you sure the new prop is the right size (shaft diameter). If too small it won't slide far enough along the taper.
Yes. The nuts screw on. They are all 1".
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FWIW not ALL shaft tapers are the "same" - although any American made ones should be. We recently had to have a new hub machined for a Max prop for that reason.

Some years back we removed a Martec for a fixed Campbell and we had the same issue.. we drilled and threaded the nut for set screws but I don't think that's quite as secure. If you decide to drill the shaft for a proper pin try to get some carbide bits.

btw Jim's point 'sliding all the way on' is well taken.. if the taper doesn't match you may have unexposed threads inside the hub. You shouldn't see any shaft taper behind the hub.
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Drilling a hole through the nut and shaft is not an impossible task ... for an experienced machinist and a portable drill press. Drilling such 'by hand' will inevitable lead to ..... .
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If you decide to drill, here is what you need to do. Don't bother with carbide, but cobalt is nice, or titanium nitride coated if it good quality, brand new. The secret to stainless drilling is LOTS of pressure. Stainless work hardens, if the bit stops cutting the stainless hardens and destroys it. If it keeps cutting then it keeps cutting!

Here is how to get the pressure you need with a hand drill. First pick the right drill. Forget battery drills, the battery isn't the problem. It appears that when they started designing battery drills they fired everyone that knew anything about drilling! You need a drill with the proper grip. You'll recognize it because it will have a groove on either side for your thumb and forefinger. You'll notice that almost all corded drills have this feature, and almost none of the battery drills! This is very important to drilling stainless. Grip the drill between thumb and forefinger, and pull the trigger with your pinky. You'll notice you can get centerline of the drill bit lined up with the center of your forearm. So you can push very hard and not put side pressure on the bit, which would bend and break it. This is why a drill press works so much better than hand drilling.

On a threaded boat shaft you are going to want to use a dremel grinder to produce a flat spot on the thread that you can then center punch to start the bit. Buy some tapping fluid, the thick kind that will stay on the bit, not the thin watery stuff. Use low speed, about 250 rpm would be good, brace yourself and push as hard as you possibly can. You want to keep a chip coming out at all times. Stop and rest and lubricate the bit every so often. It will seem like forever, but an inch of stainless will take less than five minutes.

It would be good to practice the grip and the pushing really hard on a piece of scrap, even regular steel to get the technique down before doing the shaft. I've drilled and tapped thousands of holes this way and it does work. The secret is really in the grip!

Gary H. Lucas
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