lapping on shaft tapers

[Paul45c]

Figured I'd post a new thread on this one, since it's not exactly about mounting props.

What, exactly, is the technique for lapping props on the tapers? What do they call the grinding compound, and where do you get it?

I know my wheels were done when I first got the boat, but I've never done it.

 

[Genesis]

You can get valve grinding compound at NAPA.

The idea is that you clean up the bore and shaft as best you can to remove all debris, gunk, etc.

Then you put some grinding compound on the shaft, and put the prop on the shaft (no key)

While applying force forward, you rotate the prop on the shaft. This effectively grinds the two together with the compound between them, fitting them to one another.

It may take 200 rotations - or more - to do a good job, depending on how out-of-round and true the tapers are.

To check it, you clean all the grinding compound off the shaft and bore, then put some prussian blue on the taper and rotate the shaft. You will see where there is no contact by where the dye does not transfer.

You're aiming for 100% contact. You probably won't get there, but you can get quite close (80+%)

 

[CARL GUZMAN]

Just to recap on the past ? there's no way to do this under water so I should pull my boat out and doulble check asap? right?

 

[yachtsmanbill]

You can get valve grinding compound at NAPA.

The idea is that you clean up the bore and shaft as best you can to remove all debris, gunk, etc.

Then you put some grinding compound on the shaft, and put the prop on the shaft (no key)

While applying force forward, you rotate the prop on the shaft. This effectively grinds the two together with the compound between them, fitting them to one another.

It may take 200 rotations - or more - to do a good job, depending on how out-of-round and true the tapers are.

To check it, you clean all the grinding compound off the shaft and bore, then put some prussian blue on the taper and rotate the shaft. You will see where there is no contact by where the dye does not transfer.

You're aiming for 100% contact. You probably won't get there, but you can get quite close (80+%)

Would you believe the lapping compound we used on tapers was SPECIAL NAVY GRADE? Probably about 1200 or so. ws

 

[Walter P]

Guys,

Karl is absolutely correct in the procedure, however be sure you are using DIS-SIMILAR metals. Stainless shafts with NiBral or Bronze props is fine. Stainless shafts with stainless props will gaul and you will defeat the purpose of lapping. What happens is that the tiny metal particles that are being removed from the lapping process tend to stick to each other and form clumps that seize between the two surfaces being lapped. I'm not quite sure but I think what happens when you lap bronze or Nibral to stainless, the softer bronze only can adhere to the softer metal. Whatever is happening I can assure you that it's risky to lap SS to SS.

Walt

 

[luckydave215]

For those who aren't familiar with prussian blue, it's a cobalt blue ink mixed with grease. Apply it sparingly to one surface only, spin the prop a turn or two, and look for the color transfer on the other surface.

 

[Paul45c]

Great replies. I'm going to guess it would be best to apply the Prussian Blue to the shaft and not the prop, since it's easier to see it on the shaft (just slide the prop back).

Do you find you have to lock the shaft down, or does this not apply enough torque to rotate the shaft?

 

[Genesis]

Normally there's not enough torque to rotate the shaft, but it depends on your setup and how worn the cutless bearings are. If yours are a bit loose hten you might need to, but you really ought to think about changing them if you get in trouble doing this.

As for not being able to do this in the water, you're correct. Its impossible to do this with any reasonable amount of accuracy wet, and most valve compounds are water-based.

The note about stainless props is also correct - it can be done with them but it takes a LOT of care and frequent cleaning of the removed material. Fortunately most props are made of Nibral.....

$1200 for grinding compound eh? Why do I suspect it was the same stuff you get at NAPA, but marked up to "military" prices?

 

[Paul45c]

Normally there's not enough torque to rotate the shaft, but it depends on your setup and how worn the cutless bearings are. If yours are a bit loose hten you might need to, but you really ought to think about changing them if you get in trouble doing this.

Nope, my cutlesses are almost new. No probs there. Thanks, Karl.

 

[yachtsmanbill]

Normally there's not enough torque to rotate the shaft, but it depends on your setup and how worn the cutless bearings are. If yours are a bit loose hten you might need to, but you really ought to think about changing them if you get in trouble doing this.

As for not being able to do this in the water, you're correct. Its impossible to do this with any reasonable amount of accuracy wet, and most valve compounds are water-based.

The note about stainless props is also correct - it can be done with them but it takes a LOT of care and frequent cleaning of the removed material. Fortunately most props are made of Nibral.....

$1200 for grinding compound eh? Why do I suspect it was the same stuff you get at NAPA, but marked up to "military" prices?

C'mon Karl--that was a #1200 and it is OIL based. CLOVERLEAF is the brand and you can get it at GRAINGERS. A 4oz. can should be enough for a hundred jobs. Not to sound fecisious (sp), but the way I learned to lap was not to spin the joint (or valves for that matter) around and around, rather 1/4 turns back and forth, lift the part and advance the index, set it down and repeat. You really dont want rings around the bore. It also wouldnt hurt to give the shaft a shoe shine with 1000 emery to break any crud off first.The key and way should probably get dressed also to facilitate the lapping job. I would also recomend a dye check around the key way. I had 2 aquamet shafts made and the knucklehead that did the keyways cut them with square corners setting up a fracture zone. The keys and the way should have a 1/16th radius. Mine failed 100% at mid taper.
BOAT US ws good enough to buy a new wheel and 2 shafts. Of course at that time I went through the stuffing boxes,cutless's and alignment along with 2 new couplings as they were originals. Alignment can be roughed in on the hard, but a final should be done after the hull settles out in the water.I I do try to be thorough. I was at the dry dock this morning and watched them put the new Kahlenberg wheel on and will try to squeeze some pix in later of the nutting arraingement. I know how fastidious true yachtsmen can be when it comes to their running gear without becoming BANAL. We all know there is a right way, wrong way and my way to approach various repairs on our yachts, with the latter usually taking precedence. Although mistakes can usually be remedied with an ounce of experience, I personally feel that there are certain areas that wont tolerate compromise. A failure is bound to occur at the worst possible time--usually when a collision is imminent or your running a hot inlet.
As far as the lapping conditions are concerned on stainless steel you are absolutely right on! Discretion is the key word here. Lap, clean and lap some more is the order of the day. I really feel that you would be struggling to use enough pressure by hand to cause a metal to metal galling. On a brand new pair of Michigan wheels I bought I found "seating reliefs" distressed in the bore, much akin to rifling. I would have to assume that since these were raised in the neighborhood of about .001- .0015" they would sqeeze in upon bore stretching. I think they aid in the bore squarley seating on the shaft.These marks were barely evident when I used DYKEM blue. Anyone that uses any bluing should be aware that it will stain your fingers for a long time. I prefer to wear double plastic gloves.
I want to wish all the fellow HATTERAS owners a nice day. I sincerely hope you are all enjoying this beautiful fall weather!! Although it is 50 and gray here in Chicago, it sure beats the weather that I endured in New Orleans all summer working on my yacht. Being temporarily land based, I neglected to catch the MAFOR forecast today. Maybe one of the other well found yachtsmen here can provide us all with a national update. Best regards, and dont forget to check over your bonding systems!! Mr. William Stephan

 

[Genesis]

Oh ok Cloverleaf... I thought you were talking about the PRICE! Heh, with the military, you never do know!

Lifting and re-seating works too - its not about trying to remove material.... I know you know that, but a lot of folks don't get what you're really trying to do here - its about smoothing imperfections that are beyond the thousandth-of-an-inch arena - if you're much more out of round or off the taper specs than that you're not going to succeed with lapping and the shaft and/or props need to go to a shop and have the taper cleaned up.

I concur fully with the keyway inspection too, and for the same reason... and that key should go in AFTER the wheel is placed on the shaft - it should require no more than a couple of fingers worth of pressure. If its "tight" and you see some yard monkey hammering it in there with tools don't let 'em do it!