How Far Can You Lap Prop?

[Sailor_Grant]

I just bought a new prop, it has correct taper and fits well with no wobble, however, it does only slide up so there is a 1/2 inch of space between front of prop to taper wall, so that the second prop nut could not be put on past the split pin. I know the standard is a 1/4 inch of space between the taper wall and front prop face.

Do you think I can make up this distance by lapping the prop excessively?

[Lee Jerry]

Yes, lapping should solve your problem. And I don't think it will take nearly as much (lapping) as you think.

[leecea]

FYI, I have an old 1" shaft and did an approx. measurement of two diameters 1/4" apart and it was around 0.3mm.

[SailingHarmonie]

You might know this already, but be sure to try the fit without the key in place to be sure the key is not restricting the fit. If all is good, I think as LeeJerry suggests, I think you find this goes pretty quick. To move it 0.25" up the taper you only need to increase the radius of the bore about 0.01". Bronze is a dream to machine.

[kapnd]

When you dry fit the prop without the key, mark the front of the shaft.
After refitting with the key, if the prop doesn’t slide clear to the mark you made, the key probably needs a few strokes with a file.

[dannc]

The OP might want to check out YouTube for some videos. I just saw a video on lapping a prop... I think it was on...

Yep, it was on Sampson Boat Company's channel around the 10 minute mark,

https://www.youtube.com/watch?v=dh1JVsPsfJI

I am sure there are other videos out there as well.

[Bowdrie]

Yes, index marks and making sure the key fits properly without binding are important first steps to take care of before it's determined that lapping is necessary.
Should you do have to lap, .010", (ten thousandths,) is a lot of material.
So, what we did in the old days was rig up the hose and bucket so that the engine could be run on the hard.
With the prop removed and the high spots/areas marked, put the engine in gear and turn the shaft at idle speed whilst using strips of fine emery cloth in back-and-forth motion on the taper, (like polishing on a lathe).
Once we were down to the last few thousandths then used the lapping compound to smooth/even-up the taper by hand turning the prop.
No way was the boss going to have someone spend all day twisting a prop on a shaft with constant on/off and adding compound.

[skipperpete]

I’m just not keeping up with the changes in how propellers are measured and fitted, up till now I’d always regarded the propshaft taper as an untouchable reference point to which a propeller is mated by using Prussian blue and a bearing scraper and that (for survey) the final contact area was to be a smooth 70-80% blue marking pattern, no annular rings. The OP got the wrong taper in his new propeller, the reference point is always the small diameter, if this dimension is too large the prop will sit too far up the taper.. and if its too small it won’t go far enough up the shaft taper despite the fact that the angles match perfectly.

[Bowdrie]

^ You bring up a valid point.
"Hey boss, did I run the taper reamer far enough into this prop bore"?

Edit: my first post, #7, was based on the fact that shafts are cut and tapered by hundreds of shops of all sizes, and who knows how accurate their taper attachments on their lathes are.
Whereas props are made by a relatively few companies that you assume are using quite accurate standards for their machining operations.

[Sailor_Grant]

Thanks everyone for the replies.

I spoke with the manufacturer, and they stated that lapping may only give you a 1/16" at best.

I took out the digital calipers and confirmed the small end diameter of the ptop was too small, and therefore misbored, and they are sending me a new prop.

So for other folks on CF having this issue, take out the digital calipers and confirm the small end prop diameter is correct if not seating correctly, as these prop companies are not perfect! (this is second prop the sent me misbored)

[skipperpete]

Originally Posted by Sailor_Grant

Thanks everyone for the replies.

I spoke with the manufacturer, and they stated that lapping may only give you a 1/16" at best.

I took out the digital calipers and confirmed the small end diameter of the ptop was too small, and therefore misbored, and they are sending me a new prop.

So for other folks on CF having this issue, take out the digital calipers and confirm the small end prop diameter is correct if not seating correctly, as these prop companies are not perfect! (this is second prop the sent me misbored)

Thanks for the update Sailor_Grant, happy to hear that you got a favorable response from the prop supplier.

[CaptCorn]

What we do with larger propellers is heat the hub evenly with a rose bud and while still warm slide it on and tighten it with the first nut. Then when it cools it shrinks and does not rely upon the nut.

[sinnerman]

Originally Posted by Bowdrie

Yes, index marks and making sure the key fits properly without binding are important first steps to take care of before it's determined that lapping is necessary.
Should you do have to lap, .010", (ten thousandths,) is a lot of material.
So, what we did in the old days was rig up the hose and bucket so that the engine could be run on the hard.
With the prop removed and the high spots/areas marked, put the engine in gear and turn the shaft at idle speed whilst using strips of fine emery cloth in back-and-forth motion on the taper, (like polishing on a lathe).
Once we were down to the last few thousandths then used the lapping compound to smooth/even-up the taper by hand turning the prop.
No way was the boss going to have someone spend all day twisting a prop on a shaft with constant on/off and adding compound.

Note that in the above, you are lappping / reducing the size of the shaft.

If you use a lapping compound, the prop would be the one being "machined" as it is the softer material (bronze versus the stainless steel shaft)..

my two cents

cheers

[Icarus]

Dry fit?
You need to torque the prop nut, depending on the diameter of the threaded stub...1/2", 5/16, 3/4?

if the second lock nut pin hole doesn't line up drill a new hole for the split pin.

I would apply Loctite blue or red to the threat.