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Thread: flywheel and shaft tapers, lapping

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  1. #1
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    Default flywheel and shaft tapers, lapping

    Didn't find this in Virtual Indian:
    What is the proper taper (measurement) for shaft and flywheel tapers?
    My rough measurements, with a caliper, showed .200" per (linear) inch on the crankpin hole of the flywheel.
    likewise, the drive shaft measured .208" per lineal inch
    and the hole in the flywheel measured .214" per lineal inch.
    "Rough" means wide margin of error, ..... like with the hairy eyeball

    While I don't like the concept of lapping with the stock shafts (they are shorter than the bore length), I am acknowledging the need for a better fit between shafts and flywheels. Mine don't seem to match as well is I'd like to see. Shafts pressed in by hand, I can wiggle them more than I'm comfortable with.
    About ten years ago I tried lapping an old flywheel with an old drive shaft, wheel in the lathe, shaft chucked into the tail stock, gentle pressure in brief contacts, about 60 rpm. Had a seizure, .. galled? Seems the compound collected in a 1/8" spot on the shaft, and cut a groove in the flywheel taper.
    Glad I hadn't tried that on new parts.

    Seems lapping discussions have suggested grasping the shaft in your fingers and rotating the shaft in the wheel (with compound, of course). Gee, it took quite a while to get to "failure" in a machine without removing much metal, so how long should it take to remove a few thou with just my fingers?!

  2. #2
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    Quote Originally Posted by fillibuster View Post
    ... so how long should it take to remove a few thou with just my fingers?!
    All day and part of the night.
    Please note that whizzer-wheel cuts upon lapping shafts can eliminate a great deal of galling or grooving. Reversing often, as you would by hand is also critical.

    The circumstances I described in the VI discussion were extreme, but not unusual. The taper occasionally has to be re-trued to the wheel, as well as re-surfaced.

    None of the shafts I have on hand seem to be worth measuring.... !

    ....Cotten
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    thx, Tom, I'd hoped to get your comments.
    "whizzer wheel cuts", would these be lineal grooves cut with a cutting wheel in a 4 1/2" grinder, or a smaller wheel in a die grinder? I'd thought of that, actually. I'd envisioned about 4 grooves, maybe in a spiral effect if possible, to lessen the effects of the keyways, and to hold a little more compound. ... are we on the same page?

    I measured again today, with 12" straight edges (from a combination square) against the tapers, and measuring at the ends, got 2 5/8" per foot.
    The sprocket taper is the same as the flywheel end of the drive shaft, but being longer, this end could be used on the flywheels and wouldn't come up short of the end of the bore like the intended end would.
    And I have to report that the largest collet with my Bridgeport is a 7/8", same as drive shaft.
    and I have old shafts and flywheels to practice with

  4. #4
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    A old tool, and die maker told me one time if you lap a taper, if there is a high spot on either part, the high spot will push the part to the low side. This will give you not a straight shaft to part alignment, when you are finished lapping. As your parts have been together I doubt you will have high spots that will cause any problems. might want to use blueing to check the fit first. I wonder why the shaft has movement in the flywheel? There again check with blueing. For what it's worth. Stan

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    Quote Originally Posted by stan View Post
    A old tool, and die maker told me one time if you lap a taper, if there is a high spot on either part, the high spot will push the part to the low side. This will give you not a straight shaft to part alignment, when you are finished lapping. As your parts have been together I doubt you will have high spots that will cause any problems. might want to use blueing to check the fit first. I wonder why the shaft has movement in the flywheel? There again check with blueing. For what it's worth. Stan
    Befuddles me too, why the "wiggle", but from my observation the small end of the taper is tighter than the large end, which suggests that the degree of taper is slightly in error in either the shaft or the bore. ...... The S & S wheels fit my various shafts tighter than the new T & O wheels. After some serious clubbing with brass drift and hammer, and re-torque-ing, and true-ing again, I was able to true things and maintain torque. But I never liked having the suspicions, and on disassembly they were only a few thousandths out of true, but I want more confidence this time.

    Tom, I opened your pics, saw the whizzer cuts, like! In a couple more days I'll have a lab rat in the mill for a test run. Any suggestions on rpm? My book says 100 to 150, but the book doesn't know what I'm doing with what. And I do have an old-fashioned valve-lapping oscillating crank, but doubt such a attachment is available for the Bridgeport. Would repetitive brush applications of compound compensate for the need to reverse rotation? .... And I presume pressure will have to be slight, and judged by the sound of the process. When it sounds like the compound has turned to grease, back off, and apply more compound?

    anybody want to tell me I'm p-ing' in the wind?

  6. #6
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    Filibuster!

    As you can see in my previous attachment, the cuts are narrow; a Dremel-type abrasive cut-off wheel works great. Whether longitudinal, cross-cut, or spiral grooves are best would be a useful study. Please note that a lapping shaft should probably be only used once.

    I wish I still had the math skills to calculate the tapers, but they have faded from lack of use... .. .

    And Stan!

    That is certainly true when hand-lapping, or without a pilot. My barnyard approach was to fixture the assembly using a lathe: http://virtualindian.org/10techfly.htm
    One can actually observe the wobble of the flywheel decrease as the taper is corrected.

    Please understand that I have found some tapers so skewed from the centerline that only installing a junk shaft and severe discipline with a hammer could get them within "lapping distance". (Mostly Brand X, of course.) "Z wheels" are indeed quite malleable.

    Low tech rules.

    ....Cotten
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  7. #7
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    The taper is 6 deg. per side, from Indian factory drawings.
    The theory behind lapping is that the abrasive imbeds in the softer material and actually grinds away the harder material, so that if you do it using the hardened shaft you are actually lapping the shaft to fit the worn flywheel.
    I know many people have done it this way and it will usually be acceptable, but the best way would be to cut a piece of brass in a lathe to the correct taper and then lap it in a lathe or vertical mill. A drill press is not absolutly square and will cause runout.
    Last edited by moldthread; 12-06-2014 at 10:01 AM.
    Bruce Argetsinger
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    Bruce, I have a friend that repairs old pocket watches as a hobby and he made the same comment about fitting a staff to a jewel bearing. He said it's the soft staff that will cut the jewel in the same method you mentioned.
    Eric Smith
    AMCA #886

  9. #9
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    I agree of course, Folks,

    (That same phenomenon is what made H-D's aluminum tappet blocks wear their tappets prematurely, and why Panhead valveseats don't like to be lapped.)

    But let us balance that against what is practical and expedient. Cranking out a brass or other piece to sacrifice for each taper is costly in time and material, even if you re-cut it fresh each time.
    Perhaps it would be appropriate to anneal original shafts in a firepit overnight?

    ....Cotten
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  10. #10
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    Update: Good so far!
    With a dial indicator on the top of the crankshaft, with hand pressure downward on the crankshaft into the flywheel taper, and forcing the top end of the crankshaft away and against the dial indicator, I have reduced (by lapping) the WIGGLE from .012" to less than .001", with less than 30 minutes of lapping.
    (felt so good about it I had to report)

    I'd found a step-shaft in my junk, approx 2 11/16" dis. by 2 1/2" long, into the lathe, faced it off, bored the center to 1" for a tight fit with the crankshaft, used this piece clamped to the flywheel to hold the shaft perpendicular with the wheel, put a flat washer and the nut on the opposite end and drove the shaft with a drill and 1 1/8" socket. Variable speed drill and low rpm, about 100-150, frequent reversals and addition of compound, maybe 5# of pressure. Drill in right hand, and middle finger of left hand (in a greasy glove) pushing the shaft out-of-contact from the back side like the old boy taught me to do when lapping valves in my 45 about 42 years ago!!

    Was a little concerned with the increased "depth" I'd get from the lapping, I pre-calculated that I'd have to remove .002" from the large end of the bore (the movement was in the small end) before the small end would fit tight, and with a taper of 2 5/8" per foot then my lineal loss would be 4.5 times the .002", equals .009", ...... so each flywheel's thrust washer will have to be about .009" thinner than before. ..... achievable. .... and I'd "show my work" but I'm too lazy.

    2 5/8" per foot is 6.279 degrees, if you use the sin inverse on your calculator.

    Doing the drive and pinion may be a little trickier, but the method will be similar.

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