View Full Version : Contact area check for tapered shaft/ hubs

06-09-2005, 08:54 PM
Where I can find a detailed procedure for carrying out a contact area check using machinist "blue" for tapered steel shafts (Approx 3" nominal diameter) and matching iron hubs.
Taper is 3/4" per foot on diameter.
I do not have taper gauges so contact will be between the respective hub and shaft.
How is the percentage of contact area determined?
Thank you as always,

06-09-2005, 10:45 PM
Not sure if there is a standard method,but the method I use is to blue the shaft and slide the hub on,then twist the hub 5* and back 5*.Remove the hub and see where the bright spots are on the shaft.

Idealy you want a contact area of 2/3 starting at each end of the taper and extending to the center yielding a slight hour glass shape.The opposite of that is is a barrel shape and undesirable.

I quit using Dykem for checking tapers,the stuff I can get locally is a little too thick and it "drags" marring the contact pattern.I now use the common black marks-a-lot,I find it gets me closer to fit faster and it's cheap.

What are you fitting,prop shafts?

[This message has been edited by wierdscience (edited 06-09-2005).]

06-09-2005, 11:09 PM
I'm working on an old Cummins engine with a tapered crankshaft nose. The service manual says to lap the hub to the crank with 280 grit lapping compound. Clean throughly and blue. Place hub on crank and turn 1/8 turn and pull straight off. First 1/2 inch on large diameter should be 100% contact, remaining surface should be 70% to 100% contact.