Couplings, Lathe Or Mill?

[FLUTE HEAD]

I've been trying to make a coupling to connect two different sized shafts and I seem to be having problems. My question is, should this be done only on a lathe? I have checked my spindle to be perpindicular to around 5 tenthousandths , but I guess it would only take "a hair" off to throw the concentricity off. Have any of you been successful with this on a mill? My shafts are 3/8 to a 15/32 shaft. Maybe I should just turn my 15/32 shaft down to make things easier.

[HuFlungDung]

If it is a rigid coupling, the best method is to bore it in one setup on the lathe. Whether a rigid coupling is best is questionable: the concentricity and perpendicularity of the two shafts needs to have zero deviation, because bearing preloading and possible shaft fatigueing will occur after running for a while.

[FLUTE HEAD]

THANKS, I'll try to get that done on a lathe.

[swarfmacdaddy]

Boy, hes not kidding zero deviation!!! I had a machine shop make me some rigid couplings and it took me weeks to get them alinged and they have never been right. So i gotta break down some day and buy some flex couplings. I even spent enough at the machine shop to buy 20 couplings. Lovejoy makes real nice ones. Cheap too.

[HuFlungDung]

Randy,

Maybe they were never made right? It should be possible if you take the time to align them, to get them right. Having said that though, the ideal motor type is the C-flange (face mount), bolting to a machined-in-place face frame. This allows you to tighten up the coupling, leaving the motor bolts slightly loose. Then run the motor and tighten the bolts up when it has found its natural position. Whatever clearance they gave the coupling bore on the motor or screw shaft will equal the eccentricity that cannot be corrected. I suppose if both ends of the coupling have exactly the same amount of clearance, and the setscrews are exactly in line, when the coupling is tightened, the shafts will line up, even though the coupling itself may be a little bit eccentric. A really close fit is a must (even if you have to heat the coupling to assemble it on the shafts).

The whole setup will be more forgiving if you remove one bearing from the motor (next to the coupling) and allow the bearing on the shaft to support that end of the motor. Or vice versa. But, again, only with a C-flange motor mount.

[FLUTE HEAD]

As a matter of fact I ended up going with a c-flange. But I decided to check the shaft on the machine with a test indicator. Turns out that the shaft is out of concentricity (bent) a few thousandths. I hope I didn't do that while moving the machine. I'll try to have it turned down so that its back to good.

[ViperTX]

If you are using setscrew then that is probably throwing you even further off. You need to attach one end and turn the other end if you even want to get close.....any amount of variation is going to show up....find a flexible coupling....or buy one and bore it out....*smile*