Greetings and thanks for reading this. I have disassembled the spindle of my Enco 20 inch square column mill-drill to replace the pins that prevent the collet form slipping. Now I need the procedure for preloading the bearings. The "manual" is worthless. Any ideas? thanks, John
The preload should be pretty low, perhaps 30 to 100 pounds of axial force. If it's too loose you'll get chatter, too tight and the bearings will overheat at high speeds.
First question is how is the preload determined? Spacers, shims, adjusting nut, or something else?
Is there a single tapered roller bearing at each end of the shaft or two tapered bearings together or what arrangement? Whatever you determine the force to be, be sure to rotate the bearing several rotations in each direction as you tighten the nut to allow the rollers to align properly. Otherwise, they will align once they start running and change the preload.
-Mount an indicator to the quill with the tip on the end of the spindle to detect axial play in the bearings. You want the indicator fastened to the quill so you're not measuring deflection of the machine structure.
-Snug the preload nut while checking for relative axial movement between the spindle and quill. Use a lever between the table and spindle nose to apply a moderate force. Rotate the spindle by hand between rounds of checking and tightening to seat the rollers. When the play is gone tighten the nut only to the next notch and lock it.
-Run the machine at its highest speed and watch for overheating due to excessive preload. If you can keep your finger on the bearing or housing it's not too hot.
-Check for play with the spindle hot and again when it cools. Repeat from the top as required.
All posts are good advice. I would add that it is a good idea, on tapered bearings, to go a little beyond what would seem to be good for the preload, rotating the shaft a little as you go, to ensure the seating of the bearings, then back off and make the final adjustment. If you have adjusting nut, etc.
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