Cross Feed Screw - Insert Repair
Remove the cross feed screw from the lathe.
Measure the total length of the acme screw to the gear face and record.
Cut off the old acme cross feed screw just in front of the power feed drive gear.
Face off the end to clean up and spot drill the center.
Set up and drill and ream to .3125 to a depth of 1.250 inches.
Set up and turn down a 1.500 inch length tang on the new cross feed screw blank for a
snug sliding fit in this bore. On my new blanks run on the factory machine,
the thread stand off is set for you, just turn down the unthreaded 7/16 end of the blank.
Finish off the length to measurement recorded.
An approximate length in this step is fine, just get it close. Finish off or cleanup the thread start.
File a little flat on the side of the insert tang or mill a small weep groove so air can escape
when you are inserting the tang into your old lead screw shaft.
(I have used my lathe bit, on center, like a shaper bit and cut a small groove also, works great)
Test fit the two parts between centers in your lathe.
Set up a dial indicator to measure run out, and turn the insert blank to achieve the lowest run-out.
Mark the parts alignment.
Remove your blank and use Loctite 680 (Green- Slip Fit - P/N 68015 10ml small size) on the tang.
Put the screw assembly back between centers and align you marked parts with the low side run-out down.
The loctite will lift the tang slightly as it cures. Allow for full cure of 24 hours.
After cure, check run out again and straighten as needed.
Set the assembly up in a drill press or mill using a V block, drill( I use an Accupro 3.15mm)
and ream with a 0.1247 reamer for press fitting of an 1/8 dowel pin.
The position of the dowel pin is at the end of the gear teeth or at 1.125 from the end of the gear.
Install the dowel pin. The dowel pin installation is optional, the 680 will hold the repair in most cases.
Set up and finish off the pin area and front of the insert tang if needed.
Large dial conversion or refitting for backlash:
Follow the South Bend drawing No. ATT. 208 or ATT. 212, which are included,
as a guide for the next steps.
Using internal expanding arbors, hold the dial collar or bushing by the 3/8 bore,
Set up and face off just a thousand or two to the mating surfaces to clean things up.
Do the same thing to the mount bushing and front of drive gear where the bushing contacts.
Here is were you would counter bore the mount bushing if adding the installation of thrust bearings.
Counter bore both the bushing and the dial ring so part of the bearing is in both parts.
Install a set of thrust bearings between the backside of the lead screw gear
and the threaded end of the mount bushing. Measure and then turn off the thickness of the thrust bearing set
from the large diameter of the cross slide screw right behind the drive gear.
Assemble the complete lead screw mount bushing dial ring and handle and check the endplay in the mount bushing.
To correct any endplay use a feeler gage to measure the clearance that is causing the end play.
Machine back the shoulder that the hand crank seats up to the same amount as the feeler gage measurement.
Cleanup and reinstall the cross feed screw in the lathe with lubricant.
The object here is to have a free turning cross slide screw but without end play that gives you unwanted back lash in the screw and nut.