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CAUTION: Do not set the backlash too tightly on a worn section of the screw. The nuts are very likely to jam if the machine is traversed to a place on the screw where only slight wear has occurred.
When replacing nuts on a used leadscrew, be certain to examine the screw threads for damage, wire edging, and general wear which could result in the screw seizing in the new nuts or cause them to become prematurely worn.
If backlash may be adjusted to within a few thousandths on an un-worn portion of the screw and exceeds approximately 0.100" on the worn portions of the screw; the leadscrew is worn out and needs to be replaced.
CAUTION: Lucas leadscrews are specially designed to simultaneously maximize machine-thrusting capacity and to minimize screw wear. They utilize 'non-standard' pressure angles and thread geometry. It is, therefore, not good practice to mix Lucas lead nuts with 'homemade' leadscrews, or vice-versa.
Machines with small tables have both the fixed and adjustable nuts housed in one mounting block. Larger table sizes require each nut to be held in separately blocks, which are mounted beneath the table at a distance dictated by the size of the particular table. In all cases, the fixed nut is installed to the front of the machine table with the flanged end to the front. The adjustable, or backlash take-up nut, is held in the rear of the nut block (or the rear block when two are used).
To adjust the table nut backlash on machines whose saddle extends beyond the width of the bed; run the table all the way to the back until the rear limit switch trips off the power feed. Hand-crank the machine further, if required.
Looking up into the cored access hole in the saddle, direct a helper to hand-crank the table a few inches in whichever direction is necessary to position the adjustable nut in the most convenient position for removal of the locking segment.
Remove the locking segment mounting screw and insert a 3/8-16 screw about three inches long into the tapped hole in the locking segment. Using the 3/8" screw as a lever, wiggle the locking segment off the nut serrations and guide pins.
Turn the serrated flange of the adjustable nut until the backlash setting is at the desired minimum or the minimum dictated by wear.
Since the backlash nut on larger tables is several inches in diameter, it may be hard to turn. Pinholes on the flange of the nut are provided for the insertion of pins or the use of a spanner wrench. It will help to have another person 'rock' the table screw back-and-forth slightly with the crank on the table hand-adjusting shaft. Do not hammer the flange of the nut in order to turn it as this will damage the nut serrations and prevent use of the locking segment. To replace the locking segment, slip it into the serrations and onto the guide pins from the rear end. If necessary, use the 3/8-16 screw in the locking segment to help wiggle it into place. Tap the outside diameter of the locking segment and inspect it to see that the serrations mate and fully seat; then tightly lock the segment with the 5/16-18 locking screw. Be sure that the replacement of the locking segment is properly done; if it works loose, the adjustable nut may turn and jam on the threads.
The nut housing on the right side of the saddle may be removed for backlash take-up by removing the four retaining screws. Slide this housing back on the adjustable nut until the serrated flange is exposed.
This may be difficult if paint, dirt, or nicks are on the exposed portion of the adjustable nut. It will be necessary to clean these up before the housing can be retracted. Do not file or scrape more than is necessary; the close fit between the nut and housing provides a seal for lubrication retention.
With the nut housing pulled away sufficiently, the adjustable nut may be turned to take out the backlash.
As with the previously discussed backlash adjustments, be sure not to over-adjust the nut, causing the screw to bind. Replace the nut housing in reverse order to complete the adjustment. Be careful to properly engage the serrations of the nut block into the mating serrations in the nut.
The adjustable backlash nut for the head feed screw is located in the nut block on top of the head. Start by removing the locking segment. Then, using pins or a spanner in the holes provided in the serrated flange of the nut; turn the nut to take out excessive backlash. Re-seat and re-lock the locking segment when the adjustment is finished, keeping in mind the necessity for care in replacement of the locking segment.
For Field Service and Repair Parts Call:
Lucas Precision
13020 Saint Clair Ave.
Cleveland, OH 44108-2033
TEL: (216) 451-5588
FAX: (216) 451-5174