Logan 820: How do I lock the cross-slide and compound?

Tim,

First, to get the inner nut off, try running a die nut onto the screw threads backwards. That should clean up the damaged threads next to the keyway and allow the nut to get past the damaged area. If it doesn't, try all of the die nuts that you have. If that still doesn't do it, try an adjustable or split die nut. That should do it.

Differential adjustment of the two nuts on the (probably 3/8"-24) threaded portion of the cross feed screw is how you adjust for minimum end float of the cross feed screw. That is best done with the cross feed nut run off the end of the screw and should be done before evaluating the crossfeed screw and nut for possible replacement. You will probably need a thin pattern open end wrench to hold the inner nut while you tighten the outer one (what used to be referred to as Tappet Wrench). It will probably take several attempts of loosening the outter nut and making a small adjustment to the inner one and then tightening the outer one before you are satisfied with the adjustment. When you are satisfied with the end float (should be less than 0.003"), run the brass cross feed nut back onto the screw and use the dial to measure the backlash. With a new nut, this will probably be 0.002" to 0.003" more than the end float of the screw. With a used nut, it will be more than that. Record or remember this reading. Then crank the cross slide back to the region where it most often runs, and repeat the measurement. With a new screw and a new nut, this reading should be the same as the first one. How much more it is indicates how much wear you have on the screw (independent of wear in the nut). At this point, it is up to you to decide whether to spend the money to replace nut or nut and screw.
 
Robert --
Many thanks, really helpful and much appreciated. That's tonight's work. Hope I have that die nut.
 
You're welcome. I forgot to empathize to check what the threads actually are before attempting to run the die nut on them as I have no way to confirm that they are actually 3/8"-24.
 
Attn; Tmenyc and wa5cab
Yes the threads on the end of the cross-slide shaft are 3/8-24 UNF
Greg (AC4WF)
 
Well, I got the UNF die nut, straightened out the threads, got the nuts and handle off ok. Cannot seem to get the screw out completely, is there a woodruff key in there somewhere? The cross-slide is much better now, much less slop. BUT, the original problem of the tool not holding a DOC is still present. It seems to buck off a facing cut and just move away from a turning cut. And, there is still this small amount of south-north movement in the entire cross-slide assembly that won't go away.
Appreciate your continued help.

Tim
 
Tim,

In Downloads there is a copy of an 800 Series Operator's and Parts manual. The pages are sorta numbered but not consecutively. If you go to File page 35, you should see the LA-45-1 Carriage, with the saddle, cross feed screw, etc. There is one Woodruff key near the center of the screw that prevents the LA-190 Idler Gear from spinning on the screw. It is not obvious from the drawing whether the screw is removed to the front (after removal of the LA-689-A Bushing (called "Bearing" on most lathes)) or taken out the rear. All that I know is that on an Atlas it comes out the front, and for several reasons I would try that first. Which means removal of the LA-689-A.

However, I can't see how this would have anything to do with the movements you mention.

To temporarily lock the cross slide to the carriage, tighten down the front and rear gib screws.

Which direction are you calling "north"? Toward the headstock, toward the operator, or what?
 
Robert, Mikey --
Mikey asked me to go back to the beginning and detail the symptoms of the problem.
Context is that I'm a newbie, but an analytical type. My 820 is the mythical former shop teacher's pride and joy that sat unused for some years. So, overall it is in great condition. From January-March, as I got to know the machine in the little time I had for it, I restored it in subassemblies and really cleaned it out. It worked fine, turning, facing cleanly. The issues arose as I started my first projects.
Issue 1. Over time, I noted replicability issues; there was/is a bit of slop in both longitudinal (what I call east-west) and lateral cutting. I measured carefully each time, but could not pin down the ability to replicate a cut.
Issue 2. The compound was just too difficult to adjust. I disassembled it, discovered that both swivel bolts were bent, clearly the cause of my inability to get the swivel to work well. This appeared to have been a traumatic injury, as if something fell on the compound or the compound was used to move the lathe; everything else around it was sound.) I replaced those through the actuator.
Issue 3. When I got it all back together, it would no longer hold a cut, either turning or facing. It bucks off the work for a cut of more than 5-8 thou, and with the less resistance the tool just pushed away from the work. I noted that the cross-slide, when pushed, moved appr 1/32", you could jiggle it back and forth. Tightening down the gibs did not eliminate this (the 820 has no cross-slide lock, a project for the coming weeks with a friend with a drill press). I could not tell if the loss of lateral rigidity (what I call north-south) has the same cause of the inability to hold a depth of cut.
Issue 4. Based on the comments here, lateral slippage was excessive. Based on advice here, the next step appeared to be disassembling the cross-slide more completely. I removed the QCTP and compound again, removed the cross-slide thread nut, and this time opened up the handwheel and collar assembly. It showed that the threads between handwheel and inside jam nut were damaged, perhaps from the same traumatic injury that bent the compound swivel bolts (one can imagine someone grabbing the lathe by the cross-slide handle and compound). With advice from here, I located a 3/8-24 UNF die nut, repaired the threads, removed the nut. As noted above, I was not able during this attempt to dislodge the woodruff key, so could not get the cross-slide screw out, but cleaned out a lot of old crap and reassembled. (Robert, thanks for the download reference; I have that doc here and can now see the woodruff key.) The cross-slide slippage appeared to be much improved, showing almost no free turning of the handwheel.

I tightened down the gibs, and it held tight, no lateral movement. I stuck a test piece of steel into the chuck; it turned without slippage, but after releasing the gibs a quarter-turn and, with the first facing attempt it bucked, and now the lateral slippage is back again. In fact, it's worse; the entire cross-slide now jiggles both longitudinally and laterally. The carriage and saddle assemblies are firm and rigid. All of the motion is above, with the cross-slide. When I tightened down the cross-slide gibs again, it holds firm. Are the gibs that sensitive?

This is where I am now. Hope this description is clear.
 
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