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

tmenyc

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Having a problem with slop/slippage on my cross-slide, enough that the toolpost bucks at the slightest pressure. The slippage is completely north-south, the filister bolt holding the cross-screw nut is tight, the gibs are cleaned and tight. At the handwheel there's about .015 slop and the whole handwheel to cross-slide screw seems a bit loose. If I lock down the carriage the entire cross=slide assembly will shift, perhaps 1/64". Mikey, who has been hugely helpful to this still-newbie, has recommended that I lock down the cross-slide to isolate the problem but I can't find anywhere how to do that.
Also, this is a problem that has come up recently, after I replaced the two compound swivel bolts. It did not happen before, but clearly, with those two bolts bent I had other problems. Doesn't seem as if those would be the problem since all they do is enable the compound to swivel.
Help please?

Many thanks,
Tim
 

BenW

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I don't know whether this particular machine has a crosslide lock, but if there isn't one and you just want to isolate the problem, you could tighten the gib to lock the crosslide temporarily.

Sent from my LYA-L29 using Tapatalk
 

francist

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Any chance those two new bolts you put in are just a hair long and not drawing the compound swivel down completely? If they're bottoming out beforehand they would probably still prevent the compound from rotating but wouldn't be drawing it tight to the cross-slide. Kind of like a T-nut with too long of a stud.

If I didn't have a problem before changing a part but had a problem after changing a part, I'd look strongly at my new part as being the problem.

-frank
 

Nogoingback

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Your 820 should be similar to my Model 200. On mine, I was able to adjust some slop out by loosening the outer nut
on the x-slide handle and carefully taking up the slop with the inner nut. It took a few tries, since tightening the outer nut changed
the adjustment but I got it in the end. If you can do this, then any other slop in the x-slide will be the nut at the other
end of the screw that attaches to the x-slide itself. If it has significant wear, it will need to be replaced. Of course the
screw could be worn as well.

Can't imagine why your x-slide would move when you lock the carriage. However, the carriage has gibs that are adjustable
as well at both the front and the back. (At least mine does.). Adjusting them might help.
 

tmenyc

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Frank -- my thinking, too, except that the compound is not moving; all the motion is in the cross-slide below it. But yes, it was not present before the bolt replacement. I'll check the bolts out. They were from the Actuator, so I assumed they were milled correctly.
Alternatively, I'm wondering about the cross-thread nut. I had taken it out, cleaned it well, and reinstalled it a good month before the bolt replacement without a problem afterwards. Is there any way it could be in wrong? It is definitely bolted into place, and did not show a lot of wear, although a small amount worn off might not have shown. Would ANY wear be too much wear? I'll take it off tonight and photograph it. The cross-feed screw does not show obvious wear where it is visible, which (the two swivel bolts excepted) is consistent with the whole machine's condition.

NGBack -- I will certainly do the adjustment. With my understanding that "slop" is the looseness of the handle that results in turning the handle without changing the actual position of what the handle turns, my cross-slide handle is loose but does not turn without the cross-slide moving. The .015 slop is longitudinal, on the carriage. Will adjusting the cross-slide outer and inner nuts tighten the handle on the screw AND tighten the mechanism to possibly eliminate the lack of cross-slide rigidity?

Thanks for the help.
 

Nogoingback

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If you had the cross feed screw out, you would see that there is a gear on it secured with a woodruff key which is sandwiched
between a shoulder on the shaft and the inner end of the bushing that supports the screw. (The bushing is the part I'm
pointing to in the pic.) So, if the handle is adjusted to be loose, that allows some longitudinal movement in the shaft.
Adjusting out that slack with the nuts at the handle eliminates that movement. It's a fussy adjustment: too loose and you
get the movement, too tight and the cross feed handle binds and is hard to turn. Of course, I'm assuming your lathe goes together
the same way mine does, but I'm pretty sure it does. When you perform that adjustment, be sure that the setscrew on the
movable dial is loosened first.

The cross feed nut that moves in response to turning the handle is not adjustable. Slop in that nut indicates wear in the
nut, the shaft, or both. On my lathe, I replaced both parts which I ordered from Logan. The shaft was expensive, the
nut not so much. If you have much (rotational) slop in the handle, changing out the nut would be a good place to start.

And again, I would check the gibs on your carriage as well.


292763
 
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tmenyc

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NGB -- many many thanks! If I can get to it tomorrow evening that will be great; if not it will be (ugh) ten days, I have family stuff out of town. Either way I'll certainly report back here. Sounds very do-able indeed, however. I'm hoping the screw doesn't need replacement.

Many thanks again.
Tim
 

tmenyc

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OK, I"m back from out of town, itching the whole time to get back here and solve this problem. Tightening down the gibs did nothing except stop intentional movement of the cross-slide. I removed the nut, and as can be seen from the pictures, it looks fine, no apparent wear. Threads are clean, no chunks, only casting marks.

I removed the outer bolt on the cross-feed handle, and the handle, and then discovered that the inner nut cannot come off; there is a widening of the threaded slot, preventing it from moving further. I'm guessing this is wear or damage, but when I tightened the micrometer nut the north-south slop disappeared! Easing back a little bit, it could be turned without creating the slop. Is this the solution?
Is the widened portion a replacement need? It does not seem to get in the way, and I'll see if handle slop returns when I reassemble.
As always, many thanks for the support.

Oh, and by the way, Mikey send me a link to a video of a simple cross-feed lock, which I'll make as soon as I get this fixed.

Tim
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Chuck K

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Thread your cross slide nut onto the screw and check the fit at different points across the length of the screw. It will probably fit looser in the center than near the ends. If it's real sloppy in the center, it might be time for a new nut.
 

wa5cab

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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.
 

tmenyc

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Robert --
Many thanks, really helpful and much appreciated. That's tonight's work. Hope I have that die nut.
 

wa5cab

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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.
 

tmenyc

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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
 

wa5cab

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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?
 

tmenyc

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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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GrayTech

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You checked the replacement bolts aren't too long? (Not actually clamping.)
 

mikey

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Tim, I mean no offense but your post is difficult to understand because of your terminology. It might be a good idea to use conventional nomenclature so we all understand what we're discussing. Movements along the longitudinal axis of the lathe is called the Z-axis. Movements across the lathe from the front to the back is called the X-axis. So, when we turn a work piece we do so in the longitudinal or Z-axis, and when we feed in or face, we do so in the X-direction with the cross slide or compound. I assume that when you say "longitudinal" you mean a turning cut and a "lateral" cut is a facing cut or you are feeding in a depth of cut. If this is not correct, please let us know.

images.png

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.

Can you clarify this for us? Do you mean that you could not accurately dial in a specific depth of cut and expect the lathe to take that off the diameter?

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.

Not sure what the "actuator" is but you replaced the swivel pins (I assume you mean the swivel pins, part # 180, that lock the compound down to the cross slide) and subsequently noted that there was excessive movement in the cross slide or the compound (do you know which one is moving?), such that a depth of cut more than 0.005 - 0.008" pushed the tool away from the work.

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.

So, it appears that fixing the damaged thread on the part of the leadscrew that takes up slack between the cross slide leadscrew and nut allowed you to reduce the amount of play in that assembly but ...

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?

Which gibs did you tighten - the cross slide or compound? Assuming you mean the cross slide gibs, your issues resolved until you loosened the gibs a quarter turn and the issue of "lateral slippage" recurred.

So, from what I can gather here, it appears that the problem is that the cross slide gib is extra-sensitive, such that you have to run it tight to eliminate turning and facing issues. Is this correct? If so, it implies that the gib or the dovetail is not flat or is not adjusted correctly. I am not clear on how replacing the swivel pins that hold the compound to the cross slide affects this other than that they now work properly and are transferring forces from the tool to the wonky gib situation.

Do you agree with the problem statement? If so, then the guys can maybe help you work through the evaluation and resolution of this problem. As we discussed, it might not be a bad idea to use some Prussian Blue to see what the contact pattern looks like under there. You might also take a really close look at the gib adjustment screws to see if there is any deformation at their tips. With luck, this might all be resolved by replacing the gib.
 

Tozguy

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The bent compound screws and the buggered keyway would indicate (as you mentioned) that some severe trauma has occurred. Considering all the adjustment work that has been done without solving the problem I am starting to suspect that the top of the cross slide might be cracked somewhere. Cracks in cast iron are not always easy to see so you need to look for them.
 
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mikey

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This might be a good one to ask Richard King about.
 

tmenyc

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Mikey,
Thanks, as always. Sorry about the bad terminology; I got in a bad habit with that from the start, will do it correctly from now on.
You do certainly understand the problem statement, however clumsily it was worded.
I got the Prussian blue, will do it today. And, I'll inspect the cross-slide carefully for a crack, hoping to not find one.

Also, the actuator is the Logan Actuator, lathe.com. I believe it's either the successor or descendent firm.
Tim
 

tmenyc

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And yes, reading your response again: yes, my issue with replicating a cut was exactly as you note: dialing in a cut, after accounting for the dial slippage, stopped being predictible. For a few weeks, a cut I made, always in the .005-.010 range, was pretty close to that, usually over, .002 off. But then, the error range started growing, and then it stopped holding a cut altogether as described. Most of this was done on 12L14, at the .006 feed rate and 420 rpm, so should have been easy cuts.
The problems started after I changed the swivel bolts, and while one might think that that might have caused it, my growing belief is that disassembly upset something that was on the edge of going wrong. The compound swivel was clearly not functioning and had to be fixed, and that install was quite easy, and the compound is working fine now. On to the gib.
 

tmenyc

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here are pictures of the cross-slide gib and gib screws, presented left to right as x+ to x-. Is it meaningful that screws 1,2,and 4 are flat but 3 is rounded? All four screw indents in the gib appear the same, cleanly rounded. Do you think the three flat end screws were inappropriate replacements? The indent in the gib screw hole is approx .09" across, which matches the rounded end of the one screw, but the diameter of the flat screw ends is .154", so they would not fit fully into the holes. Could that have created enough slack for the gib to slip during turning or facing if the gib screws were loosened enough to let the cross-slide move? If so, why did it cut well for awhile but then not? Was it maybe in a perfect gib adjustment that I haven't been able to replicate?

The smooth side of the gib has two scratches I can feel, just opposite the 1 screw hole and 2/3 of the way from screws 1 to 2. There is some wear on the x- end, with the sharp edge rounded down, almost like a radius on a cutting tool.

Many thanks,
Tim


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mikey

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I'm not a Logan guy but I'm going to guess that the flat-faced gib screws are the wrong screws. If so, they would spread force over a relatively broad surface area instead of being concentrated in a tiny part of the gib like the round headed one does. This could also put more force on the upper edge of the gib strip because this is where they would contact the strip. Furthermore, it looks to me like those flat screws were made that way; the tips look like they were inserted into a hole in the end of the screw. Makes you wonder if the former owner did this.

If this was my lathe, I would either make or buy the proper gib screws. I would also replace the gib strip and hope that this works well enough that scraping the dovetails of the cross slide won't be necessary. Ideally, the gib screws would be long enough to allow a locknut to be placed on the screw so they don't move once you adjust them.

I defer to the more experienced Logan owners. I may be totally wrong on this.
 

francist

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I'm not a Logan expert and I doubt that this will be the root of the problem, however I can't help thinking about something mentioned in a few posts earlier. About backing off the gib screws ".. a quarter turn.." In my world, that's actually quite a bit to back off. I couldn't find the gib screw size from the Logan manual and parts list, but even supposing they're #10-32 which would be reasonable, say. A quarter turn on a 32 tpi screw backs that screw away from the gib nearly 8 thousandths of an inch ( 0.0078" ). That's quite a bit, and way more than ample to go from a snug fit to a sliding fit.

For what it would take, running the gib screws back in and then backing off less aggressively might yield some better results. Or not :)!

-frank
 

tmenyc

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Mikey,
I just wrote to the Logan Actuator to order the replacement gib and screws, in the hope that that will create enough of a solution. If it does, it also answers the "why now" question, as in "why did it work before"? The answer is that I hadn't touched the gib screws before I discovered the bad compound swivel bolts. IIRC, the entire saddle assembly was moved intact when we brought the lathe here. So I'll bet that however they had been set before, to accommodate the flat screws, was still in place until I disassembled it to replace the swivel bolts. Definitely hoping it's a cure.

Frank,
Your point is well taken; my quarter-turn was actually an estimate, it might well have been less, but am pretty sure it wasn't more. I'm going to be more precise with the new gib screws and nuts in hand; these nuts are pretty worn and hard to work with precisely.

Tim
 
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