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

Tim, I've only replaced 4 gib strips so I am by no means an expert at this but I will offer what advice I can.

New gib strips often come without the locating holes predrilled; that is a good thing because every lathe is different and it is better to drill them yourself. If you do some reading, you will find all sorts of opinions on which shape of screw point is best - round, conical, ball bearing, etc. Personally, I prefer the angled cylindrical insert that Emco uses because it spreads the forces from the screw over a broader area; whether this makes a difference, I am not sure but it makes sense to me. With that said, 3 of the 4 lathes I replaced the gib strip on used conical screw tips like yours and they seemed to work fine.

You will need to trim the gib strip to length. I suggest cutting to fit the length of the cross slide instead of matching the length of the old strip. Be sure to deburr the ends and all corners of the strip lightly, then sand the working faces with 400 grit wet/dry sandpaper laid on a surface plate or flat glass plate. You are just looking for a uniform surface here so go lightly and evenly.

Clean the dovetails of the saddle and cross slide really well. Get up in the corners with a knife and get all the crud and debris out of there. Also make sure there are no burrs on the inside of the dovetail where the gib screws enter and clean the screw holes out really well.

You are going to drill the four holes for the screws into the gib strip. Personally, I use a file to gently shorten and gently round the tip of each gib screw so that the sides of the tip bear on the gib strip hole, not the point. This spreads the forces out over a broader area. I use a spotting drill that is slightly wider than the included angle of the screw tip to drill the holes in the strip. Because the tip of the screw is cut back and blunted, the sides contact the hole instead of the very tip of the screw. Hope that makes sense. I use a spotting drill because it is short, rigid and only the point cuts. The flutes of a spotting drill are not sharpened so they do not cut; this eliminates the risk of damaging the threads in the saddle.

Once the dovetails are cleaned and the screws are prepped, take your drill and pass it through the gib screw hole. You only need to drill about 1/3 of the way into the strip for each screw so pass the drill through until it is in far enough to give you that 1/3 depth and mark the drill on the outside with masking tape or a Sharpie; you will use this as a depth gauge when drilling.

Now you can put the gib strip and cross slide into place on the saddle. Pull the cross slide tight to the saddle, trapping the strip between them, and then clamp the cross slide in place if I can. On all the ones that I did, I was able to use blocks and clamps to do this. You are not trying to apply a lot of force; only enough so the strip cannot move. Look at the strip to make sure it is not cocked and then you're ready to drill.

I prefer to drill the first hole, the one on the operator side of the strip. You are using the threaded hole as a drill guide and if you use a spotting drill, this works well. Shoot some cutting oil into the hole and drill to the depth of your marker. Once done, use compressed air to clear the chips and install a gib screw. Snug it down lightly; now the strip cannot move and you can drill the other three holes. Then take the whole thing down and clean all the chips out of the holes and gib space. Deburr the strip if needed and recheck to make sure no burrs were raised inside the threaded holes. Now you're ready to install the gib strip.

Most gib screws are long enough to allow a locknut to be used on the outside. If yours are too short for this, some Blue Loc-tite works well and allows you to adjust as needed without the screw vibrating loose. If you use Loc-tite, use it sparingly.

Oil everything up and install the cross slide and gib. I use machine oil for this. Install all four screws and gently thread them in until they just touch the strip, then back them off a tiny bit. Now you can adjust them. What you are trying to achieve is a smooth sliding fit with zero play. Since the saddle/cross slide assembly already has some wear, some screws may need to be adjusted more than others but you should be able to accommodate that wear.

Using just moderate hand pressure, push the cross slide away from the gib strip so it fully contacts the dovetail on the other side of the saddle. Now you're going to adjust the screws and the easiest way is to work from the center on out to the ends. I adjust all the screws until they just touch the strip; this is enough to feel drag when you turn the cross slide handle. I fractionally back off all but the second screw from the front and turn the cross slide handle; you will still feel some drag. Adjust the screw just until the handle turns freely; this may only be a tiny fraction of a turn. Then I bring in the third screw until it touches just enough to cause some drag. I adjust that one until the handle turns freely. Repeat with the first and last screw, each time feeling it cause drag and then adjust until the drag just disappears. Once you are done, the cross slide should move freely but there should be zero side play when you firmly push across the cross slide with your hand.

Done.

Hope this helps.
 
I doubt that the 1/4" difference in length will matter. But the gib should have the four flat bottom holes cut at a 30 degree angle. Without them, the gib will walk out. Also the new gib screws appear to be threaded to the end.

This is mostly tongue-in-cheek, but I wonder whether Logan and Clausing are using the same machine shop. Two or three years ago, I bought a new carriage gib for the late Atlas 12", mainly to confirm that they were still steel and not plastic like the compound and cross slide ones had become.. It was also missing the flat bottom holes. So were about 12 out of 13 on the shelf in their warehouse. The sent me the 13th one and had the remaining 12 sent out for completion.
 
thanks, Mike and Robert.
I wrote to Logan this AM to ask, based on Robert's response, if sending gibs undrilled is standard, on the chance that they'll do it for me. Otherwise, I have to beg some time with a friend with shop to use his drill press. Somehow I don't think this is a job for an unmounted DeWalt. Mike, thanks for the instructions; I'll definitely use them.
Assuming I'll have to take it to my friend, I'll take advantage of the occasion and drill the cross-slide for the lock as well.

Late-breaking news: return email notes "must be drilled after assembly".

best,
Tim
 
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Then you need to write back and get them to send you the drawing showing where the holes go, size, shape and depth.
 
Robert,
Mike's note, #41 above, seems to cover the ground, no? Although the hole difference from 820 to 820 can't be great, the only way I'd know it was correct is by using my cross-slide's holes.

Tim
 
Well, yes and no. In the first place, Logan should never have sent you the gib without instruction on how to make it usable. You've figured out, because you have asked, that you are expected to have to do something in order to make the gib usable. But you still don't know how deep to make the holes, what diameter of drill bit to use, what the included angle on the nose of the bit should be (yes, that is a variable), and whether or not you should locate the hole positions with a spotting bit just small enough to go into the tapped holes and then finish them with a larger bit (which will require being able to hold the gib at an angle).

I don't approve of doing gibs this way. It was only done to save the manufacturers a few cents. The chances of ruining one of the holes while modifying the part and later during routine maintenance are pretty good.
 
Late-breaking news: return email notes "must be drilled after assembly".

I have only done the gibs on two machined cross slides and two cast cross slides and it seems to me that the gibs for a machined cross slide could conceivably be pre-drilled. For a cast cross slide, I think it would not be practical to pre-drill them unless the maker used a consistent datum that is consistent for all their models. Bottom line is that it is probably more accurate to drill the gib holes yourself. I use a hand held drill for this - Makita, not Dewalt, but it works fine.

You only need to drill into the gib deep enough to center the cone of the gib screws. This ensures the gib cannot walk. As long as the conical sides of the screws provide the pressure instead of the point, this should be sufficient. If you use the gib screw holes as a drill guide and use a spotting drill then the angle of the holes should be close enough to be correct and you won't mess up the threads in the hole. In a properly functioning gib set up, the screws do not put a lot of pressure on the gib; they only adjust the space between the sliding components that ride on an oil layer.
 
Well, that's reassuring! But, it will be a DeWalt...

Robert, I see your point. I also see Mike's. And, probably, you're both correct. I don't know, and don't know if anyone knows, how alike one 820 is to another 820, but it's easy enough to get it right myself. Instructions would have been nice, for sure, but I have your and Mike's guidance, which is sufficient. I learned a long time ago in my world of vintage pen restoration that instructions for the brand and model and born-on-date don't necessarily fit the pen; I'm learning now that the lathe is a whole lot larger but the tolerances are a whole lot finer. With pens, with some exceptions one generally shaves a bit here, adds a bit there, which is both the beauty and the challenge. With the lathe, the challenge is getting it right to get it at all. I'll certainly post when it's done.
Many thanks to you both.
Tim
 
Pretty much all of the vintage American iron that gets discussed in these Fora originally came with flat bottom holes in the gibs and bull-nose gib screws. The only reason for changing them would be to be able to make it cheaper. And think about it - if the company building the lathe couldn't manage to get four holes to line up with four other holes, how could you expect any machine that they built to be able to produce decent parts?

I'm sure that the cheaper gib they sent you will work OK after you finish making it. But this is an example of what happens when the bean counters get the upper hand. :alien:
 
It certainly would have been nice if the gib had the holes in it. But, let's keep in mind, the company that built the lathe
no longer exists, and hasn't for many years. Scott Logan told me that he doesn't possess the original drawings for the older
machines, and so he may not know what the hole spacing is on that gib. I suspect that has more to do with it than "bean
counter" shaving pennies. I could be wrong, but my impression is that there aren't any bean counters involved and that
Scott makes all the decisions. He supplies the parts he can, but they're parts for 75 year old machines that went out of
production decades ago. If this lathe were a Sheldon or South Bend, the conversation would be about how to make a
gib from scratch.
 
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