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- Dec 20, 2012
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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.
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.