Tailstock Modifications
I completed 3 different modifications to make the tailstock easier to adjust and use: Modified offset locking screws, adjustment guide and cam lock.
Modified offset locking screws
Adjusting the offset of tailstock is a little challenging with the main locking screw located on the bottom of the tailstock. You need to remove the tailstock to loosen that screw, put the tailstock back on the lathe to set the offset (or center) and hope the slotted set screw holds the position while you remove the tailstock to tighten the bottom screw. Chances are the adjustment will be off and you will need to repeat the process a few times. To make this process easier, I wanted the locking screws accessible with the tailstock in place. The top half of the tailstock has a threaded hole for the locking screw and the bottom half has an oval slot that the screw head locks down on. I drilled out the threaded hole for a 10-32 clearance completely through the top half of the tailstock. I put a 10-32 screw in from the top and used a square nut in the bottom slot that won't rotate.
I also replaced the slotted set screw (opposite the headstock) with a 10-32 cap screw. This allows me to use the same hex key for both locking screws and slotted heads tend to get ruined through use. I faced the end of the screw, added a bit of chamfer and turned down the first 0.100" of threads so it won't move the tailstock when it is tightened. I thought all the hardware on this lathe was metric, so that hole either has sloppy 5mm x .80 threads or it was actually 10-32. Either way, the 10-32 screw threads smoothly all the way in.
Adjustment guide
To make adjusting the tailstock offset easier, I made an adjustment guide. I cut T shaped piece of aluminum out of 1/4" plate and squared up the surfaces with the mill. The outer holes are drilled and tapped for 8-32 and the center hole is drilled for a tight 8-32 clearance hole. I drilled and tapped an 8-32 hole on the backside of the tailstock in the middle 'post' on the bottom half. The middle screw threads into this hole and clamps the guide to the bottom half of the tailstock. The 2 outer screws are brought in contact with the top half of the tailstock. Precision adjustments can be made (with the locking screws loose) by tightening or loosening these 2 screws and knowing that each full turn is 1/32". The 2 screws also allow a bit of rotation about the locking bolt axis. With the use of a dial indicator, this allows you to ensure that the quill travels parallel to the spindle.
Cam lock
Moving the tailstock normally requires using a wrench to loosen a nut on the locking bolt. Because of the slight angle cast into the surface that the nut rests on, I would often need to loosen the nut 2 full turns so the foot wouldn't bind on the bottom of the ways. This gets a bit tedious when you consider the holes I drill usually require at least 3 operations (center drill, pilot hole, final hole), each with a different tailstock position. I had seen numerous cam lock designs on the web and liked the version on gadgetbuilder.com the best.
I started by crudely leveling the top surface using a rotary tool with various grinding bits. If you don't mind using a wrench, you could stop here. After doing this, I only needed to crack the nut and the tailstock would slide without the foot binding. I took a 3/8-16 bolt, parted the head off, and cross drilled a hole per gadgetbuilder's specs. I didn't have any steel on hand, so I made my thimble out of 7075 aluminum. I made the diameter of the thimble about 0.850" so I have larger bearing surfaces since it isn't steel. If the bearing holes start to elongate, I'll have to remake it out of steel. The thimble was drilled out and cross drilled to gadgetbuilder's specs.
I made the cam shaft from some nice turned, ground & polished (TGP) shaft that was rescued from an old printer or scanner. I don't know what kind of steel this is (1045?), but it turns easily and has a great surface finish. No sandpaper cleanup was required. Once I had the minor and intermediate diameters turned, I followed gadgetbuilder's method of marking the cam location and offsetting the shaft by inserting a 0.040" shim between it and one of the chuck jaws. I removed 0.035" from the cam (this was later proven to be perfect for my design). I cross drilled, spot faced and tapped the end of the cam shaft for a handle. I used a smaller TGP shaft for the handle and left the polished finish. I only turned down the end and threaded it with the lathe so it would screw into the cam shaft.
I cut out a 1-1/2" square from some scrap 1/4" steel plate for the foot. My Sherline mill doesn't really have the rigidity to make working with steel easy, especially this mystery meat, so I just cleaned up the ends with a file. It was cut pretty square, so this wasn't a problem. I marked the hole for the locking bolt based on the original. I drilled and tapped this for 3/8-16. I assembled everything for a trial fit (with the handle on the front side of the tailstock). Since the hole in the foot is offset, it needs to be rotated in 360 degree increments to change the height. There is only 0.035" of travel in the cam and every rotation on a 16 tpi thread equals 0.0625", so there is only one "proper" height for the foot. If this proper height doesn't allow the tailstock to lock, material must be removed and the foot must be rotated one thread higher. Alternatively, material (such as brass shims) could be added to the clamping surface of the foot if there was a good way to secure them. I got lucky with the orientation of the tapped threads, since my tailstock locked into place with the handle rotated 45 degrees and moved without binding when the handle was vertical.
I took everything apart and put a jamb nut on the locking bolt to keep the foot in the correct orientation. I put the locking bolt and thimble in place and used a transfer punch through the cam shaft hole to mark the back web of the tailstock. This is where I ran into a problem. I squared up the tailstock on the drill press and used a small bit to drill a pilot hole. I couldn't use a center drill since it was too short and the chuck would interfere with the bottom of the casting. I figured I would be fine since I had a decent center punched divot. After drilling the pilot hole, I placed the thimble back in place and realized my hole was off center by about 1/16". My endmills were too short, so I couldn't use them to recenter the hole. I struggled with ideas for a bit before I settled on turning a plug and pressing it into place. I remarked the hole location and created a huge divot with a center punch. I set it back up on the drill press and took very small pecks at the hole, frequently checking to make sure I was still on center. This time the hole stayed on center and I drilled it out with the final size bit. The location was relatively critical, since I wanted a tight clearance (0.3125" hole and 0.305" intermediate cam shaft diameter). If I would do this again, I would either make sure I start with a large divot and buy a long center drill, or take accurate measurements, transfer the location to the back side and drill on the flat surface with no interference. I used a spring on the locking bolt between the foot and the bottom of the tailstock. This keeps the foot centered (locking bolt vertical) and prevents binding when the tailstock is unlocked. I used grease on all of the bearing surfaces when I did the final assembly. I can lock and unlock the mechanism with one finger. I am pleased with the end result and learned some valuable lessons (use the right tools, don't try to outsmart conventional wisdom, things that can go wrong probably will at the worst time).
Click the pictures for larger images.
Modified offset locking screws
Adjusting the offset of tailstock is a little challenging with the main locking screw located on the bottom of the tailstock. You need to remove the tailstock to loosen that screw, put the tailstock back on the lathe to set the offset (or center) and hope the slotted set screw holds the position while you remove the tailstock to tighten the bottom screw. Chances are the adjustment will be off and you will need to repeat the process a few times. To make this process easier, I wanted the locking screws accessible with the tailstock in place. The top half of the tailstock has a threaded hole for the locking screw and the bottom half has an oval slot that the screw head locks down on. I drilled out the threaded hole for a 10-32 clearance completely through the top half of the tailstock. I put a 10-32 screw in from the top and used a square nut in the bottom slot that won't rotate.
I also replaced the slotted set screw (opposite the headstock) with a 10-32 cap screw. This allows me to use the same hex key for both locking screws and slotted heads tend to get ruined through use. I faced the end of the screw, added a bit of chamfer and turned down the first 0.100" of threads so it won't move the tailstock when it is tightened. I thought all the hardware on this lathe was metric, so that hole either has sloppy 5mm x .80 threads or it was actually 10-32. Either way, the 10-32 screw threads smoothly all the way in.
Adjustment guide
To make adjusting the tailstock offset easier, I made an adjustment guide. I cut T shaped piece of aluminum out of 1/4" plate and squared up the surfaces with the mill. The outer holes are drilled and tapped for 8-32 and the center hole is drilled for a tight 8-32 clearance hole. I drilled and tapped an 8-32 hole on the backside of the tailstock in the middle 'post' on the bottom half. The middle screw threads into this hole and clamps the guide to the bottom half of the tailstock. The 2 outer screws are brought in contact with the top half of the tailstock. Precision adjustments can be made (with the locking screws loose) by tightening or loosening these 2 screws and knowing that each full turn is 1/32". The 2 screws also allow a bit of rotation about the locking bolt axis. With the use of a dial indicator, this allows you to ensure that the quill travels parallel to the spindle.
Cam lock
Moving the tailstock normally requires using a wrench to loosen a nut on the locking bolt. Because of the slight angle cast into the surface that the nut rests on, I would often need to loosen the nut 2 full turns so the foot wouldn't bind on the bottom of the ways. This gets a bit tedious when you consider the holes I drill usually require at least 3 operations (center drill, pilot hole, final hole), each with a different tailstock position. I had seen numerous cam lock designs on the web and liked the version on gadgetbuilder.com the best.
I started by crudely leveling the top surface using a rotary tool with various grinding bits. If you don't mind using a wrench, you could stop here. After doing this, I only needed to crack the nut and the tailstock would slide without the foot binding. I took a 3/8-16 bolt, parted the head off, and cross drilled a hole per gadgetbuilder's specs. I didn't have any steel on hand, so I made my thimble out of 7075 aluminum. I made the diameter of the thimble about 0.850" so I have larger bearing surfaces since it isn't steel. If the bearing holes start to elongate, I'll have to remake it out of steel. The thimble was drilled out and cross drilled to gadgetbuilder's specs.
I made the cam shaft from some nice turned, ground & polished (TGP) shaft that was rescued from an old printer or scanner. I don't know what kind of steel this is (1045?), but it turns easily and has a great surface finish. No sandpaper cleanup was required. Once I had the minor and intermediate diameters turned, I followed gadgetbuilder's method of marking the cam location and offsetting the shaft by inserting a 0.040" shim between it and one of the chuck jaws. I removed 0.035" from the cam (this was later proven to be perfect for my design). I cross drilled, spot faced and tapped the end of the cam shaft for a handle. I used a smaller TGP shaft for the handle and left the polished finish. I only turned down the end and threaded it with the lathe so it would screw into the cam shaft.
I cut out a 1-1/2" square from some scrap 1/4" steel plate for the foot. My Sherline mill doesn't really have the rigidity to make working with steel easy, especially this mystery meat, so I just cleaned up the ends with a file. It was cut pretty square, so this wasn't a problem. I marked the hole for the locking bolt based on the original. I drilled and tapped this for 3/8-16. I assembled everything for a trial fit (with the handle on the front side of the tailstock). Since the hole in the foot is offset, it needs to be rotated in 360 degree increments to change the height. There is only 0.035" of travel in the cam and every rotation on a 16 tpi thread equals 0.0625", so there is only one "proper" height for the foot. If this proper height doesn't allow the tailstock to lock, material must be removed and the foot must be rotated one thread higher. Alternatively, material (such as brass shims) could be added to the clamping surface of the foot if there was a good way to secure them. I got lucky with the orientation of the tapped threads, since my tailstock locked into place with the handle rotated 45 degrees and moved without binding when the handle was vertical.
I took everything apart and put a jamb nut on the locking bolt to keep the foot in the correct orientation. I put the locking bolt and thimble in place and used a transfer punch through the cam shaft hole to mark the back web of the tailstock. This is where I ran into a problem. I squared up the tailstock on the drill press and used a small bit to drill a pilot hole. I couldn't use a center drill since it was too short and the chuck would interfere with the bottom of the casting. I figured I would be fine since I had a decent center punched divot. After drilling the pilot hole, I placed the thimble back in place and realized my hole was off center by about 1/16". My endmills were too short, so I couldn't use them to recenter the hole. I struggled with ideas for a bit before I settled on turning a plug and pressing it into place. I remarked the hole location and created a huge divot with a center punch. I set it back up on the drill press and took very small pecks at the hole, frequently checking to make sure I was still on center. This time the hole stayed on center and I drilled it out with the final size bit. The location was relatively critical, since I wanted a tight clearance (0.3125" hole and 0.305" intermediate cam shaft diameter). If I would do this again, I would either make sure I start with a large divot and buy a long center drill, or take accurate measurements, transfer the location to the back side and drill on the flat surface with no interference. I used a spring on the locking bolt between the foot and the bottom of the tailstock. This keeps the foot centered (locking bolt vertical) and prevents binding when the tailstock is unlocked. I used grease on all of the bearing surfaces when I did the final assembly. I can lock and unlock the mechanism with one finger. I am pleased with the end result and learned some valuable lessons (use the right tools, don't try to outsmart conventional wisdom, things that can go wrong probably will at the worst time).
Click the pictures for larger images.