As I use my Hendey lathe, little things stand out to me that I want to modify. One of these things was the use of set screws to lock the scales to the cross slide and compound screws. Most lathes have some kind of thumb screw so you can quickly reposition the scales while working. Maybe my lathe did too and they were simply lost over the years. My compound passes over the cross slide scale which would sometimes block me from getting an Allen wrench on the set screw. Here’s what I’m working with.
I’m going to make my thumb screws in the style described by MrPete222 in his Machine Shop Tips #106 video. I’ve followed him on YouTube for a while and had seen this video long before I had my lathe. I recommend his videos to anyone interested in hobby machining. This style of thumb screw involves making a knurled nut and attaching it to the threaded rod.
I started with a 3/4″ piece of HR steel and faced the end.
Next, I drilled a starting spot with a center drill.
My lathe had a 1/4″-20 set screw for the cross slide. Using my Machinery’s Handbook I found the right size tap drill bit and proceeded to drill the hole.
The diameter of the thumb screw head doesn’t matter and I arbitrarily picked a size a little under 0.6″.
I chose a medium sized knurl for this thumb screw. I’ve founding using the tail stock when knurling with this style knurling tool keeps the work from deflecting too much and produces a better result.
The next step was to tap the hole. I got to try out my spring loaded center that I made just for this purpose. You can see it held in the Jacob’s chuck. The spring center has a spring loaded rod with a point on the end of it that fits into the center hole on the back of the tap wrench. This helps keep the tap aligned when starting to thread.
Here’s the piece I was left with after parting it off.
To figure out how much thread I needed protruding from the bottom of the screw, I threaded my knurled nut onto a bolt and moved it to a satisfactory position. Once there, I moved the knurled nut up, applied some red Locite, and then moved the knurled nut back into position. I should note, that I put a small piece of brass between the thumb screw and the cross slide screw shaft. This saves the shaft from getting deformed when the thumb screw is tightened.
Once the Loctite had dried I cut the waste part of the bolt off and filed the top down flat. Finally, I put a nut into my lathe chuck and threaded the thumb screw into it so I could radius the top edge. Typically a collet would be used to hold the part instead of a nut in the chuck.
Here’s the two thumb screws I made. I made the smaller one for the cross slide but didn’t take any pictures because it was made using the same process for the larger thumb screw.
Here they are in place and ready to be used!
At some point I need to made a depth stop for the cross slide. It was missing when I got my lathe but you can see where it goes in the picture above. I’d to to the left of the cross slide dove tail where the hook shaped piece of metal can rotate on to it. That’ll have to wait for another post though.