Boring Bar Holder for a Sherline Lathe

I have the boring bar holder for the Sherline quick-change tool post for my Sherline lathe. I find that it is quite hard to use it. Specifically, when I use a boring bar in the holder the tool post rotates under normal use. This causes the bar to back away from the cutting point. This happened no matter how hard I try to tighten the hold down bolt for the tool post.

I decided to make my own boring bar holder that would not rotate.

The way that I ensure that the holder will not rotate is that I have two tie-down bolts that use the same channel in the crossslide.

Figure 1 shows the holder mounted on the crossslide of a lathe.

Figure 1: boring bar holder on lathe

I started with a 1 ¼” x 1 ¼” bar of 6061 aluminum. I cut off a 1 ¼ “ long piece (making a cube) and drilled a 3/8 hole through the center. Since the 1 ¼” height of the bar does not position the center of the hole at the right height. I added a piece of 5/16” thick aluminum to the bottom of the cube and that provides the right amount of height. See figure 2.

Figure 2: bottom of boring bar holder

You can see in Figure 2 that there are two holes for hold down bolts, one on each side of the through hole, that use T nuts to hold the holder to the crosslide. Note that these holes are #11 (body drill for 10-32 screw) and are counter bored from the bottom to ¼” to a depth of ¼” to clear the T-nuts. The hold down bolts are 1 3/4 “ long. You can also see the slot I made perpendicularly through the 3/8” hole down to just above the bottom of the cube. (The top of the slot is rather messy because I tried to use a slotting saw first and that made a mess – I used a band saw to cut the bottom part.) You can also see the slot in figure 3.

Figure 3: side view of holder

The final part of the holder is the clamp that holds the boring bar in the holder. This can be seen in figure 4.

Figure 4: top view of holder

You can see the two bolts at the top going across the slot. The part of the holes to the right of the slot are #11 (body drill for 10-32 screw), the parts of the holes to the left are tapped 10-32. Thus, a tightening the two bolts going across the slot will close the slot and clamp down on the boring bar in the through hole.

To use the holder, you first slide the holder into a slot on the lathe crosslide and tighten the hold down bolt furthest away from you. Then insert the boring bolt and tighten the two clamp bolts to secure the boring bar. Finally, you tighten the other hold down bolt.

2024-09-05