I had quite a bit of trouble with slipping QCTPs. They would tend to twist under load. I tried a longer T-Nut and relieving the center of the QCTP. These steps helped but there was still some slip. This is a disaster for CNC work, the computer needs to know where the tool is.

I decided to make a QCTP riser to match the Sherline spindle and tailstock risers. I built it to have a raised "key" on the bottom to catch the table T-slot. That should keep that portion from rotating. In the top I cut a square recess to keep the QCTP itself from rotating. The pictures below show the parts involved. This size is for use with a 1" riser.

The body is clamped to the table via a long T-nut and two socket head cap screws from the top. The QCTP post is clamped onto the riser block. The final installation then looks like this.

I also made a short one for use without the Sherline riser block. It uses the same concept as above but the mounting is slightly different. The post goes through the plate and is attached to the T-nut via a set screw threaded to both. This is the configuration the QCTP came with from LMS, but with a newly machined post. The top nut pulls the assembly together holding all solidly to the table. The key fit to the T-slot and the square cut out on top is what prevents the QCTP from rotating. Here are two pictures of the short tool post.

They both work quite well and eliminate (hopefully) any twisting of the QCTP.