I needed a mandrel for the slitting saw. Built it with the previously made 3/8-24 arbor in mind. The key to making this run true is to mount it on the arbor for all finishing operations on the lathe.
Cut off a 1 1/4" length of 1" steel rod that was already faced and center drilled. Drilled with #O drill bit to a depth of 9/16" and tapped it 3/8-24. This was then mounted on the arbor, held in the end mill holder, and mounted to the lathe. The steel was faced and turned true for its length. The first 1/16" was reduced to 5/8" for a tight fit to the slitting saw. This same face was then center drilled, drilled with a #21 drill bit, and tapped 10-32 for the retaining screw.
The cap was made on the end of a 1" round steel bar. The bar was center drilled, and drilled 7/32" for clearance on the 10-32 screw. This end was then bored to a depth of 1/16" and diameter of 5/8" until it was a tight fit on the body. The cap was cut off first with a parting blade and then with a hacksaw. The cap was mounted on the body/arbor setup and faced and trued.
The body/cap assembly was removed from the arbor and held in the vise on the mill. Center was located by 2 passes with the edge finder.
See the "Osborne Calculation Tool" listed on the left.
The part was then offset by 5/16" and drilled with a spot drill. It was then drilled 3/8" deep with a 1/8" bit. A reamer was used to ensure an accurate size. A 3/16" long piece of round steel bar (1/8") was held in a collet in the lathe. It was faced and then glued (Locktite) into the hole in the body. All pieces had a nice fit with minimal movement of the blade when the cap was even loosely attached.
Made a similar mandrel for the gear cutters purchased from RDG Tools, but with a square key glued into place. Runout on both mandrels with a cutting tool in place was excessive. I was able to bring both down to respectable runout by careful filing. The runout on the gear cutter is now < 0.001" and on the slitting saw < 0.002".
