Vettepilot
Plastic
- Joined
- May 9, 2020
Background: Bridgeport mill, older manual machine. Bed just trammelled, machine seems tight and very repeatable. I just used it to machine out two 80% lowers with no problems and perfect results. Now working on a Lee Precision aluminum two cavity mold.
The mold was a 9mm that I wanted to mill out to cast 50 caliber round nose bullets, .800" long. I got everything all set up and indicated/dialed in, and started work with a new .500" round nosed milling bit. I set moderate tension on the quill lock. (Moveable, but with drag.) I then came up .100" with the bed and then down with the quill slowly but steadily to a zero stop. Raise the quill, brush the bit, blow out the chips, lubricate the work/bit. Raise the bed another .100", come down with the quill to zero stop, and repeat until reaching .800" depth. I have found this to be a good technique, especially for smooth holes in aluminum.
So the cavities in the mold came out really great, with a very smooth finish that I wouldn't even need to lap. BUT: Both mold cavities measure exactly .4995" perpendicular to the parting line, but .504" at the parting line. Mold was VERY securely clamped tight together for the milling process, and besides, the oversize is perpendicular to that axis.
What went wrong??
Thanks!
Vettepilot
The mold was a 9mm that I wanted to mill out to cast 50 caliber round nose bullets, .800" long. I got everything all set up and indicated/dialed in, and started work with a new .500" round nosed milling bit. I set moderate tension on the quill lock. (Moveable, but with drag.) I then came up .100" with the bed and then down with the quill slowly but steadily to a zero stop. Raise the quill, brush the bit, blow out the chips, lubricate the work/bit. Raise the bed another .100", come down with the quill to zero stop, and repeat until reaching .800" depth. I have found this to be a good technique, especially for smooth holes in aluminum.
So the cavities in the mold came out really great, with a very smooth finish that I wouldn't even need to lap. BUT: Both mold cavities measure exactly .4995" perpendicular to the parting line, but .504" at the parting line. Mold was VERY securely clamped tight together for the milling process, and besides, the oversize is perpendicular to that axis.
What went wrong??
Thanks!
Vettepilot