BABore
10-13-2005, 10:27 AM
I'm pretty new to casting and have only acquired 5 molds. My latest mold is a Lee 476-325 2-cavity. It casts a 0.477 dia GC bullet roughly to the LBT design. I know, I know, but I figured I'd take a chance. After getting it I prepped it for a first tryout. I chamfered the top edge of the blocks to allow better venting under the sprue plate and gave it a general deburring. Lapped the way too thin sprue plate flat, lubed it according to Lee, and left it on the loose side. I inspected the goofy alignment system and criss cross vent lines, shuddered a little, and went to casting.
I started with straight WW's at 750 F. Used a ladel with 0.200 spout hole and a pressure pour. One cavity would fill out but the second wouldn't. Switching them around also switched the results. Played around with different pouring techniques, but could only get a decent bullet on the first pour. Tried alloy temps up to 925 F with similar results. The good bullets had good weight variance but the GC shanks seemed a bit small. Figured I had a venting problem. On a positive note, both cavities dropped bullets right out.
I tried to open up the silly vent lines with limited success. It cast a tiny bit better, but still rounded bands. Sometimes both bullets, sometime just one. I was getting around 55% useable castings. I laid in bed trying to figure out how to improve the venting. As I own a machine tool shop, I have access to lots of methods. Since the blocks don't come off of the handles readily a mill was out of the question. I thought about using a series of 1/8 parallels to scribe in Lyman style horizontal vent lines that matched on the mold halves. Then it hit me. We have several 24" digital height gauges with carbide scribers. I took off the sprue plate and lapped the top of the mold flat. I put the opened mold on a granite plate, sprue side down. I set the height gauge at 0.0625 and scribed each block with several passes each. I did the scribe lines in 0.0625 increments until well beyond the nose. Following the scribing I lapped the block faces lightly to deburr and used a hand scriber to touch things up.
I casted a bunch more bullets using ww's at 750 to 900 F. Fillout was better, but only by degrees. I was probably up to 65% now. Next I tried adding 1 1/2% tin to the mix. This brought me up to about 75% good bullets. I was still getting small sections of bands that weren't sharp. What to do now?
Took the sprue plate into work to open it up. I measured the existing holes at 0.140. I drilled a couple of 0.140 holes in a 3/4 thick piece of aluminum and deburred them. I then set the sprue plate over the hole and used the drill bit shank as an alignment dowel then clamped the plate to the aluminum block. I then clamped the works in a drill press vise and used a carbide 45 degree chamfering tool. The holes were opened up to 0.180" and the bottom of the sprue plate was lapped flat with a diamond hone. Backing up the sprue plate, with the aluminum, reduced the bulging alot. Now back to the pot.
Using WW's + 1 1/2% tin at 725 F things worked like a charm. I casted up 250 bullets last night and only got around 10 rejects after the mold was up to temperature. Most of the rejects could be attributed to an oops during the pour.
When I started with this cheapy mold I swore that I would never get another. Now I've changed my mind. If and when I get another Lee it will go into the shop first. About the only other improvements I could see would be to build a thicker sprue plate and put in a stud to replace their *** screw.
Just my 2 cents
I started with straight WW's at 750 F. Used a ladel with 0.200 spout hole and a pressure pour. One cavity would fill out but the second wouldn't. Switching them around also switched the results. Played around with different pouring techniques, but could only get a decent bullet on the first pour. Tried alloy temps up to 925 F with similar results. The good bullets had good weight variance but the GC shanks seemed a bit small. Figured I had a venting problem. On a positive note, both cavities dropped bullets right out.
I tried to open up the silly vent lines with limited success. It cast a tiny bit better, but still rounded bands. Sometimes both bullets, sometime just one. I was getting around 55% useable castings. I laid in bed trying to figure out how to improve the venting. As I own a machine tool shop, I have access to lots of methods. Since the blocks don't come off of the handles readily a mill was out of the question. I thought about using a series of 1/8 parallels to scribe in Lyman style horizontal vent lines that matched on the mold halves. Then it hit me. We have several 24" digital height gauges with carbide scribers. I took off the sprue plate and lapped the top of the mold flat. I put the opened mold on a granite plate, sprue side down. I set the height gauge at 0.0625 and scribed each block with several passes each. I did the scribe lines in 0.0625 increments until well beyond the nose. Following the scribing I lapped the block faces lightly to deburr and used a hand scriber to touch things up.
I casted a bunch more bullets using ww's at 750 to 900 F. Fillout was better, but only by degrees. I was probably up to 65% now. Next I tried adding 1 1/2% tin to the mix. This brought me up to about 75% good bullets. I was still getting small sections of bands that weren't sharp. What to do now?
Took the sprue plate into work to open it up. I measured the existing holes at 0.140. I drilled a couple of 0.140 holes in a 3/4 thick piece of aluminum and deburred them. I then set the sprue plate over the hole and used the drill bit shank as an alignment dowel then clamped the plate to the aluminum block. I then clamped the works in a drill press vise and used a carbide 45 degree chamfering tool. The holes were opened up to 0.180" and the bottom of the sprue plate was lapped flat with a diamond hone. Backing up the sprue plate, with the aluminum, reduced the bulging alot. Now back to the pot.
Using WW's + 1 1/2% tin at 725 F things worked like a charm. I casted up 250 bullets last night and only got around 10 rejects after the mold was up to temperature. Most of the rejects could be attributed to an oops during the pour.
When I started with this cheapy mold I swore that I would never get another. Now I've changed my mind. If and when I get another Lee it will go into the shop first. About the only other improvements I could see would be to build a thicker sprue plate and put in a stud to replace their *** screw.
Just my 2 cents