Fins and New NEI Mould

[GSM]

Group:

I recently received a new NEI mould and "tried" to throw a few bullets with it this weekend. A few questions for the more experienced:

1. The mould was consistently dropping bullets with fins - on the sides, the nose, and the base. It looks like the RCBS handles are pushing off on one side of the blocks (where the alignment pin protrudes through). The inside of the jaws kept getting a half moon mark after using the mould for a little while. I think me and the Dremel have fixed that part of the problem (ground on on the handles, not the mould).

2. The base fins have me a little stumped though. On all the other moulds I have, both the top of the blocks and the underside of the sprue plate are finished smooth. The NEI has the circular finishing pattern on both the block tops and the underside of the sprue plate (same pattern that is on both of the block faces). The base fins aren't terribly big (0.01" or less), just bothersome right now. Should I even be worried about them?

Mould specifics: 270 cal, 100 gr GC cut down to 90 gr (#12A, I think), alloy was 80ww/20 lino, temp ~800F.

Any info or opinions would be appreciated.
Thanks.

[Bass Ackward]

2. The base fins have me a little stumped though. On all the other moulds I have, both the top of the blocks and the underside of the sprue plate are finished smooth. The NEI has the circular finishing pattern on both the block tops and the underside of the sprue plate (same pattern that is on both of the block faces). The base fins aren't terribly big (0.01" or less), just bothersome right now. Should I even be worried about them?

Mould specifics: 270 cal, 100 gr GC cut down to 90 gr (#12A, I think), alloy was 80ww/20 lino, temp ~800F.

Any info or opinions would be appreciated.
Thanks.

GSM,

You didn't ask for this, but I would contact NEI and ask their opinion. That matters more than mine.

But since you posted and answered 1 yourself, I'll say that NEI has chosen less friction on the top of the blocks as a good thing. It aids venting. Outside of varying opinion on this, it should not affect molding. Most likely you have a burr preventing complete closing of the blocks or the aluminum has warped. Happens. You should be able to see this if you have access to magnifiers.

There could be a work around. You could smoke the cavities of your mold so that you can lower the temperature of your melt so it sets up quicker. Or you could alter your mix so it has less tin in it and that will make it set up at a higher temperature which will occur faster.

But you clearly have something causing you a problem and NEI should get the first shot at solving the issue.

[44man]

It sounds like fixing the handle fit cured the fins on the sides.
The swirl pattern on the sprue plate and blocks is much better then a smooth plate for boolit fill out. They will also hold Mold Prep or Bullplate lube real nice.
You might try adjusting the plate tension to get rid of the fin around the base. Hold the mold up to the light and see if you can see light beween the plate and block tops. Make small adjustments either tighter or looser and see if you can make the light go away. If not, call NEI and ask them.
I would not try to lap the plate or the top of the mold, it is almost impossible to keep them flat or make them flat.

[9.3X62AL]

I have two older NEI 25 caliber aluminum molds, and cast a lot cooler than you do--around 675* with Taracorp alloy. After about a half-dozen pours, there are few rejects. Light smoking of the cavities is all I do.

I share the view of either warpage or closure restriction causing your finning problem.

[BABore]

I cut molds with the same NEI style circular venting cut. It's actually done with a sharp pointed fly cutter using a high feed rate. Ran into the same base finning problems. I used a diamond hone to smooth the surface a little to cure it. The venting is just a little too much of a good thing. Normal wear will eventually eliminate this. You didn't say how you were pouring this mold. If using a ladle, don't pressure pour it. If your bottom pouring you may want to not pour directly into the sprue hole. Basically lighten up on the lead stream force. Your alloy is highly fluid, especially at 800 F. Try it down around 700 F.

[44man]

I use a fly cutter on the mold faces but find the swirls from an end mill much better on the plate and mold top.

[GSM]

Gentlemen:

Thanks for the respnses.

I'll check for warpage on the plate, but I think BABore may have hit it (how did he know I was bottom pouring directly into the sprue hole).

I'll drop the temp as well - just became accustomed to running hot on the steel multi-cavity moulds (this one is the meehanite 4 banger version).

Thanks again.

[Billwnr]

I cut molds with the same NEI style circular venting cut. It's actually done with a sharp pointed fly cutter using a high feed rate. Ran into the same base finning problems. I used a diamond hone to smooth the surface a little to cure it. The venting is just a little too much of a good thing. Normal wear will eventually eliminate this. You didn't say how you were pouring this mold. If using a ladle, don't pressure pour it. If your bottom pouring you may want to not pour directly into the sprue hole. Basically lighten up on the lead stream force. Your alloy is highly fluid, especially at 800 F. Try it down around 700 F.

I had finning problems when I used my lyman ladle and pressure poured. When I switched to Bill Ferguson's bottom pour ladle I had no finning. The Ferguson ladle isn't built for pressure pouring.

Bill W

[BABore]

Yep! I use both also, depending on the mold's wants. You can file in a groove, on the Rowell spout, with a triangular file to get a fine stream. The #1, 1 pound ladle, will almost compete with a regular bottom pour pot.

You can also do a partial pressure pour, with a Lyman or RCBS ladle, then lift at the last moment. Gives you a kind of in-between method. All kinds of techniques to use when you don't have a big pot above the mold. Kind of makes me feel sorry for the bottom pour guys sometimes. [smilie=1:

[hiram]

I had an NEI mould and I had fins on the nose also. I took it off the handles and pressed the 2 halves together firmly. I slowly tried to pull them straight apart and they they resisted to separate. The alignment pins were binding in the matching holes. I took a 1/4" reamer and slowly gave each holde a few turns. VOILA---no more binding, no more fins. Easy fit, easy separation.