Sprues and the plates that cut them.

[10sandxs]

I have a number of noe molds and some have developed a poorly cut sprue which I've tracked to the sprue plates. These led to a pretty significant weight difference between cavities. While I've sent them to al, and he'll most likely replace, I decided to make a new (old) spruepate design. Taking a que from my HG molds, I cut the sprue holes at a 20 degree angle for the last 0.025". The result is impressive, at least to me.

On a 5 cavity NOE HG68 clone, bullets from "light" sprues weigh 214.7gr with a 0.399 gr standard deviation. With a "heavy" sprue, the bullet weight grows to 215.3 gr with a 0.237gr standard deviation. This for 10 castings, so a 50 bullet sample. Standard deviations within each cavity are arround 0.2 for 10 castings, and between the five cavities it drops to 0.18 or less per casting. Even at a 3 sigma level, this is about +/-0.6 grains... I'm happy with that...

I'd have posted pictures of the bases (which look perfect) but I powdercoated them already...



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[Teemu]

Nice! Those sprue plates looks like same wich NEI had years back on iron molds.

[samari46]

Nice work on cleaning up the sprue plates. I took a different approach. I have a bunch of counter sinks for different screw heads and for drilling 60 degree countersinks for my lathe. They come if different sizes and used them to enlarge the holes slightly and refine the cutting edges. Then laid a piece of silicon carbide paper on an old surface plate and lapped the underside of the plate. On my larger molds improved the fill out of the cast bullet and much easier to cut the sprue. Frank

[Valley-Shooter]

Can you post a pic of the cutter you are using to cut the 20 degree angle?
Where do you buy them?

[country gent]

While it doesn't seem like much that solider .025 edge will extend the life lot. Like a knife blade the fine angle thins the blade and also allows it to slip thru the slightly steeper finished edge forms the cut edge and a much stringer edge. I have used a taper pin reamer for this final edge. I use a 82* countersink for the main sprue hole almost to size and then the taper pin reamer to finish the edge. Last is to stone the back smooth and burr free. Another benefit of this is that the tendency of cutting the sprue to pull the plate down into the blocks is lessened.

[10sandxs]

Can you post a pic of the cutter you are using to cut the 20 degree angle?
Where do you buy them?

Here is the cutter. It's just a 20 degree angled endmill. I think I got this one from Travers tool, but there are other sources as well. I picked 20 degrees as that's what I had from a previous project.

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[10sandxs]

While it doesn't seem like much that solider .025 edge will extend the life lot. Like a knife blade the fine angle thins the blade and also allows it to slip thru the slightly steeper finished edge forms the cut edge and a much stringer edge. I have used a taper pin reamer for this final edge. I use a 82* countersink for the main sprue hole almost to size and then the taper pin reamer to finish the edge. Last is to stone the back smooth and burr free. Another benefit of this is that the tendency of cutting the sprue to pull the plate down into the blocks is lessened.

Agree completely. I did do a light lap on the underside as well to eleminate any burs. Force to cut sprues does seem lower and sprues are MUCH cleaner and flatter

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