How sharp must the sprue cutters be

[thebigmac]

HOW SHARP MUST THE SPRUE CUTTERS BE ??? I HAVE A MOULD WITH SPRUE CUTTERS HAVING A NOTICEABLE (GUESS TO BE @ 1/32nd") "WALL" FROM THE TOP OF THE MOULD TO THE FUNNEL BOTTOM. AT FIRST I THOUGHT MY ALLOY WAS TOO HARD, BUT WHILE CLEANING THIS MOULD WAS WHEN I NOTICED THIS PROBLEM. I HAD TO REALLY SMACK THE SPRUE CUTTER TO CUT THEM. SHOULD I JUST TAKE THE DRILL PRESS AND DEEPEN THE FUNNEL ??? OR WHAT.... IDEAS GRATEFULLY RECEIVED. THANKS.
THEBIGMAC:castmine:

[DLCTEX]

I have used a countersink to make a sprue plate. I want mine to have a knife edge. The sharper the cutter, the smoother the cut, and easier.

[crabo]

I use a 90 degree countersink to sharpen or enlarge my hole. If you have a heavy base, you sometimes need to open the hole a little larger.

[Le Loup Solitaire]

Hi, I have made sprue cutters out of aluminum plate and cut the funnel with a countersink. Aluminum plate isn't the greatest stuff for holding an edge, but it is enough to cut the sprues with an average tap/whack or whatever one wants to call it. Anyway whatever plate that you use and its edge lasts a long time with WW. It would figure that harder alloys up to lino would be harder to cut and the edge wouldn't last as long as with a softer alloy. The diameter of the funnel hole thru which the alloy flows is also a factor. The smaller the diameter...the smaller the diameter of the sprue cut, but that subject is one of personal opinion-some casters like a larger hole (up to a point) as it supposedly enhances pouring qualities. If the sprue plate is steel then the funnel can be polished to make the sprue hole sharper, but it doesn't have to be real sharp to do a good job. The bottom of the steel sprue plate can also be honed or polished a bit if you have a perfectly flat fine stone or use a piece of glass with some fine valve grinding compound on it. Just make sure to keep the entire process totally flat. Again super sharp isn't really necessary. A "wall" as you have described isn't good as it isn't cutting...that's why it is taking considerable force to get it thru the sprue hole diameter thickness. Suggest you go slow as you can always take more, but can't put any back. You can try/practice with 1/4" aluminum plate as its pretty cheap and you might be surprised at the Alu plate's performance. Also you can always go back to steel plate anytime. LLS

[Bret4207]

Take the plate off and flatten it using a figure 8 motion on a stone or paper on plate glass. Then use a Dremel cone shaped stone and turn it in the hole WITH YOUR FINGERS NOT THE DREMEL TOOL!!!! till it creates a slight bulge on the bottom. Then hit the bottom on the stone for a stroke or two and you'll have a fine edge there/ It won't stay razor sharp, but it'll be a lot better.

[badgeredd]

bigmac,

It doesn't happen to be a RCBS mold, does it? I had a new one I bought about 18 months ago that had the same flaw. It looked like the cutter had some how been set too shallow and there was a noticeable 1/32" flat as you describe. If I recall correctly it was their 35-200-FN mold.

I used a counter sink to get most of the metal out and then as Bret said I finished it by hand with a coned wheel and polished the bottom to remove any stray burrs.

Edd

[Chargar]

I use the little Cratex abrasive cones mounted in a drill press at the slowest speed. It is not just a matter of beng sharp, but tool marks in the sprue hole can form a lock and you have to beat the snot out of it to make the spru fall free.

Once you have a mirror smooth and sharp spru hole, the world is a much better place to live in.

[thebigmac]

THANKS TO ALL OF YOU WHO TOOK THE TIME TO ASSIST ME..Mac

[theperfessor]

A sharp cutting edge is nice but a razor sharp edge isn't totally necessary and in some cases will dull faster than a slightly blunt edge.

If you use Bullshop lube to prevent lead smears you can cut the sprue just as it solidifies. It takes a lot less force to cut and puts a lot less force on the cutting edge. One of the other members here has a technique for this that allows you to dispense with a sprue hammer - he cuts the sprue with a gloved hand. I think there is a sticky somewhere on this site about it. After reading about this I do it his way and it works great.

[Springfield]

If ya gotta whack it then you waited too long for it to cool. I cut sprues with just hand pressure all the time.

[462]

Read about using the gloved hand to cut the sprue, rather than beating the plate with a cudgel, and it works quite well.

[leadman]

I had a couple Lyman 2 cavity moluds that had sprue holes like that. I used a countersink to deepen the taper and sharpen the edge. Works good.

[SciFiJim]

I too, cut the sprue with a push of a gloved thumb. It only works on two cavity molds for me. Still takes a gentle whack on four or more cavity molds.

[Bret4207]

A sharp cutting edge is nice but a razor sharp edge isn't totally necessary and in some cases will dull faster than a slightly blunt edge.



I agree, but once you take it to a fine edge and start using it, it seems to dull a certain amount and stay at that level. I have a few I did 12-15 years ago that still cut very smoothly. I think it's just getting that factory edge finished that does it.

[TAWILDCATT]

I think you will find that the edges were never sharp as a knife.I have many molds that have that.they were drilled and countersunk.relieing on the sharp 90degree edge.
some one sells an add on to the sprue plate to hand hold to cut the sprue.
it clamps on with a set screw.:coffee:

[theperfessor]

SciFIJim - A short piece of flattened tubing stuck over the sprue plate extension works good to add leverage to four cavity sprue plates.

Brett - You're right about the wear. When I grind my own cutting tools from HSS blanks I always take the "razor sharp" edge off just a little with a fine honing stone. I found out that for cutting tools it prevents chipping. And I suspect that a loose sprue plate that had any up-and-down motion would chip or bend a sharp edge from having force applied to it at a right angle to the normal motion, especially from an impact (hammer) blow.

[thebigmac]

all right gentlemen, i just tuned in here to se if i more responces.. Wow !!! All you guys are just great. Whenever someone requests assistance on this great forum, there are always plenty of members saying their thing. Much to my surprize
you all seem to know what to say. Thanks again----- big mac

[Bret4207]

Much to my surprize
you all seem to know what to say. Thanks again----- big mac

Fooled another one........




:mrgreen::mrgreen::mrgreen::mrgreen::drinks: