Anyone built a new sprue plate and faced a mold?

The used MC i bought off Ebay years ago came with 3 sets of molds, all had a few issues, but nothing that made them unusable. The main issue is that the 9mm conical has been used quite a lot, there is a wear mark on the mold where the bolt that the sprue plate pivots on and i believe the sprue plate is warped a little allowing lead to build up underneath it.

When casting, i get lead building up in the groove in the mold block that pushes the sprue plate out so the bump on the back of the projectile gets larger and larger, not cut off flat with the base like it should.

My plan is to mount the cast iron mold halves in the mill and face it, so it's dead flat, i was then thinking i should polish it so it's nice and smooth, but i'm not sure if that is a good or bad plan. I was going to also make a new sprue plate and grind the back so it too is dead flat so hopefully it will not get any lead build up. The projectiles are BB and i believe there is enough material there to not cause any issues.

Is this the right way of doing it? or should the surfaces not be polished?

I hope to use high carbon steel for the sprue plate so it will hopefully last better and keep a sharp edge to cut the sprues off.

I made a new sprue plate for a Lyman mold. Drilled the holes then surface ground the bottom. It was easy and has worked without problems for several years.
If I was going to face off the top of a mold I'd run an indicator on the top surface to make sure it is set up perfectly flat in the vise before milling. I wouldn't trust the bottom or sides of the mold to be perfectly parallel or square. I also wouldn't polish after milling, machining marks will help it vent.

I would agree with everything that Quack1 says.

For those that don't have access to a surface grinder, when you drill the sprue hole, use a SHARP drill so, you don't push metal when when it brakes through. Then stone the back side, around the hole flat. Also, you don't need a sprue hole larger than .100, it will fill fine with that size hole (.080 for 25 cal and smaller) the larger the hole, the sooner it will dull and the easier that it will cut, especially for 4 cav molds.

Frank

I never thought about venting issues if they were ploished, nice catch. Im with you on Checking flatness while setting it up I'd not assume it was square.

I too was curious about hole size, good to know I don't need them too big. It is only two cavity mold as well. Whe. I get time to attack it, ill try and get pictures.

I've done this quite a few times. Everything the previous two posters sounds perfect. The only thing I would say is that sometimes there is no flat surface on top of the mold to indicate off of, and simply holding it low in the vice jaws is the best way to grab a "happy medium" right off the bat. What I do is draw file all the blocks all the way around to bust off any dings that weren't there when it was cut originally.
use your vice to grab the stop pin in the top of the mold and twist as you pull up to remove it.
Now that you have a clear surface on top, fly cut the top of the mold till it cleans up completely. (Usually, the hinge point is the last spot to clean up).
I find that about 3/16" is the ideal thickness for a good sprue plate, and almost any steel will work, but I've had the best luck with a tool steel like 01, A2, or D2.
Make the sprue plate and finish the periphery, then pop your holes for the sprues. Make them undersized (1/16"??)
Follow the small holes with a 90 degree countersink cutter. Watch out to stop short and draw file off the burs on the bottom side of the plate. You will find that you actually went deeper than you thought, so check it often and use stops to remove, and replace.
Once you get it where you want it, if you have a surface grinder, go and clean up the top of the mold and the bottom of the sprue plate.
Replace the stop pin, put your mold back together and see if you can see light between the two. If not, make sure you can cut a hair in the sprue hole.
Works every time!

Thanks for that extra information. All very good points.

My dad have a friend that has some 4140 and 4340 square stock. I believe that will harden up nicely to hold it's cutting edge on the sprue holes.

I don't have access to a surface grinder, but my mill can take a cup wheel that i can use to grind with, i hope to be able to use it to get a nice surface finish after fly cutting it.

Hopefully after this, i won't have any more issues with lead being stuck between the plate and mold blocks.

Don't heat the sprue plate up much when grinding it or it will end up bowing. It is best to use a water based coolant to prevent bowing. Even with flood cooling on a surface grinder you can still bow it if the DOC is too deep.

I polish all my sprue plates with a rag and some Mothers polish. They clean up easier after use. I also usually lap the bottom of sprue plates working up to 1500grit wet dry to make sure they are flat. I don't need to do it for MP sprue plates though because they come flat and smooth.

Also be careful not to go too fast with the feed rate or deep with the DOC when milling the mold block. You could end up knocking off the sharp corners at the mold cavities. Cast iron can be a little brittle and chunk off.

Your not talking alot of metal removal so a fly cutter with a sharp tool and light cuts of .005 or so should work fine. feed across slow and easy. I did a lyman postell mold ( converted it to nose pour) and I used a 3/8" 4 flute end mill starting at front side and working across it in .050 steps, this gives a very flat true surface. Feed across till end mill is completly off part. As to the sprue plate once out side is finished you have the fixture to do it. Drill hinge pin hole. Indicate mold blocks in true and center cavity with indicator. Bolt sprue plate on in place against stop pin. Drill sprue hole and chamfer slow and easy. I cut a small chamfer around the holes to keep metal from being raised around them when torquing or pressing things togehter. I made my plates from D-2 finished them in manner above with 3/8" end mill and they are around .200 thick finished. D-2 grinds terrible and is a pain with heat build up, but is very impact resistant. I was lucky as I did these at work in a cnc mill and programed the shape and hinge hole then cut them out of wider longer stock stepping down every pass. Before setting up remove all burrs dings and imperfections with a fine file or stone, a surface plate and fine sand paper works great also. Getting down to the true surfaces makes set up much easier. Go slow think things thru before cutting and measure alot and cut a little.

Even more good advise. With the gear i have on hand, hopefully i can do a good job of it. I actually didn't take into consideration that cast iron is brittle, going slow is a must on something that will cost me a fair bit to replace if i mess it up. Most of the machining of cast i have done were non interrupted cuts, so chipping was not an issue.

Heat build up while grinding may be an issue. The plan was to drill the sprue holes then harden the plate, i can then flip it over and do a final pass with the grinder to flatten it just in case it warped some during heat treatment. Hopefully it won't effect the edge on the sprue hole, as the goal is to keep it nice and sharp. The only issue i see is the scale you generally get when heating up steel and dunking in oil to harden it. Hopefully the grind after this process will give a nice sharp edge though.

Yeah there is a chance it will warp during heat treat. I never made a sprue plate out of it but you try a piece of 4140 prehard. It comes hardened to 28Rc-32Rc which is still soft enough to be machined with HSS tooling.

Fly cutters are okay for some things, but also remeber if the head of the mill isnt perfectly square and true to table or vise you never get a square true cut. Using the end mill and stepping over gives a much flatter truer surface much easier. A fly cutter out of true actually will cut a radious across the part. The smaller end mill stepping over a small amount cuts a much flater surface. To help alieviate chipping try and cut with the cutter cutting into the block on the heavy side of the cut. We used to stone a small radious on the corners of the end mill to help get a better finish, unless we had to have square corners in the bottom of the part. You might also consider adding to the length of the sprue plates lever section for added leverage when cutting the sprue. Another inch would add alot there.

I'll give it a shot, see if i can avoid making a mess of it :) I have always found that using small cutters will give a pattern on the piece i'm working on, but if i was going to do the final touches with a sheet of wet and dry and a piece of glass to get it nice and smooth it won't matter about the small marks.

Hopefully i will get a start on it on the weekend.

or you could just buy some new sprue cutters from magma engineering.
lay a new one on top of the mold and check flatness with it.
you might just have the bolt too tight or a broken spring on the sprue bolt.
I tried adjusting a cutter for my MC like I would a hand mold, it don't work that way....

I would have looked at that but i am from .au, the shipping alone would possibly exceed what the part cost. I actually wouldn't mind getting a new mold or two from them.

Timely discussion here. Just finished my first set of mold blocks that copied a lee 6 banger. Could use the lee plate, but I notice that over time they seam to gall the top surface of the mold blocks. Thinking about using 3/16 O1 tool Starrett ground tool steel for the sprue plate. Thinking that hardening the sprue plate might keep it sharper longer, might prevent galling the blocks ?? I have a mill of course, no surface grinder. Reading this discussion and thinking about it, sure that after the O1 is quenched, going to need to re-surface the mold side of the sprue plate, bound to be some warping. Hoping when finished this mold throws a .380 160gr. gas check round nose with a small flat on the nose for use in a tubular magazine rifle.

Ypu could always just use the surface grinder to true up the top of the blocks. After removing any burrs, lead, with a plat faced file I would place it top down on the surface grinder then take small amounts from the bottom to true it with the top of the block. Then turn and grind the top until cleaned up.

You could also use a lathe with a 4 jaw chuck.

If the current sprue plate can be cleaned up with less than say .020" ground off, that would be an option instead of making a new sprue plate.

w30wcf

Fill the cavities with lead before machining to avoid chipping the base.
I have done a few, used a fly cutter and used a scrap of cast iron to find the right speed and feed.

Ha, never considered leaving lead in the mold, makes sense.

Sadly i don't have a surface grinder, i do have a mill that will take a cup wheel. Cover the bed and ways with rags to keep the abrasive dust out of them.

Hopefully this weekend i'll get a chance to do some cutting.

I know it has taken me a while to get back to this, life always seems to get in the way.

I got some slices of 4140 steel and machined them on the weekend, they aren't perfect, but they should do the trick. I drilled the holes then put the plates in the mill and faced them, i then cut the shapes out. Heated up to red hot and quenched in oil. I mounted them in the mill again with the flat side up, as i don't have a surface grinder i hit it with a carbide end mill, i then rubbed them over wet and dry sand paper on a sheet of glass. There are still a few marks, but hopefully it will not cause any issues. The holes have nice sharp edges, so i feel it will do well, hopefully i'll test them out on the weekend.

The pictures are not great, but hopefully should give you enough detail.

http://i903.photobucket.com/albums/a...714_073708.jpg

http://i903.photobucket.com/albums/a...714_073653.jpg

I have faced a boat load of Lyman four cavity molds. Mostly to match the molds boolit weight. I had a hand casting business for over twenty years and cast with multiple molds for production. I preferred to set the molds on a magnetic chuck, skim the base, then turn it over and skim the top. I matched the molds to drop within one grain of each other. I prefer to use a surface grinder rather than a fly cutter, but have achieved good results with both methods.

New production Lyman four cavity molds do drop boolits within +/- one grain when bought in pairs. This is based on a pair of 40-175-TCBB and a pair of 45C-250- RNFP.


I have made sprue plates from CRS and A2 tool steel. The A2 worked best.