I'm curious myself who uses this method with success? what do you use for the hammer? What do you place the bottom of the mold on? If I'm  going to try this lets get some facts that keep me out of trouble.

I have to agree that Joe might have a point...... Gee I hated to admit that. 

  I do hit the sprue plate with a small rawhide hammer with no problems that I've seen, and you know how thin those old Lyman sprue plates are. But, and it's a big BUT. I don't hit the mold blocks themselves, with the hammer or thru the sprue plate. Without any evidence to back it up I really don't want to try and see what happens.

  I figure it's no problem to go back to the mould maker and get a new sprue plate. But supposing... with no evidence to back it up.... I should damage the top of the mould blocks by doing as Joe suggests, especially around the cavity hole? Then a perfectly good mould is shot. I don't know about you guys but when I get a mould that does the job perfectly I sure don't want to screw it up.

  So, basically, if it works for me with 60 + years of casting behind me I'm not interested in seeing if what Joe says will work. But then my sprue plates are set up so they cut cleanly and leave the bases without any of those "bumps" so I have no need to see if whacking the sprue plate works. I suggest you all do the same!

Pete

Joe
The sprue plate is the most ignored part on most moulds. Good mould makers spend countless hours on grinding a cherry or lathe boring a cavity, and then slap on a Sprue plate from Lyman or RCBS. These are stamped out of relatively soft, read mailable, steel. Most of the moulds that I have that use commercially produced sprue plates have had the plates reworked by me before I ever cast a bullet in them as they are in sad shape. Few are truly flat, most have raggedy dull sprue holes. Many times I will make a proper plate for a mould and get rid of the one that was slapped on it. My material of choice is .090 bronze. I mill it to shape and drill the sprue hole in the exact center of the bullet and cut my sprue cavity with a ball end mill. this gives me a sharper edge that cuts cleanly and flat to the top of the mould. After doing all that work to make a proper plate why would I want to whack it with something? I would no more hit my mould than I would stick a steel rod down the bore of my rifle to drive a slug through it. Yes it can be done but there is potential for damage and I, for one won't take that chance. I also won't use a micrometer as a C clamp. Most guys when they are hitting the sprue plate are just flipping it on it's side and whacking it. When done along the axis of the plate little harm is done. When hit down against the block, over time it has to flex the plate. When the strike is away from the block it will tend to pull the plate up leaving a bump in the sprue and over time flexing the plate away from the mould block face making the plate  fit poorly. Most of the people who hit their plates will say they always hit it on the axis, but over the thousands of hits they gotta shank a few, some more than others. Its gotta take its toll. Your moulds are precision instruments treat them like they were and they will give you a lifetime of good service or mistreat them and see what happens.

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See 3 BULLET CASTING, PG 95

joe b.

joeb33050 wrote on Aug 22^nd, 2011 at 6:18am:


Couldnt see it Joe. Have to have an account. What kind of hammer are you using?  Has to be heat proof.  I want to try it myself.   

Normally I only hit the sprue plate with a hickory remnant.  I've almost thrown a few molds. Rebuilt and deburred a bunch.  I've done the glove thing but dont like wearing gloves when I'm casting. Has to be easier on molds. 

If the mold is out of square, hitting the sprue plate wont make it square. Neither will cutting the base with the sprue plate.   

I drill new sprue plates while on the mold dialed in in the lathe. Then the hole is dead center to the mold cavity.   

               Joe. 

position

Don't surface grind the sprue plate, lap it out. The magnetic chuck on the grinder can pull out a slight warp, you grind it flat then release the chuck and the warp springs back. Use some old glass and some lapping compound. 

40 Rod

40_Rod wrote on Aug 23^rd, 2011 at 9:21am:


If the sprue plate is galled, surface grind it and then lap on a lapping plate or piece of glass. The magnetic table on my surface grinder isnt strong enough to bend a sprue plate.  I use a fine wheel so dont have to lap after grinding.  Incorrect grinding technique can heat the sprue plate and cause warpage. Keep cool or use coolant when grinding. 

                            Joe.