Sprue screw help

[hornady]

I was casting with my Lyman 4 cavity mold and noticed the Sprue cutter loosening up. I loosened the setscrew and tried to tighten the Sprue screw, It is stripped out, I am hopping just the screw. I tried to replace the old screw from a new re-build kit, and the threads seem to be full of fouling from the old screw. I did not want to cross the treads in the mold block. I was thinking I might try running a tap in the mold to clean the threads, but this being a step down screw I am thinking the tap will bottom out before it cleans the mold block treads. Any ideas,

[chboats]

you will need a bottom tap. There are several stages of taps that the taper on the end of the tap is shorter, until there is almost no taper.

Carl

[theperfessor]

If you're careful you might be able to use a very sharp pointed object to get out the old screw thread. A sharp pin might work.

[Mal Paso]

If the block threads are buggered so much a plug or bottom tap doesn't clean it up, a Helicoil Kit from an auto supply will allow you to replace the threads.

[montana_charlie]

you will need a bottom tap. There are several stages of taps that the taper on the end of the tap is shorter, until there is almost no taper.

Carl
If you are careful not to overheat the steel, you can grind (almost all of) the taper off of a standard tap - to create a bottoming tap.

CM

[Shuz]

I've often used a steel dental pick to clean junk outta threads.

[hornady]

Thanks for the ideas, I get some spare time I will see what I can do, This 4 cavity is one of my older molds in 9MM and it gets a lot of use.

[MT Chambers]

I just drill and tap to the next larger size, preferably N.F.

[hornady]

Good news the mold block must be harder than the sprue screw. I ran a tap in and out of the mold block, it took a bunch of **** out of the treads. Sprayed the treads out with WD-40 to remove all the chips. The new screw tightened up nice. I had ordered the rebuild kit from Mid-south, mold is good as new.

[theperfessor]

Great! Good to hear a success story.

[44man]

The problem is the set screw damages threads so you can strip when you remove the screw.
I use a tiny chunk of brass under the set screw. Copper is better. A chunk of copper wire.
Another way is to cut a groove below threads in the screw for the set screw.

[Canuck Bob]

The problem is the set screw damages threads so you can strip when you remove the screw.
I use a tiny chunk of brass under the set screw. Copper is better. A chunk of copper wire.
Another way is to cut a groove below threads in the screw for the set screw.

I suspect this too. A dandy thread chaser can be made by a good quality screw, hex head cap screws are generaly good. Grind a small groove the length of the threads and advance a bit and backup to clean. I also make my bottom taps using a cutoff wheel in a dremel tool.

A good blast of high pressure air should be tried first, protect your eyes.