Sprue plate screw won't stay in.

The sprue plate screw on my old and heavily used 3118 4-cavity mold will not stay in. It doesn't come unscrewed, it just plain slides out. Rust is the presumed cause. The threads on the screw seem to be reasonably good, so I assume it is the ones in the mold body. I tried filing a recess for the set screw, but that did not hold it. I haven't tried loctite, as I figured the heat would defeat it. Has anybody tried anything that worked?

Loctite 28654 Form-a-Thread might work. Specs say it's good to 300F but I've used it to repair damaged spark plug threads on aluminum heads of air-cooled small engines...like chain saws and push mowers. Only other option I can think of (without some machineshop work) would be installing a helicoil... if you can find one with the right thread.

Bill

Not a hard fix but it needs to be done correctly. Several fixes will work. 1) loctite form a thread may work as mentioned above. 2) a helicoil should work but can be tricky to install and a kit has several inserts in it. 3) is to make a insert. not as hard a s it sounds. set up the block in a drill press locked down to the table on location. Drill out existing hole to tap drill for larger bolt. Tap to new bolt size and insert bolt with red loctite. Cut of square and close to flush. do not remove from drill press as location will be lost. Center drill pilot drill and drill tap hole for bolt and tap. Clean up to flush and transfer set screw hole thru the bushing. Clean up threads.

Once you start #3 do not move drill press table or remove mould from it. do everything with it locked down. If the tap and wrench is to long use the drill chuck to drive the tap. This maintains location thru the process. A good vise bolted down tight or a couple strap clamps are fine.

The last is to have a new bolt turned up with over sized threads to catch the last threads left. This is a lot of work for an iffy fix.

If you're reluctant to try it yourself, contact Eric at Hollow Point Mold Service.

You're talking about the pivot screw for the sprue plate right?

The way I'd approach it would be to drill the hole and tap it to accept a 1/4 cap bolt. Finding a cap bolt with a shank that wasn't too long might be an issue. You could use a piece of tubing as a bushing until a better solution was found.

I'd probably leave the portion of the the hole where the set screw goes unchanged and reduce the diameter of the end of the bolt to fit it. I don't have a lathe but it'd be easy enough with a drill in a vise/clamped down or a drill press to spin the bolt and use a dremel or a grinder to reduce the shaft then finish it with sandpaper.

I fixed a worn lee mould in a similar fashion but I put a bolt all the way through the body and put a nut on the other end. I should have drilled and tapped it but I wasn't thinking. I removed the handles and had to cut a relief for the bolt. The same might be an option for your mould but it wouldn't be as pretty

You could drill the hole deeper and tap. Then use a longer bolt. You could drill and tap for the next larger bolt diameter. You could use a larger self tapping bolt. You could drill a hole perpendicular to the existing hole tap it and put in a bolt to lock the other bolt in place.

Tim

drill a hole in from the side, tap to 10/32 and use a brass set screw to hold the sprue screw from moving

Had a thought. You could get it where you want it then drill a 3/32 hole through the side of the mould and through the sprue plate screw. Then cut the drill bit shank for the pin, leaving it 1/4" long so it can be grabbed with vice grips should it ever need to be removed.

This would be easy to accomplish without a full machine shop and easy to change when a different solution is desired.

NOT any sort of a wanna'be machinist, what I did years back with a 4-cavity Lyman mould with identical problem was to set mould on drill press table, and found the largest number (e.g., #1 - #60) drill bit which would just fit in the rusted/stripped hole. It turned out that I had to remove very little diameter of existing hole, but when at its bottom I clamped mould to table, and continued drilling all the way through. I don't recall which (and at 2* out, too cold for me to go and check ;) ) but either a 6-32, 8-32, or perhaps 10-32 bolt was the size I used, so I ended up with a nut/bolt going all the way through it. I used a large drill, then, on the bottom, to just accept the head of said (I think it may have been 8-32) flat head machine screw, and put that in from bottom up. Once done, all then needed was but to put Sprue plate back on, and I used two nuts at top, with a bent-spring flat washer underneath them. Well, you asked ;) -- I tried this; and it did indeed work. Just another option for you if all else fails....
geo

Thanks guys! You've given me some good ideas. Now just as soon as the ice storm goes away, and I can work in the shop again...

I took Bazoo's suggestion. I clamped the mold in the mill vise, centerpunched, and drilled through the side of the mold and into the screw (hopefully not much farther) with a 1/16" bit, then cut off a small finish nail and tapped it in. Heated it up and cast for a good hour with no problems. In fact, something, maybe the cutting fluid, seemed to make the boolits fall out much easier.

I had this exact same thing happen recently on my Saeco 4 cav mould. Threads looked fine on the allen headed tap screw that went through the sprew plate, but it would strip when it bottomed out. I retapped the body out, still no joy. Before I decided to drill and tap to a larger size or even try a helicoil, I just went and bought a new 10-32 steel screw. For $.82, I saved a lot of work. The threads on screws are softer than the steel mould, and wore just enough to allow stripping. Just a suggestion that might save ya a lot of unneeded work.