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Thread: Bent sprue cutter on an RCBS mold

  1. #1
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    Bent sprue cutter on an RCBS mold

    I ran across a used RCBS 358/ 180 gr GC silhouette mold at a local GS. I really did not want a GC mold but the price was right and the blocks looked good so I bought it. I used it for the first time tonight and noticed that the sprue plate was binding. I loosened it slightly and then noticed that the sprue on the rear cavity was not cutting flush. Looking at the plate closely I noticed that it was bent. Apparently the mold had been dropped with the cutter in the open position. My question is can I straighten the plate sufficiently to make a square base or will I need to contact RCBS for a replacement?

  2. #2
    Boolit Buddy
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    Since they are free, I would just call RCBS on monday and they will send you one. Probably take about a week since they are on the west coast.

  3. #3
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    I had a similar challenge a while back with a sprue-plate not flat. I "knew" my attempts to restore it with manual effort would probably make it worse.. but -- why not give it a whirl? I darkened entire plate bottom with either magic marker or Sharpie (one or the other) and then began rubbing it on some 600-grit wet/dry sandpaper I had affixed to a piece of plate glass with spray adhesive. Bion, it was not that far off, and my concern became -- while being able to make it again flat -- to not do so on an angle. A single layer of electric tape for the first couple dozen strokes took care of this. I then removed tape, and continued in circular strokes. (I kept the paper wet) After -- repeating the magic marker coloring -- it was again flat, I removed the sandpaper, and applied some valve grinding compound to the glass, and resumed. I think my pressure was perhaps too heavy, as I also ground the glass -- but, it worked dandily! Lastly, I washed it well with soap and water, followed by 99% Isopropyl alcohol. I "blued" it with some Birchwood Casey cold blue... and it has worked quite well, ever since. Start to finish, the entire process took less than an hour, and was, imho, well worth the effort. My thoughts, at the time, for the cause of bent plate was it may have been struck by previous owner at an angle with a too-heavy hammer to cut sprues while casting. Good luck!
    geo

  4. #4
    Boolit Master

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    I bent the sprue plate on one of my RCBS molds once and was able to straighten it. I tapped on it with a hammer on a flat surface and worked it on some emory cloth. I did this while waiting for a replacement. RCBS has changed their sprue plates over time and the newer ones are thicker.

  5. #5
    Boolit Master mattw's Avatar
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    What George said! The RCBS moulds have a super thick plate anyway, take a few thousands off will not kill it. Depending upon how it is bent, you might need to clamp it in a vise and persuade it against the bend once with a soft face hammer. Be careful not to peen it with anything.

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    The only thing I would add is if you have a really strong magnet or can pick one up at Harbor Freight, it makes holding the sprue plate flat much easier when dressing down the surface. Also if you have a new sharpening stone a few passes on the stone first can remove a bit more material to begin with.

  7. #7
    Boolit Grand Master

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    It can be straightened pretty close then a light polish for final clean up. Most can be saved it takes patience and time.

    1) with a straight edge locate where the bend is actually at in both directions. Its probably not square to any edge. A 6" machinist steel scale works well here. This will show high point of bend and where it actually is at. mark this with a marker or pencil.

    2) clamp the plate in a padded vise with the high point of the bend even with the vise jaw tightly and lightly tap it with a brass hammer or hammer and punch. The Idea isn't to do it in one blow but to slowly bring it back into place.

    3) lightly grease a poece of flat stock and rub plate on it this will show high spots mark and work as above

    4) when very close leave the grease on the flat stock and a piece of 220 grit paper ( the grease helps hold it) and work to a complete pattern work the plate in a figure 8 pattern turning 90* often. This is the longest sanding part of the process

    5) work thru 420 -600 grits you only need to go here to the smoother pattern of the finer grits this is simply polishing and smoothing the plate out. It will also sharpen the cutting edge of the sprue hole.

    When done with the above the plate should be flat and true, the sprue hole sharp, thru the hole process you may remove .005-.008 of material. Tt with paper dry and then oil or water to lighten cutting and even finish out before next grit. Done right and after the 600 grit with oil it will be close to a mirror finish

  8. #8
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    Thanks for the replies. I will call RCBS Monday and ask about obtaining a replacement. In the meantime any attempt at repairing this one will start with a hammer, not a stone or emery cloth. It had to have been dropped while the sprue cutter was open or at least it landed that way. In the closed position you can see where it breaks over the edge of the block. I will keep you all posted.

  9. #9
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    Update: My attempt to straighten this ended up with it bent in another place instead. I sent RCBS an email and they replied that they will send a replacement. Still good folks to deal with after all these years. I knew they used to be but had not needed any replacement parts from them in a while.

  10. #10
    Boolit Master RED BEAR's Avatar
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    straightening things can be a bit tricky. had to straighten warped and bent parts all the time before i retired. i can be a bit anal about things like this i would have to straighten it for a spare . i know it makes no sence when they are sending a new one but i couldn't help.my self.

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    Is it the sprue plate or is it the top of the mold? I've run across several Lyman molds that had warn where the sprue connected to the top of the mold (from lack of lubrication and tightening too tight), the only fix was to have a few thousanths shaved off the top of the mold, drill and tap a new sprue stop post.

    Many people hate lubricating the sprue plate screw because they get oil in the hearest cavity and it is a pain to get out an.d keep casting.

    My solution was a needle tip bottle like https://www.amazon.com/Needle-Applic...le+tip+bottles

    They have much smaller drops and are easier to control when I use STIHL High Performance Ultra 2 Cycle Engine Oil, like https://www.amazon.com/STIHL-0781-31...e+oil+additive

  12. #12
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    Quote Originally Posted by RED BEAR View Post
    straightening things can be a bit tricky. had to straighten warped and bent parts all the time before i retired. i can be a bit anal about things like this i would have to straighten it for a spare . i know it makes no sence when they are sending a new one but i couldn't help.my self.
    I have received the new part and have not had time to put it on yet so I know I will not spend more time trying to straighten the damaged one. Besides, it is unlikely that I would need another one any time soon. On the other hand, I do seem to have a serious affliction that renders me unable to dispose of such an item regardless of how useless it is. Wish I could just bring myself to toss it.

    Quote Originally Posted by Grmps View Post
    Is it the sprue plate or is it the top of the mold? I've run across several Lyman molds that had warn where the sprue connected to the top of the mold (from lack of lubrication and tightening too tight), the only fix was to have a few thousanths shaved off the top of the mold, drill and tap a new sprue stop post.

    Many people hate lubricating the sprue plate screw because they get oil in the hearest cavity and it is a pain to get out an.d keep casting.

    My solution was a needle tip bottle like https://www.amazon.com/Needle-Applic...le+tip+bottles

    They have much smaller drops and are easier to control when I use STIHL High Performance Ultra 2 Cycle Engine Oil, like https://www.amazon.com/STIHL-0781-31...e+oil+additive
    Definitely a bent sprue plate. When I looked for the source of the problem it was obvious that the mold had been dropped with the sprue plate in the open position . The plate was bent over the edge of the mold blocks similar to bending sheet metal with a break, just to a lesser extent.

  13. #13
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    Same church, different pew: E.g., I dropped a Lyman mould on concrete garage floor, also bending plate. I put it on a railroad-rail "anvil" I have, with a piece of flat steel -- maybe 1/2' thick -- atop it. After donning glasses and ear protectors, I whapped plate with an 8 pound sledge a few times. Bion, it got it allllmost flat, but no cigar! So, I stuck it to a donut magnet I keep to use as a dam for coolant while drilling though steel -- in this case, just for something to hold on to -- and put it on my 6" x 48" belt sander. The belt was pretty much in need of replacement, anyway -- a medium grit pretty worn. I was surprised how quickly and easily this went -- with my ending up with a "good-enough" surface. I finished it by circular figure-8 motion on a piece of 200-grit wet 'n dry paper I had water-held to a pane of glass. I applied some cold blue -- and the one and only thing I noted is now the pour holes in the plate -- this is a 2-cavity mould -- one is still a perfect circle, but it appears the hole closest to hinge-hole is ever slightly egg-shaped -- just a smidgeon you only notice if you really look close. E.g., while off the mould and on a piece of white paper. While on the mould -- where it now lives -- I don't even notice it, and the mould almost works better than new. Good luck!

  14. #14
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    [QUOTE=Grmps;4460688]Is it the sprue plate or is it the top of the mold? I've run across several Lyman molds that had warn where the sprue connected to the top of the mold (from lack of lubrication and tightening too tight), the only fix was to have a few thousanths shaved off the top of the mold, drill and tap a new sprue stop post.

    Also it seems on some of new manufacture molds the sprue plate has burrs on the underside that gouge the mold surface.

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