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Thread: Bent sprue cutter on an RCBS mold

  1. #1
    Boolit Man
    scotner's Avatar
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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 Master
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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
    Boolit Master
    georgerkahn's Avatar
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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.

  6. #6
    Boolit Master
    Dragonheart's Avatar
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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 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
    Boolit Man
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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
    Boolit Man
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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.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check