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Thread: Sprue Plate Hole Geometry Question(s)

  1. #1
    Boolit Master
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    Sprue Plate Hole Geometry Question(s)

    Is there any consensus on correct sprue plate hole creation when making new one?
    Lyman appear to be spot drill angle with about a .020 vertical cylinder at entry to cavity.
    Does sprue plate material affect any angles etc? AL versus 1018 vs 4140 vs A2 etc.
    Lastly, are there hole diameter suggestions for the various calibers?
    Thanks.

  2. #2
    Boolit Master

    Rcmaveric's Avatar
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    All i can offer is that material and thickness makes a big difference. Lee use a thin light weight one that some times makes it hard to cut the sprue. Conversely NOE uses a big thick steel one that takes a while to heat up affecting bases fill out till it is nice and hot. But the NOE one cuts sprues nicely like butter.



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  3. #3
    Boolit Bub
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    I've had best luck making sure the edge of the hole at the bottom of the plate is a sharp edge with no vertical cylinder at all.

  4. #4
    Boolit Grand Master

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    On the ones Ive made Ive used gage stock it already ground and flat. I cut out and fit the desired shape then drill hinge hole and spot for stop pin I then mark top layout and pilot drill sprue holes with a .100 then use a 90* counter sink to open up to just under the desired size. stone bottom to remove any displaced metal and burrs. On hole size I would recommend stating small, you can always make them bigger. While lees plates are roughly 1/8" lymans and RCBS are 3/16 I use 1/4" for the ones I make.

  5. #5
    Boolit Bub
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    Don't be too afraid to make the sprue hole some larger, especially on larger bullets, like a 54 cal muzzleloader slug
    My opinion is you need to fill the whole cavity with molten lead instantly, then cool until solid, cut sprue, empty mold repeat as soon as feasible.
    Please note that I have no problem with cooling the molten sprue with a wet rag or similar to speed up the process.

  6. #6
    Boolit Man Time Killer's Avatar
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    Ty for asking this question. I was going to do some mold and spur plate work myself and the answers will help out greatly when it comes that time. Ty for the responses. That is one of the things I love about this forum. Shared experiences and knowledge.

  7. #7
    Boolit Master
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    Currently have Lyman 2 cavity blanks cut out.
    .250-.300 thick 4140 and .25 thick aluminum.
    Those vertical walls on Lyman sprue plate just didn't look right.
    May very well be reason folks who stone bottom of plate seem to get some real benefits from that action alone.
    I think I have bull-nose mill.
    If I do I think I'll experiment with milling sprue cavity and finish with spot drill.
    Would make for bigger puddle of lead for sprue cooling and shrinking inward.
    Thanks again for all the ideas and guidance.

  8. #8
    Boolit Grand Master

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    A ball nose end mill around 5/8" dia might make a good sprue puddle that release easily. I would cut one thru to dia in a piece of scrap first then section at center line to see how good the edge will be it may be on the thin side if cut to the sharp edge. There might be a chance of deforming when cutting over time.

    One advantage to the 82* and 90* sprue pockets is at the stat of the cut the angled edge slightly lifts the sprue keeping the plate from binding and breaking the sprue loose from the plate. I believe that's part of the reason makers get away with the small cylindrical section. When I cut these I run them close then put the machine in neutral and finish turning by hand with a good heavy cutting oil. I have a wood dowel I cut the 90* point on and finish with it and 320 grit lapping compound to remove tooling marks for a good release.

  9. #9
    Boolit Master
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    I used a standard metal countersink bit to cut my sprue holes. I just guestimated the diameter comparing with others of the same caliber. I did find that like Richard B., "no vertical cylinder...make the end a sharp cutting edge seems to work best for me.
    After cutting the hole to near the "no vertical cylinder" state, I took diamond impregnated rubber burr with the proper angle and polished it to the sharp edge...and stoned the other side flat ...FLAT... making sure you do not create a cutting edge that is not at the very bottom of the sprue plate. If the cutting edge is not exactly on the bottom it will tend to lift the sprue plate which will cause all kinds of problems. Smearing lead, hard cutting, and loosening the sprue plate , maybe even bending the sprue plate. Ttttttthhhhats my ssssssstory and I'm sssssticking to it.
    AKA hans.pcguy

  10. #10
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    Ho' made sprue plates

    ...............So far as any SP design goes it mainly depends upon it's thickness, and the material it's made of. I like to use 1/4" ground steel stock for most anything.



    These are both simply a 45 countersink type. The 4 cav was a much abused old H&G dropping a wadcutter. I simply opened up the original sprue holes which originally had a simple trough running across. Still does but the sprue lead supply was greatly increased.

    If you have a milling machine you can use 5/16" thick stock to make a 'Killer' SP for large (35 cal Plus) slugs. After locating and drilling the holes with a 45 or 60 degree countersink over each cavity, you can then switch to 1/4" endmill to mill out a 3/16" deep 'pocket/puddle' over each hole, leaving a wall between them. Then use a 1/4" ball endmill to put an internal radius around the inside of each pocket. For such a thick SP you'll for sure want to use a shouldered bolt for the pivot.



    I only use aluminum for SP's on moulds for very soft lead. In this case for pouring cores for swagging pure lead for paper patching for muzzle loading. Cutting to a fairly sharp edge in aluminum for this is OK, but for anything much harder can defeat the cutting edge much sooner then a person would care for..

    .............Buckshot
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  11. #11
    Boolit Master
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    I had a few Lyman molds that had the vertical section on the sprue plate. Since I have a lathe I have a decent assortment of center drills. Most are either 1 or 2 cavity moulds. Set the sprue plate up in my drill press and drilled them so that the vertical section was gone. Naturally when drilling you get burrs on the underside of the sprue plate. Stoned them off and stuck a 320 grit piece of silicon carbide paper on my surface plate. Then sanded the plate removing any remaining burrs. One plate required some serious stoning and sanding as it was not flat even before the redrilling was done. Used a propane torch to heat blue the plates prior to installation. Did make casting the 458 gas check bullet easier due to the larger sprue hole. Frank

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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