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Thread: Lapping on dies

  1. #1
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    Lapping on dies

    I have a Redding SB 6ppc die that sizes the base area about .0015 squeeze but the shoulder/body junction is .003 sized down. Id like .0005 squeeze up there and .001 at base. Is there any slick trick lapping/polishing that would make it more betterer? Maybe .003 is ok?? Seems a lot.

    Wally

  2. #2
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    If you have a lathe, you can use 250 grit Emory paper on a piece of round stock. It will cut the case hardened die. It will take a while, and you need to concentrate on the shoulder end to take more out in that area.

  3. #3
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    I had someone who has been well known for die work open up the shoulder of a PPC die and when I got it back, with a $60 bill that I paid, it was effectively ruined because of the runout of the sized cases. This was a long time ago, but based on that I think that I would stick with opening up the back of a die, or possibly the neck of a one piece die, but evidently working so close to the point of the shoulder involves more risk of failure.

  4. #4
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    Quote Originally Posted by jackie schmidt View Post
    If you have a lathe, you can use 250 grit Emory paper on a piece of round stock. It will cut the case hardened die. It will take a while, and you need to concentrate on the shoulder end to take more out in that area.
    For best results use a Silicon Carbide abrasive. An Emory abrasive is way too soft for steel.

    .

  5. #5
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    Quote Originally Posted by WallyDog View Post
    I have a Redding SB 6ppc die that sizes the base area about .0015 squeeze but the shoulder/body junction is .003 sized down. Id like .0005 squeeze up there and .001 at base. Is there any slick trick lapping/polishing that would make it more betterer? Maybe .003 is ok?? Seems a lot. Wally
    Wally, I'm an 'aggressive sizer' when it comes to the shoulder/body junction.....especially on cases with 30 degree and greater shoulder angles. For me, .002 would be the minimum and .003 would be perfect. -Al

  6. #6
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    Makes sense !

    Quote Originally Posted by Al Nyhus View Post
    Wally, I'm an 'aggressive sizer' when it comes to the shoulder/body junction.....especially on cases with 30 degree and greater shoulder angles. For me, .002 would be the minimum and .003 would be perfect. -Al
    Since its a diameter we are actually talking .0015 clearance per side. Thats the size of my gray thinning hair. Talked me into it Al!

  7. #7
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    Quote Originally Posted by WallyDog View Post
    Since its a diameter we are actually talking .0015 clearance per side. Thats the size of my gray thinning hair. Talked me into it Al!
    Laffin', here! -Al

    P.S. The average diameter of a human scalp hair is .004, so you're waaaay safe.
    Last edited by Al Nyhus; 08-28-2020 at 11:49 AM.

  8. #8
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    AL, bring that pesky die down, and we'll lap it to within 0.000005", or, we'll have HIM buy U, "uh nu un". RG

  9. #9
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    Quote Originally Posted by R.G. Robinett View Post
    AL, bring that pesky die down, and we'll lap it to within 0.000005", or, we'll have HIM buy U, "uh nu un". RG
    Randy, I'm hackin' and slashing away at this hunk of steel trying to make something out of it that will squeeze a piece of brass to where I think it needs to go. A real machinist or a talented-type like yourself would either laugh or cry if you were to witness the carnage.

    Every time I fire up the lathe or mill, I'd swear John Wayne talks to me. Maybe He has taken up residence in some dark corner of the shop?

    Last edited by Al Nyhus; 08-28-2020 at 07:54 PM.

  10. #10
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    Roger that -HE says that the judicial use of [your beloved] BLACK JUICE may help to curb the decimals and smooth the edges some . . . RG

  11. #11
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    so being the lapping novice,
    could one apply lapping compound to a case( at the place to be lapped) as a tool and go at it..gently

  12. #12
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    Quote Originally Posted by rsmithsr View Post
    so being the lapping novice, could one apply lapping compound to a case( at the place to be lapped) as a tool and go at it..gently
    I've tried that without much luck....it's going to depend on the surface hardening of your die. In my case, the compound just reduced the diameter of the brass being used. Sure wouldn't hurt anything to try, though.

    Using a piece of brass as a lap is a slick way to touch up a Wilson seating die, though. They are a leaded steel (12L14, I believe) and cut like butter. I use common valve grinding compound and finish it with either JB compound or an old piece of 400 grit in a slot on the end of a .250 aluminum round stock or a slotted wooden dowel.

    Good shootin'. -Al
    Last edited by Al Nyhus; 08-30-2020 at 08:57 AM.

  13. #13
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    Tried this yet?

    Quote Originally Posted by Al Nyhus View Post
    I've tried that without much luck....it's going to depend on the surface hardening of your die. In my case, the compound just reduced the diameter of the brass being used. Sure wouldn't hurt anything to try, though.

    Using a piece of brass as a lap is a slick way to touch up a Wilson seating die, though. They are a leaded steel (12L14, I believe) and cut like butter. I use common valve grinding compound and finish it with either JB compound or an old piece of 400 grit in a slot on the end of a .250 aluminum round stock or a slotted wooden dowel.

    Good shootin'. -Al
    Id approach this with carbide. I cant see what your doing exactly but could you put the die into a v block and indicate it center in your mill? You can buy solid carbide blanks to size and have it ground into a single lipped cutter. Of course costs are the factor. Maybe find a 4 lip carbide endmill close and then lap the last.0000005 at Robinettes? Of course the temp controlled lab will be a bit costly but its only money.

    Wally

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