Reloading press: "Camming Over"?

[klewan]

Aaahhh, it's the linkage; not the ram. Is it like the toggle link in a Luger, something with about the same movement?

I came from an automotive perspective, a cam moves something and then falls back as the high point moves away. So "camming" on a press didn't make a lot of sense to me.

[J-cat]

Lee presses do not cam over.

Do too.

[J-cat]

The Lee die instructions say to run the ram all the way up, screw the die down into contact with the shellholder, lower the ram and turn the die in a further 1/4 or 1/3 turns and lock it in place. This is done to compensate for frame stretching and any other slop.

I'm still not clear as to whether the ram is actually going past top dead center and descending as you continue the lever movement. Lee has a lever stop; you're not going past that. But it sounds like other presses don't, that if you put a dial indicator on the shellholder and cycled the press, it would show the needle spinning in one direction and then reverse as the press went past TDC. Is that true?

You do not understand the concept.

If you raise the ram all the way up until the handle bottoms out, then the ram won't cam over because it has nothing to cam over. You need to cam over something, like the bottom of the sizer die.

If you raise the ram to TDC and then screw the die to touch, it won't cam over because the frame will spring away from it under pressure of the case being sized.

To get the ram to cam over you have to screw the die down further so that the ram touches the bottom before TDC. What happens next is the ram pushes on the bottom of the die, causes the frame to spring away, and then you have a condition where there is no gap between the top of the shell holder and the die despite a case being sized.

[ar15barrels]

To get the ram to cam over you have to screw the die down further so that the ram touches the bottom before TDC. What happens next is the ram pushes on the bottom of the die, causes the frame to spring away, and then you have a condition where there is no gap between the top of the shell holder and the die despite a case being sized.

This is what you want for the most consistent case shoulder location.

If the die and the shell holder are completely touching through the whole sizing operation, the shoulder will be in the same place regardless of press frame stretch and brass hardness.
The problem is that most dies size the case shoulder MORE then you need in this condition.

The answer is to put a shim on top of the shell holder or use the reading competition shell holders which allow you to reduce the amount of shoulder sizing while maintaining a full steel-on-steel stop.

Simply loosening the die in the press gives you a steel-on-brass stop which is not as consistent at setting shoulder lengths.

[klewan]

You do not understand the concept.



If you raise the ram all the way up until the handle bottoms out, then the ram won't cam over because it has nothing to cam over. You need to cam over something, like the bottom of the sizer die.

If you raise the ram to TDC and then screw the die to touch, it won't cam over because the frame will spring away from it under pressure of the case being sized.

To get the ram to cam over you have to screw the die down further so that the ram touches the bottom before TDC. What happens next is the ram pushes on the bottom of the die, causes the frame to spring away, and then you have a condition where there is no gap between the top of the shell holder and the die despite a case being sized.

OK, now I understand. In automotive terms, that's Pre-loading. And I can see a Lee press doing the same thing when you crank the die down another 1/3 of a turn. Only I've never seen anybody use the term camming when talking about Lee presses, only RCBS or Lyman or Redding. I can also see why Randall uses it for his long distance target brass; force the brass to the same size, everytime.

Thanks to you guys for enlightening me.

[ar15barrels]

OK, now I understand. In automotive terms, that's Pre-loading. And I can see a Lee press doing the same thing when you crank the die down another 1/3 of a turn. Only I've never seen anybody use the term camming when talking about Lee presses, only RCBS or Lyman or Redding. I can also see why Randall uses it for his long distance target brass; force the brass to the same size, everytime.

Thanks to you guys for enlightening me.

I prefer the fact that the press linkage goes past absolute TDC because you can feel it happen.
With a press that STOPS at absolute TDC, you have this "mushy" feel where you don't know if you are hitting the linkage stop, or if you are still sizing.
The little tiny bit of linkage travel past TDC is more assuring to me.

If I were to have kept the Lee press, I probably would have modified the linkage to give the same feel of the linkage camming over center.

The reason I am pre-loading the die and shellholder is that I want to ensure that the force required to size the case is LESS than the force required to spring the press open.
If the press springs open sometimes (but not always), then the shoulder on the case you were sizing WHILE the press was springed open was NOT sized as far down as a case which did NOT spring the press open.

[J-cat]

You're right. Preloading is a better descriptor for what's happening. There is alot of confusing firearm terminology floating around.

FWIW, I don't set my dies that way. I feel that places alot of stress on the press frame and the linkage. What I do is screw the die way past that "cam over" point and allow my strength and the press leverage to compensate for the frame springing. I also use Redding competition shell holders to allow me to size precisely in .002" increments from +.010" to +.002" over whatever the standard shell holder does.