press cams over center

[blueridgeMTNs]

I've always wonder *exactly* what is this? When setting up dies I set up by screwing down the die until it touches the shell holder when the shell holder is fully upward. And then I lower the shell holder and turn the die further down 1/8 to 1/4 and set the large nut. Why do they call this "press cams over center"?

When the die is screwed down initially and touches the shell holder why cannot we leave it like that? When we have to screw down a little more (1/8 to 1/4) the handle very slightly "bumps" over center...for lack of better explanation. Is this what is called "came over center"? Will this damage the press body?

 

[nettlle]

I always screw the die down until it touches the shell holder and lock it there. The extra 1/8 to 1/4 turn isn't going to help anything. It's just working the linkage on the press harder.

 

[rcmodel]

No, actually it isn't 'Cam Over' in most presses anymore.

I always screw the die down until it touches the shell holder and lock it there

Press frame flex, and linkage compression make your method not work to 'fully' FL size bottle-neck rifle cases.

'Cam-Over' is a term that applies to some presses, but not most.

Most modern presses have a built in stop that stops the handle at 100% full toggle extension! then no more.

Some older designs, and a few new ones I can think of, actually did 'cam over' after full extension and almost start to pull the case back out of the die on the way back down!

I think today, it is just a term used to say, yes, I screwed the sizing die in a little past shell holder contact to take all the press frame and linkage compression out and get truly Full Length sizing to push the shoulder back where it came from after firing.

My old RCBS Rock-Chucker doesn't Cam Over center.

But it definitely 'bumps' at full ram extension when the FL sizing die is adjusted properly and the linkage snaps to full brace extension.

NONE of this applies to carbide insert handgun dies.
Adjust them to very light shell holder contact, or you might break or loosen the carbide sizing ring in the die.

Hope this helps!

Rc

 

[Walkalong]

Whether a press "cams over", has a stop, or neither, it it the point of no return where pressing down on the handle doesn't raise the ram any more. At this point more pressure is only stressing the components.

The extra little bit we turn the die down after contact takes up the slack/flex in the mechanisms, but I never blindly turn a die "X" amount and call it good. I adjust it down a hair at a time until I get it where I want it.

Not to mention the fact that very few dies need this done.

 

[243winxb]

Cam Over RCBS

My old RCBS instructions. The difference from just touching to full cam over may be between .002" to .004" additional set back when measured head to datum. Note that the lock ring is tightened during contact. This squares the die with the shell holder.

 

[Andrew Leigh]

My Rockchucker cams over and I set my dies such that cam over is achieved.

What is cam over? My press does not have cams but linkages, both do the same thing, they provide additional mechanical advantage to the lever so that your arm does not work as hard as with a direct 1:1 ratio. The term cam over refers to extending the linkage past 180deg. as they can move a little past when at the bottom of the stroke. When they move past the pressure on the die reduces slightly as when they cam over the press is on the return stroke that is it neither designed for or can do past fractions of an inch.

If the cam over pressure is set too high then you could face metal fatigue in time to come but it is highly unlikely.

So why do I set to cam over. Simple, my arm is not a calibrated torque wrench and is unable to provide the same pressure on each stroke. Having the press cam over means that every stroke will be subject to the same pressure as it reaches the bottom of the cycle and then releases, the same on the return stroke.

Now, one can argue the merits of this technique but I have found that it does make a difference for me, especially when using the Lee Neck Sizing Die. Variable pressure on the handle causes variable neck tension, camming over reduces the variations significantly.

 

[fguffey]

Why do they call this "press cams over center"?

I do not know who 'they' are, I have at least 4 Rock Chuckers, none of them cam over, all of my Rock Chuckers lock up, jam up or go into a bind, my Rock Chuckers do not cam over.

I have 7 Herter presses, all of my Herter presses cam over, long forgotten is 'WHY?' The last RCBS press I used that cammed over was an A-2. Adjusting a die to the ram with a cam over press requires a different technique for adjusting the die to the shell holder.

What does a Rock Chucker do when the ram is raised to 'TDC' top dead canter? The linkage locks up, goes into a bind and limits ram travel meaning TDC is it. So I suggest a reloader that wonders and or is curious remove the die then raise the ram and watch the top of the ram when it reaches the top of its travel, All of my RCBS rams on all of my Rock Chuckers presses kick the ram and cause it to tilt.

I have modified a Rock Chucker to cam over by grinding the linkage in an effort to prevent the linkage from making contact before the ram got to TDC.

Kicking the ram to tilt: Not something I worry about, when sizing a case the case prevents the ram from tilting and when sizing a case no more than necessary the linkage does not get tangled up.

Then there are cases that have more resistance to sizing than the press can overcome. I have two original 'Come-Alongs' they lock up with the same leverage offered when using vise grips, in the old days 'they' used a term called 'leaver lock'. The pliers did not cam over, nor does the original come-along, made in Tulsa, Oklahoma.

F. Guffey

 

[243winxb]

my Rock Chuckers presses kick the ram and cause it to tilt.

Wore one out, ram would tilt forward. Not good for bullet seating. RCBS replaced press for cost of shipping to them.

 

[ironworkerwill]

Guffy, I like mention of ram "kick". Obviously if brass is particularly difficult to resize or die is bottomed out too hard kick could occur.

I never noticed it but have pondered the situation.

* that just shows how slow I type, or think, maybe both*