c'sink depth control

[B747US]

Does any body know how can we control the depth of a c’sink operation where we have +/- .002 tolerance for c’sink diameter and part being a 200” long “T” shape extrusion grabed from standing leg in the vises, it doesn’t seat perfectly flat on the jaws and resulting c’sink diameters vary which is not acceptable. Any idea will be helpful. thanks

[mayday]

submit a deviation from print

+/- .002 c'sink on an unmachined extrusion? fancy flatheads they got there

[Jim at Gentex]

It's tough to visualize this from your description, but I think I know what you mean.

 

quote:

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it doesn’t seat perfectly flat on the jaws

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You probably won't come close to .002 tolerance until you solve this problem.

 

Two possible alternatives:

 

1. Fixture it differently so you get a consistent placement of the part.

 

2. Skim cut (if possible) the surface to establish a flat plane to work from, then set your countersink Z depth accordingly. Holding .002 on a countersink diameter is a tall order, but not impossible.

 

 

edit: I LOVE MayDay's idea!

[Psychomill]

Short of facing it flat in the setup (which I'm sure you've thought of or can't), will it flex enough to force it flat when you clamp it? That could be an issue in itself since your part is 200" long.

 

Can you probe for each hole position? Otherwise, may have pick up an offset for each one.

 

I've done one similar years ago where I used a dial indicator in the spindle and starting from the first hole, noted all of the changes in the part at the feature location. Then wrote a macro that changed the Z as it ran the program. A lot of typing though, and sux if you have quite a few to do. A probe would simplify this.

[MACHINEMASTERG]

ive made a stop that fits the c-sink out of plastic and csunk the hole buy hand and relied on the stop to controll the depth on a casting job..im sure not much help on a part that long !!

[JG]

I've had to do similar things by positioning over the hole, M0, manual jog to a block, cylcle start with a incremental cycle. kinda defeats the whole CNC thing, but it worked.

 

Jg

[CAM-mando]

I agree with above ...

 

If you can do a manual secondary operation look a microstop countersink tool.

http://www.gouletaircraft.com/PDF/prod/micro.pdf

 

Short of that, the only way to get close would be some pretty elaborate fixturing to force the topsurface against work stops which would only be an option for high production I would think.

 

±.002 on dia is ±.001 on depth

[B747US]

thanks guys for the comments, we c'sink them (some 190 holes) manually and have no other choice, I cannot machine that surface at the same time I c'sink the holes since that surface needs to be machined to hold other dimensions in prior operations.