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Ghost images when milling.

Forestgnome

Stainless
Joined
Aug 2, 2008
Location
Californeeeah
I was milling a surface that had holes drilled through, when I noticed I was getting "images" of the holes approximately 3/8" above the holes. These images are the same diameter as the holes, 1/8", 1/4", etc. I'm using a 2-flute, 2" LOC, 1/4" diameter cutter. Anyone experience this, and how can you stop it besides drilling the holes after milling?
 
I was milling a surface that had holes drilled through, when I noticed I was getting "images" of the holes approximately 3/8" above the holes. These images are the same diameter as the holes, 1/8", 1/4", etc. I'm using a 2-flute, 2" LOC, 1/4" diameter cutter. Anyone experience this, and how can you stop it besides drilling the holes after milling?

That's caused by a slight play in your spindle bearings allowing the cutting tool to move up and down as it hits the hole. The same principle allows those
moving Star Wars images of Tie Fighters to be encoded in the grooves of an LP record's surface or an image of the gloved hand on the surface of a car's bonnet after hand polishing.

I would be experimenting to see if I could encode writing into the machining swirl marks with a removable sacrificial text in relief beside the job, but that's just me.
 
Am I reading that right? 2" LOC & 1/4" diameter? If so, then that skinny little thing will vibrate at the slightest provocation, like passing by a void, or sneezing, or dropping a Kleenex :crazy:.

Regards.

Mike
 
I agree, but I would have expected to see a vertical line above the hole rather than a circle.

"I would be experimenting to see if I could encode writing into the machining swirl marks with a removable sacrificial text in relief beside the job, but that's just me." I like the way you think!
 
"I would be experimenting to see if I could encode writing into the machining swirl marks with a removable sacrificial text in relief beside the job, but that's just me." I like the way you think!

Not yet you haven't.

But I gave him a "like" for creative out-of-the-kleenex-box thinking..

:)

NB: I have seen this before, and "tighter" tool & spindle may not eliminate it entirely, just make it less obvious.

So yes, IF the surface is a critical one, the holes should be placed last. If possible.

Next-best, where one cannot, might be post-op abrasive finishing - ordinarily more resistant to "ghosting" - given that blindfolding the customer's QA munchkin is generally a non-starter.
 








 
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