Spotfacing on Castings

[derekkarp]

I'm sure someone here has ran into this problem before.

We have to put counterbores, or spotfaces, whatever you want to call them into a cast surface. The dimension is held from the cast surface. Since our castings vary more than the tolerance given on the depth of the spotface, we're having to set the tool length for each new hole. We can either use probing, but will need custom styli, or a right angled head with a probe, OR....

I need to find some kind of spring loaded micro-stop tool that will let me program to worst case scenerio, and the spring will take over once the depth is reached. Any ideas? Keep in mind your regular micro-stop will not work because there is no 'feel' on a CNC.

Thanks,
Derek

 

[MikeHalloran]

If you have control over the design... you're doing it wrong, and should dimension the spotfaced surface from some other feature that you can control, instead of from the casting surface.

If you don't have control over the design, you have to gently suggest that maybe the designer is doing it, uh, not perfectly correctly, and should at least be able to loosen the tolerance to equal that allowed for the cast surface.

If you're stuck with no design changes allowed, then you either mess with the tools constantly, or fixture the part so it's located from the cast surface adjacent the spotface.



Mike Halloran
Pembroke Pines, FL, USA

 

[derekkarp]

None of those options are acceptable.

1. Its not our part. Its for a large jet engine company. The part has been in production for 15 years. Getting a print change is impossible.

2. We HAVE to cut major hours (200+) out of this part. Fixturing it from that surface is impossible. Messing with tool lengths have doubled our run time on this operation. Manual intervention is killing us.

Thanks for the input though
-Derek

 

[MikeHalloran]

Okay, so probe it, and offset the tool depth per part or per spotface.

I'm guessing the probe doesn't _really_ have to be the same shape as the tool, it just has to touch one point on the cast surface, and that should tell you where the surface is, relative to the surfaces of similar parts, if the surface is not sharply curved.



Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

Is there another operation that preceeds the spotface? Can you get a feedback from that operation for a reference for the spotface?

Ted

 

[unclesyd]

If you can program you tool for a small standoff at each position you may be able to take a reading on machine amps to ascertain when to start the measuring aspect.
We did these on some of the early cnc machines. I don't recall how this was fed back to the machine controls.

This approach was also used on a large horizontal boring machine with glass linear encoder. This system just reset the encoder to zero.

 

[mrainey]

Put a manual machine (Bridgeport, drill press, ...) beside your CNC and have the operator machine the counterbores while the machining center runs everything else?

Software For Metalworking

http://closetolerancesoftware.com

 

[unclesyd]

Take a look at these two systems to resolve your problem.

http://www.renishaw.com/en/6075.aspx

http://pdf.directindustry.com/pdf/renishaw/probing-systems-for-cnc-machine-tools/5200-3649-_46.html

 

[derekkarp]

Thanks guys. The part is too big to use a BP or drill press. The features also have to be bought off on the machine also. Our designer is coming up with a spring loaded micro stop for a CNC machine. I'll let you know how it works.

-Derek

 

[wmalan]

Probing. As others have said. That is pretty much industry standard for production machining of castings. I've used them for everything from best fitting the casting for machine home, identifying surfaces with extra stock for more cutter passes, and of course the spot/hole drilling on cast features.

--
Bill