Perfect Spot Faces

[Fraserjj]

Hello

Right we have a job that requires oil pathways to be drilled through steel forgings, with a 1/4bsp thread at each end, a 9mm deep 32mm spot face is also required.
According to our customer the spot faces have to be almost mirror finished.

we are using an XYZ mill cnc, and our results so far have been on the borderline of acceptable.

What tools or methods should we try to get a mirror finish and perfectly flat?

any help would be very grateful

 

[ProEDesigner00]

Hope your getting paid really really well for polishing techniques

 

[Chappy2]

http://www.sugino.com/products/db/e_yotoprod_b.asp?seq_no=11517

We have had much success with this companies tools.
also Cogsdill

 

[Tmoose]

BSP threads don't seal, so need a sealing surface. If an o-ring sealing is doing the sealing then a 32 RMS finish made by plunging to produce circular, not spiral tool marks should be fine (enough).
I can picture some spiral marks giving them trouble, and the repair required going to a highly polished surface.

standard O-ring finish specs here -

http://www.allorings.com/gland_static_radial.htm

 

[tripleZ]

Jig grinder and bonded cup wheel (if I'm visualizing this correctly)? Definitely not optimal from a production standpoint. But you'll get flatness values better than .0005" and, depending on the hardness of your material and wheel grit selection, pretty near a #10 finish on the surface. I never used one of the Sugino concepts, but it looks promising.

 

[mrainey]

Can't you run a small inserted cutter in there after you machine the counterbore? Just take a few thousandths off the face with high RPM's and a low feed per tooth.

Software For Metalworking

http://mrainey.freeservers.com

 

[steveh]

I agree with Chappy2. If the material is at all malleable, try a roller burnish tool to finish the spotface. I have used them on fairly hard grey cast with good results.

 

[kagan]

If you use super finishing machines for surface grinding such as Supfina, you can reach a flatness of under 1 micron and Ra 0,2. But this is the expensive way. I don't suggest you to make grinding operation at your CNC because of the grinding wheel granules.

Also you can first make a spot face operation without interpolation. This will give you circular traces that are required from many companies for o-ring sealing surface. Then you can apply a silicon carbide brush with 80 grit to soften the trace. You can get a flatness that comes from the spot face insert. So you should check it before the operation. Also I should say that you can't reach the surface like mirror with silicon carbide brush (brush with abrasive flament). But please consider that may be you can reach the technical drawing specs with a dull surface.
Burnishing is also a good solution but you can carefull of the tool life because of high contact force on the pins.

 

[QuaziFawad]

I would be careful with the burnishing tool because of flatness requirement. What is the Hardness (at the spot face after you take the skin off). If you are circle interpolating, I would suggest trying Wiper Insert.