How to hit 32RMS on an oring gland

[dingo0722]

I have a job that requires a 32 rms finish in 6061-T6 on the floor and wall of an oring gland. After roughing it out what would be the best way of hitting that finish value. I was thinking of using a carbide ball endmill with a small stepover. are there any other techniques that would work

[HuFlungDung]

I'm not visualizing how you'd get a ball endmill down into the corners?

I would just take a very light cut, at a very slow speed, with a new endmill, not the one that roughed open the groove. If your cutter is running perfectly concentric with the spindle, then you can feed faster, but if there is any miniscule amount of runout, then essentially, you have to 'single flute feed it', because the highest runout flute needs to take its cut everywhere in order to reduce the scallop effect.

Note, that not every new endmill that you pull out of the carton is good enough. The end flute grinding needs to be excellent to get a good finish. I'd suggest one of the more high end endmills, in hopes of starting out with a better grade of tool.

[RICHARD ZASTROW]

Be careful using an end mill for "O" ring grooves. If you're dealing with high pressure, you might be producing a leaky surface due to the "cross hatching" effect of the face of the end mill.

We tried it and ended up changing to porting tools, trepanning tools and hollow mills form ground to "O" ring groove dimensions. This was in high pressure applications, 2500+ PSI.

Dick Z

[dingo0722]

Richard,
I am not familiar with the tools you listed. Was the operation done on a mill and where do you buy the tooling you listed? Not sure that the pressure rating is, they just speced an 32rms finish, I doubt the pressure is higher then 250psi since it is a 6061-T6 part

[RICHARD ZASTROW]

Try "googling" Trepanning Porting Tools Hollow Mills

The corner radii and groove width etc. are ground into the tools. They are used on mills, HMC's, VMC's drilling machines and on lathes.

They are fed into the workpiece like a spot face or counter-bore, typically "Z" axis feed.

Hope that helps.

Dick Z

[fizzissist]

Originally Posted by dingo0722 I have a job that requires a 32 rms finish in 6061-T6 on the floor and wall of an oring gland. After roughing it out what would be the best way of hitting that finish value. I was thinking of using a carbide ball endmill with a small stepover. are there any other techniques that would work

A 32 finish on that material, all things being equal, is a piece of cake.

The real sealing takes place on the floor, not the walls, if that's any help...but some prints will call out the same finish on walls and floor, so to make QC happy....we'll make it all pretty.

I've done lots and lots of O-ring grooves in both 304SS and 6061 for high vacuum systems, up to the high 8's, and the leaks have always come from too deep a groove, pinched O-ring, or a hair.

I've always done a rough cut down the middle of the groove, then a rough pass on each wall, leaving a few thou for clean up on the walls and floor.

A good sharp carbide endmill, 2 or 3 flute, with small corner radius, NOT a ball mill, running up in the 1200SFM or higher range, plenty of coolant to avoid dreaded chip re-cutting, and you'll get wonderful grooves.

I've been extremely happy with the endmills from these two companies....

http://www.dataflute.com/catalogs/da...e/webfm_send/9
Whoops!!! the link disappeared when I posted this..and I'm not in the mood to go digging it up...but the company is Helical, supposedly the same exact product. I like DATAFlute's catalog better....

...was using an SGS carbide mill on a 304SS O-ring groove. Broke the tool in the first groove on the 2nd pass. Replaced the SGS with a DATAFlute and finished that part, and the rest of the parts in the batch. Was never pleased with the SGS mills, and always pleased with the DATAFlutes.

Hairiest grooves were .042wide x .026 deep, 304SS, rectangular with radius corners, about 2 linear inches each groove....4 grooves each in 16 parts on one endmill. The DATAFlutes ROCKED!!

[dingo0722]

great thanks for the info. I will proceed like you had with the corner radius 3 flute carbide.

thanks

[Algirdas]

the link disappeared when I posted this
here you are:
http://www.dataflute.com/catalogs.asp#dataflute