Piston Ring slot

Hi all,

Looking for some suggestions please as to what I'm doing wrong. I'm trying to cut piston ring grooves in a piston and I keep getting a small taper on the right side of the groove.The left side is always good and perpendicular. The groove width is 1.3mm, and i'd guess the taper is around 0.1-0.2mm, certainly visible under the magnifying glass.

I have ground the tool bit and have relief on all sides. I thought it might be one of the feeds creeping, but even holding all feeds steady it still happens.

Any suggestions?

Thanks Craig

Is the tool flexing?

possible. I'm using a 6mm tool bit and i've kept the cutting edge as short as possible. Tool bit is about 15mm out from the tool post.

If you are holding the piston in a chuck, it may be slipping a tiny bit. You might try a piece of paper wrapped around the piston for the jaws to grip on.

That seems a large overhang for a 6mm square tool bit. But why is one side of the groove fine and the other not? I'd suggest that the tool isn't ground correctly, or isn't held exactly square to the work.

Andrew

I would imagine tool is not square to the piston.

Dave W

Increase the width to, say, 1.5-1.6mm and use a parting tool? Ideally 1.6 with a 1.5mm parting tool - rough cut and finishing cut principle?

Is the outer edge of the groove coming out wider than the 1.3mm tool and the bottom to size? if so then the tool could be flexing away on the tapered side and the side rubbing on the other which would make it straight. Close up photo of the tool from above would help.

thanks all for comments and thoughts, that's the great thing about this site.

I'm practicing on a blank so have the piece firmly clamped, pretty sure it is not slipping.

I will be able to reduce the tool overhang by quite a bit, so will try that.

I'll double check squareness.

I don't currently have a 1.5mm parting tool and I already have the rings cut so that would be a last resort.

Jason, yes the tapered edge is wider, sorry can get close enough to get a photo in focus. Guess that could mean flexing.

I'll try again tonight and report progress.

Thanks

Craig

Hi all,

Success, thanks for the suggestions. I reground the tool, and reduced the overhang. Not sure if it was one or both of those factors, but I have 2 nice ring grooves now with nice parallel sides.

Have tested the piston in the sleeve with one ring fitted and certainly feels like a good seal.

Thanks

Craig

nice job....whats it for....?

thanks clogs, this is for the WT2527 15cc glow engine, detail over on the work in progress thread.

the method I use on stationary engine pistons ,is on new pistons is to use a short stiff parting tool to rough out the ring groove to undersize on width and go in to full depth,then grind up very narrow left and right hand turning tools from HSS and machine each side of the groove (not at the same time) this gives dead square groove sides and good control over groove width.