1/3 Scale Ford 289 Hi-Po

[petertha]

Thanks for your detailed writeup, Terry. Even though I've bookmarked your prior builds regarding rings, I always learn another tidbit or two.


Lapping the rings isn't for cosmetics. Smooth sides are important because during combustion the bottom face of the ring must seal against the lower face of the piston groove so combustion gasses behind the ring can push and seal the ring to the cylinder wall.
- I always assumed the lapping was more related to dealing with the parting off operation, specifically more variation in thickness dimension & higher potential for edge burr. I didn't consider the seal aspect. So dumb question, now you have a nicely lapped flat ring face. So how does one ensure the quality of the mating ring groove face in typically aluminum is of similar quality? Do you have a preferred tool or treatment for that?


I use 1050F which is a compromise of what others with more metallurgical knowledge than I have recommend. Controlling this temperature in a home shop without a suitable oven can be difficult...

- maybe you mentioned elsewhere, but do you make your fixture & expansion pin from same type of CI

- what kind of oven do you use yourself & what is your recipe for minimum heat/soak duration time? I've seen some documentation specifying time per volume on Durabar grey CI equivalent post #27 https://www.homemodelenginemachinist.com/threads/piston-rings.36318/page-2#post-415318 )


- you mentioned using uncoated inserts steel/CI alloys before(which I assume are the ones engineered for aluminum type alloys) on certain. I have used them myself in steel for similar reasons. The only downside seems to be a bit more fragile (sharper nose radius) & they wear faster (lack of coating?). But my question is more why do they work? I noticed I could actually order coated/steel inserts with the same sharp nose radius as my aluminum ones. In fact it made me look at some 'for stainless' ones I bought out of curiosity which cut better than the regular ones in more typical steel. But another parameter is I think aluminum inserts have a higher rake angle. This is not always easy information to quantify (at least on my tooling back alley locations). One would think this would not be conducive to a better finish or dimensional control in a tougher material. Anyways, any thoughts on this subject as to WHY the uncoated work as they do or you prefer them?

 

[mayhugh1]

Thanks for your detailed writeup, Terry. Even though I've bookmarked your prior builds regarding rings, I always learn another tidbit or two.


Lapping the rings isn't for cosmetics. Smooth sides are important because during combustion the bottom face of the ring must seal against the lower face of the piston groove so combustion gasses behind the ring can push and seal the ring to the cylinder wall.
- I always assumed the lapping was more related to dealing with the parting off operation, specifically more variation in thickness dimension & higher potential for edge burr. I didn't consider the seal aspect. So dumb question, now you have a nicely lapped flat ring face. So how does one ensure the quality of the mating ring groove face in typically aluminum is of similar quality? Do you have a preferred tool or treatment for that?


I use 1050F which is a compromise of what others with more metallurgical knowledge than I have recommend. Controlling this temperature in a home shop without a suitable oven can be difficult...

- maybe you mentioned elsewhere, but do you make your fixture & expansion pin from same type of CI

- what kind of oven do you use yourself & what is your recipe for minimum heat/soak duration time? I've seen some documentation specifying time per volume on Durabar grey CI equivalent post #27 https://www.homemodelenginemachinist.com/threads/piston-rings.36318/page-2#post-415318 )


- you mentioned using uncoated inserts steel/CI alloys before(which I assume are the ones engineered for aluminum type alloys) on certain. I have used them myself in steel for similar reasons. The only downside seems to be a bit more fragile (sharper nose radius) & they wear faster (lack of coating?). But my question is more why do they work? I noticed I could actually order coated/steel inserts with the same sharp nose radius as my aluminum ones. In fact it made me look at some 'for stainless' ones I bought out of curiosity which cut better than the regular ones in more typical steel. But another parameter is I think aluminum inserts have a higher rake angle. This is not always easy information to quantify (at least on my tooling back alley locations). One would think this would not be conducive to a better finish or dimensional control in a tougher material. Anyways, any thoughts on this subject as to WHY the uncoated work as they do or you prefer them?

Peter,
When I cut ring grooves, I use a sharp insert with back clearance, and I practice on the end of a piece of scrap to get the feed and speed for the best surface finish. The insert also needs to be perfectly perpendicular to the axis of the piston. If the measured width of the groove doesn't perfectly match the width of the insert, the insert isn't mounted correctly and the surface finish will suffer.

I've never made the fixture from CI, but I think I'll try it this time. I've typically used 12L14 and 303 stainless. Matching the coefficients of expansion is probably a good idea.

My oven is a Ney Vulcan dental oven. My particular model isn't manufactured any more, but similar ones can be found on ebay.

I like using the high rake inserts on cast iron because they give a good surface finish even though they don't last very long. I'll some times use them for finishing passes on steel and stainless steel as well. On lathes without a lot of rigidity their peeling action seem to give great surface finishes without the chatter.

Terry