Ring grooves

[Gordon]

I seem to have a problem with ring sealing. Usually after a lot of screwing around I finally get the rings to seal. I think that the problem is the finish on the side of the ring groove. The finish on the side of the groove has to be smooth, especially on the lower side of the groove. A good finish on the side of the ring is fairly easy because it can be lapped on a flat plate. The finish on the side of the groove is pretty much determined by the machined cut. Usually the groove is too narrow to get inside with any kind of file or stone to smooth it out. I have been cutting the groove with a cut off blade. I square up the blade to the chuck and plunge cut and move the tool over to get the final width. Any words of wisdom on the proper method? Tips?

 

[Vietti]

I agree the ring groove sides are important. I think though that the top of the ring groove is more important but either way, make them as true and smooth as possible.

 

[danallen]

The best way to get a good finish in a groove is to have back clearance on the tool in addition to side clearance. You don't want any part of the tool rubbing or dragging chips.

 

[Charles Lamont]

Just to be crystal clear, when you say plunge then move the tool over, do you back it out before moving it over?

 

[Gordon]

Yes I am backing out the cutter before moving it over to widen the groove.

I am wondering if the reason why I am successful sometimes and not at other times is because I have the cutter set at a slight angle to the part. This could give a better cut on the bottom of the groove and a worse cut on the top of the groove. The bottom of the groove is more important than the top because the bottom controls compression while the top controls intake suction. I have not been too successful at grinding side relief in a narrow cutter using only a hand grinder on a .040 wide cutter. Perhaps I should try making a better grinding fixture. I have seen illustrations of a "fish tail" shaped cutter and that is probably what is required.

 

[Brian Rupnow]

Gordon--Just a crazy thought here--You can buy grinder cut-off wheels (I've heard them called Zip-cut discs) 1/16" thick. If you mounted one of them on a toolpost grinder, and used it to cut the ring grooves, wouldn't the fact that it is grinding the cut leave a smooth finish on both sides? You might have to true the face with a diamond dressing wheel to get sharp bottom corners in the ring groove. I don't really know this to be true, but I was thinking of it.---Brian

 

[peterl95124]

I have always cut my ring grooves using a "Nikcole Mini Thin" carbide grooving tool, they are ground with rake, relief, and side relief, and have never had any problems with them, they cut clean. I also use them for grooving the top of my valve stems for "E-clip" keepers. (have had lots of problems using them as general purpose lathe bits, they're too fragile (and $$$) for that, but never a problem with ring grooves in aluminum, and only broken a couple doing valve stem grooves in stainless). I make my grooves the grooving tool width and then make rings to suit, my most recent engines have .027 width grooves and .025 width rings.

Also I don't use 6061 aluminum for pistons, it doesn't machine cleanly (some would say its
"gummy"), I use 2024, much harder so much cleaner cutting.

I always use (TapMagic EP-Extra) tapping fluid as a lube when grooving <=== Always !!!

PS, the best grinder (IMHO) for lathe bits is the Glendo Corp Accu-Finish, its a slow wet diamond grinder / polisher. they sell about seven grades of disks, and I bought one of each, but I only ever use the coarsest for roughing and the finest for polishing and resharpening.

 

[Steamchick]

Just a couple of observations. If you are using o-rings all 3 faces in the groove must be of good finish. But if using Iron or steel rings there should be No Contact between the inner diameter of the ring and the bottom surface of the groove. Metal rings seal on the flat faces of the groove, so the cross-slide determines the finish of the faces - I propose a sharp tool, fine cut and slow feed rate.
Hope this helps?
K2

 

[Gordon]

Gordon--Just a crazy thought here--You can buy grinder cut-off wheels (I've heard them called Zip-cut discs) 1/16" thick. If you mounted one of them on a toolpost grinder, and used it to cut the ring grooves, wouldn't the fact that it is grinding the cut leave a smooth finish on both sides? You might have to true the face with a diamond dressing wheel to get sharp bottom corners in the ring groove. I don't really know this to be true, but I was thinking of it.---Brian

I have never tried them for ring grooves but I have tried them to cut off rings from a blank and my observation is that the wheels flop around like a paper snow bird.

 

[Gordon]

I will probably have to just invest in some carbide grooving bits. I have looked at them before and hesitated because of the cost but that is probably false economy.

Thanks

 

[kuhncw]

Gordon,

Little Machine Shop sells a line of HSS indexable tooling manufactured by A R Warner of Latrobe, PA.

HSS grooving/cutoff inserts are offered in 1/16, 1/32, and 1/64 widths.

I've used both the Nickole carbide inserts and the A R Warner HSS inserts and either do a nice job on ring grooves.

Chuck

 

[Gordon]

Gordon,

Little Machine Shop sells a line of HSS indexable tooling manufactured by A R Warner of Latrobe, PA.

HSS grooving/cutoff inserts are offered in 1/16, 1/32, and 1/64 widths.

I've used both the Nickole carbide inserts and the A R Warner HSS inserts and either do a nice job on ring grooves.

Chuck

The inserts look good at $17 but the price of the holder will shock you. $140 for a 3/8" square with a corner notch seems kind of excessive. I have one of the other type which clamps from the top which is more complex and those are only about $35. 1.5mm is the narrowest insert though. I wonder if it would be possible to make a holder.

 

[kuhncw]

Gordon,

This is an AR Warner HSS grooving tool holder I made for my
Sherline lathe.

Chuck

 

[Gordon]

Gordon,

This is an AR Warner HSS grooving tool holder I made for my
Sherline lathe.

View attachment 144965

Chuck

Thanks. I will probably order a couple of inserts and make a holder. I don't understand why the holders are so expensive. I just got a Traverse flyer and the holders are only $82 which is $60 less. Inserts are $23 instead of $17.

 

[Richard Hed]

The inserts look good at $17 but the price of the holder will shock you. $140 for a 3/8" square with a corner notch seems kind of excessive. I have one of the other type which clamps from the top which is more complex and those are only about $35. 1.5mm is the narrowest insert though. I wonder if it would be possible to make a holder.

People make holders all the time. I haven't yet, but I have a shiteload of a certain type of carbide insert that I cannot fine a holder to buy. I will soon make my own. you can buy the screws for inserts with holes in the middle or use a lever type that holds from the top. Easy peasy. don't forget to harden it.

 

[Richard Hed]

Gordon,

This is an AR Warner HSS grooving tool holder I made for my
Sherline lathe.

View attachment 144965

Chuck

Whoa! I likes it. How did you get the hole in the cuttyer?

 

[Richard Hed]

Are they military-industrial? If so, that's why. If not, just taking enormous profits. No doubt some tools are higher quality than others, but it doesn't seem justifiable to me to charge 140$ for 20$ item.

 

[ShopShoe]

Richard, and others,

The inserts have the hole already:

AR Warner: https://www.arwarnerco.com/Default.asp

Nikole Mini-Systems are similar: Nikcole Mini-Systems – Niko Nikcole

I have no relationship with either company or any vendors.

--ShopShoe

 

[l.dullum]

Checkout the Thinbit line of inserts from the Kaiser Tool Company. They range from .004" on up in 001" increments, and work great for ring grooving.