Thread: Pistons and machining

I was imagining something along the lines of a parting off tool, for the grooving , but I see that LOGS tool is more rigid , and would be more effective , the ring grooves are only shallow anyway in most cases , not deeper than 3/8" mostly .

Yes I was worried about the piston moving , particularly if it is long and unsupported and the chuck isnt that big . It would be a disaster if it moved as it would make the tool dig in and make a real mess

The mandrel would be great I think- specially if you only have smallish chucks with short jaws , not much grabbing power .

I might even be game enough to do the Morris 6 pistons one day ..I worked out they will take 3 and 1/4" Dodge rings , but the Morris ring grooves need deepening slightly as the Dodge rings are deeper than the Morris ones .

I will download that PDF file at the library .. looks to be interesting .

I spotted that piston grinder on EBAY too ..it was there for ages

MIKE

Originally Posted by Log

Just for interest. The gadget I was describing earlier, well I just found a couple of pics of one. Perfect Circle Manulathe Piston Regroover | eBay
I'll have to lift the pics to save in my files, just for historical interest.

Cheers.

I've never seen one of those before ! Would it be effective on harder materials eg cast iron alloys

Not cheap is it

Originally Posted by morrisman

I've never seen one of those before ! Would it be effective on harder materials eg cast iron alloys

Not cheap is it

From memory the tools had tungsten piece brazed on the end so though I didn't ever do cast iron pistons on it I'd imagine cast iron would be do-able.

Sure isn't cheap, surprised me, I wonder what it will go for eventually. I'll put it on my watch list just for interest.

Cheers.

Machining cast iron pistons is easy enough with HSS tooling.
I have used tools ground from square or parting blades ground down the last 20mm on a surface grinder. 32 x 5 parting blades are plenty strong enough and can be ground to cut most ring grooves. Carbide groove tools are available in both brazed and insert styles. Practice on some scrap pistons, the mandrels are quick to make and can be recycled after use. A piston catalogue or two is handy for finding rings

Crossfeed is right morrisman, as I said earlier I just about always used tool steel. I always used as wide a tool as possible depending on the rigidity of the holding of the piston etc.

Cheers.

Just for interest sake: I have a 1925 or 1926 Van Norman cylindrical grinder with a piston turning and grinding attachment. It's not yet restored, but has moved into my shed for a "soon" project. RayG ans Josh helped me get it here..... The attachment Bolts to the T-Slot table.
(Photos here)
Joe

Originally Posted by jhovel

Just for interest sake: I have a 1925 or 1926 Van Norman cylindrical grinder with a piston turning and grinding attachment. It's not yet restored, but has moved into my shed for a "soon" project. RayG ans Josh helped me get it here..... The attachment Bolts to the T-Slot table.
(Photos here)
Joe

Thanks, very interesting grinder, wow so early too, nearly 90 years old. Does it look like the piston grinding attachment operates on a cam?. Might be too early for cam ground pistons, dunno. Irrespective, it's a nice interesting machine.

Cheers.

Yes, Log, it has a master cam which the drive arbour and centre (at the other end) pivots against - spring loaded - as it turns.
I'll take photos when its cleaned up. So far nothing moves and I'm still feeding it with penetrating oil.....
I'm hoping it has enough movement range to grind camshafts - maybe - off other master cams.

Cheers,
Joe

In answer to how pistons are usually mounted for machining, I worked for an engineering firm that made pistons and rings in the early 80's. Even then roughing was done in NC's. They were turned to a finished oversize for the largest size needed (ie 0.80" oversize) then finished turned and cam ground as needed. The ring grooves were all turned to full depth during roughing.

The turning and grinding was done with the piston held on a tapered or stepped mandrel in the lathes main spindle taper, which engaged the bottom of the skirt. It was held in position by either a spring loaded live centre or on one lathe some form of internal locking system which clamped the piston onto the mandrel via a pin passed thru the gudgeon hole. From memory you pulled the locking lever while held your hand under the gudgeon hole, catching the pin as it fell out. Swap pistons and pull lever again while holding pin in the hole. Centre pin and release lever. Spring pressure kept piston tight. I don't remember but probably operated from the outer end of the spindle.

This machine also from memory had a very interesting set of traverse gears. What was left was sitting in a box behind the lathe at one time. The result of an earlier crash. All manual on this baby.

The cam grinders also had the same type of mandrel but the piston was held in place by a spring loaded flat rotating centre.


Dean

Originally Posted by shedhappens

Instead of using ring spacers you could buy the cast iron and make your own rings to suit, I haven't done this myself but my brother has, I don't know where he got the cast iron bar from but I could find out. I have cut ring grooves a few times to fit non standard rings to something you can't get parts for, thinking about that the last time was probably 15 yrs ago I opened up the grooves on a compressor piston and fitted a set of Briggs & Stratton rings. A thing to consider is that these days many newer engines have a chromed top ring.

I always keep a look out for big diameter cast iron just in case I find some that would suit some rings I want to make. I have not suceeded yet. Making new rings is something I would like to attempt one day. There is a formula. Make the ring over diameter by a certain percentage. Cut a slot to enable the ring to close up to just oversize. Close it up and clamp it in a holder which will enable you to machine the closed ring to finish size. Grind the final part if possible. Remove the ring and grind the slot for final fit in the bore.

Lots of you probably know this but I thought someone may be interested in this very simplified explanation.

As mentioned in my previous post I worked an engineering firm that made pistons and rings in the early 80's.

I was never involved in any of the ring making but was working around the area at times. I don't recall where the ring blanks came from but I remember watching a stack a foot or so high fed into a tube to close them up then a clamping bar passed thru and clamping from each end. Remove from the tube, place in a grinder and grind to size.

A Mrs Smith did the ring sizing afterwards. She sat at a table with a machine to grind the gaps by small amounts and a gauge to test the fit. I remember her mostly because she was very old and she was the only person I have ever seen with a full length cigarette in her mouth after it was smoked. She did it continously.

They had a machine to make oil control rings. A large roll of spring steel fed into this machine which was adjusted to produce slinkies of various sizes which could be cut up into rings. I am sure this was where the idea for slinkies came from.

Dean

Are pistons made here anymore ?

I can think of the old POLSON and ROLLOY Australian brands , and REPCO of course , these piston brands are long dead I think.

JP is one , but very expensive

MIKE

Thanks Oldnewengine for the insights on both the piston machining and the piston rings.

I did visit manufacturer of pistons, piston rings etc once in Melbourne quite a number of years ago. I remember the semi-finished rings(a heap of em) being pushed into a cylinder then a mandrel passed through then a plate put on and the nut tightened up and then the cylinder was removed. The cluster of rings were then ground to size on the OD. I did see a lot of stuff there but can't remember a lot of it.

I remember seeing the pistons being cast in an automatic machine. Something like this; the dies were sprayed(I think by a little robotic arm sort of thing) with a release agent, they then automatically closed up and rotated around to the pouring station, then around(can't remember what cooling time of if they were cooled somehow) then the inner pieces of the dies(that would be inside the piston)closing up some how and retracting etc and then the dies opened up and the piston dropped out. Some thing like that anyhow.

Thanks again for your explanation, brought back my memories.

Cheers

Mike.

I worked for an engineering firm that made pistons and rings in the early 80's.

However JP would be the one. I don't know if they still make make pistons etc but I know the site is still operating from driving past. My Step son used to live around the corner.

At one point they claimed to be able to make any piston or ring set you wanted within a size range. Max of about 10inches I think. Bring in an unknown sample they would copy it.

Log.

Thats about it. We had a casting guy who did all that work by hand. Sometimes with a helper. Five piece mould. Two outers and three inners I think. Pull out the centre one and the other two then came out.

JP also made high performance high compression racing pistons from a special alloy. They made 12:1 compression ratio pistons for the holden grey motor that were really something to see.

Dean

Though the thumbnail pics don't show(at least for me) if you click on the thumbnail the pic will show up, then just back-button to the story.

How pistons are made

Cheers