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Steady rests and surface finish

M

motorfixer1

Aluminum
Joined
Nov 14, 2012
Location
Illinois, USA
Hey all I've been away for a while (works been crazy) but I was searching today for some answers. I routinely machine an electric motor shaft on our Kingston HD 22X90 manual lathe. The shaft is about 5" for half and about 3" on the other half and 60" long. Material is 4140 HR. I use a steady rest in the center of the shaft to prevent chatter and it works well for the most part but I have noticed that the rollers cause their own vibration influence on the workpiece. After roughing out the shaft in another machine (American Pacemaker 26X96) I move the workpiece into the Kingston for finishing. In the center of the workpiece I start out by machining a spot for the steady to ride on with a TPG 320 insert taking light cuts until the surface cleans up and runs true with the centers. After a light polish with sandpaper I adjust the steady to contact the freshly machined surface. No matter how smooth the surface looks there always seems to be some audible vibration from the steady as well as some effect on the final surface finish of the part. The inserts for finishing are Kyocera VNMG 331 cermet. These inserts produce cadillac finishes on steel and last FOREVER. I was thinking about posting a video of the part in action as I am in the middle of making one. I am wondering if anyone has any advice in deadening these vibrations or stopping them all together. I make some brass caps for the fingers of the steady but they aren't really practical for higher speed, extended turning operations. http://www.practicalmachinist.com/vb/general/kingston-hd-lathe-steady-rest-bushings-w-pics-262562/
 
Have you tried some lube oil on the rollers, I always lube mine and sometimes it helps.
Is this a problem that has just started or always been there? If its new-Try new bearings.
 
I do use a few squirts of way oil on the surface where the rollers ride. I also made a cardboard slinger that goes around the shaft between the tool and the steady to keep chips and the like out of the path of the rollers. I am probably going to try and replace rollers just as a precautionary measure and go from there.
 
Run pads with air holes instead of lube if at all possible make it a pass through.

Personally I would loose the steady on that short of a piece(going to be a steep learning curve to get finish though)
 
Never had perfect running with rollers.. Used brass or bronze solids setting with a .003 shim then adding a drop of lubrication oil for many years... Then I replaced with nylon and used a .001/.002 shim for best running. Nylon can run touching if RPM is not too high.

I have a nylon block with a V on the opposite side small block attached to a finger to be used as a backer for use as a follower or rider for thin work.
*Also have a home made steady that has sealed bearings for rollers.. that works well.

5" and 3"dia x 60" sounds like a hefty part.. how are you holding it on ends? and speed turning? Seems best would be between trued centers.
 
How about junk and chips getting on the surface?

The rollers roll over them, "bouncing" the shaft, but fixed tips often just wipe the junk off. Tips that have a "pinch point", like flat tips on a round shaft might pull them in though. Lots of old time steady tips have a more-or-less radial edge to the tip, might scrape off junk.
 
You don't want to use brass, gotta be bronze, but oh boy if you keep it oiled and set them just right they will handle the speed well.

How straight is the shaft if just spun between centres? I have seen a slight bow cause massive grief and something akin to what your describing with a steady in the middle.
 
you say you are turning between centers, with a dog to drive work? a chuck has allways seemed to be more rigid in my experience. you can get great concentricity, .0005 easily, you just have to be really careful with your set up. as far as steadies, bronze pads definitely way to go, like others have said careful adjustment and lube is a must. anyone ever use a strip of emery cloth between pads and work? when I first heard of it I didn't think it would work, I was wrong it makes the bronze pads a little more forgiving and keeps them from marking the work at all. take a strip of emery long enough to wrap around work piece and catch both ends in opening of steady. you put grit side out so cloth side touches work. bring fingers down to just lightly compress emery cloth. oil it up and go. it is not the most rigid set up as the emery has some squishiness to it but its great for set ups where you just need to stop vibration and like I said it wont mark up work at all. final thought, if things are heating up, your probably to tight on your adjustment. brass is not ideal but should work ok if lubed well and not to tight.
 
a steady rest is rarely perfect aligned. if off center every time chuck goes around it and the steady rest are fighting for control of part. if using a 3 or 4 jaw chuck that (the jaws) will cause vibration itself. to lower vibration i
.
1) move close to chuck with steady rest to help set steady rest jaws then slide steady where you want it . if a steady rest is off enough a part can walk out of the chuck
.
2) slow rpm down. just saying sometimes vibration is speed related that is more rpm, more vibration. you might get a crappy finish just from turning at lower rpms with carbide
.
3) me i normally turn .001" big and sand it to size check with a bearing or ring gage
.
i have turned 60" long shafts that were under 1" diameter. got to say the smaller the diameter the harder it gets to get a good finish. try turning 0.5" dia and 60" long
 
I agree with Derek Smalls. I observed a professional machine shop years ago regularly using lubricated emery cloth inside-out on a steady rest to prevent chatter.
Best wishes --- Allen
 
Wood can work, but unlike the emery cloth idea its pretty insulating so gets hot pretty fast even at low speeds. The emery being thin and only really having 3 point contact does not suffer from that issue anything like as much
 
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