Lathe chatter on shaft

I had a shaft to rework yesterday in the shop. It is for a walk-behind
concrete saw. I had to build up a worn spot with weld and turn it back
down. The shaft was 1-1/4" and shouldered to 1" for a few inches on each
end. I removed all the parts (washers, spacers, pillowblocks, nuts, etc),
but could not get the pulley off to save my life.
The customer brought his own replacement pillow blocks. He said he tried to
order a new shaft, too, but is no longer available. The new pillow blocks
were 30mm, so I had to turn the whole shaft down in order to slide the new
pillow blocks on from one side.
I have the "non-pulley" end in a 1" 5c collet in the spindle, and the pulley
end on a live center in the tailstock. The lathe is an 11" Logan model
955. The shaft turned just fine until the few inches before the pulley. I
got some pretty rough chatter when I was turning the part that goes inside
the pillow block. It shook the entire machine. I tried different speeds
(270-500 something), different tool height, different feed speeds, but
still the chatter. I also tried a center rest. I could not used the
follower rest because of the proximity to the pulley on the tailstock side.
The thing just barely fit in the lathe. I couldn't put the part in the
other way because the pulley assy. extended over the 1" part, so it
wouldn't slide all the way into the collet.
Any ideas why the chatter?
Thanks!
Reply to
John L. Weatherly
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Could that end have been welded before?
Reply to
Tom Gardner
It is likely that you hit a hard spot.. possibly previously welded. It is likely, also, that the area that chatters makes a harmonic with the distance from the tool to the collet. Add a steady rest at some position just outside of the middle of the above distance or... better, use a follow rest.
Reply to
Gene Kearns
Tool post grinder?
Reply to
jack
Snip
Well, a long shaft can act like a tuning fork and vibrate. It must be just the right length to produce some serious harmonics.
I have some 3/8-inch lead wire, here, that could probably help you if only there were not the problem of distance.
If I had a chattering problem with a shaft I'd try putting a steady rest, somewhere, and wrapping my lead wire around it in an attempt to cut down on the harmonics.
Are you using carbide or HSS? If you're using HSS, use as small a radius as you can on the tip of your cutting tool.
Let us know how things turn out.
Orrin
Reply to
Orrin Iseminger
Any time there's a heavy weight on a relatively thin shaft it will be more prone to chatter. The weight will cause any small vibrations to increase dramatically as you found out. A really sharp tool and very slow speed is sometimes the only way to get around this. A steady rest can help if you can get it in the right place but that's not always possible. In this case I would of slowed down to 100 rpm or slower and used a extremely sharp pointed HSS tool. Grind the tool with lots of top, and end rake to help.
I'm not real sure that makes sense but I'm rather pooped from moving several thousand pounds of steel for the last two days.
Wayne Cook Shamrock, TX
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Reply to
Wayne Cook
That makes perfect sense. I turned it down within 10 thou, & took it the rest of the way with a file. I spent extra time on it, but the customer was happy. Thanks to all for the replies.
Reply to
John L. Weatherly
It was chattering near and on the weld that I laid. I would have thought that it was the weld but the chatter started about an inch before. My money is on harmonics. I wonder what steel these things are made from. Seemed a bit harder than regular mild steel.
Reply to
John L. Weatherly
Having turned lots of long shafts over the years as a lathe man chatter sometimes responds to increased tool pressure and sometimes to decreased too pressure. It seems odd I know. I see you have finished the shaft so maybe this will help another day. If the shaft is stout enough, and your setup rigid enough, using a negative rake tool can work very well. A fairly high feed is also usually needed with the negative rake tool. On the other hand, a limber shaft, especially if it's a tube, can benefit from very sharp tools, and a finer feed. However, you must be careful to grind the tool such the shaft will not tend to ride up on the tool. One job in particular that I used to run were tubular drive shafts for turbine engined light planes. These shafts were made from 4340 and were heat treated to about 38 Rc. The wall thickness was about .100 and the O.D, about 1,75 in the middle. They were about 44 inches long. Using a sharp carbide tool with a ,004 or .005 radius on the tip and spinning about 700 rpm worked the best. I had to use enough cutting oil to keep the shaft lubed enough that I could wrap my hand around and gently squeeze the shaft while turning. ERS
Reply to
Eric R Snow
Charge extra for the decoration. Paul Powell
Reply to
Paul Powell

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