Poor finish, aluminium

emtor

Registered
Registered
Joined
Aug 29, 2018
Messages
54
Friday evening, turned the large wheel on my lathe using carbide insert tool.
Saturday I turned a smaller wheel (placed on top of the large wheel).
I started the lathe and I got something that sounded like the belt is slipping (a short squeak every revolution).
Squeaking gets worse when the tension is released and also has a tendency to increase slightly with increased loads.
The finish is, as can be seen in the image, very poor. Metal looks torn instead of cut, but please note the shiny section
on the small wheel. Every now and then the lathe produces shiny sections, some of them just narrow lines and some of them wider sections.
I'm thinking this may have something to do with belt slipping.
Tried cleaning both the pulleys and the belt,- not much success. Belt has only run a few hours.
-Any thoughts on why the finish looks like it does?
The large wheel does not have a good finish, but at least it is consistent. The small wheel has a poorer and very inconsistent finish.

aluminium.JPG
 
Last edited:
Are you sure that is aluminum? It looks like steel to me. The surface finish will vary with tool height using carbide inserts. Larger diameters will be more tolerant than smaller diameters.
 
yep, that sure looks like steel. I suspect you have too small depth of cut and too small a feed and too slow a speed. You have to make carbide work to get a good finish. Get a speed feed chart for your insert. Light cuts and feeds are HSS territory.
 
You also might check to make sure your tool is on center as well.
 
I've tried the whole speed range from 125 rpm to 2000 rpm,-no change.
Light cuts, heavy cuts,- no change.
Manual feed, auto feed,-no change.
Ground a HSS tool today,-no change.
Ground a HSS vertical shear tool, took very light cuts,-still poor finish.
I've used a valve gauge blade between the workpiece and the tool tip and the blade is vertical. No tit in the center when facing . . . tool is at center as it seems. The strange thing is the fact that while turning the finish suddenly gets mirror quality for sometimes a few revolutions, sometimes half an inch of width, then goes back to poor finish.
Looking at the large wheel, the finish is not great but uniform and acceptable. Lathe did not squeal when turning that wheel.
Next day, belt squeal, probably due to slipping, and the finish got as seen on the small wheel. Varying between mirror finish to torn up.
Compound rest is locked down hard, and I could try the same with the cross slide and do a pass to eliminate movement/backlash in the cross slide.
However, I'm sure it has something to do with the squealing belt,-if it is the belt that makes the noise that is. Rotating the chuck by hand does not produce any sound or rubbing feeling, so I'm sure it's not the chuck.
 
Mine does that when I forget to tighten the tool holder on my QCTP
 
I would either tighten or replace the belt. I've seen this when the belt stretches and sets up a harmonic. The squeal/squeak also suggests a drive issue.

That aside, if this is aluminum, I would not consider that large disc a great finish but if it is acceptable and on size then that's what counts.
 
The strange thing is the fact that while turning the finish suddenly gets mirror quality for sometimes a few revolutions, sometimes half an inch of width, then goes back to poor finish.
Looking at the large wheel, the finish is not great but uniform and acceptable. Lathe did not squeal when turning that wheel.

I assume you are power feeding. If so, I think this is a clue that there could be a problem with your lathe & not the cutting tool since you have tried many options. If there is resistance or binding as the carriage is traversing down the ways, you may be picking up vibration. The bely squeaking may be telling you its seeing higher (traversing) load. Power feed bar is bent or out of alignment. What happens when you just traverse carriage by hand? Is it perfectly smooth? Does the same bad finish occur at the same position in the lathe? Need more information to help you.
 
Power feed or manual makes no difference, also the bad finish appears randomly.

The comment regarding failing to tighten the QCTP is interesting, and something to look into.
My toolpost is tight, but in order to get the tools on center I have to shim quite a lot.
(That's right . . . no adjustable QCTP here).
The shims I use are blades from valve clearance gauges. I thought that was a good idea since each blade has their thicknesses stamped on them.
(Good for future reference).
Now, these blades are tapered and not the same width as the insert holders, also there are quite a lot of them needed to get the tool up to center of the workpiece. I need to find something thicker that fills the gap without using a lot of separate shims as my current arrangement may be causing the tool to move while turning.
Also I'll disconnect the gear banjo to rule out loose/overly tight gears.

An update before going off to work: -Disconnected the feed screw gear train. One of the gears were loose,-I could tighten the nuts with my fingers.
Belt is still squealing though. After work I'll remove the belt to rule out motor/spindle problems.
 
Last edited:
Noisy belt is a slipping belt.

Belt slips due to excessive load for the transmission system.

Others suspect binding someplace.

Chuck up a chunk of wood and try it.

It will be messy but should work.

If belt still noisy repeat with nothing to troubleshoot.

Your material may be work hardened and if so will do as it is.

You state aluminum...are you sure?

Test with a hacksaw to see if the weight of the saw will be enough pressure to cut.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
Back
Top