Surface finish problems

Paul,

You're absolutely correct... I failed to ask about RPMs probably thinking the OP had tried all speeds with no luck. With HSS, a piece about 1" should be spun at 400-500 RPM and with carbide, around 1000. You're right, a piece of mild steel is a tough customer. It certainly won't cut at low speeds and untuned lathes often start shaking when you get past 600 or so (depending on how heavy the unit is). I guess my mind gravitated to that line of thinking.

Ray


samthedog said:
I have been following this thread for a bit and have not seen any comments on rpm. That piece looks under an inch in diameter so you may have too few rpms at 300 rpm. I had a piece in similar in size and spun it at 900 rpm to get a good cut. At this speed, I had no chatter to speak of and kept the cutting oil flowing to ensure a good finish.

Just be ready with a hook to pull away the swarf that builds up as this will catch between the tool and the work and give you a striated finish.

You have picked a notoriously difficult metal to machine to a good finish. Good luck.

Paul.
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samthedog said:
I have been following this thread for a bit and have not seen any comments on rpm. That piece looks under an inch in diameter so you may have too few rpms at 300 rpm. I had a piece in similar in size and spun it at 900 rpm to get a good cut. At this speed, I had no chatter to speak of and kept the cutting oil flowing to ensure a good finish.

Just be ready with a hook to pull away the swarf that builds up as this will catch between the tool and the work and give you a striated finish.

You have picked a notoriously difficult metal to machine to a good finish. Good luck.

Paul.
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Paul this is my original post, Just so you see we did cover it, thanks for posting in I do apprieciate the help. I did do some corection to the machine since then though and it is easy enough to try. so I will give it a go latter. I am pretty convinced at this point it is some sort of harmonic vibration, either a chatter, balance, or bearing, or the like.

A right I have been noticing a twisted pattern arround the part. not threading but a very faint twisted or spiral effect in the finish. About 1 twist per 3-4" reducing spead from 560 down to300 made it less. pronounsed but sill there. The effect happens on both SS and mild steel. the test parts where 3/4 . Don't know ifyou can see it in pics I can but it is hard to see and I know what it looks like.

And the first pics were of a SS part just because I know mild steel is tough. I used the mild because it was hard to see in the pics of the SS, and it showed up better in mild.
Thanks again for the help
Mark
 
READ THIS POST,please. I had a horrible time with my new 16x40" Grizzly gear head (my first gear head) lathe back in 1986. It practically KNURLED the metal. I was thinking something was wrong with the lathe. When I was leveling it,I was driving thin wedges of oak under the lathe all around. Suddenly the problems stopped. I had apparently gotten the lathe JUST off the concrete floor!!

The lathe had also sounded like a bunch of small parts going down a chute. That had also stopped. It was VERY annoying. I now have my lathe sitting on Mason neoprene pad feet. They were the cheapest,seeing as how I needed several of them,4 under the headstock alone. It adds up!!

My lathe now cuts very smooth,except for the gear "echoes" in the metal,which are in reality just a few hundredth of a thou thick.
Get your lathe out of contact with the concrete floor,if it is sitting on 1,and see if your problems don't cease.

All gear head lathes may not mind being on concrete,but we're dealing with inexpensive lathes here,which are more prone to vibration problems. I ran a Dean,Smith and Grace gear head lathe that left no gear echoes at all. But,that brand costs many,many times more than the Grizzlys. Maybe more than my house is worth in its day!!
 
George thanks I am thinking of trying some rubber roof matts under the feet to see if that helps. Was going to put it on them when I got it and thought it might be the wrong way to go. I had read that gear thing before (Not sure were) but had totally forgot about it.
Thanks again
Mark
 
George,
I put the mats under it but no help.Tell me does that gear echo show up in a spiral pattern?
Thanks
Mark
 
markknx said:
Paul this is my original post, Just so you see we did cover it, thanks for posting in I do apprieciate the help. I did do some corection to the machine since then though and it is easy enough to try. so I will give it a go latter. I am pretty convinced at this point it is some sort of harmonic vibration, either a chatter, balance, or bearing, or the like.

A right I have been noticing a twisted pattern arround the part. not threading but a very faint twisted or spiral effect in the finish. About 1 twist per 3-4" reducing spead from 560 down to300 made it less. pronounsed but sill there. The effect happens on both SS and mild steel. the test parts where 3/4 . Don't know ifyou can see it in pics I can but it is hard to see and I know what it looks like.

And the first pics were of a SS part just because I know mild steel is tough. I used the mild because it was hard to see in the pics of the SS, and it showed up better in mild.
Thanks again for the help
Mark
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Hello Mark, I went through the thread and didn't see any pictures of the tooling you have been using. Are you able to post some pictures? I was having a similar problem with stainless (super-duplex) and it turned out to be the bit. Looking at the pictures, the spiral effect is less pronounced the closer you get to the chuck. How is the spindle bearing preload? Has anyone fettled with the lathe in the past? I am wondering if the bearings may need to be nipped up a bit tighter.

If the bearings are worn and not re-adjusted, you will get inconsistencies the further from the chuck you work, irrespective of how rigid the piece is due to slop in the spindle bearings.

Good luck.

Paul.
 
Paul,
no I have never messed with the spindle bearing. not sure the proper way to adjust them. I know it would be the big nut on the back end but not sure on how tight.
The patern is the same with my home cut Hss, and different angle also several brazed carbide tip (even a couple brand new) I even tried mounting my ball turner in place of the compound rest.

Ray,
I did a test on the vibration today per your post. I did not trust my sense of feel, so I placed a glass of water on the mill at different places. The results were pretty good. On the carriage I saw nothing as far as vibration. I tapped 3 fingers on the compound and I got some light ripple. The same for the cross slide. On the head stock I had very light movement in the water and I mean like almost nothing. All of this stayed the same with the chuck off.
Thanks to both of you guys
Mark
 
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