Surface finish problems

Yes it is a good problem to have:)) And as I have stated nota real bad one. Yes I changed feed rates and did it by hand both with the carriage and the compound no notable change. Not sure how Icould measure this.
Yes I am trying to rule things out andI am pretty sure for thereasons above it is not in the leadscrew or carriage feed.
The bearing theory is notas unlikely as you may think, 1) these machines do havesome issuesthere, 2) I did crash the compound into the chuck way back.
I do have a better photo, but I think it makes it look worse than it is but at least you can see the pattern.
I think that it could be a bearing and that the reason for the spiral effect is a dent or pit itthe roller hit the pit (or it could be a raised up spot) at a different rate than the spindle speed or ratio that would cause the mark to advance in respects to the rotation of the part.(make any sense)
Well look at the photo and tell me what you think.
002.JPG

002.JPG
 
What depth of cut are you taking? Also, have you tried swinging the compound at a 30 degree angle instead of parallel with the direction of cut?
Finally, is this something that suddenly cropped-up or has it always been this way?


Ray
 
the cut is .001-.002 @ .0025 IPR and spindle speed of 300 RPM. No I have not tried setting the compound at 30deg. I will though. Not sure if ithas been here all along as I stated earlier it will go away with a rougher cut. like at .005 it is not noticable, or if I feed faster than .005. I mean it could still be there it is just masked by the rough surface. Also I just started getting a cut this nice the SS is almost a mirror finish I know the photos do not make it look that way. And the spirals are not deep more like a lazer etch or light chatter. I havebeen living with worse but also think maybe it could be better. Maybe this is the best this lathe will do. I would not tear the head down to fix it at this point that is for sure. But if we do not try to do better we never will.

Thanks again for your timeand patiance in this matter,
Mark

Ray C said:
What depth of cut are you taking? Also, have you tried swinging the compound at a 30 degree angle instead of parallel with the direction of cut?
Finally, is this something that suddenly cropped-up or has it always been this way?


Ray
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You're almost always going to see issues like that with very light cuts because there's not enough cutting pressure to keep the bit planted firmly in the workpiece. Every vibration in the machine will show-up with light cuts -especially with light weight lathes. The chuck could be slightly out of balance and the whole machine will shake with a resonance. Only a very precision and well tuned and moderately heavy machine will not show such artifacts with light cuts. As a general rule, when I'm taking a rod down to size, I remove material such that my final pass will be around 7 (minimum) to 20 thou deep.

When you need to take such a light cut and still get a perfect finish, it's customary to leave it about 1 thou oversized and bring it down with a toolpost grinder.

Ray
 
thanks Ray by the way nice looking puppies. are they some sort of bully breed love them.
thanks again mark
 
Thanks... That's only 2 of 3 pack members. I should update the photo some day. The big one is a Rhodesian Ridgeback, Pitbull mix. She loves all people and loves to play rough. Pure power -and doesn't have a clue how powerful she is but when we play fight, she knows human bounds and pain levels. The little one is a Rat Terrier, Chihuahua mix. He's very independent and the dominant one of the three. In that photo, he's wearing a sweater. It was winter and the little guy shivers when the temps get below 80. The other is a pure Rat Terrier. She's very laid-back. All great dogs. They all play and sleep together.

BTW: There are probably some "low-hanging fruit" items you can do to tweak your lathe. The obvious things are to properly adjust and lube the gibs (your ways look a little dry in one of the pictures) and balance the chuck. I've written threads on how to do that. Let me know if you any other ideas...


Ray
 
Ray C said:
Thanks... That's only 2 of 3 pack members. I should update the photo some day. The big one is a Rhodesian Ridgeback, Pitbull mix. She loves all people and loves to play rough. Pure power -and doesn't have a clue how powerful she is but when we play fight, she knows human bounds and pain levels. The little one is a Rat Terrier, Chihuahua mix. He's very independent and the dominant one of the three. In that photo, he's wearing a sweater. It was winter and the little guy shivers when the temps get below 80. The other is a pure Rat Terrier. She's very laid-back. All great dogs. They all play and sleep together.

BTW: There are probably some "low-hanging fruit" items you can do to tweak your lathe. The obvious things are to properly adjust and lube the gibs (your ways look a little dry in one of the pictures) and balance the chuck. I've written threads on how to do that. Let me know if you any other ideas...


Ray
Click to expand...
Yeah I just look back at some of your post to find one that looks like it explains the balancing, but it's been a long day and my focus is not there so I saved it for latter. Looks like the same way you balance a motor cycle tire as far as finding the heavy side.
I did try turning the compound to 30 deg. no help, but am wondering the theory befind that.
Yes the bed ways were dry, I had wiped them of because I had used sand paper even thogh I keep a paper shop towel to cover the bed I still like to wipe them down. I have been using slip-it on the ways is there something more prefered?
I saw another of your pitty in that post (her head in a laundry basket.) She reminds me of my male pitty/amstaff I had to put to bed for good this spring, cancer got him at 8 years. He was black with the same white face and pink on the nose. best dog I ever had. Oh yeah when he played he played but was gentel with the kids. when he relaxed he did that full on too. To bad they get a bad rap. I still got my girl Bull terrier/sneaky niehbor dog, and we pick up a pound mutt not a clue what he is except hard headed.
Thanks again much for the help,
Mark
 
As for 30 degrees: In this case, I wanted to rule-out the possibility that the bit was getting pulled (or pushed) sideways along the piece -possibly due to the way it was ground. With the compound at an angle, there will always be two components of force (one in the parallel direction and another in the perpendicular direction) acting on the bit to keep it stabilized. When the compound is parallel to the workpiece, it's basically free to wander in that parallel direction. In general, 30 degrees is a good angle for other reasons as well -like being able to accurately predict how much to turn the compound dial to take a specified amount off on a facing operation.

Not sure what "slip it" is but as long as you keep things well oiled it will probably be fine. I happen to use Vactra #4 or #2 way oil.

To see if your chuck needs to be balanced, run it at a variety of speeds (with the jaws closed) and make a mental note of how much vibration you feel in the machine. Repeat that process with the chuck removed. If there's a noticeable difference, it's time to balance the chuck.

Dogs: What a treat to have them. I'm the alpha pack member. They follow me everywhere I go. Unwavering companions...

Ray

EDIT: BTW: The issue really is due to taking too light of a cut. All the stars have to align to get a clean finish when you're below 5 thou. My machine is pretty well tuned and I like to think that I have a handle on most basic things -but when I get in that territory, I give it my best shot, cross my fingers and hope for the best.



markknx said:
Yeah I just look back at some of your post to find one that looks like it explains the balancing, but it's been a long day and my focus is not there so I saved it for latter. Looks like the same way you balance a motor cycle tire as far as finding the heavy side.
I did try turning the compound to 30 deg. no help, but am wondering the theory befind that.
Yes the bed ways were dry, I had wiped them of because I had used sand paper even thogh I keep a paper shop towel to cover the bed I still like to wipe them down. I have been using slip-it on the ways is there something more prefered?
I saw another of your pitty in that post (her head in a laundry basket.) She reminds me of my male pitty/amstaff I had to put to bed for good this spring, cancer got him at 8 years. He was black with the same white face and pink on the nose. best dog I ever had. Oh yeah when he played he played but was gentel with the kids. when he relaxed he did that full on too. To bad they get a bad rap. I still got my girl Bull terrier/sneaky niehbor dog, and we pick up a pound mutt not a clue what he is except hard headed.
Thanks again much for the help,
Mark
Click to expand...
 
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.
 
DMS said:
You're doing just fine. Brass is known for being almost impossible to get a bad finish on, and mild steel is known for being almost impossible to get a good finish on. The only thinh I have found that will give a nice finish on mild steel is a vertical sheer tool. Take a look at Gadgetbuilders site

http://www.gadgetbuilder.com/VerticalShearBit.html

This is a tool for finishing pass only. Don't push it more than 0.004". It will leave a very good finish even on mild steel. Another bonus is they are easy to grind.
Click to expand...

When i see that sort of suface issue on mild steel i use the vertical shear tool , their amazing, i tend to take multiple passes till it gets all the variations off.

ive had problems using them on longer thinner work pieces (8-10mm and smaller) where i find i have to use a follow steady.

Stuart
 
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