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Question of finish on manual lathe

slimpick

Plastic
Joined
Nov 4, 2023
Location
Detroit, MI
I am trying to teach myself how to use a lathe after learning some basics from an old timer. Please see my pictures. I expected a much better finish both turning and facing. So I have a couple questions:
Is the angle of the tool to the work piece correct?
I am at 140 rpm which would be about right for a HSS tool and this diameter. But should I use a different speed for this insert?
I am taking off 0.010 each pass.
Maybe I am missing some other factor? Chuck rigidity?

Thanks for any help.
 

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Your speed is way too low. If that's carbide, you need to be running at least about 4-5x the speed as for HSS. Probably higher yet with that light of a cut. Maybe even higher yet if that's something like 1018.
 
Good finish on facing with a manual lathe is pretty hard to achieve with many materials because as you traverse the diameter the effective SFM drops continuously. Sometimes you can alter feed as it drops and mitigate some effects but generally speaking some of the face will look good and the rest not so good. The advice above to speed things up will help a lot.
 
Yes you are missing something. And it's not a about a surface finish which you are trying for at such a low,low,low rpm.
The square plate should be turned down round first before you get hit by a corner.
Spin at 750 rpm or higher.
 
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Good finish on facing with a manual lathe is pretty hard to achieve with many materials because as you traverse the diameter the effective SFM drops continuously. Sometimes you can alter feed as it drops and mitigate some effects but generally speaking some of the face will look good and the rest not so good. The advice above to speed things up will help a lot.
Nice to have a CNC machine which can do all that.
 
You may actually be taking off too little finish depth with that carbide insert and radius. For a manual lathe, very sharp tools work best, sharp HSS or polished positive rake carbide. I also occasionally turn/modify small titanium parts on a hardinge lathe--honed and polished HSS tools work best, and on soft stainless if a good surface finish is a priority.
 
Using carbide insert ,you dial up the revs ,and increase the depth of cut until the chip turns red hot ........then you get a mirror finish ..........Doesnt matter how soft and draggy the steel is .
 
I think for learning insert tools should be banned!, HSS cobalt etc only and learn to grind, slight rad on the tip
You learn more I think about front side and top rake, speed feed lube etc, besides most small lathes don’t really have the power or rigidity to benifit a lot.
Good luck
Mark
 
Brazed carbide tools are how I learned. Not expensive and I did get experience altering profiles with diamond stones and wheels.
 
I think for learning insert tools should be banned!, HSS cobalt etc only and learn to grind, slight rad on the tip
You learn more I think about front side and top rake, speed feed lube etc, besides most small lathes don’t really have the power or rigidity to benifit a lot.
Good luck
Mark
For mild steel and aluminum one-ups and few-ups one can learn much by using and sharpening HSS.
Many problem jobs are best run with the correct rake angles, clearance angles, radius size and what angle of the tool leads into the feed. One can learn and experiment using hand sharpened HSS bits.
Don't get me wrong, I am not against carbide.
I used to be the specials grinder hand, one up and few ups lathe bits and inserts were priced like gold.

One old school thought war. If the cutting tool dulls or chips, or if the part work hardens and so swings the tool holder, will it cut deeper and scrap the part, or cut less and so save the part.
Considering that the part is more valuable than the cutting tool this can be important.
Your photo #1 made me think about that.

*Yes, If the flange is to be round, not hacking the corners is an accident waiting to happen

*Yes, If thr flange is to be round, not hacking the corners is an accident waiting to happen.
 
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That finish is terrible. Is your insert even sharp? It should shave your fingernail.

The face and turning photo suggest the insert is dull or the part or tool is not solid.
Has this lathe ever cut a decent finish?
Is the material able to cut with a file?
Is the part bouncing about by the way it is held?
Can the lathe spindle pry test to less than .003?
Is the tool holder loose, or far extended left on the saddle?

Sharp Test: Take a sharp knife and set the blade on your thumb nail, then try to slide it sideways. 1. if it slides easy the knife if dull 2. if it seems to stick in place it is sharp
That is a simple test for a lathe insert or tool bit for mild steel and aluminum.
 
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Oh another thing.. Is that tool hold down method clean and solid or tipping the tool holder to an tilt angle, Off being solid? If so that could be the something loose..

QT (if the speed is too low with a honed insert)...and a honed insert is not proper for steel.
 
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Oh another thing.. Is that tool hold down method tipping the tool holder to an tilt angle, If so that could be the something loose.

QT (if the speed is too low with a honed insert)...and a honed o=insert is not proper for steel.

Not with that light of a cut, anyway. It will still work but the speed needs to go way, WAY up.
 
I think for learning insert tools should be banned!, HSS cobalt etc only and learn to grind, slight rad on the tip
You learn more I think about front side and top rake, speed feed lube etc, besides most small lathes don’t really have the power or rigidity to benifit a lot.
Good luck
Mark
I once did a test on a large lathe that was equipped with an ammeter. One tool - a throw away tip that was recommended for steel, the other tool - a brazed carbide tool hand ground for steel. The component was a long steel rotor casting, same speed and feed rate.
The throw away tip pulled twice the amps that the brazed tip did

Regards Tyrone.
 
Thanks for all of the replies! I tried a faster speed - now 840. Much better finish. Also tried varying depth of cut. Now I can see the chips getting hot.

I do not know if this insert is carbide or ceramic. I am using what is currently available at work. The material is unknown. It is an old fixture out of the scrap bin. But if I had to guess, I would say it is probably 1018.

How do you determine the best speed for this insert? Do the manufacturers have a table of speeds/feeds? Or a formula?
 








 
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