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Old 06-21-2020, 07:49 PM   #1
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metal lathe tooling ?


i need to know what type of inserts to use to get as smooth a finish as reasonably possible. right now i am using pointed bits, no matter what i do i have to sand sand sand to get a finish thats worth polishing. i need an easier way.

thanx
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Old 06-21-2020, 08:15 PM   #2
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Re: metal lathe tooling ?


If this link isn't helpful because you've tried all of these angles, consider ceramic if you haven't. I was taught to leave extra material then use a file before emery tape of various grits.


https://smithy.com/machining-referen...turning/page/1
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Old 06-21-2020, 11:11 PM   #3
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The material you're cutting matters considerably. What are your speeds and feeds?
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Old 06-22-2020, 06:24 AM   #4
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Re: metal lathe tooling ?


I think its probably more your speeds and feeds rather than the insert. Unless your insert is totally out of wack for rake or relief angle or the such, for the material you are cutting. Or maybe if your insert is not on center.

At the very least, you probably need to decrease the feed rate.
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Old 06-22-2020, 07:30 AM   #5
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Re: metal lathe tooling ?


The depth of cut can be critical for finish. Often when attempting a fine finish, a cut too light is taken. The machine being used can play a role with this.


EDIT: EDIT:
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Old 06-22-2020, 07:55 AM   #6
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Re: metal lathe tooling ?


thanks for your replies

right now i am mostly working brass. but the copper, aluminum, bronze and resin(hard plastic), all show the same results.

my speed is fast, idk exactly what it is, 3000rpm perhaps.
feed = by hand. and no matter how slow i go, makes no difference. seems odd, but true.

i am just a humble hobby machinist, so i am not claiming to know a lot. but i honestly thing its the inserts. they are a 3 point and quite pointy.
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Old 06-22-2020, 09:04 AM   #7
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Re: metal lathe tooling ?


Quote:
Originally Posted by Fix'n it View Post
feed = by hand.

There lies about an estimated 95% of the problem. The tool is running in and out.


About the only hope is leave enough ruff material to work with a good selection of files, emery tape grits and down to polishing if necessary with a wide selection of compounds.


EDIT: EDIT:

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Old 06-22-2020, 09:28 AM   #8
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Re: metal lathe tooling ?


Is it one of those small hobby lathes that you have ? I have one of those. While I can't say I have a particular issue with surface finish, the cross-slide is nowhere near stiff enough that I can ever expect professional results. If you have one of those, at least check that the gib screws on the cross-slide are tight enough to remove any play.
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Old 06-22-2020, 09:34 AM   #9
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Re: metal lathe tooling ?


Quote:
Originally Posted by SeniorSitizen View Post
There lies about an estimated 95% of the problem. The tool is running in and out.


the work that i do, idk if i could auto feed. its pretty small pieces that the cut would be over as soon as i start auto feed.

these are what i have. i would like something a little rounded on the end.
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Old 06-22-2020, 09:47 AM   #10
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Re: metal lathe tooling ?


Quote:
Originally Posted by SPS-1 View Post
Is it one of those small hobby lathes that you have ? I have one of those. While I can't say I have a particular issue with surface finish, the cross-slide is nowhere near stiff enough that I can ever expect professional results. If you have one of those, at least check that the gib screws on the cross-slide are tight enough to remove any play.
yes. i have this pos, smithy cb1220 xl. i have had it over 25 years. and have work "on it" almost as much as using it. a lot of the work i did on it was deburing so i could tighten up the tolerances. so yes, the gibs are pretty tight and i keep it well lubed.

web pic
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Old 06-22-2020, 09:56 AM   #11
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Re: metal lathe tooling ?


Quote:
Originally Posted by SPS-1 View Post
Is it one of those small hobby lathes that you have ? I have one of those. While I can't say I have a particular issue with surface finish, the cross-slide is nowhere near stiff enough that I can ever expect professional results. If you have one of those, at least check that the gib screws on the cross-slide are tight enough to remove any play.
i'm not expecting professional results. but a finish that i could start using 1500gt on, in stead of 400.
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Old 06-22-2020, 11:37 AM   #12
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Re: metal lathe tooling ?


Looks more rigid than my cheap thing. Mine likes aluminum a lot more than steel. I use mostly brazed carbide tool bits. Hand feed like you.

But still, I did manage to make this ball trapped in a cube:
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Old 06-22-2020, 01:07 PM   #13
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Quote:
Originally Posted by Fix'n it View Post
thanks for your replies [IMG class=inlineimg]https://www.diychatroom.com/images/smilies/smile.png[/IMG]

right now i am mostly working brass. but the copper, aluminum, bronze and resin(hard plastic), all show the same results.

my speed is fast, idk exactly what it is, 3000rpm perhaps.
feed = by hand. and no matter how slow i go, makes no difference. seems odd, but true.

i am just a humble hobby machinist, so i am not claiming to know a lot. but i honestly thing its the inserts. they are a 3 point and quite pointy.
You should read up a bit on machining basics. It will help you out long term.

"Fast" doesn't equate to smooth. The speed the work needs to move at depends entirely on the feed rate and depth of cut, and to some degree the cutter. Finish requirements will determine your speed and feed rates, so find a chart with your material and the desired finish for guidelines.

Your cutter is probably fine, assuming it's not broken. You might need to slow your speed down and increase your feed rate. Keep in mind that it's very difficult to get a nice, smooth finish without some sort of automation. Feeding by hand makes it difficult to achieve. Also consider machine stiffness and how the work is chucked. If you're using a cheap hobby machine it may not be able to achieve smooth finishes due to instability inherent in the machine. Also, if too much work is exposed and not supported, the material can flex while being cut, leading to chattering and an undesirable finish.
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Old 06-23-2020, 08:53 AM   #14
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Re: metal lathe tooling ?


Quote:
Originally Posted by SPS-1 View Post
Looks more rigid than my cheap thing. Mine likes aluminum a lot more than steel. I use mostly brazed carbide tool bits. Hand feed like you.

But still, I did manage to make this ball trapped in a cube:
how is that made ?
lets see your machine.
i have some brazed, but they are dull, thats why i switched to inserts.
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Old 06-23-2020, 08:59 AM   #15
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Re: metal lathe tooling ?


Quote:
Originally Posted by Joeywhat View Post
You should read up a bit on machining basics. It will help you out long term.

"Fast" doesn't equate to smooth. The speed the work needs to move at depends entirely on the feed rate and depth of cut, and to some degree the cutter. Finish requirements will determine your speed and feed rates, so find a chart with your material and the desired finish for guidelines.

Your cutter is probably fine, assuming it's not broken. You might need to slow your speed down and increase your feed rate. Keep in mind that it's very difficult to get a nice, smooth finish without some sort of automation. Feeding by hand makes it difficult to achieve. Also consider machine stiffness and how the work is chucked. If you're using a cheap hobby machine it may not be able to achieve smooth finishes due to instability inherent in the machine. Also, if too much work is exposed and not supported, the material can flex while being cut, leading to chattering and an undesirable finish.
i have gotten nice results on this machine. but that was when i was grinding my own tool steels. now i would rather just switch out inserts, the problem is finding what i need. and they are out there, but if i don't know exactly what i am looking for, it doesn't show up in search results.
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