Newbie - Buying first metal lathe

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

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Re: Newbie - Buying first metal lathe

Post by Harold_V » Mon Jul 22, 2019 3:19 pm

Well done. You're wise to take baby steps, as there are some rules of thumb that you most likely don't know yet, and they can keep you from making fatal mistakes.

One thing that you should know right off the top, is the diameter to length ratio when holding an item in a chuck. To prevent the part from climbing the tool, don't attempt to machine a part that extends more than three times its diameter in length. The usual result is a tapered turn and often chatter, but with a limber lathe, the part can deflect enough to climb the tool, which results in less than desirable results.

Do yourself a favor and study tool geometry until you understand its importance, then apply what you learn by grinding your own turning tools. Said another way, don't turn to insert tooling in an effort to avoid the learning curve, as without this knowledge, you'll be held captive by the limited number of insert types and holders you own, plus, without understanding the geometry, you most likely won't be able to resolve issues when a cut isn't performing as you desire.

The Resource Library on this board has some good information on grinding tools and selecting grinding wheels. Using the wrong wheel can be very discouraging. If grinding is a stranger to you, you'll benefit greatly by reading the pertinent threads.

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Re: Newbie - Buying first metal lathe

Post by dbfletcher » Mon Jul 22, 2019 6:02 pm

I do fully intend to grind my own HSS tooling... but i figured insert tooling would take at least one variable out of the equation right from the get go. I've watched enough YouTube on grinding HSS that I think i understand most of the concepts, but I have yet to even attempt it. At least once i get a little familiar with how the lathe operates, I figure i'll better be able to judge how poorly or well my grinding tools perform. Is is common for newbie to post pics of work asking about surface finish, chip formation, chip breaking, etc.. or is that not really encouraged.

I'm very thankful for everyone who has offered their opinions and advice... i just dont want to wear out my welcome too quickly. I will certainly make time to check out the resource library you mentioned in your post.


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Re: Newbie - Buying first metal lathe

Post by mihit » Mon Jul 22, 2019 7:25 pm

I'd warrant that most people are glad to offer help, and if you do ask something that's been well covered, or too basic, you'll get told to RTFM!
Lathes have been around for hundreds of years, going back to treadle lathes driven by a rope wrapped around the spindle and to a sprung tree branch. Tis an ancient art. So you have a bit of learning ahead but once you get the hang of it and can bang out the parts you need you'll be one step closer to zen. :D

I still quite enjoy peeling 10 foot long blue chips on a cut. And while I wouldn't claim that there's nothing left I don't know, I would claim I can get the maximum out of a machine. "Creative fixturing", running tools upside down from the back to cut tapers the machine otherwise cant, so many tricks to learn. But once you get your head in the game and start coming up with your own solutions for things you'll be a better human, and people will come out of the woodwork, to you with their problems. Don't forget to bill them!

Be mindful (as you seem to be) and avoid crashes (I'm sure a small chinese machine will not tolerate them well)

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Re: Newbie - Buying first metal lathe

Post by mihit » Mon Jul 22, 2019 7:30 pm

As to the insert tooling, they like to be run hard and faster than you may be comfortable with, starting out. Some shapes can be fussy with lead/clearance angles.
Very generally i'd say it's easier to get a good finish with HSS.

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Re: Newbie - Buying first metal lathe

Post by BadDog » Mon Jul 22, 2019 8:00 pm

Based on smaller lathe and relatively undeveloped skill level, I agree with generally avoiding carbide tooling, both insert and brazed. For smaller/lighter lathes, unless there is a very good reason (like very rusty/abrasive material without access to something like Tantung or Stellite), carbide anything should be largely avoided.

When I first got started, I bought a small lightweight lathe (Griz 4000). I got it because it was available, cheap, and was capable of making the main items I thought I would want to make. But I struggled, and the easiest path seemed to be pre ground brazed carbide or inserts. And still I struggled, particularly with brazed carbide bits. I generally got where I wanted to be (very low tolerance), but it took forever, and was unpredictable in every way except for consistently horrible finish. As has happened on a variety of subjects, I was called out on it here (by Harold_V in this case) and strongly encouraged to learn to grind HSS.

I was a little reluctant, after all, I didn't buy the darn thing to make bits, I wanted to make parts (spacers and bushings mainly at the time). But given I was getting nowhere fast, I read his extensive posts on the matter, and soon was making much better parts with less drama, even on a lathe that is widely known for being only slightly more rigid than an over cooked Lasagna noodle.

And that success was really the turning point for me where I became completely infatuated with machining for several years. Over that period of time I upgraded lathes a few times, bought mills, a surface grinder, and on and on. It completely changed my shop, and my approach to my primary hobby.

Hmmm. Now I have a whole shop of machine tools to go along with my fabrication tools. On second thought, maybe you shouldn't follow my advice. ;) It gets expensive in terms of both time and money (and space!).
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Re: Newbie - Buying first metal lathe

Post by spro » Mon Jul 22, 2019 8:27 pm

Every gear in the train should lash by pressure angle and the holder tight. New lube is a requirement.
Our mentor Russ has a great reply previous to mine, so I'm saying simple things Don't get cocky or assume anything now. One loose bolt somewhere will change everything. I think that one of the most important attitudes is to look at the center of axis as it relates to the saddle. The cutting tool should not extend too far out from that center of support. There are ways to reduce that by your slides.

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