How do I know SB9 Lathe I just bought is a good one?

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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Carlos
Posts: 28
Joined: Sun Nov 03, 2019 9:53 am

How do I know SB9 Lathe I just bought is a good one?

Post by Carlos »

Hi all
I just bought a SB9 A. And would like to know if there is any good way to know in which condition the machine is.

What are wear points to check? And how do I know they good or bad condition?

How do I know the ways are ok?

Regards
Karl
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Harold_V
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Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: How do I know SB9 Lathe I just bought is a good one?

Post by Harold_V »

How the lathe performs routine machining operations will speak volumes about its condition. It's difficult to do precision work on a clapped out machine. It is also difficult to do precision work if you lack experience, at which time you achieve success more by happenstance than intention.

A few simple things you can do to determine wear in a machine is to look at the way surfaces. Are they pristine, or do they show signs of rounding and damage, often caused by being struck. Do you find horizontal streaks? Rounding of what should be crisp edges?

The area near the spindle is often a good place to start. Compare the general condition of the ways against the same surfaces at the tailstock end of the machine. They should have the same general profile at each position. If they don't display dents and other flaws, pretty good chance the machine has little wear.

A badly worn machine will often display so much wear that it is obvious by eye. Place a straight edge on the way surfaces. Any light showing under the straight edge, assuming it is properly applied, is a sure sign the machine is worn. It should make absolute contact along its entire length if the ways are pristine.

Backlash in screws is a good indicator of wear, but doesn't necessarily equate to a bad condition unless it is not uniform. If you find that the screw/nut assembly has more backlash in the center than it does at the ends, that's a good sign the machine is well worn. Same thing goes for the slides. If you can't adjust the gibs of the machine such that it isn't tight on the ends of travel, but is loose in the center, that's a sure sign the machine is worn.

When turning without a center, assuming the machine has been properly leveled (to ensure that the bed is not twisted), you should be able to make a straight cut on a piece of material that is projected no more than three times its diameter in length. However, several things can cause that to fail, including a poorly ground or dull cutter. Loose bearings (improperly adjusted, or well worn solid bearings) can also cause that condition, as can a badly sprung chuck, which often permits material to oscillate, creating three sided turns.

Experience on the machine will be very revealing. If you lack experience, it may be difficult for you to determine the condition of the machine. That's often due to one's inability to discern why there's a problem. Is it the machine, or your lack of experience?

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Andy R
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Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

How to keep your SB9 Lathe in trim

Post by Andy R »

In addition to what Harold wrote, you might try to get a copy of "KEEP YOUR LATHE IN TRIM" by South Bend Lathe Works.
It was their Bulletin H-4 and was reprinted by Lindsay Publications Inc., in 1994.
Carlos
Posts: 28
Joined: Sun Nov 03, 2019 9:53 am

Re: How do I know SB9 Lathe I just bought is a good one?

Post by Carlos »

Good info, thanks a lot to you both.
pete
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Joined: Tue Feb 10, 2009 6:04 am

Re: How do I know SB9 Lathe I just bought is a good one?

Post by pete »

Do an online search for a pdf of the Dr. Georg Schlesinger book Testing Machine Tools. Read through that enough times until you fully understand what's being tested and why. The maximum allowed deviation numbers within that book would be for high quality new or fully rebuilt industrial level machines, so a worn light duty lathe in a home shop will obviously be different. But what is important is it will teach you the importance of the various lathe parts and just how interrelated they are to a finish machined parts accuracy . The subject is a whole lot more complex than most with a home shop seem to think. In my opinion the better you understand the concepts and test methods then the better you'll be at trying to adjust or compensate for the inaccuracy's your own machine might have. Any alignment checks on your own machine STARTS with the bed in a true non twisted condition bolted down on the most rigid surface you can manage. Without having that any other testing is just about pointless. But as Harold mentioned measuring machined parts and what the lathe is currently producing can indicate where there's issues that need addressing. Figuring out what might be causing and then possibly correcting those inaccuracy's is the tough part and that's where the information in Schlesinger's book is invaluable.
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