1340gt surface finish problem

I dont see a problem with that stand at all, that looks nice and solid, no problem there. And yes I know that you are getting a good finish with the drill motor, but so was I with that motor on a lathe here.

BUT I did not know that it was on a stud floor like that. I just assumed concrete, never even crossed my mind. I ran in to this same exact problem a few years back (actually 10 years or more probably now) with a customer putting a machine in to a trailer for a mobile shop. He used an aluminum plate to save weight, but other than that, almost the exact same set up. That has to be it, its the same problem that he was having, and we even swapped machines back then because we went through everything and I didn't know much about VFD's back then. I tested the heck out of the replacement lathe before sending it out, sent to him, and same thing. His came back here,I set it up, and and it cut fine. It was the PM-1236. He ended up coming up here and I eventually got him set up with a PM-1127V at the time, and it worked just fine in a trailer. Its a variable speed DC motor on that one. That has to be it, and I bet that VFD will be a big help though. That just has to be it, its the same thing. I didn't even think to ask that, looked like a concrete garage floor to me.
 
Is it possible to wheel the lathe out to a concrete floor just to test? (If its not on the same level to just wheel it out then dont do it, but if it is easy, give that a shot)
 
are the gibbs on you cross-slide and compound tight?
 
Place a glass of water on the floor and run the lathe. Any vibrations will be seen on the water surface. Any vibration shows that the floor is not stiff enough.
Pierre
 
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rherrell said:
Several of the previous photos show two speeds side by side, .0055" and .0027", the .0027" is the slowest feed this machine has. All it does is make the ridges closer together and it also seems to change the angle of them as well. That seems odd to me, why would the angle of the ridges change direction when you change the feed rate???
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This can be understood if we assume a forward-backward vibration of the stock at the tool tip. The slanting direction of the lines depends on the feed speed. If the feed speed is above a certain critical speed that is proportional to D/T, where D is the stock diameter and T is the period of the vibration, the lines slant backward and if the feed speed is below the critical speed they slant forward. The horizontal distance between the lines equals feed speed times the period of the vibration. This gives a rough estimate of the vibration frequency of about 1 Hertz from the pictures of the pattern and feed rate. This frequency is way below the motor frequency of about 30Hz (assuming 1800RPM), so motor cannot be a direct source of the problem, even though it provides energy to the vibration. This suggests converting to VFD may not help, unless it somehow reduces the energy transfer of the motor to the vibration. Harmonics of a few Hertz must be of mechanical origin, so as Matt suggests, putting the machine on a firmer floor may help.
 
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I have a question on the stand, are the uprights connected in the area marked in red? It looks like the frame is a "C" shape with that area an open span.

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The drill motor does not necessarily mean its electrical problem, it could easily be that the drill motor does not deliver near as much torque, hence setting up less vibration. I like Matt's idea, roll that lathe out to some concrete and turn it on. If you are going to be on wood floors I suspect you need a lighter weight table top machine, I believe the 1340 is too heavy to sit on a flimsy floor. Matt listed the variables to check, when they are all checked, moving lathe to solid footing should rule out the last likely source of trouble. Ten thousand small southbend lathes run on single phase motors and cut fine, I seriously doubt a 3 phase set up is going to solve this for you.
 
Doubleeboy said:
I believe the 1340 is too heavy to sit on a flimsy floor.
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I wouldn't say its to heavy, more like to powerful.

My little 8x14's bench migrated back against the wall once, and just the intermittent contact with the timber wall caused harmonics similar(not as severe) to this. I moved the bench back out away from the wall and the problem was solved. Something like the 1340 can probably turn the floor into a sound board.
 
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Not all single phase motors are built the same. When I took the cheap 2 pole single phase motor off my 1414E-LB and replaced it with a quality 4 pole Baldor single phase motor my problems went away. Before the switch I tried everything mentioned in this thread and nothing corrected the problem. Since the motor change nothing I can do will make the pattern return. I can cut any speed, depth or feed rate and do not get the pattern. I'm totally convinced a good quality motor will solve his problem.
 
Badspellar said:
I'm totally convinced a good quality motor will solve his problem.
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They already tested a known good motor, and it had no effect, on the issue. Buying an expensive replacement would be a waste of money.
 
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