1340gt surface finish problem

Have you tried different materials? How about a different diameter?

Is your tool post tight to the compound? Your toolholder tight? what about tightening the lock on the compound. That should be snug anytime you don't use the compound.
 
The spirals on your stock are classic resonance marks. The stock is vibrating at a set frequency and the tool is alternatively cutting deeper then shallower as the cutting tool moves down the stock.

Try a larger diameter piece of stock, say 1.5''OD bar, and start turning no more than 3 diameters from the chuck. If it gives a smooth cut surface then the lathe is probably fine just too much overhang for the stock diameter. If the cut is still rough then you have a lose tool/tool holder or something is out on the lathe.

Is this a new problem or did it just start?
 
A good place to start is holding the compound and trying to twist it from side to side, back and forth and try rocking it. You might find a loose gib this way. It could be on the compound, the cross slide or the saddle. If you feel or hear any clicking you have likely found the culprit.
 
I had the same problem with my PM1440E-LB. I tried every combination of material, tools, speeds and feeds and nothing helped. I did some searching and found the following post by Forrest Addy.

http://www.practicalmachinist.com/v...ase-motors-their-effect-lathe-finishes-73684/

To try to prove the single phase motor was my problem I did the following 2 experiments
1. I cut a short distance to establish the pattern and turned off the motor leaving the feed engaged. I then hand turned the chuck and I got a good finish with no pattern.
2. I made an adapter that fit inside the motor pulley that I could chuck up in my 1/2 inch drill. (My pulley extended about a half inch beyond the motor shaft.) I again ran the lathe to get a pattern and turned off the motor and spun the lathe with my drill. Again a good finish with no pattern at all.

I bought a new Baldor single phase motor and installed it with rubber vibration mounts and have had no problems since.

This was the finish I was getting before the motor swap
2016-01-08 BadSpellar.jpg
 
rherrell said:
That makes perfect sense, the problem is WHAT is loose!:) I've checked the motor and the external gears, the only thing left is to tear it apart. I shouldn't have to do that on a machine that's only 3 months old!
Click to expand...
The lathe should still be under warranty if it is only 3 months old. Matt, the owner of Quality Machine Tools, is posting in this thread. Contact Matt off group and get some help from the source until the lathe works to your satisfaction. From the posts I see here on H-M, Matt appears to be a good seller who helps his customers after the sale. We here on H-M are of course willing to help you as well.

Try looking at the drive and driven pulleys and the belt(s) while the machine is running, and while the machine is feeding and look for runout or other issues in the pulleys and for other than smooth running of the belt(s). A pulley may also be loose on it's shaft. Something loose between bed and tool could also be the problem, as posted multiple times already to this thread.

You did not state if your issue has been happening since new, or if it has started after you used the lathe for a while. If it is something new, think about anything you had changed around the time it started happening.
 
WOO HOO!!!! THANK YOU BADSPELLAR!! I did as you suggested, turned a little with the power feed and then shut it off and continued by spinning the pulley with a drill motor, here's the result...

005.JPG


On the left is with the motor engaged and on the right is the lathe being turned with a drill motor.

Man, what a load off, I know I just created another EXPENSIVE problem but at least I know WHAT the problem is.

I guess the next step is another single phase motor, if that doesn't work then maybe a 3 phase motor and a VFD, if anyone has a cheaper option I'm all ears!
 
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If you read the attached link he included, there are alternatives to replacing the motor. I would inspect the current motor, mount, pulleys, and belt for tightness, condition, alignment and adjustment. A new link belt may solve your issue.
 
A bit surprising, although I have seen a number of posts with a similar finish issue with the single phase G4003G, just haven't heard of it with the 1340GT. In addition to belt/pulley issues, I am wondering if there is a problem with the motor run capacitor if this would cause a problem? You could do a 3 phase motor with an RPC, cost wise it would be similar to a VFD with a single relay setup. The latter requires rewiring the control system. There are a number of different options.

If going to a 3 phase motor, there are a very limited number of 2Hp 3 phase motors that will fit, and they all require some redrilling of the mounting holes motor/mount to fit and a different pulley (or bore the stock one to 7/8"). These motors are all TENV, these are ones that others have used Marathon E467, Y551, Y526. The Y551 and Y526 have a small encoder shaft on the back of the motor that needs to be cut off. The motors come up on eBay occasionally, and I have seen the Y551 (145THTN6046) new, go for as little as $100 plus shipping,
https://www.mrosupply.com/ac-motors/severe-duty-motors/2270020_e467_marathon-electric/
https://www.mrosupply.com/ac-motors/inverter-vector-motors/2270267_y551_marathon-electric/
 
I have a link belt installed right now, I bought several different kinds of belts while trying to fix the problem. All the motor mounts are tight and lined up correctly, the motor sounds and looks fine while running without a belt. Even with the belts on it all sounds and looks fine, no excessive vibration or anything that looks out of place.
If I can find some rubber washers I might try that but it's still under warranty so I think I'll ask Matt what he wants to do.
 
mksj said:
A bit surprising, although I have seen a number of posts with a similar finish issue with the single phase G4003G, just haven't heard of it with the 1340GT. In addition to belt/pulley issues, I am wondering if there is a problem with the motor run capacitor if this would cause a problem? You could do a 3 phase motor with an RPC, cost wise it would be similar to a VFD with a single relay setup. The latter requires rewiring the control system. There are a number of different options.

If going to a 3 phase motor, there are a very limited number of 2Hp 3 phase motors that will fit, and they all require some redrilling of the mounting holes motor/mount to fit and a different pulley (or bore the stock one to 7/8"). These motors are all TENV, these are ones that others have used Marathon E467, Y551, Y526. The Y551 and Y526 have a small encoder shaft on the back of the motor that needs to be cut off. The motors come up on eBay occasionally, and I have seen the Y551 (145THTN6046) new, go for as little as $100 plus shipping,
https://www.mrosupply.com/ac-motors/severe-duty-motors/2270020_e467_marathon-electric/
https://www.mrosupply.com/ac-motors/inverter-vector-motors/2270267_y551_marathon-electric/
Click to expand...
Do you think I ought to try another single phase motor first? It's still under warranty so Matt would probably send me one.
 
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