ML15 x axis problems

[Hickory]

I have a ML15 lathe made in 2003. The machine was purchased with less than 200 hours on it a couple of years ago, and has mostly sat while making the sometimes painful transition from manual Monarchs to the CNC world.
This machine has, in the past week, reduced me to a point of savage frustration dealing with accuracy in the x axis.
What happens is this: The diameter of the part being turned will randomly vary. It will not be a consistant amount from part to part or from varying diameter steps on the same part. Furthermore, a program can be tuned perfectly one day, and upon startup the next day be way off. We're not talking a few tenths, but .005 to .01. The setups are rock solid, I've been a machinist for 30 years, and the machine, with its low hours, seems tight. Milltronics machines have served me well, have two mills, so I have high hopes for this machine. Any help or advice would be greatly appreciated.

[single phase]

Only thing that I can think of is the timing belt pulley is loose. Or if it is direct drive the coupling is loose. Did you check that?

[Tomorrow_man]

I have a ML15 also.

I agree, something is loose.

How is your toolpost mounted?
I have one that holds 4 BX2s and I manually index the tool.
This was where I was having the same problem you are having.
Everytime I'd index, the toolpost would spin a tiny bit no matter how tight I had the stud.

Our other CNC lathe would spin the post a little whenever a long boring bar was used. We fixed that one by cutting a pocket in the riser block and the toolpost sits in the pocket, no spin.

On the ML15 I'm going to cut a keyway in the riser block to match the key slot on the toolpost. This should fix that problem.


TM

[LYN BYRD]

ARE YOU ROUGHING AND FINISHING WITH THE SAME TOOL? I HAVE HAD THAT PROBLEM BEFORE AND STARTED USING TWO TOOLS AND IT SOLVED IT.

[Hickory]

Thanks for your replies.
It is possible that a pulley may be loose. I'll try to do some dis-assembly this weekend to veryify whether or not this is the case. It would surprise me if this has happened as the machine apparently has seen little use.
The toolpost is an Aloris BXA. I have been in the habit of taking light cuts till I get to know the machine. At the start of this job I indicated in a threading tool parallel to the x axis. I just rechecked this and am confident the toolpost hasn't shifted.
Using a different tool for finishing operations is not something I do often because of outright laziness, but it is worth a shot. However, after the turning operation, there is a threading operation and this tool varies in x location as well.
This lathe has Yaskawa motors and controls. A little surfing has revealed that the encoders use a battery to save information. Could a dying battery cause this sort of thing?
Jim

[jpawelk]

Originally Posted by Hickory Thanks for your replies. It is possible that a pulley may be loose. I'll try to do some dis-assembly this weekend to veryify whether or not this is the case. It would surprise me if this has happened as the machine apparently has seen little use. The toolpost is an Aloris BXA. I have been in the habit of taking light cuts till I get to know the machine. At the start of this job I indicated in a threading tool parallel to the x axis. I just rechecked this and am confident the toolpost hasn't shifted. Using a different tool for finishing operations is not something I do often because of outright laziness, but it is worth a shot. However, after the turning operation, there is a threading operation and this tool varies in x location as well. This lathe has Yaskawa motors and controls. A little surfing has revealed that the encoders use a battery to save information. Could a dying battery cause this sort of thing? Jim

Jim,
Your ML15 lathe has Yaskawa Sigma II motors and drives. These motors that were installled on your machine do not have absolute encoders. (Thus the reason you need to home the machine everytime you power off) There are no batteries within the axis drives and/or motors.
In my experience with mispositioning, it is usually mechanical with the info that you are giving us. The Yaskawa drives would fault out if anything went wrong electrically. Check out the gib on the X axis, as well as the Z axis. 1 gib for the X, 2 for the Z. After checking your gibs, ensure that backlash is checked and adjusted. Then if you still are having issues, then check the belt and pulleys. On the X axis, it is belted 1:1. Good luck.

[Hickory]

I checked the pulleys and belts for looseness and lost motion and everything is tight. A test with a dial indicator showed the machine repeating very well, zeroing to the same spot. What did become apparent though was the axis was only travelling .798 on a .800 jog move. This can add up, I said. After tinkering with the backlash settings the lathe seems much happier. Thanks to all for the help.
Jim