NTX2000 accuracy issues

[Bob W.]

We are having some issues with our DMG-Mori NTX2000 and I would like to get some input from those with more experience with these, since I am new to turning.  If we run the machine easy during the day and set a tool at 5:00pm before shutting the machine down, then come in and set the same tool first thing in the morning we see an offset change in X and Z by 0.002" and 0.001" respectively.  This machine has a coolant chiller and glass scales on the XYZ axis of BOTH upper and lower turrets.  We have begun investigating this but I was curious what others have seen.

I should also add that the shop is temperature controlled to +/- 2 degrees.  The times I have checked the temp at 5:00pm and 8:00 am there has been zero change from 72 degrees.

[JParis]

Bob,

I can't speak to that particular machine, only my experience with late model Mori's...

We had NV5000's that would grow on the Y axis by similar amounts as the machine warmed up during the day....I wound up writing a macro that would run for several minutes before going into production or after a break longer than 30 minutes...thermal variance can be a PITA..

[Colin Gilchrist]

I can't speak to the Mori equipment Bob, but I always run at least a 20 minute warm-up cycle in the mornings, for a machine that has been sitting more than a few hours.

I recommend getting a machine power timer if possible. On most machines, you can set the timer to turn on the machine, and then run a warm-up program. That way your machine is warm when you walk in the door, instead of you having to warm-up the machine manually. Personally, I like to stroke the machine's axes, and also warm-up the spindle at the same time. Some machines will not allow you to move the axes before warming up the spindle. Other machines have a limit where if you command a "high-rpm", the machine will pause while the spindle speed ramps up. I'm not sure what options your Mori has available, but once the machine has fully warmed-up, I would expect those tool measurements to be more like +-0.0002, and actually closer to nominal, from when you measured the tool the night before (after running all the previous day).

It is great that you already have good climate control for the shop. That is always a primary concern I have when talking with a customer about ordering a new machine. As you can see though; you will still need to get the machine up to operating temperature, in order to maintain that part-to-part accuracy, when allowing the machine to thermally cycle during the night when it isn't running.

I believe that most of the growth you're seeing is on the Spindle, but you'll still likely be getting some from the other linear/rotary axes as well.

[YoDoug®]

What is the material? Even the best thermal comp machines don't account for coolant temp and material temp. I have seen aluminum parts change size and go out of tolerance from adding coolant to the machine. 

[Colin Gilchrist]

17 hours ago, YoDoug® said:

What is the material? Even the best thermal comp machines don't account for coolant temp and material temp. I have seen aluminum parts change size and go out of tolerance from adding coolant to the machine. 

Hi Doug,

I think Bob is talking about performing a Tool Measurement (Setting a Tool Offset Value) on the machine. (Tool Probing)

I could be mistaken though, but it sounds like Bob is setting a Tool Offset at the end of the shift, and then in the morning when the machine is cold, he is running the Tool Offset Measurement Macro again, and is getting 0.001-0.002 differences in the measured offset values.

[Newbeeee™]

Bob

How big is your coolant tank?

IME it's the coolant that is predominantly the problem maker.

[CADCAM3D5AXIS]

Hi Bob

just to chime in , in the past with out coolant heater and chillers  whatever is causing the grief at least part of it as in the coolant and anything else about the Temps even a few deg of change will have you chasing   ghosts. so taking these into account and eliminate them one by one  and document the time of day and night  for weather changes and set the devices you want to control to keep things were you want them . also when not running the machines that are holding close tolerances  we would run a warmup cycle the whole time that they  are not making parts  just to keep everything nice and  warm so they do not change. we would run the machine full range of motion and cycle the spindle rpm up and down also . This way its ready to go when you start making parts  and you have it all warm and ready.  As said above it sucks when they are not running how you left them . But it all helps if things are moving  and they are ready to go.

HTH