lathe thermal compensation

[Sbarner]

Greetings all,

 

I was looking for some guidance about thermal compensation in the lathe. We have a Haas SL-20, that appears to change size as it warms up. This is extremely frustrating when trying to hold a .0005" tolerance. There are some settings to adjust the amount of compensation and the time that it takes effect, but I don't know where to begin. I guess I was looking to see what you guys do...if anything.

 

Do you have a program that runs the Z and X back and forth to warm up the screws? Do you have anything set in the thermal comp settings to begin with? Is it as simple as measuring a part, then running the machine for an hour and measure again to note the difference? I'd love to hear anyone's thoughts on this. Thanks.

[Dave.L]

Steve,

 

We have the same issue with our Mazak lathe and I think Mazak's are know for this. Once the machine is warm, it is consistent all day.

 

For this reason, we run the machine thru lunch just to keep it warm.

 

On the other hand, our Mori can sit for a week and the first part will measure within .0001 of the last part.

 

Two very different machines and a cost difference of about $145K.

[Sbarner]

Do you do anything at startup then, Dave? Or do you just know from experience that the machine is going to be off and adjust your comp then?

[Dave.L]

Steve,

 

In most cases the parts we are running that are that tight are bar fed parts. We do a combination of things:

 

1)Run with no bar to simulate and that is our warm up.

 

2) Run and watch close for a while till she settles, this method however generates scrap.

 

If you are trying to do a low quantity job and cannot afford the scrap, I would suggest a warm up program and you will need to test your machine to see how long to run it. My guess would be at least 15-20 minutes.

[Philcott]

We run a warm up program that moves the X and Z axis while cycling through some rpm changes. We still need to adjust the offset for tight sizes when running the first parts of the day. You get to know each machine and how much to adjust it. It is only about .0002 in dia. so most jobs it's not much of an issue for. Then just make offset changes when needed.

 

We also just spin the spindle on tight jobs at breaks.

[YoDoug®]

We went through this on a Haas SL20 at my last job. We would see .003-.004 swing from morning to afternoon in X axis. Always many small adjustments of a few tenths. There is a parameter to compensate.(I don't remember what number but it is easy to find looking throught the parameter pages in the controller for the axis you need) The papers I got from Haas said the parameter is normally between 0 to 1000 from the factory but you may have to set it up to 4000 for .001 to .003 total drift and up to 8000 for .004 or more drift. We ended up going with 8000 and it took care of the problem. It only took 10-20 minutes after that to get the machine warm and holding size.

 

The number (8000 in our case) is a variable in an algorythm that the controller uses to adjust for thermal drift, but there is no real time feedback going on in the machine. it simply follows this warm up algorythm. We were told that shops with big temp swings from summer to winter may need to adjust this parameter seasonally.

[Sbarner]

Where would one get these papers from Haas? Do we contact them directly, or is it something on their website?

[YoDoug®]

We got it from our dealer in Tulsa.