Haas st20 y losing alignment

Hi guys

we have a hass st20y which we have had for a couple of years now. Ever since we have had it we have had issues with it losing alignment (around 4-6mnths each time)
haas have been out it every time and to their credit they always re-align it FOC. They have carried out investigations into why this keeps happening and cannot find anything un-towards.
There are no error codes and our operator as far as we know has not had any crashes or collisions.

Has anyone had similar issues? Any advice would be greatly appreciated!

I have seen this happen on other brand name machines. 1) how thick is the concrete floor it's sitting on? 2)Is it sitting on one slab and not two? 3) I have seen moment in ball screw thrust bearing is loose. One time on a machine that had to reset the off-sets every so often we discovered the bearing bracket was suppose to use 3 thrust bearing but this one had 2. Someone must have made it on a Monday when they had a hangover. LOL as far as concrete floor being thin. The dirt under the machine settles. You can discover this by get a shaft of steel about 1 1/2 to 2" dia x 36" long and tap on the floor in several places. The one where it setles will have a hollow sound. If that's the case. put some 8 x 8" x .375 or .5 steel plates under the OEM leveling plates. If this helps, please tell us how you cured it. Oh 1 more thing putsome mag base with indicator on them and home your slides. put mag / indicator against the slide and set at fast feed....move away from indicator say 2" and reverse and see if it comes back to zero on indicator. that should tell you if the ball screw thrust bearings are tight. Just thought of something else. If you can check to see the ball screw nut and housing are tight. Ore put indicators on machine and manually cycle the lube pump and see if the slide moves. Might be a loose gib or hold down. Rich

thanks Rich for your reply.

The concrete floor reinforced but I will give what you've suggested a go cos you never know!

In regards to the bearings they have had the machine apart and replaced various bits numerous times and never found anything. I will get the indicator on there first thing Monday.

Can you elaborate on "losing alignment"?

What specifically is not aligned? What are the symptoms?

The turret is losing alignment. This is then causing issues when using the y axis, for example when drilling pcd holes they are out of concentricity with the centre of the work piece.

Darko84 said:

The turret is losing alignment.

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You need to be a bit more specific before anyone can give informed answers.

The turret is losing alignment to what? Y-centreline? X-centreline? Z parallelism? Turret rotation? X/Y perpendicularity?

Darko84 said:

...for example when drilling pcd holes they are out of concentricity with the centre of the work piece.

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You're drilling a PCD using only X-Y with C in a fixed position?

So you mean Y zero is drifting off of centreline? Or X zero?

From what I can see of your machine from google it's a wedge Y, which adds a layer of complexity to the troubleshooting.