help me choose a good vertical machining center

[Adept]

Hello all
Our shop is looking for a new vertical machining center. The other day, I asked a CNC operator about what he thought we should go for and he suggested a HAAS machine. I haven’t used this machine before so I went forth to research about this machine. I found out that people experienced problems when using this machine including; the machine not able to work for 24 hours a day, a lot of repairs required and the likes. I would like to hear your opinions before I make a decision.

[bluemoon]

Hello OP
Our company is planning to get rid of the last HAAS VMC in two months’ time. Here it is.

Haas.jpg (41.29 KiB) Viewed 1130 times

It don't know where to begin with. I guess my piece of advise will be not to buy something that has been used before - especially a CNC machine. It is a dump for money and time, seriously speaking.

[Adept]

Why? What is the problem?

[bluemoon]

The machine is just trouble by itself since the axis and the spindle is limp therefore you can only use about 2hp when cutting. We started out with fadal and used it for a couple of months. During this time we restructured our HAAS and leased it out for 2 ½ years.
Both machines had their weakness and we purchased a new machine. Upon delivery of the new machine, we tried running a program that was run by Fadal, (which we should not have done because it destroyed some of its tooling and scrapped out some parts). Interestingly, we had to reprogram the machine to run a 1 ¼ inch face mill instead of 2 inch.

Since we couldn’t reuse HAAS anywhere, I built another tool so as to compare the spindle stiffness of several machines. For HAAS VF2 with less than 100 hours of use, I realized that it has a deflection twice that of any other machine when tested with .0005 movements with 50lbs of tangential load in any direction chosen. Therefore, it translates to .001 out of roundness on any circular interpolation and a force more than 2hp or 50lbs when cutting.

[yesman]

Man, what else can I say other than the fact that you are a genius. I had no idea you can built DIY machine to test spindle stiffness. In fact you should be running those big companies. So did you reveal your results to Haas factory?
I have also read some not kind remarks about Haas machines. One of them was that Haas spindles are disposable. I would also like to confirm if this is true.

[bluemoon]

So did you reveal your results to Haas factory?
I have also read some not kind remarks about Haas machines. One of them was that Haas spindles are disposable. I would also like to confirm if this is true.

I’m flattered.
Not exactly, what I actually did is, I took the tool to their plant so as to test other machines to show them how them how inefficient their machine was. Surprisingly, neither the Selway dealer nor the Haas plant showed any interest in fixing the problem but instead they paid for my travelling expenses. So, i finally decided to write off the machine, the manufacturer and the dealer and I will continue avoiding them just in case they come up with other machines.

[yesman]

Wow, no - that was the last thing I expected them to do. Other manufacturer would have just informed you that they have realized the mistake and there is an ongoing team working to correct that. I think a simple apology always works so as not to ruin the reputation of the company.

[cocodancer]

I must admit that was a cool tool you built man. I want to raise my concerns and ask you a few questions about your spindle test. I think you must have limited you radial load to 50lbs and maybe you further compared your results between good and bad machines. I am not trying to rule out your findings but I am just raising my imagined concerns.

[FireCNC]

I know that you can also test the spindle stiffness by applying the load several inches from the face of the spindle. You can also apply the same method to test the tooling and interface stiffness.

So, an overhang built into the spindle which has bearing moved back from the spindle space can clobber the stiffness. You could also consider using tool overhang since it clobbers the stiffness faster.

[Hyatt]

You did an ingenious job there though it looks like your tool might have tested the combined system stiffness of the entire machine other than the spindle stiffness.

I am not saying that testing the system stiffness is not very important. My point is if your tool has a rubber lead screw then there is a higher probability that it add in the deflection. More over a grounded reference to the spindle housing assists in isolating the spindle shaft or bearing stiffness.

I thought that uniform radial or tangential stiffness would result in diameter variation and not out-of-round. I would also expect the bearing radial and the spindle shaft stiffness to be fairly uniform but not the housing, column or table. That stiffness should be hugely different X,Y or Z.