Another Haas issue - maybe...

[Bob W.]

Well, I was making some round parts on the new machine (vf2-ss) and they were coming out a little obround (.001" wider in Y than X). The part is 1.25" in diameter and I was cutting with a .38" MA Ford end mill @12k RPM and 150 IPM with a .05" depth cut and a .003" multipass finishing cut. Is it unreasonable to expect better accuracy at those feeds?

 

Anyways, I got the indicator out and measured the table's reaction to jogging back and forth at .0001" increments. The X axis was fine with what appears to be .0002" backlash but the Y axis was doing funny things. When I reversed the direction of the jog wheel the table would jump back .0005" with a bit of a clunk, though not very loud. I ran the same tests on the Mini Mill and both axes were the same as the VF2's X axis, tight and predictable. Any ideas?

 

I'm not an expert at this stuff and I'm asking so I don't just accept this machine as is when I maybe shouldn't be. Any thoughts? Are my expectations too high or is my technique flawed?

 

My whole purpose in getting this machine was to run parts faster. My Mini Mill would produce great parts all day long, though only as fast as the 6k spindle would let me feed. It is kind of a waste to have a 12k spindle if there is no accuracy at the higher feeds.

 

Thanks,

Bob

[Guest]

EVen on our Mori Seiki's which are by far a better machine that the HAAS, hold dead round at those feeds is a tall order.

 

The larger the circumference of the part the less noticable it is, however smaller diameter the variance in t he ball screws keep up becomes very apparent.

 

If you play around with slowing your feed rate a bit down some you will find a spot where all is well.

 

I find the higher RPM machines are really geared towards stock removal, holding tight/fine finishes still requires some "finesse"

[Thee Dragracer1951]

True that!

Going 150 ipm around a 1.25 dia is WAY fast. You can rough it that fast but finishing requires slowing that thing down. My Mini Mill will interpolate a dia within tenths is I program the finish at a proper feed rate. So wil my 2412 Sharp. I just sent some work to a friends shop where he has a Fadal and had trouble holding roundness on a .160 boss. He "knew" he had a little backlash issue. Slowed it down and the problem went away.

I thought very seriously about a VF2ss when I bought my latest mill, what I found was that in order to get those high feeds, Haas increased the pitch of the ball screws without upgrading the encoders. There have been many comments made about Haas's SS line of machines inregards to accuracy. I don't own one so I can't say that for certain, but that is what I have been led to believe

[Lee.]

Bob,

 

I would suggest doing some repeatability tests on your Y axis.

 

Set up your dial indicator and then jog away say 5 inches and then back again to Zero, and then check your indicator.

 

HTH.

[Brad MacKinnon]

I have a Haas VF-OE (7500 MAX RPM) and I had similar problems as you Bullet Bob. I found when using a 2 flute 1/2" Sowa EM interpolating a 2" OD (Alum) I achived the tolerance I wanted with 6200 RPM and 34 IPM. This is with leaving .030" for finishing a 3/4" wall.

 

Like John said you will have to find out at what feedrate your machine runs out. I found when re-running the tool on a finished OD anything over 35 IPM would produce a chip.

 

Now this maybe close to what you come up with but every machine is differnt.

[Bob W.]

Thanks for the replies. Glad to hear it is not the machine :-) I will make sure I leave a healthy amount of stock for finishing and I will slow the finishing cuts down considerably.

[Chris Rizzo]

quote:

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in order to get those high feeds, Haas increased the pitch of the ball screws without upgrading the encoders. There have been many comments made about Haas's SS line of machines inregards to accuracy.

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it IS the machine. call vince selway and tell them to take that g*ddam boat anchor back. they took our ss machine back for that very reason. coarser ballscrews + same encoders = a POS. sorry to say. you could bang your head on the wall for a long time with all sorts of parameter adjustment, but fact of the matter is it's the hardware. selway even sent a full set of regular pitch ballscrews to us...that was their attempted remedy (needless to say, I said, "if you want to switch the ballscrews, take the machine and do it in you own dam shop")

 

there are usually HUGE (.00085+) bumps at the quadrants of a interpolated circle on an ss . we interp alot of 1 to 2 " circles.

[htm01]

we went through this with Haas and did many test cuts on the SS,it stops following after about 40 IPM. we ended up trading it in for a moldmaker that has a 6mm pitch ballscrew ,the SS has a 12