VF-2 Z-axis flex

friesen · Nov 30, 2016

If I put a dial indicator against the bottom of the Z and push up and down, 25 lb force flexes about .0005 up or down. I can indicate some movement between the rail and the truck, but is some flex par for the course?

http://www.practicalmachinist.com/vb/haas/chatter-when-interpolating-inside-circle-96-vf2-237388/

Note how the new haas trucks have less preload, it worries me that I'll go to the trouble to change these out, and have the same problem. Can anyone try this on known good stuff or give some advice here?

Its a 1996 haas vf-2, pretty sure there are some crashes in its history before I got it. X rail has a .0015 movement too.

geoffw · Nov 30, 2016

Sounds about normal to me!

All of our machines are the same way.

X rail is a bit excessive. Any more than .001" deflection is a sign of wear.

-Geoff

friesen · Dec 1, 2016

Hmph. Well, I ordered some different balls from bal-tec, I am going to try re loading slightly larger balls in the trucks.

Speedie · Dec 1, 2016

friesen said:
Hmph. Well, I ordered some different balls from bal-tec, I am going to try re loading slightly larger balls in the trucks.

Seriously! That would be something to watch. Just getting those trucks out from the big casting would be a pain. Good luck and please post up when you have completed the mission....or if you fail.

friesen · Dec 1, 2016

Unbolt and slide them up or down. It easier than changing the rail, probably takes 20 minutes to get off.

friesen · Dec 6, 2016

The old star X rail bearings were .24995, so I upsized to .25015, the Z were .25015, upsized to .25040. The old rails didn't have much preload, it tightened them up about right. I'll have to see what happens after running a while.

The Z still flexes, perhaps not as bad. I think perhaps that 35mm rails are a bit small for this application or something?

I made rail slide on/off helpers out of balsa wood.

Not sure if my measurement is wrong or not, but both sizes measured smaller than baltec specs. The .25028 measured at .25015, the .25048 measured at .25040 according to my mitutoyo mic.

charlie gary · Dec 6, 2016

When you're applying pressure to flex the Z axis, are you leaning on the sheet metal in the front of the machine? If so try just putting an indicator in the spindle, bringing it down to read zero on the table or vise or anything attached to the table, and then press down on the sheet metal in the door opening. You may find some of your flex has nothing to do with pushing up on the Z.

friesen · Dec 7, 2016

The two methods I have used are a haimer 3d to vise, dial indicator from bed to casting.

Think about it, X and Y have about 1/4 the type of load of the Z. The Z has 20" of leverage, with a good portion of the truck preload loaded with Z weight.

charlie gary · Dec 7, 2016

All that is true about the Z vs. X and Y. I just wanted to point out you might see indicator movement just by leaning on the sheet metal enclosure. I don't know if it will happen with your VF-2, but it will happen with the VF-2 in our shop.

geoffw · Dec 10, 2016

Flex is typical on any Haas machine, even brand new... they this is the reason finish passes are light and usually much slower than roughing passes.

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VF-2 Z-axis flex

friesen

Cast Iron

geoffw

Aluminum

friesen

Cast Iron

Speedie

Stainless

friesen

Cast Iron

friesen

Cast Iron

charlie gary

Stainless

friesen

Cast Iron

charlie gary

Stainless

geoffw

Aluminum

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