'92 VF-0 Tool Clamping Problem

Mike K · Jul 14, 2010

Our VF-0 has been very slow on the unclamp/reclamp process during tool changes for a while. Now it sometimes won't even finish clamping. The big piston comes up about 3/4 of the way and just stops. If I disconnect the small line (I think it is an oil mist line to lube the piston) on the right side the piston will come all the way up.

The system consists of a solenoid valve, shuttle valve and some mystery valve I don't understand that hooks to the above mentioned oil mist line. We changed the shuttle valve, solenoid valve and also dismantled the piston for cleaning. I took apart the mystery valve and didn't see any gross problem but I wasn't sure what to look for.

Any thoughts?

Walt @ SGS Inc. · Jul 14, 2010

'92 VF 0 Tool Clamping Problem

Mike,
When the cyclinder is moving up to allow the drawbar to clamp, can you reach into the plunger area of the cylinder and pry up on the plunger. What I am trying to determine if the cylinder is hanginup or is it the drawbar itself.
Seems like I remember the cylinder forcing the draw bar down and the beleville springs pushing the cylinder back up and then a small spring in the cylinder raising the cylinder plunger up further for clearance on the end of the drawbar.

Maybe you have some broken beleville springs. Have you checked tool retention since this problem started?
Another area of possible problems might be the drawbar itself. Broken springs and or grooves worn in the drawbar causing it to bind on the springs.

I can't remember, is that air unclamp or hydraulic? Never the less, check your pressure gages and look for a plugged filter.
Regards Walt...

landm1 · Jul 14, 2010

Piston

Hello,

Try removing the brass muffler on the Mac valve above the spindle. Those can get clogged up and not allow the air out of the piston. If that dose not help I think I have rebuilt the Mac valve before using good o-ring greese. A new Mac valve setup is not too expensive either.
There is no oil/air mix going into the piston, more than likely you are looking at the "pre-charge" system which uses low air pressure to engage the piston on the draw bar.
The steup is actually pretty cool for what you paid for.

Good Luck!

LandM1

The Energy Rebel · Jul 14, 2010

We've got a VF-0 at the shop, a little newer (1999?)
Most of the Haas mills have a separate regulator for the tool clamp. It's usually about 6 pounds, I think.
Ours is located at the back of the machine,behind the other regulator and the sheet metal support.
On some of the other larger ones, it's on top of the spindle and they don't always have a regulator with a dial that you can read, but you can adjust them by "feel".
Try seeing if you can find this and turn up the air a little, that may do the trick.

Walt @ SGS Inc. · Jul 15, 2010

Tool Clamping Problem

Me thinks turning up the air a little may help unclamping the tool however, this would not help with the tool clamping.
Me thinks the belleville springs do the clamping and the only thing the unclamp cylinder has to do is get out of the way.
The mufffler being plugged up might be the answer or a pinched or kinked line in the area of the exhaust.
Of course, that don't splain the slow unclamping of the tool holder.

Anybody know what maybe water in the line or cylinder would act like?
Regards Walt

Mike K · Jul 15, 2010

The problem seems to be in the precharge (thanks to landm1 for identifying that) system. During a tool change, the first thing that happens is precharge pressure goes to about 14 psi to gently move the piston against the drawbar. Then the solenoid valve opens and high pressure air releases the tool.

The problem is that the precharge usually stays on. The belleville stack has enough force to overcome it, but the small spring that takes care of the rest of the piston return doesn't. This prevents the limit switch from telling the control that the tool is clamped and it all hangs up.

Does anyone know what tells the precharge to turn off?

landm1 · Jul 15, 2010

Precharge system!

Hello,

Going by memory, I think the precharge system comes off the Mac valve behind the sheetmetal stantion. I think it then runs through the valve with a knob on it right by where the spindle fan plugs in. If I remember correctly, the valve with knob on it might control the flow to the precharge system.

By the way, did you pull the plunger setup off the top of the spindle to check for physical obstructions. You can also take the plunger assymbly appart or you can get a new one from Haas for about $400.
But I will say we have a machine that changed tools much slower than our other machines, it did turn out to be a pluged muffler on the Mac valve, that went on for years, I wounder how much money that cost me?

Good Luck!

LandM1

Mike K · Jul 21, 2010

It's running again! It was exactly as you described, landm1. I replaced all 3 of the small mac valves (one was labeled "precharge") and all is well again. Much faster tool changes and it just plain sounds right again.

Thanks for the help!

haastec · Jul 23, 2010

Glad you are back up and running.

I just wanted to clarify a couple of thing. The precharge pressure should only be at about 5-6 psi. This is adjusted by the valve behind the spindle motor near the fan plug as previously mentioned. To much psi and you can have a premature tool release. (hate it when that happens

)

Next, the small regulator that is behind the lube panel which I beleve Energy Rebel was referring to is for the spindle air/oil mix for the bearings. This should be set to 17 psi.

Mike K · Aug 4, 2010

We certainly have a lot more pressure than 5 - 6 psi. No premature tool ejaculation though.

You describe a valve that adjusts the precharge pressure. Do you mean a regulator?

haastec · Aug 9, 2010

Yes, you are correct; it is a regulator that is behind the spindle motor. Good catch.

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'92 VF-0 Tool Clamping Problem

Mike K

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landm1

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The Energy Rebel

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Walt @ SGS Inc.

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Mike K

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landm1

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Mike K

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haastec

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Mike K

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