Fixing my machine - Help me understand

[Robert Davis]

Brown & Sharpe Validator
PC-DMIS 3.5 MR2

One of my air hoses to the Y axis that supplies the air bearings broke. I ended up replacing both hoses as they were getting pretty old and brittle. For those not familiar with my model, there are 2 rails on the right side of the table that hold the bridge between them and the left side of the bridge is free and floats on 2 air bearings.

There are 6 air bearings on the right side of the bridge... 2 against the right rail which is vertical, 2 underneath the right bridge column to raise/float it, and 2 against the left rail, which is angled to capture/hold the bridge down to the table.

I had to take off the angled rail that holds the bridge into the right side rail to change the hoses, as it's underneath the bridge. I indicated the distance and attached stops to the table so I could put it back in the same place when I was done. I put everything back together and all seemed to work fine except now my machine won't stop once it starts moving in Y. Normally if I let go of the joystick, the machine stops. Not abruptly, but it stops pretty quick and smoothly. Now, if I move in the Y axis, the machine maintains the same speed unless I move the joystick in the opposite direction. Then it won't stop in that direction. Unless I press the e-stop, the machine will not stop, no matter how slow/fast it's going in Y.

My questions are these...

What's stops the CMM normally? Is it the pressure against the rail and I have the distance too loose so it won't stop? Or, does something else stop the machine? I tried changing the distance between the rails. Too loose and you can hear the air leak out of the side of the air bearings. Too tight and the machine gets a lag error and trips the breaker because it can't move freely enough between the rails. Or, is this a software thing?

If it's the distance between the rails that stops the machine by creating drag, I guess it's super critical and I need to mess with it. But, the motor keeps on spinning no matter what after it starts moving. If I try and hold the bridge still to create drag as the rails would if they were closer, the Y axis motor keeps spinning. Even if I get it to stop spinning, as soon as I let go of the bridge the motor speeds up even faster to catch up to where it thinks it should be, like a loaded spring.

I'm confused and could use the advice of the resident sages.

Thanks,

Robert

[Tim Hindsman]

You may have to adjust/replace your joystick. Ours did simular to that and all it needed was adjusting. One other time the scale had a hairline crack init and it would not stop until it hit the limits. Hope it is just the joystick in your case.

[Matthew D. Hoedeman]

Dude!!!!!!!! I can't believe you took one of the rails off the machine! I too have a validator and I would not even think of removing one of those. At this point, you are no longer in calibration, not at all! You need to call in someone who does calibrations "old-style" that can get that rail adjusted correctly all along the length of the table. Unless you had a micron indicator zeroed out at EVERY bolt for that rail, you do not have it back where it was. Also, those rails are not 'straight', thus ONE of the reasons for so many bolts in the rail, for adjusting the straightness. Just thinking about it scares the crap out of me. A variation of a couple microns will throw the bridge out of square to the table and at the far end of the bridge, it will mount up. AND, it will not always be in the same direction, it will depend on which way the machine was moving, if it is moving to the back, then the 'free' foot will be towards the front and if moving to the front, it will be to the back, thus giving a DOUBLE amount of error. And, after it gets re-done, the machine will need a new table map as well. Everything, absolutely EVERYTHING will have changed.

This is VERY scary. Your machine now needs a major, complete, 100% physical and electronic calibration.

[craiger_ny]

I can't say WMS enough! And probably WTS too. You need to get a tech in pronto. Consider your machine down because the calibration is gone, no doubt about it, gone! You'll be LUCKY if it is straight. While the tech is there have him/her look at your jog box too. It is likely that what Tim said is the case but may as well make sure as long as someone is there, which you need to do (get someone in there). Both of these guys answered your question but I am replying to get my post count up and especially to emphasize that your machine for all intensive purposes is UNUSABLE at this point until you get someone in there to look at it and square it up/calibrate it.

Craig

[tking]

This is gonna hurt! Pal, your problem with the system moving is electronic / servo related not physical. As for removing the rail, woops, bad choice, to replace air lines? Fess up and get the service rep on site. Your machine is an anchor at this point!

Luck to ya,

TK

[Mr.Natural]

Robert, we have an Excell that needed re-hosing a few years back & one of our pipefitters sais a piece of cake..... i told my boss DON"T EVEN LET THOSE GUYS TOUCH THAT THING !!!! he took my advise on that one but a few months later we were going to re-locate that machine about 40' from where it was. i told him get riggers thru B&S to do this, anyway out millrights looked it over and said NO PROBLEM, i told them there is NO WAY you can move this machine with a crane...... well within a matter of seconds they caused $ 35,000 worth of damage & we had to call in real riggers & ship the machine to RI for 4 months.... i know it looks simple to do, re-hosing it that is, & there are a few connections that you can do, but there are some that require the removial of the bearing/rails to do. Tha us why B&S made it that way.... how does that saying go.... You can pay us now or later.....

[djayne]

As far as the axis drifting goes - it does sound like a problem I have with one of my machines now. We have a loose wire in the jog box - if we shake the box or bump it in our hand sometimes the drifting will stop. But this sounds like the least of your worries now. Sorry dude!

[Robert Davis]

Regardless of who changes the hoses, they needed to be changed. You can't change them without removing the rail. You cannot get to the hose connections under the bridge any other way. It's either remove the rail or slide the entire bridge off the table out of the rails, which is totally unrealistic.

I appreciate all your responses, but on a realistic level, this needed to be done. Either a tech comes and changes the hoses and calibrates it as well, or he comes and calibrates it only. I see no reason to pay a tech extra to change the hoses. Techs are expensive.

Obviously my machine will be calibrated. I'm more concerned with the drift problem and whether or not it's a function of the rail alignment or the motor not completely stopping.

Anyway, thanks for the supportive replies.

[Matthew D. Hoedeman]

I had a hose either pop off or break, I don't remember which, in the same place, between the rails, under the leg. I did not have a tech come in and I didn't do it myself. I had the maintenance guy do it. He did it by ONLY removing the end cap from the 'leg' of the machine (that little flat plate). Yeah, it is very tight confined space and YEAH, he had to build himself a tool to get in there and do it, but he did it without removing the rail. Some klind of long, pliers, griper kind of thing, possibly similar to surgery equipment hemostats (sp) of some kind.

The rail itself is only a 'guide' (only?) and has nothing to do with it stopping, starting, or drifting, unless it is too tight, then it won't move and if it is too loose, it moves in directions it should not. Do you still have the OLD controller on the thing or has it been upgraded? That will determine a LOT as to what kind of answer you need for the drift.

The old controller had 2 joystick, one for XY and one for Z, each one had little 'knobs' on the sides for 'centering' the movement of the machine. By sliding the 'knobs' in one direction or the other, it would move the 'zero movement' position of the joy stick. When it was in the right place, it would not move when you pushed the 'enable' button, if it was off center, when you pushed the enable button, it would take off without a finger on the joy stick.

The new controller has 1 joy stick, XY and twist for Z. I have never had a problem with any kind of drift, EXCEPT when I had to tighten the Z axis twist portion of the stick, and that has a screw in the center to adjust for that.

[Gregl]

As for the machine not stopping,

There are sensors at the end of the rails to tell them to stop, if either one on any axis is not connected or broke it will not stop in that axis

[Robert Davis]

Thanks for the replies. Yeah, Matt. I hear you. If it were at that point under the bridge, I could change it with pliers and some sweat.

The problem is that the hose broke off inside the right bridge. There's a small hole in the bottom of the bridge and a slot at the top. Trying to fish a line is virtually impossible without access to the underside. I tried. It's can't be realistically done. You can't fish a line 90 degrees from the top slot to the bottom hole.

So, anywhosit, I can't figure why the jogbox would be different now and not stopping the motor. The thing about the motor is that it goes whatever speed you move it at continously. If you move it super slow, it keeps going super slow. If you move it fast, it keeps going that speed. I don't know how and/or if adjusting the jogbox is possible. It's the newer style, with a single stick and twist for Z. It's got the xyz combo move button, as well as the individual axis move/enable buttons. Does PC-DMIS have anything to do with the jogbox or it's calibration? This thing must be able to be calibrated in some way, I would think.

Thanks,
Robert

[T Miller]

Tape a string to the end of old airline... how we did ours pull the new air line

[Robert Davis]

I got everything back together and it all works great. Just waiting for calibration and I'm off and running again. This machine needed it anyway, so in the end I saved money and time by changing the hoses myself.

You guys are a great source of info and I always appreciate it. But, and I say this with all due respect and no ill will, you guys are a bit melodramatic sometimes.

This machine was easy to fix. The distance between the rails is not critical. As long as there is adjustment room for the bearings, the gap can vary by quite a bit. You just adjust the bearings to fit the gap.

The things that ARE critical are the rails' linear alignment front to back to the table, and the parallelism between the 2 rails. Since I only removed the dovetail rail, the straight rail has never moved, so the linear alignment was unchanged. All that I had to do was set the other rail parallel. Not simple, but very doable with some patience and good tools.

As far as the machine not stopping, I'll look into that Monday. I suspect the reader.

Cheers and cold beers,

Robert

[KBearden]

Robert,
We just had B&S come in to do a rehose and calibrate. The problem you are most likely having is with the decoder not being aligned with the scale. A trained technician connects an OSCILLOSCOPE to the controller and aligns the decoder with the scale to insure there is a good signal being delivered to the controller. This will most likely be your problem.
And as a rule of thumb, if an airline breaks and you can easily get to it without disturbing anything else - fixit, but if it requires removing air bearings - let the trained folks do it.

[Lawrence Hardtacke]

We just had a similar problem (two hoses replaced) and the cost of replacing the hoses was included in recalibrating and aligning the machine. So dude you most likely saved nothing by doing it yourself. Also now, your machine is for all practical purposes down until it is realigned.