My experience buying an old/cheap CMM and getting it up and running

[mikethezipper]

I decided that I should document my experience getting an old CMM into our shop, and getting it up and running.

A big problem I had during this whole venture was fear. Every thread I can find on CMM's makes them out to be mystical beasts that no mere mortal could hope to comprehend, much less work on. My experience was in stark contrast to this. Maybe I was lucky, maybe not.

The beginning:
We wanted to get a CMM. Due to how much money the shop doesn't make, we couldn't justify spending $16+k on a used unit, much less so on a new unit.

So I ended up being seduced by the "deals" on ebay. I ended up getting a Brown & Sharpe Validator 7101 on ebay for around $3,100. It was advertised as being in good working condition, with updated electronics and software in 2004. It has QCT-2000 on it, and uses Scazon interpolator box and PCI card.

I bought the unit, and then the fun began. Every place I could find was quoting over $4k for just moving it to Tampa from Alabama, and that was without insurance or shipping costs. I decided that for the price I paid, I would just move it myself, especially because I couldn't find anyone for under $6k that would be able to move it in a reasonable time frame.

Well, it wasn't in working condition when I got there. The machine hadn't been used in years, and there had been oil contamination in the lines, so they were turning to dust. Hooking up air to the machine instantly lead to every hose exploding. I decided that since I had already bought my flight etc, I would just re-hose it myself and haggle down the price.

I welded up some brackets to hold the Y bridge in place, and I blocked under the Z axis. I then made a skid for it from some 2x4s and half a sheet of plywood.
Funny side-note: I ended up welding the brackets in my hotel room.... And even the crappiest car works for transporting the lumber to make the skids





From there I went to HF and bought a 4 pack of ratcheting straps for $7, and criss-crossed all of them across the machine. I then used an entire roll of shrink-wrap around the sucker, pulling pretty tight as I ran around it in circles like a madman.



It was then loaded on a flatbed and shipped to Florida (From northern Alabama). Apparently on its way here on a plain old trailer (not air suspension), the axle fell off the trailer, and it had to be transferred onto another trailer.

It got here undamaged.

I ended up doing 3 nights in a hotel for $60 a night, plus $300 for a plane ticket, and I severely overpaid someone to ship it on what ended up being nothing more than an F-250 with some POS trailer ($800). The rental car plus tools and materials purchased were $200+$200 Total price : $1680 + opportunity cost of 3 days of my labor

Total price paid so far: $4780

 

[mikethezipper]

Next Topic: Re-hosing

I thought it would be easy. I was wrong. I got about half of the hoses replaced, and from an overall system standpoint, it was pretty simple. The routing was self-explanatory, and nothing complicated from that perspective... except for one big problem. The hoses had been routed internally on the X axis. After hearing horror stories on the internet, I decided I couldn't do this myself.

No local places wanted to take on the job of re-hosing so I ended up getting it done by a gentleman in South Carolina who "specializes in Brown & Sharpes" and had re-hosed many machines. The total costs of having him come to re-hose the machine and calibrate it was $4k.

The problem is that I did half of the work re-hosing it myself. Hell, it would have taken me half as long to re-hose it than it took him. I was terrified of removing the air bearings, and he just went to it. Then I ended up having to help him for days because he took out all the air bearings at once (derp, it would have worked so much easier to just do one set at a time). My advice to others is that the labor of replacing the hoses is something you can do, and there is no need to be terrified of the procedure.

Once it was rehosed, it then came to light that the Z axis wasn't reading properly. The CMM specialist was useless at this point. I then had to pull out the multimeter and track down the issue. One of the contacts had broken off in one of the connectors. I was able to repair it, only to find out that the Z-axis read-head was also not working right. It was clean and I fidgeted with it for hours, but no dice. I ended up getting a new-old-stock read head from ebay for $264 (including next day shipping) and after tracing the wiring, I got it hooked up and working in a couple hours.

He then squared it up using a granite square and some procedure that I didn't see, and then "calibrated the machine" by measuring several gage blocks and verifying that the readings were within the tolerances for what he believed were good. He didn't do any spatial or linear error mapping at all. And then he disappeared.

So essentially I paid a guy $4k for something I could have done myself in two or three days.

Total Cost at this point $4780+$4000+$264 =$9044 (minus the discount I got for the re-hosing negotiation from ebay) - 1300

= $7744 for a machine with questionable calibration.
If I open the error map/compensation table, everything is set to zero. As in, he didn't do any error mapping or compensation whatsoever.

Also, one of the air bearings is completely loose, and most of them move freely when the air is off. The sucker also uses 14CFM (says 14.4CFM on the nameplate)so our 5HP compressor runs non-stop during use.

Also, this sucker has a solid granite X-gantry, so using it requires two hands, and is a total PITA since you are moving 200+lbs of weight with a tiny probe head sticking out, so I'm routinely smacking the part instead of slowly and gently setting off the probe. I'm getting form errors in the .0000-.0002" range so not sure if that's good or not.

Note that I've never even seen a CMM before this whole venture.

My advice: make whoever you are buying a CMM from show it functioning to you before purchase. If I could have saved 3k from unecessary re-hosing, it would have been a much sweeter deal. I see units on ebay now that look better than the one I have.

 

[mikethezipper]

I forgot another part: Getting rid of the water in the air-lines

I've got a 5hp 15CFM air compressor, and it runs non-stop while the CMM is being used. This also means that our are lines become essentially high-powered squirt guns. Water shoots out of our lines like crazy, and the CMM jams up and doesn't do squat because there is water dripping off of every air bearing.

SO over the weekend I pulled a coil out of an old R22 air handler I had laying around, and I rigged up an aftercooler for our compressor. Took me the better part of the weekend, but it works surprisingly well. I didn't think it would work at all, but it takes 200+F air and takes it to room temp before it hits the tank. $70 worth of materials and a waste of my weekend was all I needed to avoid buying a $400 part. I regret not just buying a pre-made aftercooler, but the hardest part of plumbing it in with the existing setup, which would have been the same with an pre-made aftercooler.

I feel real redneck right now. Kinda proud, kinda not. These posts are to warn the future generations about the problems they'll encounter.

 

[dkmc]

Interesting story, thanks for the warnings and list of pitfalls.
The machine got re-hosed but you got hosed in the process.
Did you have to pay the CMM "expert" up front??
Considering you had to help him, and he left the job incomplete, it seems like you could have disputed his charges and refused to pay the full ammount.
14 CFM sounds insane.

 

[D Dubeau]

Also, this sucker has a solid granite X-gantry, so using it requires two hands, and is a total PITA since you are moving 200+lbs of weight with a tiny probe head sticking out, so I'm routinely smacking the part instead of slowly and gently setting off the probe. I'm getting form errors in the .0000-.0002" range so not sure if that's good or not.

Note that I've never even seen a CMM before this whole venture.

.

Try and keep your elbows on the table, and move the head with both hands, with your wrists, and fingers providing most of the fine movement. Not always possible but It goes a long way to tame the movements and momentum of a heavy old manual. Congrats on the purchase, and the journey to a running machine.

There's no way I could go back to running a manual, although they do tend to teach better technique than just slambamming a probe around with a joystick hoping for good results.

 

[CarbideBob]

So the next step is to refit it to full DNC and of course you'll want to add a camera also.
How's your wallet feeling now .
I see a lot of people get screaming deals on old cmms and they end up sitting alone, holding down the floor, collecting dust.
I know a lot of small shops with nonfunctional or junk cmms.
They all keep them simply because they make for a good item to have when doing dog and pony shows for potential customers or pics on your web site.
Kind of a feel good enormous paperweight. They will do double duty as a nice sized surface plate and generally speaking most have very little wear on the plate itself

.0002 is way inside the capability of this machine even when it was brand new so real good there. Actually so tight that I have a very hard time believing it.
What do you expect from it? What was you hopes and dreams?
The upper or non gravity loaded air bearings should be loose and free with the air off along with some on the Z. If they all were tight it could not "lift up" and float when the air gets turned on.
If one is way out and wobbly with air on it did not get adjusted correctly. Bad news, adjusting in in may move your "square" as it forces the other air gaps to move.
I like your redneck air cooler. Am surprised you can run this and anything else in the building on only 5HP.

Funny how it moves easy but will not stop when you want to. Way cool, moving a 5-10,000 pound bridge or arm with a finger touch.
Fingertip gentle accel over a foot, hard to stop fast
Despite all that stuff they teach in engineering school real big cmms were the first things that made me understand inertia loads on machine tools.
Bob

 

[mikethezipper]

That's odd. I thought I included a picture of the abomination I am calling an aftercooler in the above post. Well, here it is again for your entertainment:




As for the gentleman who "calibrated" the CMM - I gave him his check as he was finishing his calibration, and before he left. It didn't hit me until a full day after he left just how wrong everything was. I had not yet made the aftercooler, and the CMM was squirting water everywhere, so I was unable to really run the machine through its paces to check everything out. I realize now how non-sensible calibration services are. We pay companies to come in and do some "mystery" calibration, slap a sticker on it, and disappear. I have no idea what methods were used to calibrate my tools, and no idea to what standard these tools were calibrated. That is rubbish. I don't understand how this is an industry acceptable practice. I have no documentation for anything in my building that is calibrated besides a sticker with an expiration date on it.

D Dubeau, The method you are describing is the method I have been using. I find that even doing it like that, it is hard not to smack into everything due to the inertia of the machine, unless I am going so painfully slow that I start giving up on life.

I found that if I go really really really slowly, and use nothing but the fine adjustment knobs, I can calibrate the probe tip to a "form error" of 0.0000", and then when I measure a 4" gage block using lines on opposing sides with form errors of 0.0000", it will tell me the gage block is 4.0000" long. Which is nice. Except it is almost impossibly difficult to go that slow, and possibly re-doing my measurement lines to get a form error of 0.0000" In a more normal use scenario, I will get a form error of a tenth on the probe calibration and on each of the lines from which I am computing the length of the gage block. This results in giving me a measurement of 4.0000" +- 0.0002"

For some reason, I was thinking that I could expect to be within a tenth of the true distance on gage blocks. For our use here, the results I am getting are good enough. My only fear is that I don't have a 12"+ gage block so I can make sure I won't be a full thou or more off over greater distances. I don't want to inspect a base plate for something and say that a hole is within location specs, and it isn't.


As to Carbide Bob's comment, I have been thinking of converting it to CNC after spending just 5 minutes moving that thing by hand. We are supposed to do full inspections for every part we send out, and it looks like we'll be spending more time doing this by hand than actually machining the parts. I sprang for a manual because we don't make more than 10-20 of most parts we machine.

Herein lies my problem, and possibly an opportunity to nerd out some more. I've made a few pieces of automated CNC machines for assembly of product and pick n' place, so I feel like I should have a decent base upon which to make this sucker CNC.

My main problem is that it is so heavy. After much thinking I think I have a somewhat elegant solution. Using cheap brushed drill motors with their built in gearbox. This way I can get a lot of torque to move the weight around (slowly so I dont' destroy everything) without needing any huge motors. Also, I would be able to just make some adapters to hold the motors directly onto the fine adjust screws, so it wouldn't really be that hard.

Am I just a bit too crazy at this point?

 

[DavidScott]

Put the after cooler in a water bath to drop the compressed air temp below ambient, it makes a big difference. Putting a water trap between the after cooler and your compressor tank will keep most of the water, 99%?, out of your tank.

In my neck of the woods I start to see moisture coming out of my blow gun when the ambient air is 80 degrees or above with an air cooled after cooler. I don't see any moisture in the air with a water bath after cooler even when it is 110 degrees outside. This is running a 4 hp 2 stage compressor 70% of the time.

 

[specfab]

To the OP -- I admire your perseverance in getting the machine operational. I think there is a difference in recovering the raw functionality of the motion of the axes coupled with the information display, and having a machine that really provides a result you can trust. It has always been my feeling that anyone running a machine of this nature needs to have as many useful verification tools at hand as possible, as you are seeing also. In this way, you don't end up operating "blind" between annual calibrations. When I was doing some work with a Zeiss machine some years back, I routinely checked the machine's Z-axis accuracy against an 8" optical glass flat, just to see that the plane measured by the CMM was "about the same" as the known shape of the flat. (It helps to have the additional lab instrumentation around to check the flat, of course).

Having some long gauge blocks is an excellent investment in being able to make sure you know what your machine is doing. This is the same calibration method that the Zeiss tech used on our machine. Ideally, you have blocks sufficient to cover the volumetric dimensions of the working envelope, in X/Y/Z/diagonal (for confirming squareness of axes). In the case of a factory tech cal, the gage blocks were ceramic, but standard steel blocks would do well, if you have known lengths for the blocks.

 

[Mike1974]

Mike, as to your calibration question. The sticker should reflect the item was calibrated to a known spec. You are not completely wrong in your thinking however, it is just a sticker, but someone usually wants to see that sticker. It should be able to point the auditor to an NIST source/code/documentation that states said device is calibrated to a known standard. That is really what you are paying for, a sticker saying your item is calibrated, and could be verified if someone were to track it down.

All of that said, I watched a calibration tech do some of our stuff in-house, like mics and such. He took a 'master' set of gage blocks to check mics with, and a digital bench mic (super mic?) to check some gage pins. Did not seem like their was much to it... The 'high precision' items like our class X gage rings were taken to their facility. I have no idea how they checked those. Honestly, it is not really my concern how they did them, I just need to be able to point to an auditor that such and such was calibrated on this date, and not due until this date. I guess it is just faith that the items are correct as I can't really verify anything more than a couple tenths in the shop.*

* Our shop is climate controlled to a pretty good stand IMO. I think the shop runs 72-73deg, probably within a couple degrees, although I don't think I ever remember it being much cooler... Our cmm lab is I think +/-1 deg..(?) Humidity in the shop varies a little more, but the lab is held pretty tight around 45%.

 

[mikethezipper]

I understand the importance of the sticker, I'm more bothered by the fact that is the only thing we receive when we get something calibrated. When I order gage blocks, I am expecting to get a sheet with the actual measurement of each block, as well as a NIST traceability information.

Our calibration guy came in, and he "calibrated" a harbor freight caliper. That is terrifying. The sticker he put on that caliper is the same sticker he put on our Mitutoyo calipers. I just want to be sure the tools I am using for an inspection are the proper tool to use for a given tolerance, but without knowing to which standard something was calibrated, I have no idea how accurate any of my metrology instruments really are.

Back when I did calibrations (scary that they let me do that), we would have to record at least ten measurements of master gages, and ensure that the tool was accurate to its rated specifications, all while recording all applicable NIST traceability items. That was useful. The data that testing gave was invaluable. I'm thinking I'll do all my own calibrations, at least that way I can know and trust my tools better.

 

[specfab]

I understand the importance of the sticker, I'm more bothered by the fact that is the only thing we receive when we get something calibrated. When I order gage blocks, I am expecting to get a sheet with the actual measurement of each block, as well as a NIST traceability information.

Our calibration guy came in, and he "calibrated" a harbor freight caliper. That is terrifying. The sticker he put on that caliper is the same sticker he put on our Mitutoyo calipers. I just want to be sure the tools I am using for an inspection are the proper tool to use for a given tolerance, but without knowing to which standard something was calibrated, I have no idea how accurate any of my metrology instruments really are.

Back when I did calibrations (scary that they let me do that), we would have to record at least ten measurements of master gages, and ensure that the tool was accurate to its rated specifications, all while recording all applicable NIST traceability items. That was useful. The data that testing gave was invaluable. I'm thinking I'll do all my own calibrations, at least that way I can know and trust my tools better.

I'm with you on wanting to know the actual facts and details about repeatability/accuracy/uncertainty of all measurement tools, and the process used for getting to the results. Be cautious in your thinking about doing your own calibrations, IF you need outside verification for the sake of customer's piece of mind, or ISO standards, or any other sort of external judgment of your quality system, whatever it is. Unless you set up your own metrology facility and jump through all the hoops for NIST traceability, a customer who is ISO-minded won't look kindly on self-calibration, I would suspect. Here again, it's largely appearance and formality, rather than substance and function, but it's the framework a whole lot of people use.

 

[gregormarwick]

I also went the route of used machine + DIY retrofit, but with much more success than you seem to have had. FWIW ours is an LK G80 with renishaw PH9/TP20 probing, I retro'd with a Deva controller and servo drive and run PowerInspect. Works nice. We already had a screw compressor and dryer, so no problems there. I also repiped ours when I did the retro, and replaced most of the regulators, solenoids, and much of the pneumatics in the self levelling/anti-vibration mounts.

The machine and the retro kit cost slightly less than the seat of PowerInspect. I put a lot of hours into it but I enjoyed the experience.

Regarding calibration;

Ours is calibrated annually - it's now on it's third calibration since I brought it into service. When the guy comes to calibrate he brings an interferometer, length bars, and a large granite square. With the probe removed he uses the interferometer to check straightness, squareness and linear accuracy of each axis, then uses the probe to check the length bars and granite square. Throughout the process he updates the error map as required.

When he leaves he puts the sticker on the machine, but a couple of days later we get the document package by mail. There is an A4 certificate that we copy and include with the inspection results to our clients, but the full document package includes the Renishaw interferometer report, the length bar and granite square results, full traceability of each piece of calibration equipment and the environmental conditions at time of calibration.

 

[DanielG]

I understand the importance of the sticker, I'm more bothered by the fact that is the only thing we receive when we get something calibrated. When I order gage blocks, I am expecting to get a sheet with the actual measurement of each block, as well as a NIST traceability information.

You calibration guy should give you a certificate that has the same ID number as the sticker. This tells you all the details and gives you the NIST traceability. They should have them on file; I would ask.

 

[The real Leigh]

Our calibration guy came in, and he "calibrated" a harbor freight caliper.

Sorry, but IMO that doesn't work.

For a proper calibration, the standards and the instruments must be kept in the same environment for at least 24 hours before the calibration checks are done to ensure they're all at the same temperature throughout, not just at the surface.

- Leigh

 

[The real Leigh]

When he leaves he puts the sticker on the machine, but a couple of days later we get the document package by mail. There is an A4 certificate that we copy and include with the inspection results to our clients, but the full document package includes the Renishaw interferometer report, the length bar and granite square results, full traceability of each piece of calibration equipment and the environmental conditions at time of calibration.

That's the same way it should be done here in the States.

You have full traceability if anybody asks to see it.

- Leigh

 

[Mike1974]

I just checked, our CMM does have a file folder full of reports from the last calibration. I did not look to see what everything was, noticed one sheet stating volumetric accuracy with relating ISO standards, temperatures, graphs, and all kinds of small numbers.

We also have certificates for the other tools such as mics. These are much less detailed, noting temp and humidity, inspection method, etc, just one sheet of paper.

 

[Mike1974]

http://www.practicalmachinist.com/vb/metrology/nist-certificate-proof-322886/

This thread is going on too which is related.

 

[B-Mathews]

Mikethezapper if you paid via a credit card I would be looking at doing a dispute with your card company as it sounds like you got screwed by the so called CMM specialist.

Not that this matters but was this work done at your home shop? If so maybe he thought he could take advantage of the home shop type guy. I know his method of cal. would not file in most shops.

Like I said I think I would be calling my card company and see what can be done. I would try to dispute the full $4k myself.