Checking a gage

[cmmmike]

I am laying out a gage and would like a few ideas on doing this

This is what I have done so far.

I have cad for the part that goes on the gage. I created 3 spheres and set them to the coordinates by the spheres. I did this in manual mode. Then I did an Iterative alignment for the tooling balls. Then went and checked the 2-way & 4-ways on the gage and they were off to their nominal to the part cad. I then did an Iterative alignment with the 2-way & 4-way pins and a vector point to set the gage in the correct car coordinates. Then recalled the tooling balls and they were out. I changed my numbers at the beginning of the program to reflect what I had got from setting it to the car coordinates. I then redid the program with the tooling balls up dated and my 2-way & 4-ways were almost perfect this time. The 2-way for the gage is out (.16 long) in X so I think I have to lower one of the tooling balls to bring it in. All the other dims 4-way and vector point are almost perfect. The X direction for the part is a slot.

Some of the questions I have are:

When you get a gage in and are not sure of the tooling ball locations or the stamped numbers on the gage how do you begin with verifying the gage?

If you layout a gage and your nominal for your 2-way & 4-way do not match your part print how do you go about setting it so they do?

I use 3.5mr2

Thanks for the help.

[\v/inston]

i think the fixture shop has to measure the locations of the tooling balls by aligning to ABC, then stamping the numbers on there. so i think your on the right track.

this may also help...

Ford Checking Fixtures General Construction Tolerances.


These tolerances are to be used in the construction and certification of stamping and Assembly checking fixtures unless otherwise specified by Ford Motor Company Dimensional Control Department.


1) CMM starts to machined edge of base = +/- 0.125mm.
2) Surface locators to CMM starts = +/- 0.05mm controlling direction.
3) Surface locators to CMM starts = +/- 0.2mm non-controlling direction.
4) Positional tolerance of Pin locator to CMM starts = +/- 0.05mm.
5) Nominal Pin diameter is .07mm undersized from product design.
6) Pin diameter tolerance is +/- 0.0127mm.
7) Check rails profile to CMM starts = +/- 0.15mm.
8) -4- way (H) Locator Pin to -2- way (h) Locator Pin relationship = +/- 0.05mm controlling direction
9) -4- way (H) Locator Pin to -2- way (h) Locator Pin relationship = +/- 0.1mm non-controlling direction
10) Template (Flipper details) surface profile = +/- 0.15mm
11) Probe bushing for Data Myte measuring points from CMM starts +/- 0.20mm non-controlling direction.
12) Probe bushing for Data Myte measuring points from CMM starts +/- 0.10mm controlling direction
13) Base must have a flat and parallel to +/- 0.10mm
14) Base must be level to 0.l25 total overall tolerance.
15) Generic holding fixture - Columns machined flatness and parallel hole to hole = +/- 0.05mm.
16) Generic holding fixture - Columns square to base within 0.075mm
17) Master Body Gage (Blue Buck) overall tolerance from front to back = +/- 0.13mm all directions.
18) Master Body Gage locating pin relationships, Pin to Pin = +/- 0.13mm all directions.
19) Check rail Flush check trim line 90 Degrees to surface of metal when angle is over 7 Degrees.
20) Check rail Flush check trim line 90 Degrees to surface of base when angle is under 7 Degrees.
21) Scribe line details to CMM starts = +/- 0.125mm

EDIT: i have the offcial doc if you want me to email it to you.

[kbotta]

I don't use the tooling balls. Just the datums. I set up from them (dcc), and manual from a square corner.
kb

[Matthew D. Hoedeman]

Well, last first: What is master? The cad or the print MUST be master. Which ever is master is what you need to use for nominals.

First time the gage comes in. Well, Iterative is NOT the way to go, as you are finding out right now. What number gets adjusted and which way to get the part locators in tolerance? So, start out by measuring the tooling balls. Construct a plane through the centers and a line through the two that are in line (in theory). Too many build sources are using Iterative alignments on the part locators, then measuring the tooling balls because they can't hold the required tolerance or don't want to bother trying, so this is their 'easy' way out (and it dumps more work and fuss and bother on the QC people). So, look at the numbers for the tooling balls. There should be a number that is common on all 3, or real close to it. If it is NOT common, then average it out and use that. Then, the two balls you used for the line should have a common number (or close to it). Now, you have a level feature (the plane) and a rotate feature (the line) and an origin feature (one of the balls). Do the Level, Rotate, Origin using those 3 features in a regular alignment, NOT iterative. Then do the OFFSET DISTANCES using the values on the ball you used for origin. Now, go check the part locators. EVERYTHING has a tolerance, USE IT! Most common for sheet metal fixtures is 10% of the part tolerance to a maximum of +/-0.002" (this is for the locators). If the nets all check 'low', you can simply adjust the offset value in the alignment by that amount, DO NOT UPDATE when it asks you if you want to after you change the number in the alignment (do this from the edit window, do NOT F9 the alignment). If both pins are off in one direction, do the same there. If you can get all the locators to balance within the tolerance, there is NO need for an iterative alignment and the regular alignment is MUCH easier to tweak. Also, after you change the offset in the alignment to balance the locators, AND BEFORE you use the cad data again for any features, you MUST do a CAD=PART AGAIN by placing the cursor just below the alignment, then click on CAD=PART (it will be under OPERATION ~ GRAPHICS DISPLAY WINDOW).

I do this everytime a fixture comes in here. I do a regular alignment using whatever the fixture has, tooling balls, datum edges, whatever. I then check every part locator on the fixture, then tweak the alignment values until they all come within tolerance. After the manual measurements, I do make a DCC alignment and that is the only one I tweak around, the manual one does not matter that much.

[\v/inston]

matt excelent post! i tried to add to your reputation points, not sure if it worked.

do you guys check your parts on the fixture or freestate or both?

[Matthew D. Hoedeman]

Well, that depends on the customer. About 95-98% of the time they are checked constrained on the holding/checking fixture. Once it a great while the customer wants to 'know' how something checks in a free state. And then sometimes, they just won't make a fixture for a part and I hold it with magnets. Right now, I have a part that I am trying to get someone elses program running on my machine to check. No fixture, no road map, and programmed almost 100% wrong. Vector points to check edges, about 48 alignments and alignment recalls that I can see in the program, some of them to get no more than a 3-D distance of a point to a plane (they had to align to the plane, then dimension a point! ???) and it is one that there is no fixture for and will not be a fixture for. Big part, about 2 foot square, about 6 inches high, and checks on all sides and top and bottom. And, one end if flat on the bottom, so it can sit on blocks, the other end is curved, and the part is very flimsy, so how do you hold it with any repeatability? I HATE working without a fixture! So, I mostly do fixture-held, but do some free-state.

[\v/inston]

i was checking some gas tanks recently (~3 sq. ft.) and at first they wanted them checked in the free state. the tanks where so flimsy, i was resting on the four nets and you could lift the middle of the tank and see about 5 to 6 mm of sag. naturally the parts check like crap. i put a couple jack screws in the middle where the sag was, raised them close to nom and the parts checked perfect, offcourse. they ended up having to get fixtures made and put rests in the middle area because four nets on a part that size was clearly not enough. sometimes there is noway to check a part with out a fixture and get good results.

as for the program you have to decifer, it sound like it would be easier to just rewrite it. lol vector point for edges :eek: , must have been newbie.

[rebeldude]

I always align right off the datums of the fixture. I figuire that is what is actually holding the part, so normally I can't go wrong. The only time I come off the balls are when I have no other options. The customers that have been in the CMM room while I have came off the datums have all agreed with me that it reduces room for error. I agree with Matthew though. 1st thing you need to do is find out what is "Gospel" as we call it here in Tennessee. The cad or the print.

[cmmmike]

I will check parts in free stat or with a gage as a holding fixture. It all depends on what the print has for measurements. In car or from a datum on the part.

Thanks for the help. I am checking an F250 hood hinge final assembly gage to make sure everything is in the correct location. I like using the tooling balls because I can put the gage on the table and measure them and be set to go. I am using the cad as the master. I was always told in automotive that cad is the master. The gage has these numbers stamped on it.

Sphere 1 1650.05, -639.97, 22425.01
Sphere 2 1650.00, -1000.00, 2425.00
Sphere 3 2165.06, -1000.00, 2425.01

After I measure the 2-way & 4-way and do a vector point they read this

Sphere 1 1649.860, -640.099, 2424.854
Sphere 2 1649.989, -1000.057, 2424.798
Sphere 3 2165.038, -999.783, 2426.004

I changed them to this and my 2-way & 4-ways and vector point were all less the then .003mm. Except for the X direction of the 2-way pin. Matt I am going to give your way a try to see how it works. I am trying to find something that will work all of the time and try to do it the same way gage makers would do it.

[Matthew D. Hoedeman]

One thing that I am sure you are aware of, but maybe only in the back of your mind, is the spread. I currently have 5 fixtures for little parts (less than 3" in X and Y) that sit on a big fixture (18X18 base) with tooling balls located on an average spread of 12". Now, you check those 3 little nets that are almost on top of one another and call them 'level' then check the tooling balls, you see error in the 0.5+ mm range. However, if you measure the tooling balls and call them level, then measure the nets, you see less than 0.01mm. Now, which way makes more sense? To me, it is the balls as level. The more distance between the master alignment features, the less error you are going to put into your measurement. I mean, what happens to your level plane when that floating piece of dust falls on the net just as you are measuring it, then you measure 2 more nets 1" away and call that level? A whole lot more than if that piece of dust fell on the tooling balls that have a 12" spread. This might be over the top to some, but that is the way I look at it.

[kevin strine]

Winston: I would love to get ahold of the Ford Checking Fixtures General Construction Tolerances.

Thanks in advance.
kstrine@vicount.net

[cmmmike]

OK matt

I set the gage up the way that you said to. Works great but now I measured my locators and they are off as follows.

Datum B is out in X=- 0.111, Y= 0.136, Z= 0.155

Datum C is out in X= 0.105, Y= 0.064, Z=- 0.093

Do I have to tweak the tooling balls now because the X & Z locations are out in different directions?

Thanks for the help.

[Matthew D. Hoedeman]

What locators are those? Are they the locating pins or are they nets? If they are pins, and the Z axis is along the shaft of the pin, I would not ever report the Z value. As for the X, that is a simple shift, the Y is borderline, but both could be gotten within the 0.05mm (one would be +0.036 and the other -0.036). If those are Z axis vector points then you will probably have to tweak the alignment or go to an iterative alignment (YUCK) OR, you could put 0.010" of shim under the low one to bring it up to the same height as the other, then do a common shift. Without knowing which 'direction' those locators locate in, it is hard to say.

IF the Z axis is the locating axis for those pins, you can also do a rotate in the alignment to bring them into line. I would rather add a rotation to the alignment than use an iterative alignment. Simple trig will give you the angle you need and the command goes after the LEVEL and ROTATE and ORIGIN lines in the alignment but before the AXIS OFFSETS. Here is an example of the added rotation in the alignment, I just add it in the edit window. Yes, this way can take a little longer than doing an iterative alignment, BUT, it is SO MUCH easier to adjust the touch-offs than an iterative alignment. You will probably have to make a second set of adjustments to the ORIGIN OFFSETS after you add the rotation. This is because Pcdmis rotates around the CURRENT origin, which is why you have to add it AFTER you set the origins and BEFORE you offset them.

ALIGNMENT/START,RECALL:STARTUP, LIST= YES
ALIGNMENT/LEVEL,XPLUS,TOP-OF-FEET
ALIGNMENT/ROTATE,ZMINUS,TO,FRONT-OF-KEY,ABOUT,XPLUS
ALIGNMENT/TRANS,XAXIS,BALL
ALIGNMENT/TRANS,YAXIS,BALL
ALIGNMENT/TRANS,ZAXIS,BALL
ALIGNMENT/ROTATE_OFFSET,15,ABOUT,ZPLUS <<<<<<added rotation
ALIGNMENT/TRANS_OFFSET,XAXIS,0
ALIGNMENT/TRANS_OFFSET,YAXIS,0
ALIGNMENT/TRANS_OFFSET,ZAXIS,0
ALIGNMENT/END

[Bill McCafferty]

Ok as a gage maker CMM guy let me shed some light on this subject about tooling balls and datums on a gage.

First The tooling balls are the ONLY thing that stay the same on a gage from initial check through final when a gage is being constructed. When the gage first comes in ALL of the nets will be full, ALL of the datum locators will be undersized qualification holes, ALL of the flush and feeler checks will be CNC cut but who knows where they REALLY are. So here is what happens:

The tooling balls are at some designers "nominal Car" position on the gage. The CMM guy picks up the tooling balls and origins on them to get into CAR. THEN he measures the flush and feeler surfaces and "bumps" the tooling ball numbers to get as much of the gage in tolerence as is humanly possible without going back to CNC and recutting the flush feeler rails. Then he will pick up the nets and locators and mark moves to get them on location as compared to the "bumped" tooling balls. The gage goes back out to the gage maker and he makes the adjustments to the gage to bring all of it in to tolerence. It then comes back into CMM and is checked AGAIN against the tooling balls. If its good, THEN and ONLY THEN can the CMM begin using the datums to check the gage. If your tooling ball numbers are messed up one of two things has happened. Either some bone head tried to START building the gage from the approximate datums, messed it all up and measured the tooling balls at the end and stamped BS numbers on the gage OR the gage has purposely been rotated out of CAR position.

I recommend using the tooling balls to get "in the ball park" on a gage. As soon as you are clsoe, go measure your datums and then adjust your alignment to bring in your datums after that, load your part and start checking.

If you're doing a second party cert or a recertification then aligning to your datums is MANDITORY. Using tooling balls for anything except initial build is just looking for trouble. On a gage that is 3 feet long, a change in temp of 3 degrees F can cause .002 -.003" change in over all gage size. How is that going to effect a 4 way that you're trying to hold at +/- .002"? My room STAYS at 70 degrees F. What is yours at? If it's at 73 then your checks are not going to be the same as mine. When was your machine last calibrated? There are a lot of variables to look at. Be smart folks thats what we get paid for.

Bill

[kbotta]

I cut my teeth so to speak as a gage maker, then moved intot eh CMM lab, so I can appreciate what you say Bill. At my current employer, it is written policy that gage's be check to and aligned to from the datum simulators. no tooling balls, unless otherwise agreed upon.
The TB and datum argument has been going on for years. Know what ASME Y14.5M-1994 says?

4.2.1 Application
As measurements cannot be made from a true geometric counterpart that is theoretical, a datum is assumed to exist in and be simulated by the associated processing equipment. For example, machine tables and surface plates though not true planes, are of such quality that the planes derived from them are used to simulate the datums from which measurements are taken and dimensions are verified. See Fig. 4-10. Also, for example, ring and plug gages, and mandrels, though not true cylinders, are of such quality that their axes are used to simulate datums from which measurements are taken and dimensions verified...
Partial excerpt from ASME Y14.5M-1994 (Datum Referencing ch.4)

KB

[cmmmike]

Matt,

Here is what I get for my results. Datum -B- & -C- are my 4-way & 2-way pins. They are running in X and -C- is offset. How I am picking these up is plane on my net pads, then probing a cone for the locator and creating a point and I am dimensioning it to find its location. Sorry I did not give you the correct information. I hope this work better.


DIM LOC5= LOCATION OF SPHERE SPH1 UNITS=MM
AX MEAS NOMINAL +TOL -TOL DEV OUTTOL
X 1650.050 1650.050 0.000 0.000 0.000 0.000
Y -639.970 -639.970 0.000 0.000 0.000 0.000
Z 2425.010 2425.010 0.000 0.000 0.000 0.000

DIM LOC6= LOCATION OF SPHERE SPH2 UNITS=MM
AX MEAS NOMINAL +TOL -TOL DEV OUTTOL
X 1649.982 1650.000 0.000 0.000 -0.018 0.018
Y -999.868 -1000.000 0.000 0.000 0.132 0.132
Z 2425.010 2425.010 0.000 0.000 0.000 0.000

DIM LOC7= LOCATION OF SPHERE SPH3 UNITS=MM
AX MEAS NOMINAL +TOL -TOL DEV OUTTOL
X 2165.050 2165.060 0.000 0.000 -0.010 0.010
Y -999.868 -1000.000 0.000 0.000 0.132 0.132
Z 2425.010 2425.010 0.000 0.000 0.000 0.000

DIM LOC3= LOCATION OF POINT DATUM -C- UNITS=MM
AX MEAS NOMINAL +TOL -TOL DEV OUTTOL
X 1805.705 1805.613 0.030 0.030 0.092 0.062
Y -807.375 -807.438 0.030 0.030 0.063 0.033
Z 2370.580 2370.557 0.000 0.000 0.023 0.023

DIM LOC4= LOCATION OF POINT DATUM -B- UNITS=MM
AX MEAS NOMINAL +TOL -TOL DEV OUTTOL
X 1699.993 1700.086 0.030 0.030 -0.093 0.063
Y -800.353 -800.519 0.030 0.030 0.166 0.136
Z 2358.242 2358.239 0.000 0.000 0.003 0.003

[Matthew D. Hoedeman]

So, the pins are pointing the the Z direction and the 4-way locates XY and the 2-way locates Y, right? From what I see of the dimensions, the Z has a zero tolerance for the locators, so they are NOT locating in that direction. Both have a Y nominal that is almost the same while the X values are quite different, so that tells me the 4-way is XY and the 2-way is Y. The X value of the 2-way locator, IF it is locating in a slot, has a higher tolerance for the X axis, the non-locating axis. In fact, if it is for a slot, I wouldn't even report the X value. Nor would I report the Z values if that is the direction the pins are pointing. Based on actual to nominal readings you are getting, they are off angle to the tooling balls by 0.051 degrees, so that would be the value you would use in the ROTATE_OFFSET line in the alignment (see below). I do not know if it will be + or - for the rotation, but that is easily changed after you try it once. One way will put them in line, the other will make the difference worse.

ALIGNMENT/ROTATE_OFFSET,0.051,ABOUT,ZPLUS

One other thing, the spread between the actuals to the nominals is different by 0.192mm. So, unless the 2-way is a slot, there is no way you can get both pins in tolerance, unless you have a +/-0.1mm tolerance for the fixture.

[J Temmen]

You can still iterate to the tooling balls and use the offsets, which make it easier to adjust later, at the same time. Measure and iterate to the spheres then simply place X,Y,Z origin on the sphere you used three times in the alignment, end the alignment. Do another alignment tha translates back the excact value of the origined sphere. This works when the tooling balls do not have common values, (which seems to be more often than not). Now you can adjust the:D offsets to bring in the locators.

[kbotta]

I believe tooling balls have there place in the Check fixture industry. I do not however believe that measurements should come from them. Consider this attachment:

[Bill McCafferty]

Well written Kevin. It expresses exactly the points I was trying to convey.

Bill

[cmmmike]

OK I read the Datums vs TB's and it makes sence. How about this. I use the tooling balls as my manual alignment the go to DCC mode and probe my 2-way & 4-way and do a vector point next to my 4-way and offset all of those or would doing an iterative alignment be closer since I have started with the tooling balls as a 1st alignment?

[kbotta]

A rule of thumb I try to stay with: If you start with an iterative, stay with an iterative. If you start with cad=part stay with that.
Me personaly, I like to do the cad-part thing. Again, thats just my ism.
But, It sounds like you are on track now!
Kev
(Test your alignment when done to make sure you are still perfect on the datums - or darn near close...microns)

[J Temmen]

I agree with using the actual fixture nets to align to when chacking the part, but I was under the impression he was trying to verify the gage. Do you verify the nets from the tooling balls then locate to the nets to verify flush, clearance and SPC points?, or do you stay with the tooloing balls all the way through the fixture check?
:

[kbotta]

datums, datums datums....

[rebeldude]

Thats how I look at it... Keep it simple... The part locates on the datums... Do your alignment to the datums and save alot of time and headaches!

[ufo_pilot]

Did You say toolingballs - MANUAL??
well, that takes time.
How about:
after you have taken the toolingballs manual ( just this ONCE), use an iterative to align to them.
Then under that alignment ( still in manual mode) catch a corner of the base of the fixture; 3 points for a plane, 2 points for rotation, 1 point for origin.....
NOW:::::::: take those six points=====> CUT=====> Paste ===>In front of the toolingball alignment. Use these 6 points for a new iterative alignment (eg named :CRNR)
Now make your toolingball alignment DCC ( place a DCC command behind the manual points alignment , but before the first toolingball.
All set up with clearplanes and Labels in the correct spots, you can now run totally in DCC, until the fixture is moved.
After the toolingballs, you can still hit off on your actual datums, nets, etc on the gage itself before loading a part.

[cmmmike]

I am trying to due 2 things at the same time. Verify a tower that is on the gage that we use to check a mounting hole is in the correct location to the datums. The second thing I am trying to do is check the location of the tooling balls to the datum points and check the numbers stamped on the gage so I can use them to do a quick setup when they come in screaming that the parts are not correct I can use the tooling balls and know they would match with the datums. I always thought that the tooling balls and the datums or the edges all got you back to the same in car location. I guess I was wrong.

Matt can you tell me how you trig the numbers out to get the .051 rotation. I forgot to put a tolerance in for the Z direction. Its is +/-.03 and the 2-way has a slot going over it.

[Matthew D. Hoedeman]

Well, to tell the truth, I personally do not use trig, I make the computer do it, in Cadkey, a design software. I created points at each nominal, connected them with a line, the the 2 actuals, and connected them with a line, then asked it what the angle was between them. You can do it with trig, but it takes a few more steps, so I do it the easy way, I cheat, I use cad software.

[Bill McCafferty]

Matt,

I've done the same in PCdmis.. Key in the actual locations and snap a line between them and then dimension the angle within the program.

J_T,

In my not so humble opinion, tooling balls are there for the gage build process and nothing else. You can use them to get close, but after that you HAVE to hit your datums and make an alignment that puts your datums on location.

Here is an example of why.. A got in a gage a few days back, one that Kevin used to run in fact, and the tooling balls were smashed. Two were at about 10 degrees from perpendicular to the gage base. Had I not been able to do an alignment from the datums I would have never gotten the gage measured so that we could update it to the latest revision. Also, does your part ever touch the tooling balls? What about the datums? If it doesn't touch the tooling balls then you shouldn't use them as your final alignment. As I said, just my 2 cents worth and in my opinion worth every penny.

Bill

[J Temmen]

I must really be missing something other than my mind. Lets get as simple as I am. What do you verify the fixture nets and Datums to? ,the base or tooling spheres or themselves?:confused:

[Bill McCafferty]

Part CAD if possible the Print otherwise.. Whichever is master.

[Matthew D. Hoedeman]

Well, the other thing you must keep in mind, and this may be going a bit farther than anyone thought about, is your part touching the nets where you measured the nets for the alignment? Quite possibly it is NOT simply because nothing is perfect, neither part nor fixture. So, if you really want to get down to the brass tacks, absolutely EVERY part must be aligned, not the fixture, not the tooling balls, only the part. AND, what do you do when they call out an area of 1" square for the net area? Do you scan each of these 1" squares or do you take one point on them. It all depends on (in my opinion) how silly you want to get with it. Nothing in this world is perfect, nothing, and with that being so, everyone must make a choice on how they are going to give these 'perfect' check results when everything they do is in reallity flawed. If you are working in aerospace, you will have different requirements than if you are working automotive. But, there is rarely fixtures in aerospace. Now, checking fixtures are different than holding fixtures, but a checking fixture CAN be a holding fixture. A checking fixture is what the guy on the stamping line will use to take manual measurements to keep track of the process, a holding fixture is only for CMM use. Now, I have never had a customer tell me I had to align each part as I check it. Now, what is the purpose of a fixture R&R? Most of us have done one at some time or another, so what is the purpose of one? It is to determine IF the fixture (the fixture, NOT THE CMM) can position the part the same way, every time, with different operators. SO, that means NO CMM ALIGNMENT of the part, that means the alignment is on the fixture. So, now we are back to the fixture certification. All the old lay-out boys will understand this one, the fixture SHOULD (actually, the fixture MUST) be in tolerance to the fixture pick-up features so that the part on the fixture CAN BE LAYED OUT ON A PLATE with a height gage, ya know, SCRIBE LINES ON THE PART. If the alignment of the fixture is only off the locators, howinthehell do you set that up on a plate and scribe a line? You CAN'T! So, unless you can really come up with a flat plane on the base and a square side of the fixture (or a known offset or angle), it is useless for the basic, down-to-earth inspection that quite a few places still require. So, certify the fixture to the bases (or tooling balls as a flat plane) and once you get it balanced, check the part in that state or you will never be able to back it up with basic checks that anyone can do, then where are you?

[John Kingston]

Excellent answer Matt. Nice to know that some people remember SCRIBING LINES. That is how I've shown people (new inspectors included) the beginnings of CMM work. Most of our work is aerospace. Customers usually require variable data in our first articles. It makes it fun when we hire someone who has always used fixtures to check parts. Amazing to me how many people can't use mics, calipers, etc. (Oops, going off on a tangent.)

[Matthew D. Hoedeman]

Thanks, John. I know I am a little old fashioned, but when I started in this business, CMM's didn't do iterative alignments, heck, it was real hard to get them to move along a vector! (remember B&S VAL-MEAS 200?) So back in the "good 'ole days" the machinists actually had to do their job right to begin with and not depend on the CMM operator make their work come out right no matter what kind of mess they made out of it. As far as I am concerned, that fixture should be flat and square off the base and edges to begin with, and everything should check good to that, period. In fact, I have a customer that I do certifications for the fixtures he builds and that is exactly the way it is done. Flat to the base, square to the front, origin to a tooling ball or at the corner, and everything checks to that. Now, I am NOT saying that the corner comes out X0Y0Z0, but that is part of what I am checking. The base IS flat, the front IS square, only the actual corner values float (and the worst I have seen from him is about 0.002 to 0.004"). Now, people will say that NOT allowing the CMM to do the iterative form of certification is wasteful of time and money, but it is NOT. If the machinist cuts corners on a fixture to get it up and done, what else is he going to cut corners on? Where will his next error be that he hopes a CMM operator can 'fix' (and that the 'boss' will demand he make check good)? Will it be on that shuttle engine component or the Mars orbitor component? Or will it be on the bracket that holds YOUR seatbelt to the car's reinforcement strut?

[rangerboat72]

I don't know if any of you do work for DaimlerChrysler (my former employer), but this is a link to their AME Gage Standards...

https://gsp.extra.daimlerchrysler.com/mfg/amedd/gages/index.htm



:rolleyes:

[\v/inston]

nice link RB! i have sold dies to DaimlerChrysler and they seem to be much more lenient and understanding than Ford is when it comes to buying off a prog die. maybe it was just the die engineer we had but they would check the parts for function and if the parts worked then they didn't care if small things were out and they didn't care as much about Ppk & Cpk as they did Pp & Cp, they wanted consistency for weld cells.

Now ford was a diffent story, they would do a functional build, the parts would work fine but if they did meet 1.67Ppk we would have to fix them, they wanted perfect parts, which is really hard achieve when you are dealing with metal stampings.

[kevin strine]

Winston;
I'll remember that next time we have to hold 1.67 on a trimed edge with a +/-.2 tolerance. You know where I am coming from on this.

[\v/inston]

heh, ya that is a totally rediculous tolerance on that part. i ran a 30pc cape on it and the worst range was about 8 grand but wasn't even close to 1.67Ppk, on a couple points that were right at the USL. totally absurd to put ± 0.2mm on a developed trim.

that part is not going to get any better, and i think it looks pretty **** good the way it is and have no doubt it will consistenly fit their weld station.

EDIT: *pretty darn good

[rangerboat72]

I'll have to agree with you about Chrysler being lenient. Our plant was a Chrysler plant until about five years ago when they sold off a few of their component plants. Even though we had the written standards, our plant would tend to follow their own standard if you know what I mean. Now that we are no longer a Chrysler or DaimlerChrysler plant, they expect quite a bit more from us.

I'll have to say the last three or four years has been quite a learning experience. Our plant has picked up quite a bit of business from Ford, GM and BMW. It has been quite interesting just comparing the drawing that you receive from one company to another. One may expect a large plastic part to meet a diametrical tolerance of +/- 0.02mm while the other thinks +/- 0.25mm may not be enough tolerance and the different applications of GD&T is also QUITE INTERESTING. German drawings, Russian gages, it's all been quite a challenge to adapt to. Well, my machine stopped BEEPING (good thing the boss is not around), gotta get it goin' again so I can earn that time and a half pay...

Have a good weekend (what's left of it)!