Standard (Or Generally Agreed) Method For Measuring Run-out
Standard (Or Generally Agreed) Method For Measuring Run-out
(OP)
First post in this forum - starting with a question I hope someone can help me out with; hoping there might be a definitive answer to this one.
The company I work for currently measures run-out (TIR) on 16 cylinder diesel engine crankshafts by using a steel-topped table, two vee-blocks (not solid vee-blocks, but with rollers) and a dial indicator. Now, some have suggested that a level, solid granite table should be used and others have also suggested that solid vee-blocks should be used instead of vee-blocks with (little bit worn) rollers. Furthermore, because of the length/weight of the crankshaft others have suggested that multiple vee-blocks are required to counter possible deflection of the crankshaft under its own weight.
My question is this - is there a standard method (ISO, ASME, BS, etc.) for measuring crankshaft run-out (TIR) using vee-blocks and a dial indicator? Any insight into standard methods and/or other methods and practical considerations?
Any help would be greatly appreciated.

The company I work for currently measures run-out (TIR) on 16 cylinder diesel engine crankshafts by using a steel-topped table, two vee-blocks (not solid vee-blocks, but with rollers) and a dial indicator. Now, some have suggested that a level, solid granite table should be used and others have also suggested that solid vee-blocks should be used instead of vee-blocks with (little bit worn) rollers. Furthermore, because of the length/weight of the crankshaft others have suggested that multiple vee-blocks are required to counter possible deflection of the crankshaft under its own weight.
My question is this - is there a standard method (ISO, ASME, BS, etc.) for measuring crankshaft run-out (TIR) using vee-blocks and a dial indicator? Any insight into standard methods and/or other methods and practical considerations?
Any help would be greatly appreciated.





RE: Standard (Or Generally Agreed) Method For Measuring Run-out
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
I hope the top of the steel table is at least a couple of inches thick, and reinforced beyond that, i.e., a foot or two deep overall; you need a reference surface that stays pretty flat under the considerable weight of a large crank. I.e., it should look like, or be, part of a large machine tool.
It's probably possible, if a little inconvenient, to rotate the crank within its own block, and remove the bearing shells and caps at the journal you want to indicate. ... but you have to make sure the block is properly supported and leveled on a big rigid table, because the blocks of big engines are flexible, too.
>>> What does the shop manual say? <<<
Mike Halloran
Pembroke Pines, FL, USA
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
As it was already stated solid v-blocks (even placed on perfectly stable granite table) are not the best option for establishing repeatable and reliable datum axis especially when form errors of portions of the shaft assigned as datum features are significant (e.g. three-lobbed). If rollers you want to use instead v-blocks are worn, the measurement uncertainity will not be smaller, that's for sure.
As for usage of additional v-block to limit the deflection of the shaft, keep in mind that whenever possible a method of supporting the part for inspection should reflect how the part is supported in working conditions. Is your crankshaft supported in 5 places in reality? If yes, then your supplier is correct. But if not, you will be checking a geometry in really non-functional condition, which may cause a lot of troubles in a future.
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
V-blocks for checking runout does not really follow the requirement since, usually, the datums are developed from full diameters rather than a V contacting the surface of the datum feature at either 45 or 60 degrees. If one diameter is a bit larger than the other, it would also throw off total runout (not circular though) since the readings would increase as we move along the surface of the feature towards the larger size. In other words, the center of the datum feature would be higher on the larger size datum feature. The use of chucks on each end is much better.
The dial indicator must contact on 90 degrees to the surface when measure either runout so move the indicator and base until one finds the high point (center). I have enclosed a picture and more info that might help.
Dave D.
www.qmsi.ca
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
What is the reason that your chuck or collet is not covering whole length of datum feature D and why is the whole technique you described reserved for small coaxial products?
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
If you cannot place the product in a chuck, then one cannot confirm either circular or total runout. That is the reason that I mentioned that it is reserved for small coaxial products. The crankshaft in question may be relatively large but can be placed in chucks at both ends.
Total runout combines off center, roundness and size distortion along the feature relative to the datum structure, probably datums A-B in the crankshaft case. Since the feature is a feature of size, it must meet the size tolerance first and then the total runout requirement.
In my example, the datum feature is inserted into the chuck full depth of the chuck which give a rigid datum and it is as far as it could go inside the chuck. If I were to have the crankshaft set up on chucks rather than V blocks, then I would only insert the datum feature just inside the chuck jaws on both chucks just in case the centers are not exactly the same.
Dave D.
www.qmsi.ca
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
Number: ZERO
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
Plastic v-bearings can be found in printers.
If the assembly does not use v-bearings then I'm generally with the others who have brought up collets or chucks as datum feature simulators. On the other hand, if the cost is too high for such things, and if the size, orientation and form of the datum features is controlled well enough relative to the runout tolerance value, then the additional uncertainty added by supporting the part in v-blocks may be acceptable. It's no worse than the uncertainty introduced by approximating a hole's axis by using the center point of two circles within the hole, or approximating a hole's mating size by measuring a best-fit diameter... Those sorts of atrocities are committed thousands of time every day. In some cases the parts are nice enough, relative to the position or size tolerances applied, that those practices may be acceptable ways to save a bit of inspection cost. Doing these things without understanding the issues isn't OK, but as long as one understands and considers the issues as measurement set-up and process decisions are made then all should be OK, or possibly even optimal.
Dean
www.d3w-engineering.com
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
It's total indicated run-out (TIR) I'm trying to measure, not circular run-out (not entirely sure what circular run-out is though?).
If the number of vee-blocks (and noted the discussion on this) is supposed to mimic the number of points that the crankshaft is supported on when installed in the engine block, then ten vee blocks would apparently be needed when taking measurements on the 16 cylinder crankshaft out on the table.
I'm not a mechanical engineer - I just thought there would be a standardised method somewhere out there? Would prefer to use a "certified flat" table and just the two vee blocks for cost reasons: some people are saying this should be fine, whereas others are saying that the crankshaft will sag and this will affect TIR measurement (the crankshaft supplier method calls for five vee blocks, but no explanation as to why).
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
Measuring runout requires that the axis of rotation be held constant through rotation. Vee blocks all but guarantee that this will not be the case. If you are dead set on using vee blocks, you would have to first verify roundness of the datum features. Verifying roundness is a far more tedious, time-consuming (and thus expensive) proposition.
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
Dave D.
www.qmsi.ca
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
Assuming that full diameter is shown as the datum feature and there is nothing on the print specifying that only limited portion of that feature should be used to establish a datum axis, how should datum feature simulator A look like? I mean, what should be the length of that datum feature simulator in axial direction?
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
The theoretical datum feature simulator should be round and full length of the feature excluding the inside rad in RMB. I guess we would try to fulfill this requirement as much as possible with the chuck closer to full compliance than the V blocks.
Dave D.
www.qmsi.ca
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
I assume V blocks would be a reasonable alternative.V blocks are usually bought in matched sets, so using 3 V blocks will throw another variable in the whole mess.I feel a fixture is needed to keep the V blocks linear. A lathe bed type of arrangement would work.I've seen opposing " blade" type discs used as v block replacements, argument being the small linear surface will be less prone to pick up foreign matter between surfaces.The "factory" usually calls out specs and how to arrive to accurate measuring.I have found the main idea is to measure journal to journal, not journal to V block. So if journal #1 runs out .003",mark on journal high or low spot,one not both, Go to #2 journal, measure an see if the runout, if any, coincides with #1.Go down the row of journals, record the findings.I all sag the same way, then its probibly sag caused by weight.You could put crank on V blocks and check runout of machined centers on ends of cranks also.If checking cranks is fairly often, investing in perminent fixtureing may save a lot of time and confusion in the long run.
RE: Standard (Or Generally Agreed) Method For Measuring Run-out
Peter Truitt
Minnesota