Chromium Carbide / Croblox gauge block material
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    Default Chromium Carbide / Croblox gauge block material

    The recent thread about the Starret Webber gauge blocks got me curious about Chromium Carbide / Croblox as I had never really consciously recognised that they were something different. Starret Webber seem to be the only company that makes them with everyone else opting to make their higher grade gauge blocks out of Tungsten Carbide or ceramic Zirconia.

    Starret Webber make the claim on their website that chromium carbide is the very best material for making reference standard gauge blocks out of, and then provide a table comparing the different materials. This table makes some assertions that honestly come off as somewhat spurious/snake oil to me. For example that the extremely low rate of thermal expansion of tungsten carbide is an objectively bad thing. And that chromium carbide is the "the most stable of all gage block materials" while admitting in their chart that they have "no long term data" for the stability of either ceramic or tungsten carbide.

    I couldn't find any Mitutoyo literature that acknowledges the existence of chromium carbide gauge blocks. Tesa/Brown and Sharpe mention it briefly in a dismissive manor in the literature for their tungsten carbide gauge blocks - "Three times more wear resistant than chrome carbide"

    I skimmed through the literature from Opus Metrology (the manufacturer of most of my gauge blocks) and found no mention of chromium carbide. Same with a few others.

    The NPL's primary publication on gauge blocks mentions chromium carbide in passing but never elaborates on it. Same with the NIST handbook from a quick glance.

    Is anyone aware of any objective third party literature on chromium carbide as a gauge block material?

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    Quote Originally Posted by gregormarwick View Post
    The recent thread about the Starret Webber gauge blocks got me curious about Chromium Carbide / Croblox as I had never really consciously recognised that they were something different. Starret Webber seem to be the only company that makes them with everyone else opting to make their higher grade gauge blocks out of Tungsten Carbide or ceramic Zirconia.

    Starret Webber make the claim on their website that chromium carbide is the very best material for making reference standard gauge blocks out of, and then provide a table comparing the different materials. This table makes some assertions that honestly come off as somewhat spurious/snake oil to me. For example that the extremely low rate of thermal expansion of tungsten carbide is an objectively bad thing. And that chromium carbide is the "the most stable of all gage block materials" while admitting in their chart that they have "no long term data" for the stability of either ceramic or tungsten carbide.

    I couldn't find any Mitutoyo literature that acknowledges the existence of chromium carbide gauge blocks. Tesa/Brown and Sharpe mention it briefly in a dismissive manor in the literature for their tungsten carbide gauge blocks - "Three times more wear resistant than chrome carbide"

    I skimmed through the literature from Opus Metrology (the manufacturer of most of my gauge blocks) and found no mention of chromium carbide. Same with a few others.

    The NPL's primary publication on gauge blocks mentions chromium carbide in passing but never elaborates on it. Same with the NIST handbook from a quick glance.

    Is anyone aware of any objective third party literature on chromium carbide as a gauge block material?
    Not sure how "objective" it is but, Webber Gage wasn't always owned by Starrett who bought Webber around early 1960's as an already respected outfit. May have been a side-component of buying Herman's granite surface plate line? Route-step as they are, I'd not be surprised Starrett never bothered to take-on a full understanding of what they had gotten into.

    Trade catalogs from Webber Gage Co. | National Museum of American History

    May have been a good deal more than 60 years ago Croblox were already established as the cat's best mink lined pajamas for good as it gets for gage blocks.

    AFAIK Webber Gage was the only maker of Cromium Carbide blocks. Maybe "ever"?

    AFAICS, there is still nothing better for PRACTICAL shop-floor use, whether at STP or reasonably workable ambient shop temp. They are just the right balance of stable and durable.

    Just not also CHEAP!

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    Quote Originally Posted by thermite View Post
    May have been a good deal more than 60 years ago Croblox were already established as the cat's best mink lined pajamas for good as it gets for gage blocks.

    AFAICS, there is still nothing better for PRACTICAL shop-floor use, whether at STP or reasonably workable ambient shop temp. They are just the right balance of stable and durable.
    Yes, that's effectively what it says on the S-W site.

    However I can find nothing to back it up.

    Quote Originally Posted by thermite View Post
    They are just the right balance of stable and durable.
    Durability it seems is demonstrably inferior to tungsten carbide, and stability is apparently unknown beyond that it's "better than steel".

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    I don't think it's inferior. It's used in valve body facing where tungsten carbide doesn't last. Mainly due to better corrosion resistance I think. Probably either one is pretty bulletproof as a gage block. Chromium carbide is a ceramic, so it's pretty wear resistant stuff. It's not very clear if they (Starrett/Webber) make the gage blocks as a sintered matrix with other stuff or what. They probably won't tell you either.

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    Quote Originally Posted by eKretz View Post
    It's not very clear if they (Starrett/Webber) make the gage blocks as a sintered matrix with other stuff or what. They probably won't tell you either.
    I hadnt thought of that - Webber lists the CTE as 4.7 ppm per degree C. According to the references I find, chromium carbide (Cr3C2) has a CTE of ~10.4 ppm per degree F, so 5.7 ppm per degree C. The difference could be due to some small percentage of binder, although I doubt any binder (metal) would have a lower CTE than that of a ceramic. Difference could be measurement errors.

    While the surface finish of a gage block is pretty good, I doubt it would be good enough for true metallography where one could use a microscope to see if there are two phases (ceramic chunks glued together with binder). Anyone have an XRF gun they can point at one of these blocks? If any element other that Cr and C is read, then you can be reasonably sure there is a binder. Assuming they use pure Cr3C2 that is.

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    Quote Originally Posted by LAmachinist View Post
    I hadnt thought of that - Webber lists the CTE as 4.7 ppm per degree C. According to the references I find, chromium carbide (Cr3C2) has a CTE of ~10.4 ppm per degree F, so 5.7 ppm per degree C. The difference could be due to some small percentage of binder, although I doubt any binder (metal) would have a lower CTE than that of a ceramic. Difference could be measurement errors.

    While the surface finish of a gage block is pretty good, I doubt it would be good enough for true metallography where one could use a microscope to see if there are two phases (ceramic chunks glued together with binder). Anyone have an XRF gun they can point at one of these blocks? If any element other that Cr and C is read, then you can be reasonably sure there is a binder. Assuming they use pure Cr3C2 that is.
    I doubt there is any "binder". Traces elements that are more accurately classed as "modifiers", rather. Go and check the several ways the material is manufactured. It has several Isotopes and crystal structures. It is used for a LOT more than just gage blocks!

    Wear plates, valve seats, and sealing surfaces have been mentioned.

    It is also applied "on a grand scale":

    Steel Plate Supplier, Birmingham, AL - Alabama Hardsurfacing, Inc.

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    My two cents worth: I have an 88 pc Grade 1 set of Croblox that I bought used. Original manufacture date is 1982, and it came with a copy of a 1992 calibration lab report. I had to replace two missing blocks (not cheap is right) and when I had the set verified/calibrated in 2018 the results were almost identical to the 1992 report. I had read through some Starrett catalog material and figured it was typical "Bow-wow, ours is best, yada yada". But, even though I am a jaded inspector, I called the gage division and said something like "Wow I'm impressed" and maybe threw some virtual confetti at them. They came back from the lab oiled but that is not necessary. From reading I know that wear and growth are the usual causes for replacement. I have used a variety of steel blocks, usually Mitutoyo or Webber and I feel the Croblox are best for long term durability and are easy to wring. Probably not being able to find a lot of specific information is due to the companies themselves, i.e. trade secrets.

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    Nobody has offered anything compelling yet...

    What actual, quantifiable, not anecdotal, benefits does chromium carbide offer over zirconia?

    According to Webber's own table that I linked earlier, the only benefits over zirconia are lower surface roughness and higher thermal conductivity.

    I find both of these claimed benefits to be misleading at best;

    Surface roughness - both tungsten carbide and zirconia gauge blocks wring very readily, much different to steel, so any difference there is almost certainly purely academic.

    Thermal conductivity - effectively every practical use-case of reference gauge blocks requires maximal thermal stability. Why would a high CTE and a high thermal conductivity ever be considered anything other than a bad thing for a reference artifact in a controlled reference environment? The thermomechanical properties of chromium carbide therefore seem more suitable to working gauges, but Webber are promoting it as the best material for "reference gauges". Doesn't make sense to me.

    Summary of above; Tungsten carbide - low CTE, low thermal conductivity
    Zirconium - high CTE, low thermal conductivity
    Chromium carbide - high CTE, high thermal conductivity

    From another angle; why has every other manufacturer of reference standard gauge blocks settled on tungsten carbide and zirconia, and ignored chromium carbide. There's no way that Webber or anyone else holds any enforceable patents on the material.

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    Gregor, why don't you send this question to Starrett/Webber? They are probably more qualified to answer than any of us. If they will answer anyway.

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    Quote Originally Posted by gregormarwick View Post
    Nobody has offered anything compelling yet...
    Folks seem Hell-bent on treating heterosexual relations the same way, despite them having worked well ...and for a long time, already.

    I don't give a damn. I'm sticking with my respect and affection for healthy wimmin'!

    And Croblox.

    Each being "good enough for MY needs", thanks!

    Some things just have to be experienced ... and still remain hard to explain?

    How's that for a-neck-dote-all?


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    Depending on when Webber first started making croblox gauge blocks, zirconia may not have even been an option for the company to consider - I suspect the zirconia gauge blocks are actually partially stabilized zirconia. Making large sintered zirconia parts was a technological challenge due to a phase transformation in the pure material that induces cracking on cool down from sintering temperatures. The key is to stabilize the cubic phase so that there is no phase transformation and associated volume change, and thus no cracking. I think this was a relatively recent (last 60 years) development in materials science.

    Not having experience with either gage block material, I certainly cant say which is better. I suspect that arguing over zirconia vs chromium carbide is splitting hairs - they both are non-magnetic, much more wear resistant than steel, and corrosion resistant. Each company sticks with the technology they developed and/or patented and naturally insists it is the better than their competitor. Everyone loves easy answers, but when it comes to material selection for a given application, blanket statements like "X is always better than Y" are darn hard to make and seldom defensible.

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    Quote Originally Posted by LAmachinist View Post
    Depending on when Webber first started making croblox gauge blocks, zirconia may not have even been an option for the company to consider - I suspect the zirconia gauge blocks are actually partially stabilized zirconia. Making large sintered zirconia parts was a technological challenge due to a phase transformation in the pure material that induces cracking on cool down from sintering temperatures. The key is to stabilize the cubic phase so that there is no phase transformation and associated volume change, and thus no cracking. I think this was a relatively recent (last 60 years) development in materials science.

    Not having experience with either gage block material, I certainly cant say which is better. I suspect that arguing over zirconia vs chromium carbide is splitting hairs - they both are non-magnetic, much more wear resistant than steel, and corrosion resistant. Each company sticks with the technology they developed and/or patented and naturally insists it is the better than their competitor. Everyone loves easy answers, but when it comes to material selection for a given application, blanket statements like "X is always better than Y" are darn hard to make and seldom defensible.
    Meahh.. I'll plead guilty to "nostalgia."

    When I was young in the craft, only a COMPANY could afford Croblox. And few who COULD afford them bought them! So it was sort of a near-religious experience to be privileged even the sight of them - in use by the top-hand, not we peons and middlings!

    Gregor isn't "wrong" in pointing out a shortage of hard evidence.

    But it is hard to overcome that "legendary" reverence. At least for MY generation - vintage of '45.

    Mind, we are-too, well aware - VERY WELL aware - that newer tecnology has made the classical gage block a great deal less relevant.

    But whatever else?

    Never yet met a gage block gone tactically hors de combat useless... for lack of a special BATTERY they don't have on the blister-pack board at Food Lion, Big Box, or CVS/Walgreen's, locally!


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    I think maybe I wasn't very clear about my line of thought right from the beginning.

    Specifically, the use of chromium carbide as a reference set. Webber make the claim that it is the best material for such.

    My objection to that is that the properties they cite appear to contradict* that claim directly.

    Their table shows a relatively high coefficient of thermal expansion and a relatively high thermal conductivity, both of which are generally undesirable traits in a reference artefact specifically.

    Zirconia and tungsten carbide both exhibit much better thermomechanical stability compared to steel. Demonstrable under a 0.1μm resolution comparator and a pair of fingers. From the numbers alone, it appears that chromium carbide should exhibit thermomechanical stability similar to steel. I'd be interested if anyone who has some could prove this.

    And that no comparative data exists as to the general stability over time between the materials (I suspect that in reality all three materials are approximately comparable in this respect, at least compared to steel, but omitting that data allows them to score a point in their table)

    I'm not trying to rain on anyone's parade by attempting to prove that croblox are shite, there's no need for anyone to get defensive about it. It's clear that they are functionally close to zirconia, which absolutely makes for extremely good gauge blocks. If anything, my gripe is about marketing and obfuscation, and that table...

    * and that the "poor, good, best" crap in the table is also misleading and contradictory.

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    Quote Originally Posted by gregormarwick View Post
    Their table shows a relatively high coefficient of thermal expansion and a relatively high thermal conductivity, both of which are generally undesirable traits in a reference artefact specifically.
    How, on EARTH, could it possibly matter if there IS NO significant temp delta?

    Room a "reference" set is used in might have a temperature swing of but plus or minus half a degree F, block handled with tweezers and / or allowed to re-stabilize to 68 F / 20C if touched with 95 F human fingers.

    I can hold my poor-boy metrology / layout area within plus or minus only TWO degrees F off a target 68 F, year-round. Plus or minus four degrees F is cheaper and good enough.

    Chasing the least important characteristic? Unless you expect to tote these buggers out in the field to oil rigs or such, tropics to the Arctic.

    I just don't see that - nor even my wider swing shop floor - all that likely for a "reference" set of blocks.

    Brand-new set of El Cheapo's serves the shop .. where hammers and cutting tools and other nasty stuff shares space. The Dearborns don't GO out to play there.

    Nor would the Croblox if I had those to vet an El Cheapo stack - or Pla-Check, Digi-Chek (that one is metrifuckated), Hite-Icator against.

    "Reference" set. Top of the food chain.

    Control the temp. Or wait for the right time of day? Which isn't as clumsy as all that, BTW.

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    Quote Originally Posted by thermite View Post
    ...
    From the top, this is an academic argument only.

    The claim is made that it is the best material for reference purposes, the data supplied* appears (to me) to be contradictory to that claim, and zero corroborative (to me) data is supplied.

    *and I absolutely agree that it is not the most important characteristic - simply that it's about the only real data supplied that particularly relevant to the claims made, so discussion of any other characteristic is not yet possible.

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    Quote Originally Posted by gregormarwick View Post
    From the top, this is an academic argument only.

    The claim is made that it is the best material for reference purposes, the data supplied* appears (to me) to be contradictory to that claim, and zero corroborative (to me) data is supplied.

    *and I absolutely agree that it is not the most important characteristic - simply that it's about the only real data supplied that particularly relevant to the claims made, so discussion of any other characteristic is not yet possible.
    I've nooo idea how well they sell againt Mitutoyo. Or Hexagon? Or whomever else is doing other ceramics or Tungsten Carbide.

    I'd go so far as to guess they are not in first-place, nor even close. They were NEVER "common".

    But WTH? If I remember them from late teenage years and they are still being made?

    SOMEBODY must have figured they got the job done.

    So "academic" it is! AKA "Too late NOW!" ... to tell them they should give it up as a bad idea?


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    Quote Originally Posted by LAmachinist View Post
    I suspect that arguing over zirconia vs chromium carbide is splitting hairs - they both are non-magnetic, much more wear resistant than steel, and corrosion resistant. Each company sticks with the technology they developed and/or patented and naturally insists it is the better than their competitor. Everyone loves easy answers, but when it comes to material selection for a given application, blanket statements like "X is always better than Y" are darn hard to make and seldom defensible.
    Bingo. For any selection of anything there is seldom a choice that is superior in every aspect. You take the one that has the most ideal characteristics for the situation. It may still have some drawbacks in certain areas compared to other choices. Whether Croblox is superior for a reference block application compared to ceramic blocks is probably down to a "six of one, half dozen of another" type of situation.

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    I can identify with that.

    I always wanted a two-ton Master Pink surface plate because it looked totally cool, like a 12-foot shelf of Thomas Registers. Our gage blocks are steel Johanssens because I could afford them at an estate sale and they are close enough to calibrate our stuff so that parts we make will fit other parts we made 20 years ago.

    In a way, I envy people who have to care about higher standards...

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    I bought a pile of gage blocks a couple years back for a low price that had been in storage for many years in a uncontrolled environment. Out of about 350 blocks only a couple had no rust or staining on them. They were Croblox blocks. The one's with the worse rust were Brown & Sharpe. The others with spot rust here and there were mainly Starrett, DoAll, and P & W. There were a few of other old brands mixed in, too. There were no Mitutoyo blocks in the batch. The Croblox blocks had no rust what so ever on them. They are used, you can see some superficial scratches on them, but they still wring together with other good blocks.
    As for determining what kind of material Starrett uses for these blocks, well you have to go up the ladder way past 52100 grade to one that poses a lot of chrome, Tungsten, who knows what else. Probably not so much nickel, and still capable of being harden in the 58-62 HRC range be my guess. Anybody willing to give up a block to get a spectral analysis done to identify key elements used in the steel used?

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    Good anecdotal evidence there. The blocks are a type of ceramic, not a steel alloy. The ceramic is chromium carbide.

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