Measuring 1 to 2 foot long objects accurately - how?

I have a flat sheet part that is spec’d to 15.217 inches. If it was more like six inches, I’d just take a caliper and gauge it with that. How would one go about precisely measuring something that is too large to fit inside of calipers? Thanks in advance!

What’s the tolerance?

I suspect there is some clever way you could clamp it onto the bed of the Bridgeport, and use the edge finder at both ends and calculate the length that way.

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During a prior career in mechanical design I never specified sheet metal parts to better than ±0.005 - with ±0.01 being the more common tight specification.

Is a long Vernier caliper available?

Let’s say +/- 0.005 if that’s feasible. I am guessing one way to do it is to put it on the Haas and then probe it from there but I don’t have clearance on the Haas so hoping there is some other magical tool at the space (really hoping for a comically large caliper!) that would make this pretty straight forward.

Unfortunately the specs do state 0.005". I am guessing this might be their boilerplate laungage that I never pushed back on. Lesson learned. The parts are water jet cut so with the variable kerf of a water jet I guess I was begging for trouble like this.

Early on in my prior career I got a talking to calling out 3-figure dimensions for simple parts that could have been ±0.03 without issue.

There may be some large calipers laying around, I think they used to be in a wooden box under the blue table back before expansion, but I haven’t really looked around to see if they’re still there since.

Before expansion?! Ha OK I will try and search around for it. I do recall seeing large calipers a while ago but not 15" large.

There were some 12" calipers but they were destroyed and not replaced because they were super expensive.

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Well, as Michael stated, we have vernier calipers under the granite surface plate. They are 24” best I remember. Additionally you could theoretically put it on the Bridgeport & use the DRO as Chris said.


I think you may actually have a two fold problem. Do you intend to CUT that sheet to that specific size with .005" tolerance? Measuring it is one thing… cutting it to that size is another. You MIGHT get that tolerance using the Bridgeport DRO and then make the cut using a fairly new milling bit. Short length cuts would certainly be accurate but any error or slop in the Bridgeport table will be amplified by the 15" travel. ( I HAVE heard of a machinist making parts for the US military during WWII with a tolerance of an incredible .0005" on a mechanical mill similar to a Bridgeport, but I don’t think that was a large piece.) Your actual tolerance is plus or minus .005" so a target that is .010" wide should be possible on the Bridgeport. That being said, unless someone else knows of another machine, I think the only machine at the Makerspace capable and proven with that kind of accuracy is the HAAS. So you can try cutting it on the Bridgeport but I’d ask someone to measure it (or just cut it) on the HAAS.

So I picked up another batch from the waterjet cutter. They are a professional job shop and had a pair of high quality large calipers. The new batch that I was picking up was different size from the customer-claimed faulty batch, but when we measured one of the dimenions it was +/- 0.002 from the spec (which I was surprised by, I thought waterjet cutting would be more imprecise than that; this tolerance is more than good enough) but in the other dimension it was +/- 0.01. He mentioned that they recently recalibrated the machine. I am wondering of one of the axis on the machine is out of spec a bit.

Anyway, the customer is sending the part that my parts need to fit into for me to test against so I’ll try and measure that as well