'noon all, A seemingly simple thing: Where can I buy a Ballbar? I need a 300mm (ish) ballbar, and I have a feeling this should be an off the shelf item (like gauge blocks), but I cannot find a supplier....
Yeap, the super accurate one is still in progress, thats a research project / long timescale item (its still not certain that it is possible to make such an item to the required tolerance), but I need a different (somewhere around 200mm - 300mm) long one to calibrate a pair of sensors into a single measurement volume, for a demo, for next week... I can buy such things off the shelf in the USA, from for instance:
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Id prefer to source in the UK if I can, not to mention the vagaries of shipping (customs) from the US.
A ball bar is a bar and a pair of balls, where the center to center distance is accurately known. the balls are a surface a known distance from a point (in the center) and as such you can use it to calibrate metrology equipment, usually CMMs, but in this case its an optical fringe projection system that I work on, theres a bit more info at
The pattern 150MM, 200MM in the product description confused you too much. :-) We all know that people of the US of A do have problems adopting to the metric systems. That already starts with the correct usage of units. mm, not MM (that would be MegaMega). I guess they'll catch up in some decades.
...except in the oil & gas business, where MM (or mm) is one million (M (or m) = 1000). Don't ask me why, it's completely barking mad, but it's been like that since forever and shows no sign of changing. Drives me mad (I work in that area, and trying to persuade US colleagues to use SI units is a hard job).
Some of us can do simple mathematics in order to do the conversion. The political class seems least able to understand numbers and accounts but I have a feeling that isn't just a US problem.
Wel, its exactly like it says, it a bar of fixed length with to accurate spheres on the ends.
Because the spheres are accurately round you can measure them at several points and from that get a 'virtual' point center. They are used to calibrate things like CMMs, where you know that the length of the bar is a certain distance, and so you can evaluate the measurement volume by using multiple poses of the bar a several angles etc. The renishaw device is used to evaluate the tooling, as they move, and the measurement is taken from the probe as it is forced to change length by the machines movements. If the (CNC Mill for instance) describes a circle then the length wont change, and so you can determine th emachines accuracy from the renishaw results. In this case I need to calibrate an optical metrology system, so a fixed, known length bar is required.
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