What’s A Toolmakers Vise For?
At first glance, a vise is not a measuring tool so why am I talking about this thing? Well, a toolmakers vise is a vise (duh) that is precision ground on just about all of its surfaces, certainly all six square sides, the jaws and ways are square and parallel to a high degree. The depicted vise is also a “screwless” design that uses an hex draw bolt instead of the usual screw to secure the moving jaw in both an inward and downward direction. This avoids introducing error due to jaw lift.
Suppose you have a part that you want to check for parallelism of some awkward surfaces. As an example, I have just made some t-nuts for securing things to my milling table. I was wondering how I did with my setup. An actual metrology application or, as a certain Youtuber says, “the surface plate: where dreams go to die”. As you can see, checking the vertical surfaces of the inverted T is not just a matter of plunking it on the surface plate. The darned thing won’t stand up on that face.
And so the vise comes into play. I know that it is very square and so if I clamp the t-nut in the vise, the clamped surfaces should also be parallel to the corresponding vise surfaces. If I check both ends, it will tell me how off it is. To take the reading, I leave the indicator and stand stationary and slide the vise and part around under the indicator tip.
And the answer is, in machinist terms, quite a bit, about .0015 if I am generous. The same error is present on the other nut I made so at least I have repeatably created the error. This is why one makes t-nuts for practice. The required precision is not great and you can mess things up and still have a usable result. If it was important, I would have to investigate the source of the error (milling vise alignment, mill head nod, etc…)
As is probably obvious, you can also use a toolmakers vise for workholding. I have seen various videos of this sort of vise being used to hold a part being milled.
Toolmaker’s vises come in different designs and many sizes. Mine is only about 2.5″ long overall. They can get expensive really fast.
As an alternative, you could clamp the part against a 1-2-3 block and rest it on the plate. Or use a v-block or some other way to prop it up vertically. In this case, you would likely need to move the indicator stand around which is finicky in that you can tilt things and mess up your alignment.
As always, you can spend a lot of money on a toolmakers vise if you want to. There are some beautiful makes and models out there that are breathtakingly expensive and certainly more than most hobbyist need. The cheapest 25mm/1″ version I found online goes for about $60CDN. Mine is a somewhat higher quality model but still accessible at least in this small size.