Couple of videos of my newly made height comparator in use.
A comparator doesn’t measure distance, it measures differences or deltas of distance from a plane (in this case, horizontal). This allows you to determine how flat an object is or if two objects are the same height (within the accuracy of the indicator attached to the comparator). I’m using indicators that can measure better than one thousandth of an inch.
Please note that this is entry level metrology, 10x (tenths of one thousandth of an inch) is pretty easy with mechanical methods but is getting twitchy and expensive. Smaller means electronics, then optical and temp controlled environments.
In this first video, I show what the comparator looks like and use it to check how flat, parallel and matched a pair of $12 Enco 123 blocks (1″x2″x3″) are. As near as I can measure, they exactly the same.
Note that I don’t know if the surfaces are perpendicular, the block could be a parallelepiped. To check that, I’ll need a “face” comparator (such as the pictured Taft-Peirce 9146 Comparator Square). You’ll notice that I have a machined area on the bottom of mine for just such an attachment.
I tap on the stand to “settle” it.
I put a spacer in front of the comparator so I could use to check squareness (two parallel planes with a perpendicular plane is self proving; when flipped, both planes have to be the same distance from a fixed point. In the above photo, as the cylinder is rotated, the indicator must not move). Anyway, the blocks are wildly out of square, just awful. The blocks can only be used as spacers or door stops.
In the second video, I check to see if an aluminum block I machined at 25° is really at 25°. To do this, I set the block on a known 25° surface and check to see if my block is level (ie parallel to the surface plate). To create the reference angle, I use a sine bar. Mine is 2.5″ so I need 1.065″ under one of the rolls, which I create with four gauge blocks (Suburban Tool has a video on how to use gauge blocks). Looks like I have some remedial machining to do and this shows me how much and where I need to cut.
I put the block in a tool makers vise (square every which way), used the comparator to leave the high side up (the amount it is out), clamped the vise on the mill, took a pass and now the block is within a thou. Plenty good.