I’m starting this because a thought came to me while reading the new calibration brainstorming thread. What things are easy for most people to find and buy/borrow that are accurate. I believe the number and availability of such items is staggering and they may serve us well for measuring more accurately than rulers and tapes. Even calipers can be tough to get dead straight in some instances.
My first thought was drill bits. They’re available in a ridiculous range of sizes and definitely accurate enough to use as gauge pins (inserted the wrong way around) for setting cutter compensation.
Bolt heads are also accurate enough for our purposes to use as gauge blocks and easy to find.
Sockets are very round and almost everyone has those or knows where to borrow some.
Sockets would need to be accompanied by a “very near” caliper so you know what the outside diameters are, but with that information, it might be a way to use these common gauges to check calibration cuts.
I’m not sure how exactly, but this might spark some ideas in others.
For a modest investment, around $10 on sale, I have purchased a couple of digital calipers from Harbor Freight. They come in handy for all kinds of things.
Most yardsticks or combination squares are usually 1" or large framing squares are 1 1/2" x 2". If you are looking for some larger diameters I bet you can look in your kitchen and find some pans that have a standard outside diameter, I would make sure the spouse is not looking for this one.
There are a lot of things that are pretty accurate for short distances, the
problem we have in calibrating the Maslow is high precision at long distances
the big errors we are fighting tend to be at the outsice bottom corners more
than anywhere else (except for frame warping, which is worst in the top center,
but a top beam frame addresses that very nicely)
I was thinking more along the lines of cutting shapes and then having something that you have readily available to check the cuts that you just made. The less that you actually have to measure something the better off you as opposed to taking a known object and comparing it to a cut you made.
That was exactly my thought too. Cut something on a suspect part of the sheet and using a known whatever as a go/no-go gauge.
Use a drill bit to verify cutter diameter, then cut some test shapes on a sacrificial board (or the back of a spoil board). Use the known whatever to see if the shape is right.
Even if the known whatever only becomes known with the aid of an inexpensive caliper or borrowed nice caliper.
At the university we had two huge galley cameras for shooting 30x40 films for later exposure on a Printing plate. The camera’s copy board and lens plate had to be perfectly parallel. The problem was those two parts were over 6’ apart from eachother.
The camera’s came with a 7’ long fiberglass tube with a dial indicator at the end. We could, with careful adjustment, the the platens parallel to within 0.002".
Disaster struck one evening when a slightly inebriated graduate student who will remain nameless dropped then stepped on the fiberglass tube. It was ruined. The dial indicator (a very heavy brass-bodied Sterrett) survived.
The camera’s were 30 years old when I got there and the company who made them had long been gone from the industry, no longer offering replacement parts. What to do?
A machinist friend and I, facing the same challenge as we have here, decided that while it’s very difficult to make large parts accurately, small parts and their interference to other small parts is easy to control. We also had the benefit of a coordinate measuring machine with a 19" bed… but that’s nEither here nor there.
In any case, we were able to fabricate, from hollow aluminum tube, several pieces that threaded into eachother. We were confidant in the length of our individual pieces and therefore confident in the overall length once assembled. We duplicated the original part to within our ability to measure the original piece and subsequent calibrations of the machine matched the original.
Unless it was really hot… AL does expand a bit after all.
Anyway, I think we could apply the same principal here; creating a piece of known length from smaller, easier to measure lengths that can then serve as a reference for marks cut by the calibration routine.
That may be (is) the case. My initial thought was based on using drill bits to verify the size of hole or slot being cut by the router bit, for better cutter compensation accuracy. More for people who don’t have access to a caliper or rule they trust. Why not scale it up? It might not be the answer, but it might help.
The tests I’ve seen of inexpensive digital calipers say they lack durability and surviving dropability (and eat batteries…) but they are more accurate than you’d expect for the price. In the states they’re easy to find, and if you can handle the shipping delays there’s the Asian megastores and AliExpress. They’re not Mitutoyo’s but they’re a whole lot cheaper.
There’s one or more in most of the distributed Mooselake Manor shop complexes.
