When squaring things in, it is best to indicate the actual thing doing the work, not a surrogate. The back of the table and the side of the vise have nothing to do what we want to achieve, and may not be machined correctly themselves. By indicating the fixed jaw of the vise, we are directly making it parallel with the table motion, which is what we really care about for many mill jobs. It is almost certain that NO part of the table is actually dead on square or parallel with the table travel. Maybe very close, but why use intermediates that have inaccuracies and/or can move and wiggle? Using your square clamped in the vise might be useful for tramming the in and out travel (Y on a vertical mill) by indicating it, but that would also be subject to the squareness and the parallelism of the square and it's mounting. Any assumption that the parts and axes of any machine or tool are actually square and parallel with each other is just faith and hope. Test it and see...I use a machinist square for quick vise tramming. The "fat" end goes against the front of the table, the thin end goes against the side of the vise (the vise clamp is removed on that side). Tap the vise so there is no visible gap between the square and vise. This gets me to .001"/3" (the width of my vise jaws) or better. Make sure there's no swarf between the square and table/vise, eh?
My vise stays on almost all the time. It's also keyed. I can't believe everyone doesn't have a vise like this...A bit off subject here, but many people leave their vises on the mill when it would be much smarter to take it off
Yes ,very creative, but as Bob Korves inadvertently explained, the table would have to be in the exact same position every time, including tension on the gibbs.What an awsome idea. If the laser dot can be positioned within 1/16 of an inch from the dot on the wall 20 ft. away then you could expect that traming the 6" jaws with an indicator would give:
0.0625/240 = y/6
y = 0.0016"
We will have to disagree then, Mark. Nothing is machined perfectly, and tolerances can add up. I always try to measure the important surface directly when possible, and I do not trust anything to be correct as received. A single appropriate test takes all guessing away, no leaps of faith. Most work does not require extreme accuracy, and when it doesn't, then shortcuts can be taken, with often large time savings. If that type of workmanship becomes ingrained and carries over to important work, then there can and will be unacceptable inaccuracies.Bob I have to disagree with you. Vises are ground parallel on all sides, a square in the shop should be up to snuff parallell and at 90 degrees. If not give it to a carpenter.
Tables and slots are parallel to the axis on machines. Why do you think they put key slots in Vises?
If so the machine tool is junk! I have never ever come across a table in a shop out of wack as you state not parallel on there axis!
Accuracy is not what you are worried about, repeatability is what you want. The accuracy number is what it can be off from perfect level. If it is perfectly repeatable then it will be fine.Twenty feet is 240 inches. If the dot is 1/4" in diameter, .25/240 is about .001"/". I typically align my vise to be less than .001"/4" which would correspond to .060" @ 20 ft.
However, for many operations, .001"/" is sufficiently accurate enough and the 13 seconds mounting time is very attractive.
I wondered about the reproducibility because most laser leveling devices typically quote 1/8" inch accuracy.
I do exactly the same. I also use t-nuts that are carefully shop made from mild steel, and with all exposed edges and corners rounded over to smooth large radii. They do not mark the table if they slide on it, but I do try to keep them clear of the table until over the t-slot. The t-nuts fit tightly enough to have to wiggle and push down on the vise slightly to get them into the t-slots, and also into the slots on the bottom of the chuck when changing the vise from 90 degree mounting to longitudinal mounting and back again. I always get within .0001" by simply dropping the vise into the t-slots, and a simple light push in the known direction with the heel of my wrist when tightening it down gives zero movement of the .0001" needle over the 6" jaw travel. I no longer check the vise each time I put it on the table. I take my vise off regularly for mounting work on the table, or other tooling, and always mount the vise in a different place each time I remount it, to spread any wear over the entire table. I am lucky that the mill, a Millrite built in 1967, came to me having never been used before. It was quite grimy from sitting for decades in storage, but no rust at all, and while cleaning it up, there were no chips or scratches anywhere on the working and sliding surfaces. I am working hard to keep it that way.- I know of a toolmaker with 60+ years experience that has his vise set up with 1" long precision ground keyways that just fit the slots on his milling machine. He has pre-indicated in the precision ground jaws on the vise. Many hours went into this prep, and he has to force the vise down whenever he reinstalls it - but every time it is within one-tenth, end-to-end. Defrayed over the past 40 years since he made this setup, he has saved many hundreds of hours. The downside is that he has several scrape marks, where he accidentally marked the table while removing and installing the vise.