Parallel axis alignment

[Yovav]

I need to design an X axis that have two rails for a single load, the axis are 1.6 m apart, I need to align the two parallel axis so I won't get an unwanted moment on the rails, the axis are pretty long (3 m), if the alignment is wrong it will shorten the rail life expectancy, does anyone know how can I achieve high alignment for those kind of sizes?(in a reasonable price of course)
Yovav

[electronicwood]

I solved this problem with a piece of scrap wood and a dial indicator. You can set the axes parallel, but you won't know the absolute distance between them. I've attached a picture I took of this set up as I was building my machine. It is also not important that the two pieces of wood be perpendicular, just that the dial indicator be held in a consistent position. The biggest issue with this is the fact that you are assuming the first axis bolted to the table is straight. I'm sure it's not, but I work with wood so it's close enough.

I set my y-axis parallel to the table in a similar manner and set my y-axis perpendicular to the x with a pair of plumb bobs. Like I said, I'm not building a rocket.

[JerryFlyGuy]

The way I did it on my machine was to build the gantry and then after getting one rail [master rail] as straight as I could [long story as my machine is 20ft long] I used the gantry to set the spacing and alignment of the 'slave' rail. W/ the gantry bolted to the 'carriages' and the carriages on the rail as I moved the gantry along I could just tighten the rail down. Worked for the initial alignment. Later I went back after double checking that the gantry was located sqr to the X [master rail] and loosened and re-tightened the 'slave' rail. I've never had a moments problem using this install technique.

Fwiw..

J

[electronicwood]

I thought about aligning the x bearings that way, but you are assuming that the x-axis bearing sets on the gantry are parallel. Since your idea has worked, I probably could have saved myself a step.

I'm curious how you got the master x-axis bearing set straight. I never came up with a way to measure this. If you look at the pictures that show my bearings, you can see they are mounted in an aluminum bar with a machined groove. The bearing is actually three separate bearings aligned by the machined groove. It works pretty well. My x-axis bearings are 7.5" long and I could not have afforded two single-piece bearings of this length. It is the machined groove that defines the straightness of the bearing assembly, but the groove was machined 20" at a time by moving the aluminum along the mill table and locating off an edge. Who knows how straight it really is.

[JerryFlyGuy]

The process for aligning my rail was long and conviluted [its in a thread on here someplace but I'll give ya the short version].

I used a DIY version of whats called a Ingersal Tight Wire alignment tool. Basically what it is is a very fine stainless steel wire [I used a wire which was 0.009" thick] which is pulled under tension and aligned down the length of the machine [no rail on there yet] The ends of the wire are mounted in insulators so it's not electrically grounded to the machine frame. This wire has a 5vdc power supply connected to it and grounded to the machine frame. In that power circuit you put a small 5vdc buzzer [so PS-->Buzzer--> Tight Wire] that will go off once the circuit is closed [you could also use an LED instead if you prefer]. Once you've got the wire in there and it's set sqr to the machine [measure in from some reference edge at each end of the machine] then you place the rail on the mounting face and starting at one end you slide it [rail] over close to the wire and put your first mounting screw/bolt in [finger tight]. I had a small tool that I used w/ a 20 turn bolt that I used to 'jack' the rail sideways towards the wire. Between the rail and the wire I used a spacer [small pc of welder wire of known size,in this case it was 0.030" dia] once the rail push's that small spacer wire over until it touchs the tight wire the electrical circuit is closed and the buzzer goes off.. this tells you the rail is 0.030" from the wire. lightly tighten the first screw down and move up the rail to the next screw again push the rail over while holding the spacer wire against it unit it touches the tight wire and tighten the mounting screw. Just keep doing that all the way down the rail and after a few hrs it's all done. Then I went back and double checked the spacing along the length and made sure it hadn't moved and then torqued down the screws holding the rail. I've since checked it [a couple months after the initial install] and it's still as good as it was way back then.. I used a Dial indicator to see how accurate this method was and I could place the rail in position [repeatably] to w/in less than 1/2 a thou [was using a 1thou DI].

After the rail was locked down I installed small bars on either side to make sure the rail wouldn't translate on me over time.

If I was to do it again I think I'd get the mounting surfaces machine [due to other installation issues but that's even a longer story] as well as the whole frame stress relieved, it's $$ up front but worth it if you want to use the machine for any length of time. On smaller machines this may be extreme but on mine [20ft long] it would help greatly to keep things aligned and not moving over time [I haven't checked my rails in 2 years and I'm scared to now 'cause I'm sure some of the weld stress has come out of them and they aren't where they used to be , for what I'm doing w/it it goesn't matter but if I wanted to get super accurate it would..]

Fwiw

J

[RICHARD ZASTROW]

The tight wire method works quite well, actually. Back when I was functional (billions and billions of years ago) we aligned machines with the tight wire and checked it out with K&E optics.

Now it's mostly done with high priced lasers (more optics).

Just don't kink the wire!!!!!

Dick Z

[JerryFlyGuy]

Or autocollometers [didn't look up the correct spelling.. ] I think they can measure up to the millionth of the inch if needed [ breath on your knee mill and they can measure the thermal expansion from the heat of your breath, in the bed of the mill.. scary..]