Layout of centerlines

[JerryFlyGuy]

I'm faced w/ laying out some centerlines on my x axis. This normally wouldn't be a huge issue on a smaller machine, however in my case the centerline is 240" long and must be pefectly straight. I'm laying out the center line for mounting my linear rails and I've found that these rails aren't nesc. perfectly straight right out of the box. Mine have ever so slight a curve to them. This isn't really an issue as they are bolted down every 60mm and this can be taken out of them. But how do I get their mounting holes [in the sub structure] straight before the install? I'm not going to D&T their mount holes but rather just drill oversize mount holes and then add a nut to the bottom of the mnt bolt. I've got holes in the side of the mnt structure to reach through and put the nut on. This will allow me some lattitude to get things parrellel and sqr w/ the opposite rail [ which is 10' away]. However I do need to start w/ a master rail which is perfectly straight, and the second rail will then be slaved/matched to it. I thought about using fishing line and feeler gauges, any other suggestions?? I don't think a heavy pc of CRS would be straight enough would it?? Is there some trade secret out there that someone could pass on?? My sub-structure [ which the rails mount to] is composed of welded HSS, its very straight, but there are no garrentee's that there isn't a 1/32" [its small if there is any] bow in them [side to side] so measuring off the side of them isn't an option. I'm potting the rails down w/ Moglice so the elevation isn't an issue [ if there is slight warpage from welding]. I've purchased a master precision level [ 0.0005" level accuracy over 10"] which when used in conjuction w/ jig blocks that fit the rail and two set screws per jig block, I can get the rail as flat and level as it needs to be, I just don't know how to get the mount holes laid out perfectly straight. And once the rails are mounted there is still going to be the need to bolt them down straight w/out and curves in them.

Suggestions and opinions welcome as always.

Jerry

[martinw]

Originally Posted by JerryFlyGuy I'm faced w/ laying out some centerlines on my x axis. I thought about using fishing line and feeler gauges, any other suggestions?? Jerry

Hello Jerry,

You could try using a laser level and use the beam as a reference, but, from my experience, the laser dot is always too big and it is hard to detect where the edge (or centre) of it is.

Your idea of fishing line and feeler gauges would be hard to use IMHO. It would be hard to detect when the gauge is touching........hence this mad idea...

Don't use fishing line, use thin solid copper wire (not insulated) , and get it really tight. Connect one end of the wire to a small battery's positive terminal. Connect the negative terminal to one side of a small bulb or buzzer. Connect the other side of the buzzer/bulb to a flying lead which goes to your metal feeler gauge. Make sure your copper wire and feeler gauge are completely free of grease and oxide. Bingo!

It should work.

Regards

Martin

[motomitch1]

Steel Music Wire tie off one end and hang a weight on the other end

http://www.shopaid.com/music.htm

[Geof]

You are probably correct that a length of CRS would not be straight enough for what you need; but it would be stable so what you need to do is get a piece and calibrate it. If you know the deviation from straight every 100 mm that would be good enough. Use the piano wire idea; I have uploaded a picture showing how you would stretch the wire along the length of cold rolled with identical size insulated spacers each end (glass rod maybe?). You are not worried about the exact distance between the wire and the bar just the difference from one point to another so rather than feeler gauges use the tapered wedge I show in the second picture. You hold this flat against the edge of the bar and slide it in until your electric circuit is completed. If the length is around 10 inches and the taper is something like .040 over the full length then 1/4" of movement of the wedge corresponds to 0.001.

Just mark which end of the bar you start your calibration table from.

[martinw]

Dear Geof,

Brilliant!

Best wishes,

Martin

[JerryFlyGuy]

Wow, you guys really think outside the box! Some good idea's here.. I was thinking about when I layout the centerline to drill the mount holes [ this stuff usually comes to me when I'm trying to sleep.. i was having a nap this afternoon ] I currently use blue-layout paint.. And If I was to string the fishing line down the top of the frame and then spray w/ blue-layout the string would block someof the paint from getting on the structure and there-by put a line on it right?? Or.. Coat the fishline in oil, and then use it like a chalk line, the blue-layout won't stick to any oil so when it dries you can just wipe to top surface and you'd have a perfect line that way too. I know the layout won't stick to oily area's because there was some oil residue left on the tube from my last drill proceedure and the layout didn't stick in those area's.

Geof, on your CRS idea your thinking to just mark the corrected value/deviation at each location as you move along?? What about any sag in the copper line?? The CRS will only come in 12 [ or is it 10??] foot lengths so its to short to do it in 1 complete shot, you'd have to move it along, say 1/3 of the way and then continue for the next third then move it again, this way you'd have 2/3 of the crs clamped to a known straight edge and then the last 1/3 would be used to align the un-mounted part of the rail??

I'm wondering if I can't use the fish line idea's above and eliminate any of these issues, drill the holes to the proper size for a tight bolt fit [ possibly reamed holes] and be straight enough.. I'm gonna have to think on this a bit more.. maybe even test some ideas..I haven't decided what is an acceptable tolerance for this. I think though, if I had w/in 10thou over the length I'd be happy.. is that to huge or to tight??

Thanks for the idea's guys.. feel free to post more if you think of them!
Jerry

[ger21]

There's some info on this page about using highly tensioned wire to align linear rails. It starts by the 4th picture.

http://oneoceankayaks.com/madvac/machine_frame.htm

[JerryFlyGuy]

Thanks Gerry, I've read that before.. of course it was one of those " I won't ever forget that" kind of things.. which I promptly forgot about. I've emailed that gentleman to find out what multiplication value he used. Also I've been thinking more about this, I wonder if I couldn't use the same wire.. and mount a video camera to the carriage/truck and zoom in on the wire, it wouldn't matter to much how much zoom I got. then connect a screen of some sort [small tv or whatever] overlay it w/ a clear plastic overlay. Draw to lines which locate the edge of the rail and the wire and then adjust the rail as I slide the cammera assembly down the rail.. crazy idea??

I could do the same thing just w/ a microscope mounted to the truck??

Boy this is a long ways away from the route I was thinking of taking.. I gotta say that the "ZONE" is a great place.. filled w/ GREAT people!!

Jerry

[One of Many]

Originally Posted by JerryFlyGuy Thanks Gerry, I've read that before.. of course it was one of those " I won't ever forget that" kind of things.. which I promptly forgot about. I've emailed that gentleman to find out what multiplication value he used. Also I've been thinking more about this, I wonder if I couldn't use the same wire.. and mount a video camera to the carriage/truck and zoom in on the wire, it wouldn't matter to much how much zoom I got. then connect a screen of some sort [small tv or whatever] overlay it w/ a clear plastic overlay. Draw to lines which locate the edge of the rail and the wire and then adjust the rail as I slide the cammera assembly down the rail.. crazy idea?? I could do the same thing just w/ a microscope mounted to the truck?? Jerry

I have had to do this on an OEM router that never would run without a periodic servo current fault with the trucks bolted tight to the gantry. I used .025 music wire around some bolts fashioned similar to an instrument tuning peg. I first set the top straight, then from the side. Then of course used that rail as the master to re-align the other rail. The problem is where the rails actually have a slight tilt. The bearing trucks have specific class of fit. On our router, the truck specs are around .0015 rail to rail mis-alignment across the width of the truck. As ours does a rapid, you can still hear a minor change in servo load along different areas of the run. The machine runs within spec and no longer faults, but I am still suspicious of why the OEM couldn't do better.

What I do like about the link posted above is using 2 wire lines for each rail bed. If you did this for both rails, then strung another wire across all 4 wires at each end. You should end up with a decent reference plane. If it were tight enough, you could just use a light touch indicator under the wire.

Most rail manufacturers suggest the rail be set against at least 2 machines surfaces. That not always being possible, it is left up to the user to resolve mounting them aligned and free running. Then do it again after a crash.

DC

[JerryFlyGuy]

After re-reading One of Many's post. I went back and re-read the link. I dunno what I was on or smoking but it read totally different this time.. weird. Anyway what I've done.. or am going to try is using a metalurgist microscope to measure the gap between the wire and rail. I will still do the fine wire down the side of the rail and then mount this microscope to the top of the truck and focus it down the side to where the wire is. I figure w/ 10x magnification I should be able to measure the gap down to about 1/10 or less of a mm using the graduations inside the microscope. I'll let ya know if it works.

Jerry

[RICHARD ZASTROW]

JerryFlyGuy Or you could spend some money on an Ingersoll tight wire alignment kit complete with battery operated sound sensor / headset, micrometer/light indicator etc. Then find some Federal electronic levels for more big bucks. Then, rent them to the rest of us who can't afford them. JUST KIDDING

[energyforce]

See picture attached. These are for shafts instead of rails but maybe it will give you some ideas.....

We used something like piano wire yes, attached to a boat winch. We made a notch on one end and the same for the other end. We made sure the notches were accurate to 1/32 of an inch (just use tape measure). We then put the piano wire over the notches, secured it at one end and then used the winch to make it real tight. We then put a tape measure across and marked the hoels respectfully. We then drilled the holes 9/16 (we had a special rotenbrauch bit that could fit on a portamag sooo we went with this route). The bolts for the linear rails are only 1/4" so we have ordered large washers.

Our gantry on the other hand is fully machined. Everything is VERY accurate so the placement of the pillow blocks are ACCURATE. So we will be aligning our shafts with the pillow block. What i mean is move the gantry back and forth and back and forth and tighten it while we do this.

Hope this helps? I am a believer in fine tuning

Also a pic of the shafts mounted on rails on the same surface as the attached pic. http://www.ubcustom.com/cnc/index.php?img=51


Erik