New DRO install Alignment Help.

[Cartierusm]

Ok So I got my new DRO installed on my BP clone. The question I have is that the instructions say to make sure the scale is within .02mmparallel to the axis. The problem with that is when I run my indicator over the body of the scale the needle move in and out all over the place, which is normal and I've experienced on other things, but I got zero on one end and zero at a couple inches from the other end (it won't go all the way to both ends becasue the limit of travel). So I just want to know two things, first since I got zero at two point fairly far away is that good enough for a DRO and second what would the symptoms be if it wasn't aligned correctly? I'm guessing the travel wouldn't be smooth and the distances would be off as the scale would be at a slight angle.

So did I do this correctly or is there some other way of alignment? I followed the instructions.

[One of Many]

What type of scales are you using?

What type of indicator are you using to align it and are you indicating off of a machined surface?

That .02mm(.0007-.0008") spec seems pretty tight for most glass scale alignment(.12mm=.005") I have worked with. The read heads have some float region.

The chinese absolute caliper type scales might not be that forgiving without the float ability. About all you can do there is to get the ends parallel to the two planes and call it good. These types of scales may not have enough strength for long spans. Droop wouldn't surprise me.

DC

[Cartierusm]

That's the point the body of the scale is aluminum sheet metal, so no it's not a machined surface. I was using a dial test indicator, like this one http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=61025586 , reads in .0005".

The scales are glass. This is a regular high end mill DRO not the cheap dial caliper types.

[One of Many]

Interesting to know the manufacturer. I guess I'd need to see it myself as to why such a tight alignment spec.

Do you mean extrusion of the spar casing. Sheet metal just doesn't sound high end. Some systems may have a sheet metal guard that goes on after the install, but that wouldn't get indicated anyways. The extrusion surfaces I have worked with are very true, but then again I am not looking at .0005 resolution as my bench mark.

The indicator looks fine for the application, although the resolution barely adequate for the spec they call out. Still, I'd think +/- .001-.002 or well within .005 total deviation should be good enough. I have yet to see Mitutoyo and Acu-rite call anything better than that for mills and lathes.

My normal precedure in a nut shell;

With the scales supported, clamped or stationed mid axis, for scale mounting/replacement/installation is to rough set the scales with a depth mic from the table top on the X and the way surface on the Y to the top of the spar at the mounting holes. The fasteners holding them will be smaller than the mounting hole in order to make minor adjustments when I get to the point of indicating each of them in that plane.

The back of the table spar mount surface may or may not take a shim to get the outer face of the spar to indicate parallel to the X axis travel. Mostly I am looking for gross error or bow in the spar. Under .005 isn't usually worth fussing with, but suit your conscience by all means. Once it is good on the outer face, indicate the top and correct as needed.

The knee mounting surface is usually a bit more involved since you will have standoffs to contend with. I indicate the spars outer face difference at the mounting points or in 10 inches to calculate what it would be between the mounting points. Then cut that difference off the taller standoff. Remount and check again. Still my goal being under .005 between mounting points. Once it is good on the outer face, indicate the top and correct as needed.

I leave the read head shipping/alignment brackets installed until I get to the point of mounting the read head to its stationary mount. The critical point here is to bring the mounting surface to the read head. Otherwise you risk pulling the read head to the mount, which can pull it out of alignment to the spar. Some read heads have jacking screws for this purpose and some mounting kits put the jacking screws in the mounting bracket, And then again, some leave it up to you to figure it out. Simply put, when it is time to bolt the read head to the stationary mount, nothing pushes or pulls on it any way shape or form. Then remove the plastic alignment brackets and note any pinching or binding getting them out. Investigate and eliminate that until its cured.

Mouting the scales really shouldn't be any more complicated than that, with the exception of a few PIA installs here and there.

If this matches what you did and no errors codes are displayed in either axis, then I'd think you did fine for a first install!



DC

[Cartierusm]

Yeah, thanks for the info. That's pretty much how I did it. The body of the scale, not the protective optioinal shroud, it's not sheet metal but it's sheet metal like, it's definately not machined. The need moves about .002" over the surface of the scale body as it has microscopic surface defects, as I traverse it. But I do start off at zero and toward the end get a zero, so I think I have it correct. I was lucky on the Y axis as I didn't have to use spacers, just one small .008 or so shim.

I think I have it right but just wanted to make sure as I'm using it to calibrate the cnc part when the conversion is finished, so I have to rely on it to make sure of the backlash and all that.

On a side note I get the same surface variance when I traverse the face of my Kurt vice when I'm setting it up on the BP. It's really frustrating to have the needle move back and forth but I eventually get a zero/zero at both ends. Since I was doing a CNC conversion on my mill I took my Kurt apart for maintanence and did a small lapping on a super fine diamond stone I have. So when I set it back up I'll see if it makes a difference in relation to dial test indicator with the needle moving around.

[One of Many]

The needle bounce is something you're going to get use to. You are looking for drift and trends in that bounce and consistancy of the pointer at rest. The smaller the stylus ball tip, the worse it will be on rougher surfaces. You can buy different sizes and some indicators come with them.

Sometimes you gotta think of these as beasts of burden, not pampered beauty queens. As you have found installing the scales, learning to pick near perfection out of the blurr.

We won't be able to lap/polish every surface to satisfy the indicator needle bounce. The chance we take there is removing a machine ground plane usable for reference, in trade for a hand smoothed quite possible no-longer-planar surface.

DC

[Cartierusm]

I realize that, that's why I really only gave it a few passes on the stone. and rechecked thickness with a mic.

[One of Many]

Originally Posted by Cartierusm I realize that, that's why I really only gave it a few passes on the stone. and rechecked thickness with a mic.

Great job .

Not everyone knows to recheck thickness with a mic after a few passes of unneccessary material removal.

DC

[Cartierusm]

Actually I know a lot about machining. Almost all the questions I ask here I already know the answers to, but I know I don't know everything and as I've never been trained professionally I rely on you people to make sure I'm not totally screwing the pooch. So thanks for the help.