Two questions about Aikron optical scales

[rronald]

I'm installing my Touch DRO with Aikron scales and have two questions about the optical scale.

1) The reader head came mounted on the scale. There are red clips attached to each end of the scale, each extends about 30mm away from the reader.
My assumption is that these clips are used to keep the read head in place during installation and that they are removed when the install is complete. I'm fairly positive they can't stay in place (since they would reduce the travel by ~60 mm and the travel won't equal the distance ordered (and shipped).

The instructions mention removing a "pad block and has this illustation (which doesn't help me at all):

Standard of reading head installation​

1.The clearance between the reading head and the height direction of the ruler​

body is 0.8mm-1.6mm after installation, and then withdraw the pad block​

​

Am I on the right track?​

​

My second question pertains to the interface. Since I have a mag scale on the cross slide and those only come with RS422, I ordered RS422 on the optical one as well. But despite ordering 5 micron RS422, some of the paperwork indicates 1 micron and TTL. I can get this working by trying both options, but I wanted to make sure that I won't burn anything out if I try RS422 and it's really TTL. Or vice versa. If it's safe to try one first and not the other...that would be really good to know!​

​

 

[ycroosh]

I'm installing my Touch DRO with Aikron scales and have two questions about the optical scale.

1) The reader head came mounted on the scale. There are red clips attached to each end of the scale, each extends about 30mm away from the reader.
My assumption is that these clips are used to keep the read head in place during installation and that they are removed when the install is complete. I'm fairly positive they can't stay in place (since they would reduce the travel by ~60 mm and the travel won't equal the distance ordered (and shipped).

The instructions mention removing a "pad block and has this illustation (which doesn't help me at all):

Standard of reading head installation​

1.The clearance between the reading head and the height direction of the ruler​

body is 0.8mm-1.6mm after installation, and then withdraw the pad block​

View attachment 468468​

Am I on the right track?​

​

My second question pertains to the interface. Since I have a mag scale on the cross slide and those only come with RS422, I ordered RS422 on the optical one as well. But despite ordering 5 micron RS422, some of the paperwork indicates 1 micron and TTL. I can get this working by trying both options, but I wanted to make sure that I won't burn anything out if I try RS422 and it's really TTL. Or vice versa. If it's safe to try one first and not the other...that would be really good to know!​

​

So, the short version:
RS422 vs. TTL in practice is a non-issue. This starts to matter when you need to run the cables for tens of meters. Signal running along the two meter cable shrouded in metal will not degrade enough to make any difference.

TouchDRO can handle both. The chip that I use can tolerate single ended signal very well.

Mixing 1um and 5um scales is not a problem.

Regards
Yuriy

 

[rronald]

I've got another problem. Mounting the scale on the bed, I have it supported on two aluminum blocks (about 3/16" thick). One at each end. This allows it to clear some raised bosses midway down the bed. I've confirmed that it's not touching anything between the two end mounting points.

I can get it adjusted so that it's parallel to the ways for the first half of travel (350 mm or so) moving from the spindle towards the tailstock. But a bit further than halfway to the tailstock, my indicator shows that the scale starts bends away from the bed. By the time it gets to the carriage stop, it's about .3 mm out of parallel. My analysis says that there must be a bend in the scale. Half the scale is parallel to the ways, the other half points outward with a consistent increase from the middle to the other end.

I have a proposed solution. I'm planning to reverse the scale (i.e., rotate it end for end 180 degrees). After doing so, the bend will put the scale center inward from where it should be. I then hope to be able to shim between the lathe bed and the scale enough to push the scale outward .3 mm. A very tiny nudge (.3 mm over 750mm is about 1 part in 2000). Goal is to get close enough that I can meet the .1 mm specification for parallel.

RR

 

[ycroosh]

I wouldn't mess with it.
Glass scales are pretty forgiving when it comes to misalignment, and this will not amount to any real cosine error. The read head is decoupled from the carriage that contains the encoder. In practice, if you are not scraping metal on metal, you are fine.
0.3mm is not a problem. Plus, this is the outside case. You are not measuring the glass strip inside (and you shouldn't be).
I would be more worried about adding any sort of strain, to be honest. You have a better chance of cracking the glass than fixing anything.

Regards
Yuriy

 

[rronald]

Just to close this thread out, I did flip the scales to see if they would be better in the other direction (without forcing them). And they were.

But, Aikron scales aren't meant to be used that way. One side of the scales (both the mag and the optical) has a bolt mounting counterbore. The other side does not. In fact, instead of a machined surface,the bolt is bearing directly on the sheet metal if you have it flipped.

So I flipped it back. And this time, I did not see the bend (or it was greatly reduced). I'll speculate that one of the two flat plate mounts I was using might have improperly constrained the scale. When I remounted, I added a washer in between the plate and the scale. With that, I was able to mount the scale and achieve the .1 mm spec for the level and the parallel planes.

I'm waiting on some gauge blocks to finish calibration and I'm going to upgrade one piece of my cross slide scale mount. But, I'm already very happy with my Touch DRO setup. When I calibrated the cross slide, I got back 25,401 counts per inch. That's only 1 micron off the exact number of microns in an inch. Pretty darn good. The carriage isn't quite as close (21 microns/inch off), but I think I'll improve when I have a better reference surface and can do a longer calibration test. I do realize that the calibration should result in higher accuracy regardless of how far off it is from the number of microns in an inch, but I suspect that closeness means that the setup and scales are good (square/true/parallel/etc).

 

[rronald]

So, the short version:
RS422 vs. TTL in practice is a non-issue. This starts to matter when you need to run the cables for tens of meters. Signal running along the two meter cable shrouded in metal will not degrade enough to make any difference.

TouchDRO can handle both. The chip that I use can tolerate single ended signal very well.

Mixing 1um and 5um scales is not a problem.

Regards
Yuriy

Aikron scales have their minus differential input "NC" (not connected) if you purchased a TTL scale. So there's no downside to connecting it as differential...even if you have a TTL scale. When I tested, they worked fine with a single input connected and they worked fine with both inputs connected. So I don't even know if they sent me a TTL or a differential scale and it doesn't matter as far as the wiring goes.