valensdiesel
Plastic
- Joined
- Apr 3, 2020
Hi all,
Found an interesting method for calibrating a rotating axis. This post is mostly for information in case someone else is searching for this idea, but I would appreciate any advice regarding an equipment maintenance question at the end.
This method basically boils down to "bolt a theodlite onto your rotary table, take a fixed reference point in the distance (church steeple, etc), measure actual table angles relative to fixed point to determine actual rotation vs indicated rotation". I think some discussion was made in a previous thread (Calibrating and Compensating a Rotary Table) of a similar method, but the setup as-described required an autocollimating theodolite. This link to a youtube video shows the method requiring "any old theodolite", subject to your desired accuracy/resolution limits: Dividing Head Accuracy: Unconventional Testing. I thought I would give it a shot on my well-loved Troyke 9" and see how well it has fared over time. In order to do that, I scored a secondhand Hilger and Watts ST-200 which, according to a trade pub I found, is accurate to 1 second of arc and can be interpolated down to ~0.2 seconds. The unit I picked up is in near-mint condition and was university surplus, so I'm not overly concerned that the absolute accuracy has changed drastically (though its of course possible to have it recalibrated), and anyway the R-9 is only supposed to be good to 1 minute of arc.
My new-to-me theodolite does have one slight issue, which is that it has hysteresis/sluggish return in the horizontal fine adjustment. The micrometer screw moves in and out smoothly, but when backing it out, the spring-loaded return seems to be encountering some friction which feels like moving through sticky grease. Since the micrometer acts as a positive stop in this arrangement, I believe it is still possible to obtain accurate readings, but it is a bit of a pain having to add manual preload to encourage the return force in the event you overshoot your target. I pulled out the return spring and it is covered in some rather tacky green grease.
Unfortunately, as with most Hilger and Watts items, manuals or other publications are somewhat thin on the ground, so there is of course no recommended lubricant for the system. Was this originally grease, or is it oil that has gelled over time? Who knows. I did find a translation of a russian document that actually describes the parameters of watch oil used in a (different) theodolite (Link, PDF is too large to upload), and I think there is probably a Moebius product (I'm not affiliated at all) that is pretty similar: Synta-Frigo-Lube 9030.
So, the question is two-fold:
1. Would you try to clean and reassemble with new lubricant, or live with it as-is? I could try to have it professionally serviced, but I'm not confident that anyone will know anything about servicing an antique theodolite (serial # marks it as 1957-1958 vintage: Theodolite Serial Numbers), and anyway this is more of a project of curiosity rather than necessity, and
2. If you were to clean and re-lube, what lubricant would you choose, and how might you go about cleaning the mechanism? I was thinking a volatile solvent like diethyl ether to sweep the grease out and then after it evaporates, insert watch oil/whatever lube is appropriate. My concern here is will I be able to effectively lubricate the entire mechanism?
Alternatively, if anyone has a manual or other info, or direct experience with this or similar theodolites, then your advice and expertise would be most welcome.
Finally, and this may be of most interest to others in the forum, the eyepieces for my theodolite look very similar to the eyepiece on my Hilger and Watts autocollimator (no surprise there). The AC looks like it has a widefield type eyepiece while the theodolite does not, but I did search around a little bit and found a company that would probably supply the appropriate eyepieces as they specialize in eyepieces for theodolites (Link, not affiliated). I haven't reached out to them because I have good eyepieces for all my equipment, but for everyone else's sake, I'll post the link in case there is need. You might even be able to get one of the OE-style 90-degree eyepieces which are so loved by the AC-using community.
Thanks for any replies, and hopefully at least you find the youtube video interesting!
Found an interesting method for calibrating a rotating axis. This post is mostly for information in case someone else is searching for this idea, but I would appreciate any advice regarding an equipment maintenance question at the end.
This method basically boils down to "bolt a theodlite onto your rotary table, take a fixed reference point in the distance (church steeple, etc), measure actual table angles relative to fixed point to determine actual rotation vs indicated rotation". I think some discussion was made in a previous thread (Calibrating and Compensating a Rotary Table) of a similar method, but the setup as-described required an autocollimating theodolite. This link to a youtube video shows the method requiring "any old theodolite", subject to your desired accuracy/resolution limits: Dividing Head Accuracy: Unconventional Testing. I thought I would give it a shot on my well-loved Troyke 9" and see how well it has fared over time. In order to do that, I scored a secondhand Hilger and Watts ST-200 which, according to a trade pub I found, is accurate to 1 second of arc and can be interpolated down to ~0.2 seconds. The unit I picked up is in near-mint condition and was university surplus, so I'm not overly concerned that the absolute accuracy has changed drastically (though its of course possible to have it recalibrated), and anyway the R-9 is only supposed to be good to 1 minute of arc.
My new-to-me theodolite does have one slight issue, which is that it has hysteresis/sluggish return in the horizontal fine adjustment. The micrometer screw moves in and out smoothly, but when backing it out, the spring-loaded return seems to be encountering some friction which feels like moving through sticky grease. Since the micrometer acts as a positive stop in this arrangement, I believe it is still possible to obtain accurate readings, but it is a bit of a pain having to add manual preload to encourage the return force in the event you overshoot your target. I pulled out the return spring and it is covered in some rather tacky green grease.
Unfortunately, as with most Hilger and Watts items, manuals or other publications are somewhat thin on the ground, so there is of course no recommended lubricant for the system. Was this originally grease, or is it oil that has gelled over time? Who knows. I did find a translation of a russian document that actually describes the parameters of watch oil used in a (different) theodolite (Link, PDF is too large to upload), and I think there is probably a Moebius product (I'm not affiliated at all) that is pretty similar: Synta-Frigo-Lube 9030.
So, the question is two-fold:
1. Would you try to clean and reassemble with new lubricant, or live with it as-is? I could try to have it professionally serviced, but I'm not confident that anyone will know anything about servicing an antique theodolite (serial # marks it as 1957-1958 vintage: Theodolite Serial Numbers), and anyway this is more of a project of curiosity rather than necessity, and
2. If you were to clean and re-lube, what lubricant would you choose, and how might you go about cleaning the mechanism? I was thinking a volatile solvent like diethyl ether to sweep the grease out and then after it evaporates, insert watch oil/whatever lube is appropriate. My concern here is will I be able to effectively lubricate the entire mechanism?
Alternatively, if anyone has a manual or other info, or direct experience with this or similar theodolites, then your advice and expertise would be most welcome.
Finally, and this may be of most interest to others in the forum, the eyepieces for my theodolite look very similar to the eyepiece on my Hilger and Watts autocollimator (no surprise there). The AC looks like it has a widefield type eyepiece while the theodolite does not, but I did search around a little bit and found a company that would probably supply the appropriate eyepieces as they specialize in eyepieces for theodolites (Link, not affiliated). I haven't reached out to them because I have good eyepieces for all my equipment, but for everyone else's sake, I'll post the link in case there is need. You might even be able to get one of the OE-style 90-degree eyepieces which are so loved by the AC-using community.
Thanks for any replies, and hopefully at least you find the youtube video interesting!