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The micrometer is stiff to turn.
I have checked the grating, the issue is with the former.
How can I fix this ?
Regards,
JackThere is a knurled collar at the base of the micrometer held in position with a tiny cross head grub screw which is used to lock the micrometer at a given setting. Has that got tightened down? Mine is fully wound off (anticlockwise) and locked down with the grub screw.
Cheers
RobinRobin,
I can’t loosen the tiny crosshead grub screw which must be very tight.
Is there a particular type of screwdriver or extractor?
Regards,
JackI just used a Jeweller’s screwdriver but if the grub screw is tight then it seems unlikely that the collar has moved so it probably is not the reason for the micrometer becoming tight. With mine the locking collar is close to the spectrograph body when engaged and there is a definite gap with it disengaged. I will take a couple of photos.
Cheers
RobinPhotos with the collar engaged and disengaged
Robin,
Thanks for the photos.
I will have another go at removing the grub screw.
I have another Lhires could swap micrometer shafts see if that works.
Regards,
JackIf the grub screw was not loose and the locking collar cannot be turned even after loosening the screw it is unlikely that this is the reason that the micrometer had become tight. (Did it suddenly become tight or has it becoming increasingly tight over time). Can you tell from my photos and comparing with the other LHIRES if the collar is engaged or disengaged ?
Other than that I guess it needs an overhaul, removing it, unscrewing the barrel cleaning and re-lubricating. Mine is still fine after 18 years though (I recall you have a remote adjustment, could this have been preloading it causing premature wear?)
Robin,
It became increasingly tight over time.
From your photos and comparing with the other Lhires the collar looks engaged.
I will overhaul it as you suggest.
Question 1; What lubricant should be used and is there a risk of it getting on the grating?
The remote adjustment is the motorised collimating lens.
Regards,
JackIf the locking collar is engaged and you have the locking screw loosened, it could be worth trying to release it first. (Screw anticlockwise) I just tried mine and when the collar is engaged it can be quite tight to then disengage. Try it with your spare, engaging and disengaging the locking collar does not affect the calibration.
Re lubricant the internet suggests clock oil for micrometers. (not silicone which creeps and could end up on the optics)
Robin,
I have released the collar. When tightened then slackened a fraction of a turn the micrometer is easier to turn.
It may be worth an overhaul as you suggest.
Thanks for your advices,
JackRobin,
‘I recall you have a remote adjustment, could this have been preloading it causing premature wear’?Are you advising against motorising the micrometer ?
Regards,
JackI have released the collar. When tightened then slackened a fraction of a turn the micrometer is easier to turn.
Then I think you have found the cause of the problem. You can slacken it right off. If it turns freely then, there is no overhaul needed. I find the micrometer setting does not move on its own in normal use but if you want to be 100% sure you can always clamp the locking collar back down after you set it at the wavelength you chose. No need to lock it with the grub screw though. That is really for use in an industrial machinery where the micrometer might be used as a set stop which must stay in position under vibration etc
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