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Hi everyone ? There have been a few threads regarding how to tune or reset the spring-loaded worm ? As many of you know, we have a video on the basics of adjusting the spring-loaded worm here: ? ? There have been a few questions around this process I wanted to add to the record: ? 1.?????? I NEED TO RESET THE SPRING, HOW FAR IN/OUT DO I NEED TO ADJUST IT?
When we adjust this at the factory, we use 1/3¡± (~8.5mm) as the length of the spring, measured between the bottom of the top screw and the top of the bottom screw. 1/3¡± is also the width of the ¡°back off¡± spring mechanism screwhead, so you can use that as an impromptu way to measure and set it.
2.?????? THERE IS TOO MUCH (OR TOO LITTLE) BACKLASH, HOW DO I ADJUST THE SPRING-LOADED WORM TO ADDRESS THIS?
You adjust backlash/stiction by adjusting the SECONDARY screw. This acts as a limiter to how far/hard the worm will mesh.
The primary worm screw (the one with the spring) does not impact this. Adjusting this screw tighter can tune it to be more like a traditional ¡°non-spring¡± worm gear
3.?????? I UNDERSTAND THE BOLTS THAT HOLD THE WORM BLOCKS IN PLACE NEED TO BE LOOSE, BUT HOW LOOSE OR TIGHT? HOW CAN I TELL?
The worm blocks should be loose enough to allow the worm block to slide to and from the worm gear, but not so loose that you can rock/rotate the block on the plate. In general, if you are making this adjustment, you probably want to remove the cover and ¡°start from scratch¡± as shown in the video above
4.?????? CAN I/SHOULD I USE LOCTITE ON THE SCREWS?
Yes, we use a small amount of Loctite Blue (242) on these screws to keep them from backing out. As with any type of glue/adhesive, you want to use it conservatively and be extremely careful not to let it seep onto other surfaces. You want just enough to keep the screw in place, but not so much that it becomes hard or impossible to adjust.
? ? Thanks ? Brian ? Brian Valente Losmandy Astronomical ? Losmandy.com Tutorials and vids at ?
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Thanks Brian.?
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Jim W
Phoenix, AZ. USA
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Thanks for that summary.? Can you confirm clarify .... there are large cap screws that hold the worm blocks to the frame. There are smaller screws that hold the worm blocks to the "cover plate". From previous exchange with Jim, I am assuming your #3 refers to the big cap screws that Scott never touches in the video?
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Edward
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On Thu, Jun 10, 2021 at 10:12 PM, Edward Plumer wrote:
From previous exchange with Jim, I am assuming your #3 refers to the big cap screws that Scott never touches in the video?
Correct? Brian
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In relation to Number 3 by Brian.? I used Loctite (Blue) and a 0.005 gap gauge and 'snugged' them down.
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Jim W
Phoenix, AZ. USA
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Thanks Brian.?
I don't have the Losmandy SLW but have experimented with my own design and wanted to know what the "back-off" screw was for (AKA the secondary screw).? According to your description it is to prevent backlash and stiction.? I presume the stiction is caused by the spring pressure of metal on metal, and the backlash is the up and down motion resulting from a loose block screw gap driven by the stiction?? How does the setting of the secondary screw depend on configuring the SLW at a high point vs. a low point of the ring gear?? If it is set at a low point it looks like it mostly does nothing, and if it is set at a high point it mostly acts like the non-SLW unfortunately with loose screws, I think.? Am I correct?
I suggest that a better SLW should not have loose screws on one side with gaps but a solid rotation axis on the motor side that also prevents the up/down motion.? Loose screws leave a small gap that can cause the blocks to wobble in two directions (towards the ring gear and perpendicular to the ring gear's axis).? These are the issues that I have identified with my solution, which I believe is similar to your design minus the back-off screw.?
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Sorry to bump up an old thread, but I would like to confirm if the 1/3" (8.5mm) spring length applies for both axes. In my mount RA came with the factory 8.5mm but DEC is at 6.7 mm and I suspect that this is some of the tweakings made for the vendor to eliminate play in DEC (RA was also "adjusted" but touching only the back-off secondary screw).? The fact is that I have seen recently DEC Heavy Duty Tr messages that I think are caused by overtightening.
Best regards,
Daniel
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Yes, both axes have the same tension measurements leaving the factory
Sorry to bump up an old thread, but I would like to confirm if the 1/3" (8.5mm) spring length applies for both axes. In my mount RA came with the factory 8.5mm but DEC is at 6.7 mm and I suspect that this is some of the tweakings made for the vendor to eliminate play in DEC (RA was also "adjusted" but touching only the back-off secondary screw).? The fact is that I have seen recently DEC Heavy Duty Tr messages that I think are caused by overtightening.
Best regards,
Daniel
-- Brian?
Brian Valente astro portfolio? portfolio astrobin?
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Hi Brian,
Thank you for your answer. I have tried to adjust the DEC SLW starting with resetting the spring length to about 8.4mm . What I have found is that the secondary, i.e. back-off screw, does not seem to have any effect, that is, regardless of its position the resistance offered by the spur gears is minimal. If you want the gears offering resistance you have to screw on the main spring screw and in any case the back-off screw does not seem to have any effect. I have screwed and unscrewed the back-off screw and its regulation effect is zero. Is anything wrong with my DEC SLW ???? ?
Best wishes,
Daniel
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Daniel
How are you measuring this effect??
It's impossible for the backoff screw to have no effect if you have the spring tension set correctly - or at least I've never encountered a situation where that's the case
if you loosen the backoff?screw completely?
This is the procedure to check/adjust the spring loaded worm:
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If you continue to have questions about this, please use the open support case you have with us. I will probably ask you for a video demonstrating what you see
Hi Brian,
Thank you for your answer. I have tried to adjust the DEC SLW starting with resetting the spring length to about 8.4mm . What I have found is that the secondary, i.e. back-off screw, does not seem to have any effect, that is, regardless of its position the resistance offered by the spur gears is minimal. If you want the gears offering resistance you have to screw on the main spring screw and in any case the back-off screw does not seem to have any effect. I have screwed and unscrewed the back-off screw and its regulation effect is zero. Is anything wrong with my DEC SLW ???? ?
Best wishes,
Daniel
-- Brian?
Brian Valente astro portfolio? portfolio astrobin?
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If I unscrew the back-off screw I should see that the gears offer great resistance as a consequence of the worm getting pushed to the gear, right?? Well, this is not the case. If I unscrew the back-off screw the gears continue to spin freely.?
Best regards,
Daniel
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Daniel - please use the support ticket you have open and send a video
Thanks
Brian
If I unscrew the back-off screw I should see that the gears offer great resistance as a consequence of the worm getting pushed to the gear, right?? Well, this is not the case. If I unscrew the back-off screw the gears continue to spin freely.?
Best regards,
Daniel
-- Brian?
Brian Valente astro portfolio? portfolio astrobin?
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On Fri, Aug 19, 2022 at 11:45 AM, Daniel wrote:
Hi Brian,
Thank you for your answer. I have tried to adjust the DEC SLW starting with resetting the spring length to about 8.4mm . What I have found is that the secondary, i.e. back-off screw, does not seem to have any effect, that is, regardless of its position the resistance offered by the spur gears is minimal. If you want the gears offering resistance you have to screw on the main spring screw and in any case the back-off screw does not seem to have any effect. I have screwed and unscrewed the back-off screw and its regulation effect is zero. Is anything wrong with my DEC SLW ???? ?
Best wishes,
Daniel
If your back off screw doesn't seem to be working it could be that the bottom cap screws are just a bit too snug to let the OPW move. If they are just a little bit too snug they lock the OPW into position and the worm can't float on the worm gear.? ? -- Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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¡±If your back off screw doesn't seem to be working it could be that the bottom cap screws are just a bit too snug to let the OPW move. If they are just a little bit too snug they lock the OPW into position and the worm can't float on the worm gear.¡±
- that is exactly what happened to mine; they were screwed down tight enough that the worm could not float. Slightly loosening them restored the float for the worm gear and resolved the spikes in my guiding.
Geoff Chapman
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There is nothing else that can cause this in a clean undamaged unmodified G11 or GM8 mount with tucked servos and sprung Gen II OPWs.?
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Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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That's exactly what Brian says. He only refers to the far end screw that it is beneath the big spring screw though. Unscrew a little and that should free the worm enough to float over the gear.? However, I'm not sure if I'm going to get much benefit of it. Currently DEC is guiding just under 0.4" RMS over 3 hour sessions and it is the RA axis what is limiting the guiding accurary (I get around 0.6" RMS).
Best wishes,
Daniel
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Did you get those spikes in RA too?? ?I'm considering too slightly loosen the far end bottom screw to try to improve my RA performance. Peak values in RA are over 2.5" and those concern me more than the RMS number.
Best regards,
Daniel
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PE spikes can be caused by stiction which may be visualized as force ramping upward with a sudden release as the level of force applied overcomes the resistance present. There are two possibilities here, the bottom of the deck plate cap screws are just a smidge too tight or you have a bit too little lift. I would start by adding some additional worm lift using the lift adjustment may fix it but be aware the lift adjustment usually needs to be very small to maintain optimum worm tooth engagement and these are not fine threaded fasteners. So I would make the smallest possible adjustment to the lift adjuster, observe and if needed continue to adjust. It sounds like your worm is close to optimum so with a small adjustment you should be GTG. If you don't see any change the bottom side cap screws are the next place to adjust. I suggest changing the outer or left side first, test, observe and adjust, if after two cycles you see no change try cracking the inner cap screw a smidge.?
You can verify the cap screws are letting the OPW move by wiggling the end of the counter weight and feeling for movement on the outer end of the OPW where the worm bearing block is attached to the OPW. There should be some movement felt on both axis or chances are you need to crack the outer bottom side cap screw a bit. Keep in mind that a little adjustment goes a long way on all of these coarse threaded fasteners.?
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Keep us posted.?
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Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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The spikes I mention can be seen in this excerpt of a PHD2 log:
As you can see the error is most of the time in a band of +-1", but there are occasional spikes. Even without the occasional spikes, I do not like too much the performance, too much oscillations with just 9 lbs of equipment (Sharpstar 76EDPH with all the typical add-ons).? With the 343mm focal length of the 76EDPH? the resulting images are perfect, but? I would like to be able to image with longer instruments (with 1200mm fl as the maximum perhaps).?
I think that oscillations could be related to stiction and may benefit from a fine adjustment of the worm gear.
Best regards,
Daniel
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Danial, please post your PHD2 log file and I'll look at it for glues.
Peter
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Edward Plumer
Chip Louie