Guiding Issue - Forums

Recently I disassembled my HEQ5 for lubrication and bearing replacement.

However, after putting it back into operation, the guiding is not behaving as it should.

Without guiding, in 120-second frames, about one out of every five shows a star trail.
But with guiding, all frames show trailing.

Could something be mechanically too tight or too loose, or could it be a software issue?

Here are two comparison images — one with guiding and one without. In the PHD2 graph, there are no spikes that would justify the star trail.

The trail is perfectly aligned with the movement of the RA axis.

Has anyone ever experienced something similar?

I’ve already tried various settings, both mechanically and in PHD2.

Thank you very much!

📷 guide.jpg📷 guide2.jpg

Without knowing your guiding setup, this smells like a flexure issue between the guide scope and OTA.

It would help us figure things out a bit better if we saw a photo of your setup, at least a little more details on what you’re using to guide with.

Without knowing any details at all - this sounds like either Flexture as Brian said, or you need to re-do your calibration…

Though, given you say that the PHD2 guide graph shows no movement - I’d say Brian will be correct - this will be flexture somewhere in the system.

Guide scope/Camera wobbling, imaging camera moving in the focuser or imaging scope focuser has some slop in it… something to that effect… Make sure everything is bolted down/tensioned tightly…

Hi Ari,

How did the mount perform before the rebuild?
Post rebuild, what did the PHD2 calibration graph look like?
Did you change anything in the guiding setup?

Brian Puhl · Nov 12, 2025, 04:25 AM
Without knowing your guiding setup, this smells like a flexure issue between the guide scope and OTA.

It would help us figure things out a bit better if we saw a photo of your setup, at least a little more details on what you’re using to guide with.

📷 Imagem do WhatsApp de 2025-11-12 à(s) 08.33.08_f7f55671.jpg📷 Imagem do WhatsApp de 2025-11-12 à(s) 08.33.20_40e1ae7a.jpg📷 Imagem do WhatsApp de 2025-11-12 à(s) 08.33.45_2e608da7.jpg

guiding details:

60 f4, FL 240mm

asi 220mm +uv ir cut.

I went to double check the guide scope again and noticed that one of the screws holding the dovetail to the shoe was a bit loose... (It wasn’t completely loose, but maybe just enough to cause the problem).

When I have clear skies to test, I’ll come back here with the results. I’ve also left a few more images in case they help identify the problem.

Alex Nicholas · Nov 12, 2025, 05:24 AM
Without knowing any details at all - this sounds like either Flexture as Brian said, or you need to re-do your calibration…

Though, given you say that the PHD2 guide graph shows no movement - I’d say Brian will be correct - this will be flexture somewhere in the system.

Guide scope/Camera wobbling, imaging camera moving in the focuser or imaging scope focuser has some slop in it… something to that effect… Make sure everything is bolted down/tensioned tightly…

📷 image.pngI recalibrated several times. Some turned out better than others, but none of them seem to fix the problem.

It might be caused by a slightly loose screw I found, which I described in the comment above.

Jim Raskett · Nov 12, 2025, 10:56 AM
Hi Ari,

How did the mount perform before the rebuild?
Post rebuild, what did the PHD2 calibration graph look like?
Did you change anything in the guiding setup?

It was showing some guiding spikes, and I noticed the grease wasn’t great, so I decided to take it apart. It wasn’t performing perfectly before, but it was definitely better than it is now with guiding.

What confuses me is that it’s producing good frames without guiding (something it didn’t do before) and bad ones with guiding hahaha. If it were the other way around, I’d understand!

Looking at the calibration graph, to me it looks like there was a bunch of backlash in DEC???
with the amount in the home position and the clutches locked, can you move the vertical rod shaft and see any movement?

have you run the PhD2 guiding assistant and checked DECbacklash?

If it isn't the guide scope (which incidentally is poorly mounted) then it is well possible that the primary mirror is shifting. Mine used to do that in summer, not all positions obviously.

Jim Raskett · Nov 12, 2025, 12:51 PM
Looking at the calibration graph, to me it looks like there was a bunch of backlash in DEC???
with the amount in the home position and the clutches locked, can you move the vertical rod shaft and see any movement?

have you run the PhD2 guiding assistant and checked DECbacklash?

You are right. That was one of the issues I was expecting to solve with the hypertune hehehe.

Ari Paulechen Junior:
Jim Raskett · Nov 12, 2025, 12:51 PM

Looking at the calibration graph, to me it looks like there was a bunch of backlash in DEC???
with the amount in the home position and the clutches locked, can you move the vertical rod shaft and see any movement?

have you run the PhD2 guiding assistant and checked DECbacklash?

You are right. That was one of the issues I was expecting to solve with the hypertune hehehe.

How did the worm adjustment go post rebuild?
Were you able to adjust the worms where there was no obvious physical movement when moving the axis back and forth with your hands while not binding the worm?

The reason I am asking is because when I rebuilt mine, I could not adjust enough to eliminate the axis play before the worm started to bind. At best, there was noticeable play in DEC.
I disassembled the mount again and started from scratch. This time, the DEC axis worm adjusted perfectly. There was no obvious play in the axis and the worm moved easily when turning the gear by hand.
The mount has been running great since.

Jim Raskett · Nov 12, 2025, 06:26 PM
Ari Paulechen Junior:
Jim Raskett · Nov 12, 2025, 12:51 PM

Looking at the calibration graph, to me it looks like there was a bunch of backlash in DEC???
with the amount in the home position and the clutches locked, can you move the vertical rod shaft and see any movement?

have you run the PhD2 guiding assistant and checked DECbacklash?

You are right. That was one of the issues I was expecting to solve with the hypertune hehehe.

How did the worm adjustment go post rebuild?
Were you able to adjust the worms where there was no obvious physical movement when moving the axis back and forth with your hands while not binding the worm?

The reason I am asking is because when I rebuilt mine, I could not adjust enough to eliminate the axis play before the worm started to bind. At best, there was noticeable play in DEC.
I disassembled the mount again and started from scratch. This time, the DEC axis worm adjusted perfectly. There was no obvious play in the axis and the worm moved easily when turning the gear by hand.
The mount has been running great since.

My case seems very similar to your description. Even after adjusting to the binding point, there's still play when moving the DEC axis. This play already existed before and continues now, even after replacing the bearings. When you disassembled it the second time, do you remember doing anything different? (It's a problem I want to solve, but first I need to look into the RA issue.)

Ari Paulechen Junior:
Jim Raskett · Nov 12, 2025, 06:26 PM
Ari Paulechen Junior:
Jim Raskett · Nov 12, 2025, 12:51 PM

Looking at the calibration graph, to me it looks like there was a bunch of backlash in DEC???
with the amount in the home position and the clutches locked, can you move the vertical rod shaft and see any movement?

have you run the PhD2 guiding assistant and checked DECbacklash?

You are right. That was one of the issues I was expecting to solve with the hypertune hehehe.

How did the worm adjustment go post rebuild?
Were you able to adjust the worms where there was no obvious physical movement when moving the axis back and forth with your hands while not binding the worm?

The reason I am asking is because when I rebuilt mine, I could not adjust enough to eliminate the axis play before the worm started to bind. At best, there was noticeable play in DEC.
I disassembled the mount again and started from scratch. This time, the DEC axis worm adjusted perfectly. There was no obvious play in the axis and the worm moved easily when turning the gear by hand.
The mount has been running great since.

My case seems very similar to your description. Even after adjusting to the binding point, there's still play when moving the DEC axis. This play already existed before and continues now, even after replacing the bearings. When you disassembled it the second time, do you remember doing anything different? (It's a problem I want to solve, but first I need to look into the RA issue.)

My apologies for my faulty memory, but it was the RA axis that had play.

Unfortunately, I didn’t see anything upon disassembly but after re-assembly, the worm axis adjusted easily and there was no apparent play in the axis.
Sorry for the confusion!

Whenever I would get something like this, it was almost always some sort of flexure from the guide scope. The rings might not be tightened down enough, the shoe might not be tight enough, etc.

Did tightening the screw fix your issue?

Paul Macias · Nov 13, 2025, 06:26 AM
Whenever I would get something like this, it was almost always some sort of flexure from the guide scope. The rings might not be tightened down enough, the shoe might not be tight enough, etc.

Did tightening the screw fix your issue?

I dont know yet, we are in the rain season here… maybe next week some clear skies show up

Update: The “loose” guider wasn’t actually the problem.

I took more frames, both with and without guiding, and I found that there’s really no pattern, sometimes guiding is bad, sometimes unguided is bad.

When I reassembled the mount, I noticed that unlike in the video I followed where after releasing the RA axis the mount would make 3 or 4 full turns when a torque was applied to the counterweight shaft (with no counterweights), mine was only making about 1/3 to 1/2 turn.

I decided to open it again and put the old bearings back in. Now I’m getting a little over one full turn.

I’ll try using it like this over the next few days, and if I still don’t have success, I’ll open the bearings and remove all the original grease. (I suspect there’s an excess of factory grease, which for our application ends up dragging the axis.) What do you think?

Did you shim the mounting when reassembling. I mean that shims are required on each shaft. The shims provide the exact spacing for the worm alignment to the respective axis gear. Without, the worm might not seat or mesh correctly causing backlash during operation and adjustment…

Tim Ray · Nov 16, 2025, 03:26 PM
Did you shim the mounting when reassembling. I mean that shims are required on each shaft. The shims provide the exact spacing for the worm alignment to the respective axis gear. Without, the worm might not seat or mesh correctly causing backlash during operation and adjustment…

📷 Imagem do WhatsApp de 2025-11-10 à(s) 09.41.14_086d22f2.jpgWould it be this red washer like in the image? If so, when I disassembled mine it didn’t have one on either axis. Since it’s a second-hand mount, maybe the previous owner lost it.

Yes, Since you can only adjust the worm basically in and out towards the main gear, you have no adjustment on the height of the worm to get it to seat properly with the main gear. That shim moves the main gear instead to make that adjustment… I hope that makes sense… Tim

There are many videos on YouTube about reassembly of these mountings. An Atlas or EQ6 video would work as well. Look for how to measure for that shim. You need a micrometer (analog or digital, nothing fancy) and a little math. I might have a few extras. I redid my Sirius mounting several years ago and might have a few shims left of various thicknesses I could send you.

Tim Ray · Nov 16, 2025, 03:37 PM
Yes, Since you can only adjust the worm basically in and out towards the main gear, you have no adjustment on the height of the worm to get it to seat properly with the main gear. That shim moves the main gear instead to make that adjustment… I hope that makes sense… Tim

Thank you for your help and willingness, but I live in South America hahaha. I’ll see if I can find something here that works for this purpose.

But I noticed that this washer is located after the main gear and the worm. It seems to serve to keep the two bearings from making contact with each other.

In your case, the washer would go here so that both the center of the worm shaft and the main gear shaft line up in height (green line). This makes it necessary to add a washer (in red) to raise the ring gear relative to the worm and keep them aligned on the same axis.📷 image.png

If I remember I reassembled without a shim. then measured the distance from the center of the teeth on the main gear to the surface the worm gear housing mounts on. Then disassemble. Add shims to the front of gear (like your image) to raise it to match the same distance as the worm is to that housing surface. Reassemble and the two gears should line up. then adjust worm in and out as not to bind…

I found these pictures of my HEQ5 Pro back when I disassembled the RA axis.
You can see the position of the red shim washer in relation to the RA worm wheel.