AZ-EQ6 Dec belt has snapped

[Jonk]

As it has been raining all day, I pulled my AZ-EQ6 mount apart to give it a clean, regrease and reset the worms.

After about 3 hours work, I put it back together and started to test when I heard a clicking noise from the dec axis.

Turns out the drive belt has snapped - although not completely as it's metal reinforced.

I don't know if I did it without realising, but it's definitely now useless.

Does anyone know where I can get a replacement?

I've emailed Optical Vision and hope they can help with a part number or even supply one.

The wording on the belt is MEGADYNE T2,5 177,5 2412

 

[Dr_Ju_ju]

have a look @ BeltingOnline, the 2.5mm, 177.5 mm, should be right one http://www.beltingonline.com/t2-5-synchroflex-timing-belts-2903

[wimvb]

Ouch!

The belt tension may have been set too high. you can check it when you get a new belt. Julian's post is a good start for a replacement if the mount vendor can't help (might get two, just in case).

 

Good luck

[Jonk]

Thanks very much for the link, I've ordered 2 to replace both belts.

It didn't feel too tight when I took it apart and didn't notice the break, but if there was a weakness there, I've probably found it at the best time.

I'll update once delivered and fitted.

[kendg]

So, the belt is 2.5mm tooth pitch, 177.5mm length. What width did you order?

[Jonk]

I measured the original with a set of vernier callipers, and it was roughly 6.5mm.

On the order page, you manually type the width, and it didn't complain at 6.5mm so hopefully it's ok.

The number of teeth match the original, so it should be fine.

[kendg]

Perfect. Thanks.

[Jonk]

The replacement belts have arrived, seem to be ok.

Here are some pictures.

 

 

[Jonk]

I also received a reply from OVL:

For such belt, the BOM is 5.13.006.0039 and unit price is £17.85 including P&P for UK delivery

We can order a replacement DEC drive belt for your AZ-EQ6GT with delivery in approx. 4 months.

Hmm 4 months and 4x the price per belt? No thanks!

[StuartJPP]

7 hours ago, Jonk said:

I also received a reply from OVL:

For such belt, the BOM is 5.13.006.0039 and unit price is £17.85 including P&P for UK delivery

We can order a replacement DEC drive belt for your AZ-EQ6GT with delivery in approx. 4 months.

Hmm 4 months and 4x the price per belt? No thanks!

Rather pathetic that. I could stomach the excessive cost but 4 months? Nations have risen and fallen in less time.

[Jonk]

I know! The belts I bought from the link above took 2 days.

My guess is that OVL would have them come in on a regular stock shipment from China... Literally on a ship.

Even then, I suspect the belts only cost a pound or so each for Skywatcher, if that.

Nevermind, the replacements are fine, I'm just running them in.

 

[Fred_76]

Hi!

 

It should have been better to replace the 71 tooth belt by a 72 tooth belt on the RA axis. The difference in length is minimal (2.5 mm) and the play in the motor's shaft position is enough to tension the belt.

The big advantage is that with a 72 t belt, the motor pulley, worm gear pulley and belt are back in the same position every 3 turns of the worm gear instead of 71 turns with the 71t belt. It is then much easier to do a PEC : you just have to enter the period of the 72t belt x 2 (i.e. 1436 s).

Here is a list of associated periods.

AzEQ6 with 71t belt (original)

- motor pulley (12t) : 119.7 s
- belt (71t) : 708.1 s
- worm gear pulley (48t) : 478.7 s (use this value for PEC but it will not correct belt errors)
- combined pulleys and belt : 33 986.9 s

AzEQ6 with 72 belt (modification)

- motor pulley (12t) : 119.7 s
- belt (72t) : 718.0 s
- worm gear pulley (48t) : 478.7 s
- combined pulleys and belt : 1 436.1 s (use this value for PEC and it will correct all errors of the belt drive)

Autoguiding with PEC "on" is possible with EQMod.

Fred

[wimvb]

Will you do that modification? It would be nice to see the unguided tracking performance with this mod and pec applied.

Anyhow, good to know in case a belt on my mount snaps.

[Fred_76]

No Wim, I sold all my astro equipment... here in Normandy, we have not enough good nights per year to shoot the deep sky, and I was quite frustrated to have such costly equiment standing by my garage.

I had an AzEQ6 with a SW200/1000. The PEC was working correctly with EQMod and the 71t belt, with the period set to 478.7s. I never had the time to change to the 72t belt before I sold my mount, however mechanicaly speaking, this can only improve the PEC as it will compensate the defects of more mechanical elements.

[Jonk]

Interesting... I'm not sure now I've put it all back together and put it back on the pier that I want to pull it apart again and re-tune.

Is the info above prove or just a theoretical idea?

Has anyone else done this?

[Stu]

@Tazman, at SGL we tend to favour the friendly approach, explaining your point without overly putting others down. It seems to work very well and is just as effective at getting your point across.

Welcome to the forum  

[Moonshane]

I suspect that the ability to adjust play in the worm gear (that Skywatcher install as standard - certainly in the HEQ5) would have more capacity (if done badly) for premature wear than a slightly different belt. As could overtightening the adjustment on a focuser or an adjustable objective cell in a refractor. I appreciate that the sentiment is one of trying to help people avoid warranty issues or damage/wear but I agree with Stu it could be done in a more 'SGL' way. Personally, I tend to agree with you in principle (that fiddling creates problems if you don't know what, but you really have no idea of the skills of the people discussing the issues, their background and knowledge. You clearly know a lot about motors and gears but I am sure others do and would not all necessarily agree with all you say.

 

[Stub Mandrel]

I can understand specialist suppliers bumping up the price because for holding stock of little-wanted spare parts.

But when they don't actually hold them in stock, and it's a readily available off the shelf item, that's poor.

[1DegreeN]

I have a problem with the RA belt on my AZ-EQ6GT where the teeth are coming off the belt. I opened the housing to find a fine yellow/green dust coating the bottom - this being material from the belt. One tooth was completely gone and others were on their way. I've never done any adjustments on the mount before and have no idea what caused this. I guess I may have had the RA clutch tightened too much at one point, that's the only thing I can think of. Anyway, thanks to the very helpful info in this thread I have a replacement belt on its way.

[Stub Mandrel]

4 hours ago, 1DegreeN said:

I have a problem with the RA belt on my AZ-EQ6GT where the teeth are coming off the belt. I opened the housing to find a fine yellow/green dust coating the bottom - this being material from the belt. One tooth was completely gone and others were on their way. I've never done any adjustments on the mount before and have no idea what caused this. I guess I may have had the RA clutch tightened too much at one point, that's the only thing I can think of. Anyway, thanks to the very helpful info in this thread I have a replacement belt on its way.

The clutch shouldn't have any effect, it may be that the belt tension was too high.

[sloz1664]

If you buy the belts from reputable companies like Beltingonline or HPC Gears you can order glass reinforced belts. These will not break, they are industrial quality and withstand thousands of RPM and many hundreds of hours of working life. The biggest danger for timing belts is "not enough tension" This causes the belts to slip, damaging the belt teeth and eventually rendering it useless.

Steve

[Wolfie6020]

Just wanted to say thanks for the link to Beltingonline.  Shipping to Australia for these belts cost 5 times the price of the belt but still quite reasonable.  

A very helpful read here.  Thanks to all.  

Edited February 21, 2020 by Wolfie6020

[Jonk]

Wow, nearly 3 years ago?!

Maybe I'd better think about another strip / rebuild?

It will be good to see how the replacement belts have fared, albeit the 'mileage' is probably quite low.

It will be an intresting exercise nonetheless.

[Wolfie6020]

On 21/02/2020 at 23:11, Jonk said:

Wow, nearly 3 years ago?!

Maybe I'd better think about another strip / rebuild?

It will be good to see how the replacement belts have fared, albeit the 'mileage' is probably quite low.

It will be an intresting exercise nonetheless.

Mine arrived today and replacing the old with new was a three minute job.    Just a week to Australia - very happy with that. 

6.5 mm width is perfect. 

I also tightened up the tension a little on the Dec axis as it was a bit looser than the RA.    A few minutes of slewing each axis and they seem as smooth as silk.  

The old ones had a lot of worn belt dust so it was time for new ones anyway it seems.  (The picture of my finger) 

Ordered six so that should do for the foreseeable life of the mount.  

Thanks again and yes it would be interesting to see how they have fared.   My old belts have about 5-600 hours of use over three years. 

Edited February 27, 2020 by Wolfie6020

[Jonk]

I will get round to checking mine again in a couple of months.