HTD Timing Pulley

[IanL]

I'm looking to build a stepper motor focuser for my Baader Diamond Steeltrack RT, likely based on Tekkydave's Arduino ASCOM Focuser design and software.

Now I'm pretty happy I can source all the parts and fabricate a bracket using an off-the-shelf NEMA 14 bracket attached to a DIY fixing plate drilled for the two accessory holes under the focuser.

The Steeltrack has a pulley built in to the fine focus knob already to take a HTD belt (6mm wide, 3M pitch - i.e. 3mm).  Sourcing such belts online is easy enough, but what I'm struggling with is finding a pulley for the stepper motor (5mm shaft most likely).

The Baader Diamond Steeldrive appears to use an 18-tooth, 6mm flanged pulley (looks like a single flange on the outside to me but hard to tell). I can find reasonably priced pulleys online at widths of 11mm and upwards, but no 6mm wide ones.

So question is, would an 11mm wide flanged pulley work with a 6mm wide belt? The pulley machined in to the focuser fine control knob is not flanged so it seems possible to me that the belt could walk itself off the focuser if the 11mm pulley flange is offset beyond it, or run in to the focuser body if offset the other way.

Alternatively does anyone know where I could find a stepper motor pulley (i.e. one with set screws to attach to a shaft) that is HTD 3M, 6mm wide double flanged? I've searched extensively online, eBay, etc. and the only one that even looks close is 39 quid on Amazon and even there the details are sketchy and may not be right, crazy price notwithstanding!

I guess I could try some other type of timing belt and pulley, but would be better to go with the original design for most reliable engagement and elimination of backlash.

Thanks in advance

[Juicy6]

http://www.motionco.co.uk/timing-pulleys-timing-pulleys-aluminium-c-25_35_50.html

[IanL]

40 minutes ago, Juicy6 said:

http://www.motionco.co.uk/timing-pulleys-timing-pulleys-aluminium-c-25_35_50.html

Looked at those already, for 9mm wide belts. Might give it a try if nothing else turns up but hoping I have missed 6mm wide somewhere.

[Dr_Ju_ju]

There is also Belting Online http://www.beltingonline.co.uk/

[fozzybear]

I get my pulleys from these people in the uk, for my modded eq5 mount (astroeq)

http://www.beltingonline.com/15-tooth-mxl-pulley-al15mxl025fb-5168

hope this helps they have various pulleys available and belts

[IanL]

Have taken a look at beltingonline and they only have 9mm wide HTD 3M pulleys.  The only place I have found 6mm wide is here: http://www.bearingsrus.co.uk/transmisson-products/timing-pulley/htd-metric-timing-belt-pulley-3m-5m-8m-14m/3m-3mm-pitch/18-3m-06f-pb

But that's a pilot bore pulley so would have to drill out the bore and drill and tap grub screw holes. Not sure my cheapo drill press would be sufficiently precise for such a small job. I may try a 9mm pulley with a 6mm and a 9mm belt to see if either works satisfactorily.

[artoleus]

Did the 9mm wide work for you in the end?

[IanL]

It's far from ideal as the belt wanders across the pulley. I have wrapped a length of thin wire around one side of the pulley to prevent this but it's not a good solution. I still have two (probably related) problems, in that there is a distinct 'notch' every so often, not sure if the belt is jumping a tooth or if there is excessive friction with the wire. Also the focuser seems to be slipping outwards during the course of a session - again not sure exactly why and need to do more diagnosis.

It does work well enough to do an evening's imaging provided I reset the focuser and driver software at the start, but I am unable to dial in set focuser positions for each filter between sessions. I am thinking about getting a new pulley and belt set to replace the fine focus knob. I also need to do a bit more work on the motor bracket as it's not as square and rigid as I'd like it to be, which may also be contributing to the problem.

I'd say it's a 6 out of 10 solution at the moment - useable but not something I can set up and forget about.

[Rusted]

Can't you find a local model engineer to bore you a pilot hole pulley for you?

It's only a couple of minutes work in a lathe.

Ask around the back door of an engineering company for a favour during a fag break.

Or, what about the local senior school or [even better] the local tech or skills college?

They usually have lathes in their metalwork shops.

The tutors are always happy to help in my own experience. Especially with such a simple job.

I'd do it for you but the EU postage would probably be more than buying several pulleys.

 

[artoleus]

If you can put up with 20 teeth: https://www.proto-pic.co.uk/aluminum-gt2-timing-pulley-6mm-belt-20-tooth-5mm-bore.html  Ignore not 3mm