Need a belt drive sprocket made

[glend (Glen)]

I would like to get a belt drive sprocket fabricated to replace the RA and DEC motor sprockets in my CGX mount. The stock sprockets are too short and do not allow the belt to align properly with the worm sprocket. Tooth dimensions and diametre would be the same as stock, just need a longer one.
Can these things be 3D printed? Would they be strong enough?
If aluminium fabricated, is there a well regarded IIS supplier?
Thanks

[garymck (Gary)]

Hi,

when I have needed a timng pulley, I've usually bought from the UK. Prices are cheaper and delivery is usually quicker. Here is a list of suppliers. I would be amazed if amongst them, you could not find exactly what you need.

http://www.eurekamagazine.co.uk/desi...ulleys/610983/

cheers
Gary

[cfranks (Charles)]

Queensland supplier I have used for years and highly recommend:
https://www.smallparts.com.au/store/categories/ and search for timing pulley.

[Merlin66 (Ken)]

+1 for small parts.
They supplied the timing belts and pulleys for my Skywatcher focus motor mods.

[glend (Glen)]

Thanks guys, yes i know about Small Parts, i have bought things from them in the past. I think they just sent out an email about getting out of the hobby side of the business, must check it out.

[bojan]

3Dprinting works, however you may have PE issue... (correctable with firmware).
In the past I used SDP-SI (postage was a bit expensive, and it seems Small Parts used them as supplier).
These days I am buying sprockets from ebay for couple of bucks, and adjust parameters in firmware (my recent LXD75 project using OnStep was like that).

[Octane (Humayun)]

I'm after a spare sprocket like the one that comes with the RoboFocus Mandel kit. Can anyone point me in the right direction? I don't mind spending coin on good quality rather than eBay alternatives.

The image shows what I'm talking about (the one attached to the motor): http://www.robofocus.com/store/photos/rf001.jpg

I think it's got a 5mm bore.

Thanks.

Regards,
H

[gjh1967 (Glenn)]

Core electronics sell a few sprockets
Located in Newcastle NSW and mail order

[rally]

Would a simple spacer work to extend the sprocket into its correct alignment position ?

[glend (Glen)]

Originally Posted by rally

Would a simple spacer work to extend the sprocket into its correct alignment position ?

No the motor drive shaft is too short to push the sprocket out further, the set screw would not find a shaft to lock to.

[bojan]

Perhaps you just need a piece of 5mm steel shaft and adapter like this:

http://www.ebay.com.au/itm/Brass-Sha...wTFCFOU1YiX5zg

[glend (Glen)]

Originally Posted by bojan

Perhaps you just need a piece of 5mm steel shaft and adapter like this:

http://www.ebay.com.au/itm/Brass-Sha...wTFCFOU1YiX5zg

Thanks Bojan, that looks very interesting. Itvis an option but have concerns about a shaft extension because of the load placed on the extension and joint. The belt is under tension. My preference is to find a sprocket which will fit the existing shaft well but just extend outward a bit further and preferably have and end flange. Most of these hobby timing belt sets do have flanges on the ends to help keep the belt aligned. I am going to browse through that suppliers gear.

[glend (Glen)]

This item would be ideal if i can get the gear specs to match.

2pcs 2GT 20T 5mm 8mm Bore Aluminum Pulley Gear Wheel for 3D Printer Timing Belt | eBay
http://www.ebay.com.au/itm/2pcs-2GT-..._YtzmaNWdeyWfw

[bojan]

Do you know the original timing pulley-belt specs?

As an alternative, you can change the whole assembly, only thing to take care of is transmission ratio... unless you can sort it out in firmware.

Flanges are not really needed to keep the belt aligned, it will not slip, ever.. - I used just plain pulleys made from extruded stock for my EQ6 modification, the timing belt transmission is inside and there was never any issue for the last 5 years since I did it.

Another thing you can do is to replace the motor (with longer shaft)....

[glend (Glen)]

How do i determine the motor sprocket specs? I can count the teeth ( i think it was 14) and i know the width of the sprocket and can work out the outside diametre. The shaft is 5mm.

[bojan]

I just had a look at your other thread... bad design.
Those original pulleys are coarser than the ones from ebay (that are used for 3D printers).
There is a marking on the belt (T5x165), like this one:
http://www.ebay.com/p/Milling-Machin...165/1138257840

I would replace the whole thing, both pulleys, with finer teeth and narrower belt. Important thing is to keep the transfer ratio (ratio between number of teeth on pulleys) the same.
Motor pulley has 14, how many teeth are on the other one?

Since the motor shaft is short, I would use the pulley with 8mm hole, and made the bushing long enough to match the 5mm shaft and have the proper contact with screw. I would even glue the bushing with epoxy to the motor shaft.

I would probably even consider widening the original hole on 14-teeth timing pulley, to suit bushing.

Bushing could look something like this:
https://pengeapens.myshopify.com/collections/bushings
or this:
https://www.pennstateind.com/store/PK-PENXXBU.html

Or just a simple hollow tube, 5mm inner, 8mm outer diameter - they can be made very precise and absolutely concentric, and material can be even plastic (Acetal is ideal for this.. or PVC).

SPD/SI have a calculator for timing belt diameters, distances etc... very useful for determining the belt specs.

And I wouldn't worry about warranty.. you can always put back the original parts.