Gears and pulleys

[cjdawson]

Hi all

 

im in the process of gathering parts to make a stepper driven focusser.   To drive it I’m planning on getting a nema 17 or nema 14 stepper motor and driving it with a belt feed like you get on cnc.   However,   I’d like to get a gear wheel with a 22mm inner diameter that I can fix to the focus knob of my Meade Lx-90.   Been looking all over and can only find them with a 20mm inner diameter.

 

anyone have any suggestions on what I ca: do here?

 

this is the pull that I was thinking of, but I’d need 2mm extra on the inner bore of the large gear.

https://www.ebay.co.uk/itm/XL-40-10-Teeth-1-5-pitch-Timing-Pulley-Belt-Set-Kit-Reduction-Ratio-4-1-CNC-/262648050975

 

[JamesF]

Since you're asking the question I'm assuming you don't have much in the way of power tools.  In which case the easiest solution might be to see if you can find a local engineering company or model engineering group that could take the 20mm bore version and open it out to 22mm.  There's even an organisation that provides communal workshop space that might be able to help out.  I just can't recall the name of it right now.

James

[Skipper Billy]

If you get stuck you can post it to me and I will pop it in the lathe and skim it out for you. No charge. PM me for my address if you want me to do it for you.

[petevasey]

A long time since my LX90 days and I can't remember what the focuser knob assembly is like, but worth asking: can you remove the knob from the focuser to reveal the shaft?  If so that might be 6mm or larger  and one of the stock size wheels might fit.

Best of luck,

Peter

[cjdawson]

Yeah, that’s a thought.    No chance of my being able to do that until I’m back from my hols.

 

think I’ll measure the shaft with the knob removed when I get back.   Also might be possible to have bothe the gear and knob on at the same time, for aesthetics

[JamesF]

Just to tidy up my original posting, the community workshop thing is called "Men's Sheds".  It has a website: https://menssheds.org.uk/

There appear to be a few in Yorkshire.

James

[cjdawson]

Oh my men’s shed looks fantastic.   And there’s one where I live.   Might have to travel further for metal working though.    Love the idea.

[JamesF]

I might prefer to use a lathe, but I imagine it could be done with just a drill press and a 22mm blacksmiths drill bit.  Even a woodworking workshop might well have a drill press.

James

[cjdawson]

I've got a drill at home.   didn't know that drill bits came in 22mm sizes.   sounds great.  If I order the 20mm pully, then drill it out to 22mm that would most likely work.

[Gina]

Better to attach pulley directly to shaft.

[JamesF]

5 hours ago, cjdawson said:

I've got a drill at home.   didn't know that drill bits came in 22mm sizes.   sounds great.  If I order the 20mm pully, then drill it out to 22mm that would most likely work.

Blacksmiths drill bits come in lots of larger sizes with a narrower shank (often 1/2" or 12mm) so they can be fitted into a fairly standard chuck (although some drills come with 10mm chucks these days).  You really want to use a drill press to do it though, so you get the hole perfectly square to the pulley.

James

[Davey-T]

Drilling large holes is quite tricky as the drill keeps biting and jumping and you end up with a hole with angled edges, an old trick was to drill through a piece of cloth to try and prevent this.

As said the knob should be removable revealing a smaller shaft.

Dave 

[noah4x4]

Take a look at Amazon under 'cog wheels' if you want toothed wheels and try Rapid Electronics for friction or belt drive wheels. Both sell assorted packs for hobby use (e.g. such as Robotics and remote control mechanical devices).  

[cjdawson]

19 hours ago, JamesF said:

Blacksmiths drill bits come in lots of larger sizes with a narrower shank (often 1/2" or 12mm) so they can be fitted into a fairly standard chuck (although some drills come with 10mm chucks these days).  You really want to use a drill press to do it though, so you get the hole perfectly square to the pulley.

James

Oops, thought I’d typed drill press.

 

and yeah I know that getting the hole cantered is the hard part.  I’ll be looking in the new year into doing the actual fitting.