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 large diameter pulley 
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Joined: Wed Oct 16, 2013 4:07 am
Posts: 270
Post large diameter pulley
hi all
i'm looking to build a large diameter pulley
i have a 200mm lazy susan bearing that i plan on mating with a machined piece of corian a type of hard plastic
i intend to cut a circle out of the corian and then using a dremel cut the grooves on the edge of the corian for a gt2 belt .
i am wondering if there is a formula for taking the belt measurements and working out the nearest diameter that would fit
a 200mm circle so that i end up with a equal amount of divisions or ridges so there is no jumping or jerking as a rotation is completed
i figure its going to be a bit of a mission to accomplish but i thought i'd ask before i jump in.
thanks for your time and thoughts in advance
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Thu May 10, 2018 2:55 am
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Joined: Thu Mar 10, 2011 11:38 pm
Posts: 545
Location: Exmouth, Western Australia
Post Re: large diameter pulley
Chardie,
I have a program here called 'Gearotic'. With it you can design gears, sprockets and pulleys for a variety of standard timing belts including GT-2. You can also design complete wooden clocks as well. link below.
I doubt you'd want to buy it yourself for a one-off project but if you let me know the details of the pulley I can produce a DXF drawing you can then print out and cut round. Alternately, wait long enough and I mght just have my CNC machine in a fit state to cut it out for you!

All I need to do is tell it how many teeth to use, adjust to get the outside diameter you want and export as a DXF file. I've tried to attach an example DXF file of a GT-2 pulley produced in Gearotic but the forum will not allow it for some reason. PM me with your email address of you want to proceed with this.
Note that most people with a CNC machine should be able to import a DXF file and cut out the pulley from that for you if you know someone who can help you. Anything to avoid the tedium of cutting it out by hand!

http://www.gear2motion.com/

Kit


Thu May 10, 2018 10:11 pm
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Post Re: large diameter pulley
thanks kit that would be awesome
i remeasured the diameter its 201 mm
running mums sowing tape measure around the circumference i get 638 mm so if i read the the diagram at the top of the post i get 2mm from peak to peak. if i divide 638 by 2 i get 319 teeth. not being an engineer i dont know if thats right or wrong lol. if that looks good in your gear program i will run with that. i think i may get it water jet cut next time i am down on the coast. 319 is a lot of times to do something wrong lol. i will send a pm shortly


Fri May 11, 2018 5:39 am
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Joined: Thu Mar 10, 2011 11:38 pm
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Location: Exmouth, Western Australia
Post Re: large diameter pulley
Here's a screen grab of 319 teeth in gearotic. It's easy enough to knock out a couple if you want the ouside diameter to be 201mm. Dont forget that the outside diameter of the belt round the pulley will be larger than this so if you want the whole thing to be only 201mm we will need to make the pulley significantly smaller. The drawing of the belt should give you the distance from the pitch diameter to the outer edge of the belt. It's easy to keep adjusting the number of teeth until the pitch diameter of the pulley is 201mm (or whatever you want) minus two times that distance.

The pitch diameter is the diameter of an equivalent smooth pulley that would move a smooth belt by the same distance per revolution. There should be a line along the belt drawing showing where this is within the belt thickness.

Attachment:
ChardiePulley_1.jpg
ChardiePulley_1.jpg [ 97.32 KiB | Viewed 113 times ]


Fri May 11, 2018 6:52 pm
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Joined: Thu Mar 10, 2011 11:38 pm
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Location: Exmouth, Western Australia
Post Re: large diameter pulley
Having looked at your original post again, I think the distance 'PLD' is the pitch diameter to outer diameter distance. To get an overal diameter outside the belt of 201mm you want 315 teeth.

Kit


Fri May 11, 2018 7:02 pm
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Joined: Wed Oct 16, 2013 4:07 am
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Post Re: large diameter pulley
thanks for the dxf kit. i dont't have any cad program or printer for that matter on my home computer bit of an oversight that, but not needed it before now. i do use cad at work. luckily work has picked up as i been out of work since before the commonwealth games.so i think i'll get it waterjet cut when work picks up. the cnc i use has a bug when the tooling radius approaches the radius of the program code odd thing happen and something gets smashed usually. so i couldnt do it on the cnc i run at work anyway not that i have tooling that small.


Tue May 15, 2018 2:21 am
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Joined: Thu Mar 10, 2011 11:38 pm
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Location: Exmouth, Western Australia
Post Re: large diameter pulley
I was a bit concerned at needing a 1mm bit to cut out the GT2-2mm profile. The 5mm version would be a much less tool-snapping option.

Kit


Tue May 15, 2018 3:30 pm
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Joined: Wed Oct 16, 2013 4:07 am
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Post Re: large diameter pulley
in the continued interested of having something happen in the forum ;)
i have ordered a couple of gt2 belts of around 700mm and some gt2 idler wheels. i have found some 1mm fluted ball mills just need to order them might get 6 ... just because you know :roll:


Wed May 16, 2018 7:22 pm
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