Timescapes - Digital Timelapse Discussion

large diameter pulley
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Author:  chardie [ Thu May 10, 2018 2:55 am ]
Post subject:  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

Author:  Kitwn [ Thu May 10, 2018 10:11 pm ]
Post subject:  Re: large diameter pulley

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!



Author:  chardie [ Fri May 11, 2018 5:39 am ]
Post subject:  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

Author:  Kitwn [ Fri May 11, 2018 6:52 pm ]
Post subject:  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.

ChardiePulley_1.jpg [ 97.32 KiB | Viewed 5629 times ]

Author:  Kitwn [ Fri May 11, 2018 7:02 pm ]
Post subject:  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.


Author:  chardie [ Tue May 15, 2018 2:21 am ]
Post subject:  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.

Author:  Kitwn [ Tue May 15, 2018 3:30 pm ]
Post subject:  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.


Author:  chardie [ Wed May 16, 2018 7:22 pm ]
Post subject:  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:

Author:  chardie [ Fri Jun 01, 2018 5:56 am ]
Post subject:  Re: large diameter pulley

the gt2 belts turned up this week also the 1mm fluted mills have arrived. these things are tiny. There is a better than average chance of breaking them lol

Author:  chardie [ Mon Jun 04, 2018 11:36 pm ]
Post subject:  Re: large diameter pulley

got work down on the gold coast for the next three days. silly me forgot to put the dxf file on a memory stick last week when i had a couple of days work . i have now sorted that out. :roll: . those fluted mills turned up and they are tiny i was going to take a pic but i need to break out the takumar 100mm macro lens. i am going to try getting it waterjet cut first. i really don't like my chances of manufacturing one lol. by the way i have a question about follow focus gears. i hope someone more knowledgeable chimes in. i know most people run gear motors against the gear ring , just wondering if there is a belt option for a 0.8 gear ?

Author:  chardie [ Sat Jun 09, 2018 9:51 pm ]
Post subject:  Re: large diameter pulley

ok here's an update, got my idler wheels, belts, and picked up the large diameter pulley wheel bit of an issue with the water jet cutting the top where the waterjet cuts through the top is nicely done however as it passes through the steel it seems to deform and curve away abit and by the time its exiting the steel it's more triangular. most likely may not be an issue as i will use the top part for the belt to run on. i should have specified a thinner steel perhaps 8 or 10 mm. they did ask me what i wanted it cut out of and i had a piece of corian i thought to use.however they asked me if i wanted made out of steel and i said i didn't have anything lying around, they replied we will have something lying around so that was that lol so i ended up with a 16mm thick steel gt2 gear here' a couple of pics
there is one tiny little raised edge as you can see in the bottom pic i guess that's where it entered or exited. on the whole i am happy enough and i may re purpose it as a base plate for a pan unit as its quite heavy for what i intended it to do
by the way autocad 18 didn't like working with the file you sent however the watejet had no issues with the file which was a relief

Author:  geraldft [ Wed Jun 13, 2018 4:08 pm ]
Post subject:  Re: large diameter pulley

Hi Charlie

I caught up with this late.

Re the large gear if I was to make one and had no CNC gear - I'd go back to your original theory and using the circumference, work out how many holes to drill, and at what angular distance. You would need a rotary table and to choose a diameter that will give you a degree result that will divide into 360 degrees with a round number.

Circumference = Diameter x Pi

As an example :

For 270 holes the angular distance is 1.333 degrees at a diameter of 171.89 mm

So you drill all the holes at equal angles, then machine off the outer edge to pass through the middle of the holes... (Don't try milling the grooves on the edge - you will probably end up breaking the cutters and achieve less perfect grooves.)

However drilling this many holes will be quite slow. Hence you may want to consider a longer pitch like 5mm...

Also - if you are really smart and have the time, make attach a stepper motor to your rotary table and use it to increment at the push of a button in exact fractional degrees. An Arduino can be used or even Dragon Frame if you don't want to code...

Author:  Kitwn [ Fri Jun 15, 2018 3:09 pm ]
Post subject:  Re: large diameter pulley

It's very interesting to see the way the water jet cutting degrades as it passes through the steel, but I'm still amazed that it's possible to cut such fine detail in thick steel with just water. If it proves too heavy you could always take it back and get them to cut out some holes to leave you with a spoked wheel. I'm glad the drawing worked out OK.


Author:  chardie [ Sat Jun 16, 2018 10:23 pm ]
Post subject:  Re: large diameter pulley

its all good geraldft concerning knowledge, sharing late is better than never lol. for future reference would a 3 or four inch rotary table suffice for an 8 inch diameter pulley do you think ? i realize that there would be overhang and you would need some sort of bench under the overhang so it wouldn't flex or bend when you drilled it. regarding the stepper motor i'm guessing that you would need a small pulley on the stepper and a somewhat bigger pulley on the rotary drive. the only other thought i had was whether an o.9 or 1.8 degree stepper would be better for precision. er i'm just thinking aloud for the moment :)

Author:  chardie [ Sun Jun 17, 2018 1:28 am ]
Post subject:  Re: large diameter pulley

since the trade winds decided to make a pass over Antarctica today and bless us with an arctic blast. i pulled the 100mm takumar out today just for kits visual gratification :)
some shallow focus
i'm thinking i need a hothouse after today or a heated man cave perhaps so that might be the next off topic conversation

Author:  geraldft [ Sun Jun 17, 2018 7:43 am ]
Post subject:  Re: large diameter pulley

Hi Charlie. It can't be as cold as Melbourne though can it? Maybe just relative to what you are used to, meanwhile wear thermals...

With rotary tables the bigger the better, though they can get heavy and expensive. The larger ones will give a slightly more accurate index and make it easier to mount things. Mine is at 6" Vertex brand made in Taiwan and it works well, though I often wish it was even bigger. At Hare and Forbes the 6" is the same price as a 4" so not worth getting the smaller one. I often need to make special jigs to hold things, but for your gear you could use a heavy bolt through the center so long as you can find the center accurately. If the disk blank is already turned relative to the drilled center then you can use a dial gauge on the edge to assist with that. Flexing shouldn't be a problem, though for thinner material you could reinforce it with a backing plate underneath.

Normally tables have a 90:1 ratio so they can be direct driven by a motor or a 1:1 belt. At 1:1 you have 4 deg per rev. With a 1.8 deg motor that means 50 full steps per degree or 400 steps with 8x microstepping. That should give good resolution I think... but also no harm in reducing further via belt, like another 2:1. 0.9 deg motors are then not so necessary, and they have less torque.

Main thing for drilling is a good drill press with a cast base you can bolt the rotary table securely, or better still a Vertical Mill since you can also machine the edge accurately once you have drilled the holes.

Cheers G

Author:  Kitwn [ Sun Jun 17, 2018 3:50 pm ]
Post subject:  Re: large diameter pulley

Very sexy pictures Chardie! Maybe you could sell some limited editon prints to help fund the project?

It's even getting cold up here in Exmouth, WA. We've recently had to resort to putting a duvet on the bed at night instead of just the empty cover :D


Author:  chardie [ Sun Jun 17, 2018 7:18 pm ]
Post subject:  Re: large diameter pulley

im in stanthorpe 950 metres above sea level highest part of queensland, heck it even snows here

Author:  Kitwn [ Mon Jun 18, 2018 2:29 am ]
Post subject:  Re: large diameter pulley

I remember snow. It usually looked beautiful for a few hours and then turned to three days of soggy slush. One of the reasons for emigrating to Australia.
Most of England rarely stays cold enough to make snow into the fun stuff it can be in Scotland or Canada.
We've gone from one extreme to the other and now complain about the heat and the dangerous sunshine in January instead of the cold and the sleet :D

On another note, I'm actually building my new CNC router at last. I'll have some pictures soon.


Author:  chardie [ Mon Jun 18, 2018 3:09 pm ]
Post subject:  Re: large diameter pulley

good to hear that your back at it, i like reading about you guys and your metal gymnastics lol inspires me to play with my own toys

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