PDA

View Full Version : Custom Pulley Help - ATC over hall



andy_con
07-02-2016, 08:31 PM
looking at doing a complete over hall of the 6 station atc on my triac.

I want to change the 6 tool holders to 10 and replace the slow motor that only spins one way with a decent stepper that can go both ways.

all the designing is done and ive hit a stumbling block which I need some help on - a pulley system.
the shaft of the nema isnt long enough to stick out the bottom of the mounting part.

so not sure how im going to get a toothed pulley system to do the job.
but that's all I need is 2x toothed pulleys and a belt of the right length.
as you can see from the drawing two centres are 47.5mm apart



green = part of existing atc arm
blue = new nema
black = new 10 station tool holder
red = dimensions

see through -

http://i187.photobucket.com/albums/x202/magicmushrooms1/cnc/triac%20atc%20arm%20see%20through_zpsynvdl0rl.png


solid version

http://i187.photobucket.com/albums/x202/magicmushrooms1/cnc/triac%20atc%20arm%20solid_zpsp1zb04ju.png

you can just see the atc to the left here

http://i187.photobucket.com/albums/x202/magicmushrooms1/cnc/DSC_0914_zps0tv6azwp.jpg

sorry got the white cover on

http://i187.photobucket.com/albums/x202/magicmushrooms1/cnc/DSC_0649_zpsu0hlocsd.jpg

Boyan Silyavski
07-02-2016, 08:52 PM
So basically you are saying you have place for <20mm wide pulleys with say both diameters no bigger than 20mm

so at least the belt width is clear, it could be 15mm or 10mm.

Now the big disc seems to have 20mm shaft. question is could the shaft itself be machined as a pulley or it has to be 20mm diameter and pulley over it?

andy_con
07-02-2016, 09:17 PM
correct, 20mm or less would be fine.

heres another photos to explain a bit more

http://i187.photobucket.com/albums/x202/magicmushrooms1/cnc/DSC_0598_zps7rue8dpc.jpg

you have the long steel rod with 3 holes which slides into the ally disk which holds the tools, then the cog goes on top of the ally disk. the dia of that steel rod is not changeable and will be used on the new setup. that steel rod fits perfectly into the rest of the arms and bearings etc...


So basically you are saying you have place for <20mm wide pulleys with say both diameters no bigger than 20mm

so at least the belt width is clear, it could be 15mm or 10mm.

Now the big disc seems to have 20mm shaft. question is could the shaft itself be machined as a pulley or it has to be 20mm diameter and pulley over it?

andy_con
07-02-2016, 09:22 PM
current setup

http://i187.photobucket.com/albums/x202/magicmushrooms1/cnc/DSC_0595_zpsdbuoasid.jpg

so these are the bits that will remain that I have to work with
green cast iron arm and steel rod insert which the new ally disk will mount to

http://i187.photobucket.com/albums/x202/magicmushrooms1/cnc/DSC_0613_zps56uiqygr.jpg

andy_con
07-02-2016, 11:13 PM
just been speaking to a friend with a lathe whos going to make me a little shaft extender to go on the nema so I can attached a pulley to the other end to solve the height issue.

so I just need some recommendations on two toothed pulleys with matching belt to fit a centre distance of 47.5mm

magicniner
07-02-2016, 11:25 PM
so I just need some recommendations on two toothed pulleys with matching belt to fit a centre distance of 47.5mm

simply Google "toothed belt pulley calculator" and plug in your numbers, all the major suppliers seem to have one,

- Nick

Boyan Silyavski
07-02-2016, 11:48 PM
So then you are stuck with min size pulley HTD 5m 20 teeth having in mind 20mm bore:

17543


Then we go to the belt calculato (http://www.bbman.com/catalog/belt-length-calculator.html)r, play a little with it and find that voilaa, if i am not wrong you have a hit.

17544

we search the web for the 180mm HTD 5m belt and find that indeed there is one existing in this size:

17545


So more or less problem solved. Pulleys from belting online, contact them if they have the belt if not search and buy. its a good idea to pay them to bore the pulley as they do it well and wall thickness will be alright at 3mm as per drawing above.


So problem solved? Right? if you want to mill them or to do them i could pass you a dxf drawing of any tooth count you need for HTD5 pulleys

JAZZCNC
08-02-2016, 12:32 AM
So are thinking to do away with the Geneva wheel.? If so then I'd re-think it because with such large diameter disc and lot of weight then stepper may struggle to hold position good enough, esp with higher rotating speed with more weight. You'll certainly need fair ratio on it.!

Boyan Silyavski
08-02-2016, 06:34 AM
So are thinking to do away with the Geneva wheel.? If so then I'd re-think it because with such large diameter disc and lot of weight then stepper may struggle to hold position good enough, esp with higher rotating speed with more weight. You'll certainly need fair ratio on it.!

What i wanted to say was that a stepper with a gear could do the job.

andy_con
08-02-2016, 12:23 PM
So then you are stuck with min size pulley HTD 5m 20 teeth having in mind 20mm bore:

http://www.mycncuk.com/attachment.php?attachmentid=17543&d=1454888132&thumb=1 (http://www.mycncuk.com/attachment.php?attachmentid=17543&d=1454888132)


Then we go to the belt calculato (http://www.bbman.com/catalog/belt-length-calculator.html)r, play a little with it and find that voilaa, if i am not wrong you have a hit.

http://www.mycncuk.com/attachment.php?attachmentid=17544&d=1454888551&thumb=1 (http://www.mycncuk.com/attachment.php?attachmentid=17544&d=1454888551)

we search the web for the 180mm HTD 5m belt and find that indeed there is one existing in this size:

http://www.mycncuk.com/attachment.php?attachmentid=17545&d=1454888746&thumb=1 (http://www.mycncuk.com/attachment.php?attachmentid=17545&d=1454888746)


So more or less problem solved. Pulleys from belting online, contact them if they have the belt if not search and buy. its a good idea to pay them to bore the pulley as they do it well and wall thickness will be alright at 3mm as per drawing above.


So problem solved? Right? if you want to mill them or to do them i could pass you a dxf drawing of any tooth count you need for HTD5 pulleys


that is perfect, thank you very much.not sure I understand it all but I will contact them with this detail and buy a bits.many many thanks

andy_con
08-02-2016, 12:27 PM
So are thinking to do away with the Geneva wheel.? If so then I'd re-think it because with such large diameter disc and lot of weight then stepper may struggle to hold position good enough, esp with higher rotating speed with more weight. You'll certainly need fair ratio on it.!

yes I want rid of the Geneva wheel.the current disc is mounted via bearings and once in bits the ally disk that holds the tools is very free flowing in the green cast iron arm.I don't want it to run at high speed, but a bit fast then the current setup which is painfully slow. ill give it a go and see how it works, if it becomes a problem ill have to redesign

JAZZCNC
08-02-2016, 03:02 PM
What i wanted to say was that a stepper with a gear could do the job.

Yes I know that but it's needs a High Ratio and decent sized stepper to handle the inertia of large diamter wheel fully loaded with tools and they do struggle if run fast resulting in overshooting. Which actually slows tool changing or If toolholder isn't perfectly lined up they rub and wear spindle/Pullstud resulting in dropped tools.!!

Geneva while still needs gearbox or ratio it does index perfctly and is more reliable. That's why they are used in ATC.!!