Belts and pullys

Hey guys, im in the process of designing my first CNC Plasma/Router and need some help.

I started building one thinking.... This will be easy!. and oh boy was it ever so opposite!

Anyway Im looking at building a 50x50 Plasma/router table and could do with some help along the way.

My first question is,
I want to use a belt system for control what do i start looking for and do i really need the small pulley up to the big pully (Sorry forgot what its called)

Secondly do you know where i can buy loose end belts?

Thirdly, does it have to have a certain ammount of teeth on the pulley?

If i plan to go for the pulley then i will have 4000mm worth of ball screws available for sale at some good prices along with ballnuts :naughty:

Any help would be great thanks

List of hardware i have..

2 x Nema 23
1 x Nema 34
1 x 1500mm 20mm ballscrew with 20mm pitch
1 x 1500mm 20mm ballscrew with 20mm pitch
1 x nema 34 mount with bearings
2 x nema 23 mounts and bearings
4 x Supported round rail and bearings
2 x unsupported round rail and bearings
1 x Uniport
2 x PS407 power supplies
3 x PM542 microstepping drivers

Derek, i would personally suggest that if you were going to use the machine for a router then sticking with ballscrew this way you will increase your torque over belts, the way i did it was to use a 2:1 Ratio to for every turn of the pull on the servo the pulley on the ballscrew turns half a turn. this does have its trade offs i.e its reduces your rapids if you are using steppers but will double your torque. also doing a gearing mechanism will increases your accuracy.

I overdid things but i like to over engineer things. to overcome slow rapids in my system but maintain torque i used servo motors that can spin at 3000rpm, but unlike steppers, servos maintain there level of torque through there full rev range!

Hope that helps a little buddy.

So if i keep the screw, do your recomend sticking at 1;1

also should i mount a screw on each side to stop the gantry crabbing?

I would personally use 2 screws for the X, what pitch are the ballscrews that you have? 5mm 10mm ? also whats the diameter? gearing all depends on what how powerful your motors are, pitch of screw mass of gantry and the likes. im not the best on this but there are a few peeps that may help you bit more. irving and john S to mention a few also gary from zapp.

I'd use belts....so how much are those ball screws going for???:joker:

No seriously like Ad's said if you plan to use it as a router as well then stick with the ball screws, they will be easier to setup, maintain and have better repeatability.


With regard to drive it boils down to speed and how much backlash you can tolerate. Ideally you would use a direct drive motor but again as stated you will need a powerful motor an if its a stepper then you will need a higher lead on the screw to keep the rapids up, but will effectively reduce the torque and you'll need an even bigger motor :smile:

Irving did a good motor calc sheet' so i suggest you look at that and get a feel for what you need. Don't know where it is tho. :redface:

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also should i mount a screw on each side to stop the gantry crabbing?

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If you have 2 screws available then i would use them but there are other solutions such as driving it from one side and then use belts (or cable) for the anti-racking system

Thanks Ross that sound like and idea with a screw on one side and belt on the other.

When you said ainti-racking system do you you mean the crabbing?

As for the calculator its a bit confusing to me being a newbie and dont know where to start

Maybe i should post a list of gear i have in my first post i will edit it now.

In the meantime here is the screw im using with a 20mm pitch

http://www.slidesandballscrews.com/r....html?cPath=39

The thing that gets to me is you look here > http://www.precisionplasmallc.com/My...les/Page4.html this is ideal for what i want ! but when you come to build it its bloody hard lol i think its safe to say the the CNC bug it biting at my ass to get it done lol

and looking at his machine i think this is the one im going to go for but my own version http://www.youtube.com/watch?v=fnkIG0RvVkQ

I will create a new thread in the build section

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When you said ainti-racking system do you you mean the crabbing?

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Yes. crabbing, racking, Although I thought crabbing was a permanent set out of alignment and racking is a variable shift whilst in motion :heehee:

yours will have to be quite different to that one if you want to use it as a router. twin belt or rack drive with bearings running on the ali extrusion by the looks of it. Way to light weight for a router. Just my opinion anyway.

Those belt drives always look impessive when demo'ed or for rapids, but i wonder what the resolution is like for actual cutting

Ross, i think you have made my mind up i think i will just stick with a plasma. i think im being a little greedy wanting the machine for 2 things when it will possibly cost me double the price. ive started a new thread in the build section under plasma.

Hoping to do a complete chat and build thread