View Full Version : 2 ways of mounting motor

20-09-2008, 04:54 PM
Hi all

I could do with some other peoples views please,

1/ on my "Z" axis I have 2 ways of mounting motor, one direct on top of the lead screw (12 x 3mm) and drving directly through a coupling PICTURE 1


2/ mounting up side down behind the "Z" and belt driving accross the top, PICTURE 2

I cant decide which is better, I have the plates cut for both ways, so thats not a problem. method 2, I will have to loose 10mm of travel for the bearing housing, I will still have 160mm (6"+) I dont have the belt pullys or the belt

What I would like to know is which is better and if metod 2 what belt ratio??





Thanks for your help


20-09-2008, 08:17 PM
Personally I'd go for option 2.

Given the acceleration/deceleration rates involved with a plasma table, I'd be trying to keep the centre of gravity as low as possible to help with stability.

20-09-2008, 08:35 PM
Actually I'll clarify my previous post a bit.

I'd try keeping the centre of gravity as near to the rails as possible, to minimise how much the gantry trys to rock under acc/dec (think of the motor as a big pendulum trying to pivot around the rails).
However, given that your gantry is quite 'substantial', it probably won't be as big an issue for you, than for somebody using a lightweight alloy extrusion gantry.

Lee Roberts
20-09-2008, 10:24 PM
I think i would perfre option 2 steve, cant cant really base this on anything other then how the 2 options look. Keeping to how your other motors are.

I'v also moved this question to help it get noticed.

21-09-2008, 12:19 AM
Thanks M C, Point taken, I had quickly thought of that and carried on, my view was option 2 was tidyer and a better engineering option but option 1 is easier, and I have all the bits for that, but option 2 keeps every thing the same even motors will be interchangeable i.e the top mounted one I have to drill the mounting holes whereas all the others are tapped, any views on belt ratio? all others are 4:1 on a 16mm pcd on rack this one is a 3mm pitch screw.

dont know why every one seems to think my gantry is heavy its made out of 60 x 60 x 3 hollow box it only weighs 10kg plus all the goodies LOL

Thanks Lee Just found it

Lee do you like the avatar? this was last years project,
750cc, 100mph 0-60 -3 secs we could not get out of 3rd on field no space

21-09-2008, 12:43 AM
Provided you can maintain a reasonable movement speed, then I wouldn't worry too much about ratios. It's not as though you're trying to move a big mass.

21-09-2008, 01:02 AM

I will stick to 15-60 XL that way there all the same

unless any one has any other ideas........


16-02-2009, 12:02 PM
I actually prefer option 2 and I have built my router and my plasma cutter like that. I just think it reduces the center of gravity of the whole mass and I have mine about 3:1 ratio and it works a treat. The cable chain I have with all the cables and wires in it runs over the top much better.
If you have a quick look at the router pics on YouTube you will get what I mean.
Go to 2:32 for the still shot of the Z axis

I opted to go with the linear rails on rectangular section on the X axis instead of the round bar ones as there was too much flex and I changed out the 2 start 5/8 acme screw on the X axis with a 12 start 3/4" anti-backlash one and now it is so much faster and cuts a whole lot quicker.
Stepper motors work better at slow speeds and have more torque so the 12 start thread is much better
I should take some more pictures of it one day and make a short video too.


28-02-2009, 12:12 AM
Im thinking of using belt and pulleys on my next router upgrade, mainly to reduce the width and height, and always wondered do you have set belt distances to work with? ie. do the two pulleys, drive and motor have to be a certain 'standard' distance apart?

Also do belts stretch meaning backlash would be a problem?