Twin ball screw drive on X - configuration question

[HiltonSteve]

Maybe someone out there has had experience trying this already but I am currently pondering what is the best way to run 2 x 16mm ballscrews to move my flying gantry on my machine, still at the design stage so any modifications needed would be much easier at this stage.

What would work best out of the 3 configurations below and what would not work and why...!

Option 1 - 2 x 23 Steppers running each screw independently off of the same driver card

Option 2 - 2 x 23 Steppers running each screw as above but also a toothed belt linking the two together to prevent misalignment

Option 3 - 1 x 23 Stepper (or maybe larger) running on one screw with the two screws linked with a belt.

If linking them with a belt then how do you go about getting the right length belt or do I adjust my design to suit a standard belt??

[John S]

Can't really comment on this as i have never built a twin screw machine but 4th option is single screw placed central under the bed.

If using option 3 you use an idler pulley to adjust tension.

.

[Lee Roberts]

Steve, take a look at this: [ame="http://www.mycncuk.com/forums/showthread.php?t=786"]Link[/ame]


Look for post [ame="http://www.mycncuk.com/forums/showpost.php?p=4282&postcount=9"]#9[/ame] by HS93, i'v been asking belt related questions as well, you can use that to work out what size belts you need.

I'v not seen anyone use two leadscrews on the X Axis befor, its normally the Y Axis they do it on to stop "racking", do you really need two?
If you could submit some of your design for us to look at it may help with ideas.

[HiltonSteve]

I may be calling my X axis my Y and visa versa! What i am calling my X axis runs along the table and my Y axis runs on the gantry, just seemed to make more sense this way round! Yes using the 2 leadscrews is to prevent racking.

Just in the middle of tweaking the design now but I will post some pics later. But the basic configuration is a typical flying gantry machine with two lead screws / ball screws to drive the gantry, this is why i was asking about belt configurations to prevent racking.

[HiltonSteve]

Steve, take a look at this: Link


Look for post #9 by HS93, i'v been asking belt related questions as well, you can use that to work out what size belts you need.

I'v not seen anyone use two leadscrews on the X Axis befor, its normally the Y Axis they do it on to stop "racking", do you really need two?
If you could submit some of your design for us to look at it may help with ideas.

Well you have just answered all my questions on sizing belts and pulleys! Nice one Lee.

Just need to figure out what configuration will work best, may build into my design the option to try them all and see how it works.

Just one other thing, you look way to serious in that avatar photo to the point were you are scaring my kids! Ever felt the urge to become an axe murderer???

[Lee Roberts]

Well you could be right i always thout it was that way around, looking at google images it seem i'm wrong and your right Steve:



or do we filp the 0,0,0 on its axis so we are now looking down the z axis, the pro's will have to confirm because now im :confused:.

[HiltonSteve]

End of the day if your building a machine then you decide which way round you want your X and Y, does it really matter??

All the CNC stuff I have worked on always had the longest travel movement on the bed as the X. So if your gantry was wider than your machine is long (don't really know why you would do this!) then maybe I would be calling my gantry X then you would be right!

[Lee Roberts]

Well you have just answered all my questions on sizing belts and pulleys! Nice one Lee.

Your welcome mate, i'v added those posts to the FAQ section for later use if you ever need to go looking for them.

Just need to figure out what configuration will work best, may build into my design the option to try them all and see how it works.

Indeed, ill keep an eye out for your findings.

[Lee Roberts]

End of the day if your building a machine then you decide which way round you want your X and Y, does it really matter??

All the CNC stuff I have worked on always had the longest travel movement on the bed as the X. So if your gantry was wider than your machine is long (don't really know why you would do this!) then maybe I would be calling my gantry X then you would be right!

Well that sounds about right, i think ? lol, this is for you mate anyway: .

[Smiler]

Maybe someone out there has had experience trying this already but I am currently pondering what is the best way to run 2 x 16mm ballscrews to move my flying gantry on my machine, still at the design stage so any modifications needed would be much easier at this stage.

What would work best out of the 3 configurations below and what would not work and why...!

Option 1 - 2 x 23 Steppers running each screw independently off of the same driver card

Option 2 - 2 x 23 Steppers running each screw as above but also a toothed belt linking the two together to prevent misalignment

Option 3 - 1 x 23 Stepper (or maybe larger) running on one screw with the two screws linked with a belt.

If linking them with a belt then how do you go about getting the right length belt or do I adjust my design to suit a standard belt??

Option 3 for me no question.

Using option 1 or 2, if one motor stalls, the other may continue to drive and you couldl get a bit more than racking. Slaving axes or driving from the same driver won't stop this happening unless you are introducing some sort of closed loop monitoring. Can't beat doing your alignment in hardware IMO.

Single drive with belts or rack and pinion would be how I would do it or as John suggests, drive the gantry from the centre underneath the table.

Just my opinion of course
Regards, Jeff.