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View Full Version : Twin ball screw drive on X - configuration question



HiltonSteve
19-05-2009, 11:48 PM
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
20-05-2009, 12:01 AM
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
20-05-2009, 01:38 AM
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. :beer:

HiltonSteve
20-05-2009, 02:03 AM
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
20-05-2009, 02:07 AM
Steve, take a look at this: Link (http://www.mycncuk.com/forums/showthread.php?t=786)


Look for post #9 (http://www.mycncuk.com/forums/showpost.php?p=4282&postcount=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. :beer:
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???:biggrin:

Lee Roberts
20-05-2009, 02:08 AM
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:

http://www-rohan.sdsu.edu/~stewart/3dGPAi1/png-figs/Fig03_03.png

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
20-05-2009, 02:16 AM
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
20-05-2009, 02:19 AM
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
20-05-2009, 02:21 AM
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: :beer:.

Smiler
20-05-2009, 08:24 AM
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:smile:
Regards, Jeff.

Gary
20-05-2009, 09:27 AM
Personally i would connect one motor to each ball screw and drive with its own driver, or use a belt and pulley to connect both ball screws and run from a larger motor.

Dont bother running two motors from one driver, this will cause you problems.

John S
20-05-2009, 10:10 AM
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!

Drew a part up the other day and sorted a long thin bit of spare material out it would just fit on and put it on the router with a lump sticking out.

Loaded the program and realised I had drawn it 90 degrees to how the material lay so X needed to be Y and visa versa.

Went into Mach and swapped the pins over in ports and pins, cut the job and then swapped it back.

Smiler
20-05-2009, 07:35 PM
Drew a part up the other day and sorted a long thin bit of spare material out it would just fit on and put it on the router with a lump sticking out.

Loaded the program and realised I had drawn it 90 degrees to how the material lay so X needed to be Y and visa versa.

Went into Mach and swapped the pins over in ports and pins, cut the job and then swapped it back.

Any chance of a photo of some of your machines John, you seem to do such a wide range of work with them. Are thay all self made?

Jeff.

John S
21-05-2009, 12:13 AM
Yes can do some pic's tomorrow.
Good thing is I have plenty of machines, bad thing is most are not working for some reason or other but it's all part of a plan :naughty:

I have two sides to my business, one is repair engineering where I repair anything broken in industry and some new parts.

The fill in work is converting and repairing small CNC machines hence the dead ones.

Currently I have a big Beaver CNC mill, about 3 tonnes of it that runs on an old DOS system called Ahha. That is my bread and butter machine.
I also have a Tecno Isel router with home brewed electronics, runs on mach3 and does the smaller parts like brush gear for DC motors and plastic parts.

Next is a Seig X3 mill converted to CNC, this was the prototype that was offered as a kit by ArcEuroTrade who I work closely with as well as Sieg in China. This is running but minus it's computer at the moment.
it's now a test rig to develop other X3 related add ons [ more perhaps later ]

Last machine actually running is a Sieg KC4 lathe which hasn't been released yet. Again this is a test bed for Sieg and at the moment there is a threading glitch in Mach3 that stops this being signed off.

http://www.stevenson-engineers.co.uk/files/KC4_27.jpg

That is the sum total of working machines.

In storage is a Denford Orac lathe, a Connect CNC lathe and a Connect Mill, these are for upgrades to modern controllers.

Somewhere kicking about is a Taig mill converted to CNC but lacking it's controller box.

Last machine is a Bridgeport MDI part way thru a brain transplant to have the second Ahha unit I have spare, these are very dated being DOS but they work very well and are very reliable.
The idea of having this on Ahha is twofold, one is I have already paid for it and it wasn't cheap and secondly it means both full size machines can use the same files so it will be easier to swap jobs about.

.