The Shop > CNC
The basics
Imagineering:
In my experience, the use of a Flexible Coupling is redundant. If all the Bearing Supports and Stepper Mounts are square and perpendicular there is no alignment issue to compensate for. If the Thrust Bearings are on the Stepper Motor end of the BallScrew, a little Axial play is built into the System at the support Bearing end to compensate for thermal expansion.
Copied from my reply to another Thread;
My method for lining every thing up;
Make sure the BallNut is secured in the intended centre of the BallScrew Axis.
When fabricating the End Plates which hold the Bearing, make the Mounting Holes a mm oversized. (eg 6mm Bolts, use 7mm Holes).
Bolt everything together so that the End Plates can move laterally.
Drive the Axis to the Motor end of it's travel and nip up the Mounting Bolts at that end.
Drive the Axis to the other end of it's travel and nip up the Mounting Bolts at that end as well.
Drive the Axis back and forth between limits and check that there is no binding anywhere.
If all is well, tighten the Bolts fully, and repeat for the other Axes.
I've converted two Mills and built a CNC Router from scratch, and have used this method with success on all three.
The Dual Motor Y Axis on my CNC Router and both the X & Y Axes on my SX3 are directly driven without Flexible Coupling.
philf:
--- Quote from: Imagineering on July 22, 2016, 04:31:15 AM ---In my experience, the use of a Flexible Coupling is redundant. If all the Bearing Supports and Stepper Mounts are square and perpendicular there is no alignment issue to compensate for. If the Thrust Bearings are on the Stepper Motor end of the BallScrew, a little Axial play is built into the System at the support Bearing end to compensate for thermal expansion.
--- End quote ---
Hi,
You say "there is no alignment issue to compensate for".
Everything is made to a tolerance. e.g. the stepper motor flanges may not be exactly perpendicular to the shaft and the bearings in the stepper probably aren't made to highest standards so will have some eccentricity. These errors may be very small but would have some detrimental effect. Using a solid coupling might seem to work OK but I feel sure that wear on parts would be accelerated and efficiency would suffer. I have used zero backlash couplings on my X & Y axes and timing belt drive on my Z axis.
On my machine I can push the table and turn the stepper motors (providing they are powered down). You may find that wouldn't work with a solid coupling.
I'm not saying that it won't work - it's just better to use a coupling in my opinion.
We had many machines at work (in the semiconductor industry) working to micron (or sub-micron) accuracy and, without exception, all the ballscrews were connected to the steppers or servos with couplings.
Cheers.
Phil.
Will_D:
@John: thanks for the pics. That looks like a SX3 hence the big steppers.
I would also some more info (pretty please: a drawing) of the thrust bearings etc.
Another question has raised its head: While googling Expensive pro quality UK ball screws one company was showing how to anneal the ends (with an induction coil R/F heater) before maching to suit!
Do the unfinished Chinese screws be that hard??
spuddevans:
--- Quote from: Will_D on July 22, 2016, 04:05:12 PM ---@John: thanks for the pics. That looks like a SX3 hence the big steppers.
I would also some more info (pretty please: a drawing) of the thrust bearings etc.
--- End quote ---
I used something similar to John's method, but I used a nut to hold the angular contact bearing on the ballscrew instead of using one half of the oldham coupling, see halfway down this post for a pic of the coupling in place - http://madmodder.net/index.php/topic,3535.msg40859.html#msg40859
--- Quote ---Another question has raised its head: While googling Expensive pro quality UK ball screws one company was showing how to anneal the ends (with an induction coil R/F heater) before maching to suit!
Do the unfinished Chinese screws be that hard??
--- End quote ---
They're not that hard, and the hardening is not too deep either. I used a tipped tool and had no problem - http://madmodder.net/index.php/topic,3535.msg39297.html#msg39297
Hope this helps,
Tim
Will_D:
Many thanks for the replies -all are very helpfull
This is why the thread is called "The Basics"
I am really trying to 'drill down' to the fundamental knowledge we need!
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version