Do you keep grease on the screws?
Those springs are probably not strong enough to eliminate backlash on a 50Kg gantry.
Hello guys.
I have a machine with the cheap T8 (8mm dia, 8mm pitch) ACME lead screws. Like these with the standard nuts: 8mm Acme threaded Rod Stainless steel Leadscrew+T8 Nut For CNC 3D printer Reprap | eBay
I looks like something is wearing quite fast because when it was new it was tight and nice, but now it has a bit of backlash allready and it is not used very much.
So is it worth trying different nuts?
Like thes maybee: 1 PCS T8 Anti-backlash Spring loaded Nut For 8mm Acme threaded Rod Lead screws | eBay
It is a moving gantry design and the heaviest part (gantry with all its components) weights maybe 50kg. I have the acceleration set to 500mm/s2 so there shouldn't be very high forces on the screws?
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Do you keep grease on the screws?
Those springs are probably not strong enough to eliminate backlash on a 50Kg gantry.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Hi, yes i've been greasing the screws. Maybe the assembly is a bit heavy for the T8 after all.
I guess some cheap C7 chinese ballscrews would be mich better?
I believe a realistic load for acetal nuts around 25-50lbs. Likely you're experiencing premature wear from overloading them. The ballscrews would be a great leap forward.
Okey, thanks. I think the nuts I have are bronze?
Wondering if I could keep the ACME on the Z-axis to save money and rebuild X and Y to ball screws first ? On the other hand - the z-axis is the shortest one.
My spindle is a Chinese 3kW square spindle - it weighted 7kg. I guess the z-axis sees less wear (less motion) than the other two as well.
I think you have brass nuts.
Not sure what you have available where you are, but 12mm acme with acetal nuts might be cheaper than ballscrews? But ballscrews will perform much better.
If the Z screw is working ok, then you don't need to replace it unless it fails.
But really, 8mm screws, and those nuts, are too small for anything but 3D printers.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Had thin on my previous machine and I did my own anti back lash nuts: http://www.cnczone.com/forums/linear...8-cnc-cad.html.
My machine was very light weight and the spring was stronger than the kits on ebay. Even then if the cutting force was too high, well not that high (1/4 cutter in MDF at 3/16 DOC) it started to show some backlash.
On my new built I now have chinese ballscrew on X and Y and it is light years ahead.
http://www.cnczone.com/forums/cnc-wo...rch-frame.html
I kept the Preloaded T8 nuts on the Z axis but If I use an upcut it tends to "pull-down" the cutter and downcut push the cutter up so I'm now designing an improved Z with ballscrew.
Nice work Biggs.
I guess if I am going to change I will go with ball screws on all axes.
The ACME was a mistake, but I was trying to save money somewhere Not very smart.
But I'm amazed of how fast and strong it is with the small screws.
Here is a short video of some aluminium:
https://drive.google.com/file/d/0B7_...ew?usp=sharing
Yes, the machine is mostly built with stuff I've got for free so it does not look as fancy as other machines on the planet
Maybe I just keep the T8 screws for the next project (printer).
https://www.youtube.com/c/AdaptingCamera/videos
https://adapting-camera.blogspot.com
Yes, got a quote from linearmotionbearing now on two 1610 (X and Y) and one 1605 (Z) screw.
I guess there will be an update soon, but there's also another thing I want to change on the machine so I should do that at the same time.
That is very nice to hear. Yes the speeds are good with the T8, but I guess I would like to have higher acceleration and that should be ok with ball screws.
Be careful that increased pitch is not necessarily better. If you increase the pitch you will need more force to turn the screw around and that may be more difficult with the same motor. To increase the motor speed faster (that is acceleration) you need better drivers and pulsing mechanism. Ball screws help and will give you an advantages, but some of the advantage is lost due to the increased pitch. I have 1605 screws and without problem can reach 9000mm/min (355in/min) and an acceleration of 800mm/min2 (32in/min2). I can increase the speed about 10% more but it is high enough for my as is, so I don't do it. Increasing the acceleration resulted in occasional stall, so I keep it like I have it now. Having a higher pitch would have not give me any advantage at all, perhaps only disadvantage because I'd lose force. You should consider this, especially since you have a very heavy gantry, and which is moving. My machine has a moving table, and is a fixed beam type so it is easier to move around the X and the Y.
https://www.youtube.com/c/AdaptingCamera/videos
https://adapting-camera.blogspot.com
True. I hope the reduced friction going to ball screws will compensate for the higher force needed to accelerate.
And by the way. I didn't actually weight the gantry, and it's probably max 40kg when I think about it (including all moving parts). 50kg was just a guess.
Yes, the reduced friction will definitely help in accelerating, but will actually be a disadvantage in decelerating when you have to brake the speed for that heavy gantry. It's like driving a car on an icy road versus dry asphalt. You can drive faster on ice, but you can brake faster on dry asphalt. Acceleration and deceleration works together, and while the weight of your gantry helps in braking, the low friction is a disadvantage for deceleration. Never the less, of course ball screws are MUCH better. I also upgraded my CNC at one stage from threaded rods to ball screws and never been happier... it is a move worth every penny and weighting all the pros and cons the pros definitely overweight the cons.
https://www.youtube.com/c/AdaptingCamera/videos
https://adapting-camera.blogspot.com
Don't remember how the screen looks like now, but it's only the acceleration that is configurable? The standard value for decelerating is the same as acceleration? Or is the deceleration by default higher? I'm using UCCNC.
Btw. did read some on your blog A_camera before I started putting my machine together. Nice write-up and good information you have there.
Is that 1800rpm at the steppers?I have 1605 screws and without problem can reach 9000mm/min
While that may be possible on a small machine, it's unlikely he'll get anywhere near that rpm on a larger machine, pushing much more weight around.
Gerry
UCCNC 2017 Screenset
[URL]http://www.thecncwoodworker.com/2017.html[/URL]
Mach3 2010 Screenset
[URL]http://www.thecncwoodworker.com/2010.html[/URL]
JointCAM - CNC Dovetails & Box Joints
[URL]http://www.g-forcecnc.com/jointcam.html[/URL]
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
https://www.youtube.com/c/AdaptingCamera/videos
https://adapting-camera.blogspot.com
Actually, the maximum values I can get now is 10,000mm/min speed and 900mm/s/s acceleration. On my fairly small machine I found this crazy and scary fast, so I backed off a bit and set only 8,000mm/min speed and 700mm/s/s acceleration. On Z I have limited a bit more now, and the speed there is 6000mm/min because I feel that that is fast enough already.
- Footprint (total area it is occupying in the room): 750 x 650mm
- Table height from floor: 890mm
- Y table size: 450 x 300mm
- Weight of Y: 17,5kg
- Working area: 310 x 270mm
- Weight of X-beam: 13,7kg
- Size of the X-beam (height x width): 500 x 540mm
- Size of Z: 350 x 150 mm
- Weight of Z: 8.5kg (this is increased due to a different, longer and thicker Z plate I use now)
- Z clearance from table top: 160mm
- Maximum speed: 8000mm/min
- Maximum acceleration: 700mm/s/s
The spindle and the stepper motor and the brackets are not part of the weight calculation above.
Of course, this speed would not be possible with a 40kg moving gantry, but my machine has a fixed beam and a moving table. I think this is a better solution even if it is not as sexy as a moving gantry type of machine.
https://www.youtube.com/c/AdaptingCamera/videos
https://adapting-camera.blogspot.com
The torque curve of most stepper drive systems would favor larger pitched screws (to a point). Also the momentum of the screw is lower with lower rpms.
For me at least the resolution I get with a 10mm screw is good enough (running the Gecko G540 which has a fixed microstep setting of 10).
I have to thank everyone of you for the contribution to this thread. I now know what I'm gonna do next with the machine.