hello I read through this forum but to be honest my limited knowledge about the subject prevents me from understanding some of the terms listed and how to deal with them. I built a 3m by 1.8m cnc machine and had it up and running until I decided to upgrade my 700W spindle motor to a 3.5kW one complete with a VFD. The problem I'm facing is that my carriage now weighs about 14KG (about 31lbs) and my openbuilds NEMA23 motor cant lift the spindle anymore for Z-axis movement. X and Y axes still work fine, both are also using NEMA23s. The Z axis holds the spindle motor and drops it fine but cannot lift it, i can lower the spindle motor and keep it still but cannot get upward movement, when I try it just tries to spin upwards but ends up slipping downwards. What I want to know is if I upgrade to a NEMA34, will I be able to fix this? Do I need to upgrade my driver as well for this stepper? I'm using a 24V power supply with 36amps capacity and this driver from amazon couple onto an arduino uno.(Witbot CNC Shield Expansion Board V3.0 +UNO R3 Board for Arduino+ A4988 Stepper Motor Driver With Heatsink Kits for Arduino) https://www.amazon.com/Witbot-Expan...=1496865411&sr=8-2&keywords=witbot+cnc+shield
Rather than going through all that have you considered replacing the Z axis screw with something shallower?
TR8*2 rather than the TR8*8 you currently have. It has a shallower screw angle and thus can lift considerably more load with the same motor. It only lifts 2mm per turn rather than 8mm so you will need to adjust your settings. No guarantees but it should do the trick. Definitely the cheapest place to start. 8mm 300/400/500/600mm Lead 2mm Stainless Steel Leadscrew + T8 Nut For CNC 3D Printer Reprap
Hi Ghassen, Those drivers will likely not run a NEMA34 properly. At 2amps I don't think they're capable of fully running most 23s. I agree that a different screw pitch is worth a try, but not a guarantee. You may also want to try a different driver and a larger 23 on the Z. What type of machine do you have? Joe
its a home built machine. im currently considering a sainsmart tb6600 driver and a high torque nema23 stepper (425oz.in instead of my current 175oz.in) do you guys recommend that? can i use the signals from my controller as inputs to the new driver?
If you intend to move up to a 425, you'll probably want to move up to a real driver like the DQ542MA Stepper Motor Driver An alternate suggestion would be a low amp motor that will work with your current board like Nema 23 CNC Stepper Motor 2.4Nm(340oz.in) 1.8A 23HS41-1804S - US$ 28.48. Again, these are just suggestions. Explanations of how to properly size all this can readily be found on the web if you really need a proper answer. But again, it's probably best just to start with the shallower screw and work from there.
i couldnt find a shallower screw where i live (Lebanon) i would have to ship it from the US, and as long as i'm shipping i prefer to get a new stepper and driver.
So, you can replace the 'Z' axis motor and lead with larger, while possibly requiring some serious modification. However, there may be another solution available to you. You say that the 'Z' axis carriage weighs about weighs about 14KG, or about 31lbs. Have you thought about a "Counter-Balance" weighing 14KG ? Giddings & Lewis produced several horizontal milling machine models, where, the spindle, weighing about 500 pounds, was mounted on the 'Z' axis vertical column. Basically, two cables were attached to the carriage, brought up over the top of the 'Z' axis column, riding the turns on idlers for ease of movement. The counter weights simply hung inside of the column. Because the counter-balance weighed the same as the spindle motor/carriage assembly, effectively, the 'Z' axis servo motor only had to contend with inertia the spindle motor and the counter-balance brought to the servo system, leaving all of the available power to be applied to the part being machined. Maybe you are old enough to remember the sash style counter-balance used in residential homed windows of the mid-1950s. What I have described above works under the same principal. Thus would really be a relatively mundane task to set up, compared to retro-fitting the 'Z' axis with larger components. A counter-balance system would be the more elegant solution in that you could effectively eliminate all of the vertical load (up & down) that the carriage currently adds to the system. Even if you retro-fit the 'Z' axis with a larger motor and lead, you might still need to provide some means to overcome the reduction in feed power taken away due to the upward weight load the carriage adds to the system.
Thank you Carl for the detailed description. I am reluctant however to adding weights to the z-axis setups since my y-axis is also run by a single 117oz.in nema23 using a belt drive system. so is my x-axis but that is run by 2 nema23s on opposite directions. I'm worried that the additional weight will cause my y-axis to stall as well, I have calculated that I need a 3kg counter weight for the existing nema23 to be able to lift and hold the spindle motor so i think upgrading to the larger stepper will be a better solution in the long run. I tried the counterweight system with the additional 3kg and to be honest I wasnt really comfortable with weights hanging freely on the other side of the carriage. they tend to wiggle about and might end up screwing up my alignment.
Springs? That's a pretty big spindle. Does your structure support it okay? How about a pic of your gantry.
Based on what you've got there, you might even consider M10x1.5 threaded rod which should be locally available.
what do you mean? just as an update, I purchased bigger nema23's (425oz.in) along with their controllers. they should be arriving in a couple of weeks. I'll update this thread with the results when they arrive. thank you all for your help.
I've never seen a machine like that, that's all. I think the new drivers and motors will serve you well! Cheers Gary
OK. I understand that you purchased larger stepper motors and drives. However, there is something else to consider. If I had that much weight on the 'Z' axis of my Sherline 2000 table-top mill or OpenBuilds XL machines, I would be concerned about excessive wear of the fiber lead nut. - and I would be concerned, even if I did have actual ball bearing nuts and matching lead-screws. I do agree that the increased weight of adding a counterbalance to the 'Z' axis is carried over to the 'X' and/or Y' axis. But the added weight to the 'X' and/or 'Y' axis as a result of adding a counterbalance to the 'Z' axis is mostly an inertial load on the 'X' and/or 'Y' stepper motors and it is not the same as lifting a mass load of 30-plus pounds. The added inertial load of a 'Z' axis counter-balance is predominantly dynamic because it would be place there to "ZERO" out the 30 plus pounds of the 'Z' axis and spindle motor, affecting mostly acceleration/deceleration. Whereas, in the case of a machine of this class & size, a horizontal cutting tool with an unbalanced 30-plus pound axis/spindle load affects the available power that can reliably be applied to the work piece - in this case the plus or upward direction. In your case, a difference between a plus/minus workload availability caused by the the direction 'Z' axis weight imbalance would be pretty much un-noticable but... also means that, not only will acceleration/deceleration be imbalanced, a plus rapid traverse motion of the 'Z' axis will be sluggish, relative to a negative 'Z' axis rapid traverse. So excessive wear and reduced life expectancy of the ball-nut and lead screw - especially if this machine is using an Acme type lead-screw and a fiber lead-nut, can be expected. And... there will be a noticeable difference 'Z' axis acceleration/deceleration characteristics in the 'Z' axis plus and minus directions.
Constant force springs are a far better approach than weighted counter balances. Same lift effect just without all the weight.
Thank you for your input Carl. To tell you the truth I was just thinking the other day about how all this weight is supported by just a few spirals on a "plastic" nut, and I thought that this will give out soon. I have the fiber nut and the 8mm lead screw from openbuilds, they're a pretty good match but I'm just putting too much strain on them. I'll do some research about springs and constant force springs like Rick 2.0 said and update accordingly. If you have some examples you can point me to that would be most helpful. Thanks!
Not a perfect match but the general idea. A google search should provide many more. You can use multiple springs as needed to achieve the proper weight balance. Source - Another Source
I had forgotten about using springs. As I have mainly worked on larger machine tools, any oddity such as counter-balance that I have seen in older machine tools was done using weights. I currently program/operate a small three axis machine that is used to apply liquid coating material to printed circuit boards and, as a result of this discussion, I realized that it uses springs for counter-balance. Now I'm wondering if I should experiment with counter-balance springs on my Sherline table-top mill as, the difference in acceleration and rapid traverse in the Z' axis is quite noticeable. On my OpenBuilds XL, the motors are so large (340 Oz/In, I think) 'Z' axis doesn't seem to be noticeably affected by the three pounds that the hand router weighs.
