Thanks for the question. The blackToe z-axis motor is a NEMA 24 425 oz-in stepping motor and the next step up is a NEMA 34 651 oz-in motor located here: https://buildyourcnc.com/item/electronicsAndMotors-nema34-651ozin
To make it work on the blackToe CNC machine, you would need to fabricate a new mount and the top bearing mount, or request us to fabricate it for you by calling the office.
Curious, why the need to increase the size? If the motor is having a difficult time, there may be a deeper mechanical issue at play. One issue you may have is that the bearings are needing shim washers to separate the inner and outer races. If the two races are rubbing against the coupling or collar, the bearing may be difficult to turn under the weight of the assembly. If there is too much friction between the anti-backlash nut and the lead screw, you can add some 2-in-1 oil, or other similar lubricant.
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I have added the shim washer between the bearing and coupling and have always used a light oil on the lead screw. I halved the acceleration on the Z-axis. Then I re-ran a topo that took two hours on the finish pass. No change in my results - the Z-axis slowly dropped until when the program finished and everything went back to the start point, the Z axis was lower by 0.378 inches than when it started at 0.800 above the surface.
Any suggestions would be appreciated. Maybe I need more shim washers in the assembly between all the bearing surfaces?
Before you add a larger motor, check these first:
1. take the motor off by remove only the motor screws and removing the motor as well as the coupling half that is secured to the motor shaft.
2. Turn the lead screw by hand. This will still be connected to the z-axis assembly by the anti-backlash nut, so you will feel the resistance in the upward motion of the z-axis. Does it feel relatively easy to turn, or very difficult?
3. If the resistance is relatively normal with respect to gravity and normal friction between the anti-backlash nut and the screw, then you may want to half the velocity as well on the z-axis motor tuning, and even reduce the acceleration a bit more. Doing topographical layouts should not require fast z-axis motor travel. Be careful not to lower the z-axis acceleration if you are using constant velocity as this can make the topo "too smooth" where there may be features such as cliffs present. If you need to lower acceleration drastically, then use exact stop rather than constant velocity.
Another gotcha that may be causing this phenomenon is motor cable/wire chafing. We had this same issue crop up where two wires were shorting only at a specific position because the wires moved just enough to cause these wires to connect. This was caused by a zip tie. Zip ties have a very sharp edge that can cut the insulation of the wire. A hint of this problem is if this phenomenon is only present after working successfully with the machine for a greater period of time.
I bought a new lead screw, bearings, antibacklash nut, and shim washers (WHICH NEED TO BE IN YOUR ONLINE CATALOG) and installed them. (Like another commentor on this site, my lead screw wouldn't go through the bearings. Simple solution was to chuck it into my drill press and 400 grit smooth it until a snug fit was had. Lowest RPM.)
Anyhow, I ran another Topo yesterday and got the same results. The wires are not frayed, the acceleration has been halved, the speed reduced to a crawl. When testing manually, twisting the Z axis up was very hard to do compared to lowering it.
I have thought about a counterbalance of some type, but that introduces lots of other problems.
Anything you can thing of will certainly help.
I can send pictures, etc.
What router/spindle do you have installed?
The one you sold me - 110 V, 1.5KW water cooled.
This problem of the z axis drift has been evident since I first started using the machine a couple of years ago. Lithophanes, stipples, topographic and other heavy z axis users have been particularly bad. It is to the point that I am turning away opportunities for lack of capability.
I think all options may be exhausted. We will design a new mount that holds a large motor. Please give us a call so we can arrange to send that out to you.
We just determined that the existing mount need to be adjusted by about one millimeter for the main mounting hoes for the larger NEMA 34 motor to fit. The overall mount will look the same but the outside hole spacing will be adjusted by a very small amount to match the larger motor mounting holes. This new adjustment will be included with all new machines. We will send you the new mount (consisting of two structural pieces) and the longer screws that will be needed to extend to fit the motor frame thickness.
They didn't send the longer screws, nor the new required coupling, but I finally got it together and it works just fine. It returns to precise Z zero every time.
But the motor runs pretty hot because I think it should be run at a higher voltage than the current power supply provides.
Any new sales of Blacktoe 4.1 should include this modification.