I wasn’t having any luck with the clamping arrangement of the Z nut holder. Maybe I was doing something wrong, but I couldn’t tighten it enough to keep the nut from pushing out of it. I feel like the assembly should firmly capture the nuts regardless of the direction of force in the Z. So I ended up redesigning it into two parts that capture both nuts and the spring. There’s still potential for a little wiggle but it should provide more support for your nuts.
Hope you like it.
Chris
The smaller lower nut needs to be loose or you lose the whole point of the spring. The larger coupler needs to be clamped well but the regular nut needs to just be held enough so it can’t spin. I can’t tell if this accomplishes that or not.
It does. The regular nut is free to slide up and down due to an enlarged hole but the top nut is tight. I see a problem where there can be slop if you don’t set the spring to make up the gap.
I’d like to upload models, but they were rejected… I’ll figure it out some other time.
Chris
Hmm, didn’t know that. I too had gotten tired of the Z nut slipping free on me so I printed in ABS, then superglued the nut in place (ABS chemically bonds with superglue in a way PLA doesn’t). Since then I’ve switched to a TR88 instead of the all thread ($10-15 on Amazon for the screw and nut), and upped my Z axis speed significantly. I think it’s a worthy upgrade worth considering vicious1. The TR88 came out of the bag so frictionless that if I started it turning - the nut would turn on it’s own just from gravity until it fell off. (once it’s mounted of course the tool’s weight pushes down enough that it no longer moves on it’s own) I’ve even been able to up my Z axis speed to 40mm/s. (Worked at 50mm/s too, but I didn’t like the sound of the stepper motor - so for safety I took it back down to 40mm/s). That’s travel speed - not plunge speed of course.
How is the backlash? I’m worried that the brass will wear quickly and get sloppy. Using these on a 3D printer they won’t get nearly the same loading as milling with the mpcnc. Getting another nut to make a anti backlash makes these very expensive relative to the rest of the machine.
Not having any backlash problems so far, but I don’t have hundreds of hours of use out of it yet either. I read somewhere that the nuts should last quite a while as long as you don’t exceed 500RPM (which would be about 66mm/s at 8mm per revolution) or the load limit of the nut (which should be way higher than my DW660)
Well, you were right. I used it extensively with a lot of Z moves over the past few days, and I notice some backlash now. I would get one of these http://www.robotdigg.com/product/18/Anti-backlash+Nut+for+Tr8*8+Leadscrew for $10, but at 36.5mm diameter (versus 22mm for the nut I have now) it would be way off on lining up with the Z motor mount (and would require a redesign of the Dewalt mount too for more clearance there).
I wonder if I could do what you did for the original design - take the spring, and get a 2nd cheap 22mm nut (they are only about $5 for the non-antibacklash ones) to put on the bottom of the Z nut trap.
It will work as long as the lower nut is free to move vertically but not spin.
Hmm, so I could drill out the bottom of the Z nut holder so there is no friction with the circular part of the TR8 nut, then using 2 of the screw holes mount it to the Z nut holder loosely, with the spring in the middle. Worth a try. (Although I just noticed something odd - the backlash only happens at certain heights - that means it’s the rod that has worn, and not the nut. Would the spring and 2nd nut still help in that case?)
The steel screw should not wear against brass, sounds like the screw was poor quality to start with. Not that I know of.
Hmm, I did just get it, and it was from Amazon. Maybe I’ll try RMA’ing it then.
Got a replacement, and maybe I was wrong. The replacement was very different (which is odd since it was the same item, from the same vendor), and came with a Delrin nut instead of a brass nut. I first tried swapping out the lead screw - even worse backlash right from the get go. Then I tried swapping out the brass nut for the Delrin nut, and the backlash disappeared (for both lead screws). The weird part is - if it was the brass nut the whole time - why would I have areas of height where it had sizable backlash then other areas where it had no backlash at all? I wonder how fast Delrin wears out. On the plus side - if I understand Delrin right - you can just put the lead screw back in, heat the lead screw up to Delrin’s melting temperature (since it’s just plastic - Gizmodorks even makes a Delrin/POM/Acetal filament) and it thread forms around your lead screw eliminating backlash again. Question is how fast does it wear - and how often would you need to do that.
I have some experience with lead screws. Upgraded the z axis in my 3d printer earlier in the year.
Point one to note (and probably the most critical point when talking lead screws) the must be perfectly straight PERFECTLY! The allowable run-out to prevent rapid wear of the brass nut is <0.8mm per 1000mm length (this is for T8R3 trapezoidal lead screw)
Any more than this and the brass nut will eat it’s self in a very small time frame. When any reputable company sells a lead screw they will run it through a special “straightening” machine after any cutting/machining had been done, prior to sending it out.
The design of a trapezoidal lead screw/nut assembly relies on a very small and consistent clearance between the leading edge of the thread and the drive surface of the nut. Even small variations in this will lead to rapid wear and severe inaccuracies.
I learned this the hard way. Bought a cheap setup from eBay. Had is replaced several times because it was never straight. Eventually just bit the bullet and bought a quality expensive set through a local bearing shop, and it was perfect first time.
This is one item I don’t recommend cheaping out on.
Delrin is a great material. I would hope you would never have to try and melt it. You would be best to just find a replacement.
