Hi Vivien,
I’m just starting out myself, but it seems to me that if you never intend moving to a larger spindle and for instance you never intend to (significantly) cut metal then I’d say go for the Z-Plus. Otherwise, to absolutely future proof your machine and you can afford it get the HDZ (but that might be a bit of a wait)
Relatively new user here as well and I personally own the z plus. I like it a lot, but the biggest drawback I have with the z plus is z travel. When I am using a small endmill, I cannot reach the top of my wasteboard. I have a 3/4 mdf board on top of the already supplied mdf baseboard. I’m actually considering stacking yet another 3/4 on top to eliminate this issue. That would be the main reason I would consider the HDZ over the z plus at the moment. If you’re also considering milking a lot of metal on it then I would probably go to the HDZ just to ensure you have a pleasant experience. I have not cut metal with mine yet so I can’t speak for how well the z plus will do in metal.
I’m not sure many people have had a chance to try both a Z-plus and then an HDZ, while also keeping track of the precision they are getting, but I may be wrong.
The Z-plus screw uses 200steps per mm, the HDZ is at 320 steps/mm, but I would be very surprised if it mattered in real life, precision-wise.
No, the Z-Plus includes an EZ-Tram plate, but they have roughly the same Z-axis travel as the belt-drive units and continue to have the higher mounting (so as to reduce lever forces).
The step size is tiny and you’re right, compared to the other deflections in the machine the Z step size will not be relevant.
However… The Z plus uses a leadscrew and the HDZ uses a ballscrew, those two really aren’t comparable as the ballscrew is the one designed to not have backlash, lead screws have assorted after-thoughts to work around their inherent backlash. Still, other things on the machine will dominate.
All this talk about backlash and I was forced to google it. Thinking I may not be the only one, Here is an article I found that explains it. Hope it helps someone besides me.
GJM
You are so right. It was called vaporware in my day and referred to a company announcing a product or software well before they were ready to roll out the thing. This was often done because they knew their rival was announcing a new competitive product before them. This is not the case here, it’s the nature of the enterprise. Building a low cost but reliable cnc machine we can all afford. Still, I agree with you the wait for such gripes my ever-loving you know what. I want my toys when I want my toys, LOL. As for the choice between the two, to each his own.
That’s a pretty good explanation. The linear rails and ballscrew on the HDZ deal with the backlash with a similar preload mechanism, the bearings rolling in the tracks are slightly over size and therefore don’t wobble up to a certain load, nothing is truly zero backlash.
Just in case anyone is interested, I stuck a 0.01mm dial gauge on my HDZ and heaved it around with “large cutting force” i.e. about 5kg force up, down, left and right by the spindle and the backlash I measured between the spindle mount bracket and the fixed Z plate on this sample was;
X backlash - sod all, squat, couldn’t even see the needle move
Y backlash - as above, below my measurement capability
Z backlash - < 0.005mm
I think that exceeds any performance we would require of it on a Shapeoko, nice one Luke
I don’t have one to measure, hopefully somebody else does.
Bear in mind though that it’s likely to be a small number in the context of the deflections elsewhere in the machine from the V wheels and belts.
The stock Z had some relatively large unwanted movements which the design of the Z plus removes rather effectively, it has linear rails (like those on the HDZ) so that should be X and Y deflection taken care of and the leadscrew is going to be a large improvement on the old belt drive.