Wobblycogs CNC Mk2

[JAZZCNC]

Also - I got my wrist firmly slapped by Jazz for my design with the stepper motor mounted on the Z axis front plate...he said it should be on the Y axis plate instead to help keep it out of the way & reduce the weight on the z axis.

Nah nah not having that Geeky boy I only suggest or recommend if you choose to do it different then I don't give a toss, it's your loss. . Lol

I agree having the stepper on the front of the Z-axis isn't ideal but I don't see it being enough of a problem for me.

It's not a problem(my machines like that) just from experience the other way round is better, allows higher accelerations and Velocity and reduces chances of missed steps on Z axis when working hard doing 3D work.

As I see it there are a couple of other advantages as well, it's allowed me to lift the z-axis screw up away from the chips a bit and the weight of the stepper will act as a pre-load on that axis.

No advantages here in real use only Disadvantages.?
Chips will get in there no matter unless you cover, hence why I fully cover, May not be so pretty but it's the only way to keep chips out properly and increases component life too.
The extra weight of Ballscrew, 2 x bearing mounts, stepper motor, Stepper mount, belts & pulleys makes a considerable difference to the acceleration you can achieve and extra weight will cause missed steps if motors pushed remotely close to it's corner speed.

The extra weight acting has preload is hardly worth the costs in performance and extra stress on motor/drive.

Again not saying it won't work because it does, just works much better other way.!!

[Wobblycogs]

Thanks Dean. Given what you've just said I'll stick with the stepper on the front of the Z and see how it goes. It wouldn't be the end of the world to move it to the back to get better performance if it's needed.

I've started pricing the parts up, it's looking like the build will come in around the £2000 mark. I'll put the pricing spreadsheet up somewhere once I've finished filling it in as it might be useful to people trying to decide if they can afford a build.

[JAZZCNC]

Thanks Dean. Given what you've just said I'll stick with the stepper on the front of the Z and see how it goes.

Ok but I will say " I TOLD YOU SO" when you start asking why Z axis is doing strange things.!!!. . . . . (Oh Did I forget to say My Z axis done like this uses Nema 34 motor.!!)

[Wobblycogs]

LOL, perhaps I'll have a bit of rethink about that then. I had hoped to save a bit of metal on the Z-axis by moving the stepper to the front but I ended up with basically the same amount, the price difference was only a couple of pounds so it wasn't really worth it - and it took an age to re-align everything and put the bolts back in :-). I've come to the conclusion that SolidWorks + Smart Fastners + Flexible Assemblies is not a good combination.

[Wobblycogs]

Well I couldn't leave it alone :-)

One quick re-design of the z-axis stepper placement and I can't believe I didn't just go with this all along. Trying to save a few pounds on the z-axis I think was a false economy. This design has the ease of cabling of the previous but with lower z-axis weight as well. Double win, now I've just got to plug all the numbers for the z-axis parts into the spreadsheet again...

[JAZZCNC]

Great. . . . . . Now put a proper bloody cover over the Z axis and give those bearings and screws a break. . .Lol

[JAZZCNC]

What width is your Z axis.? If you can make use of it I have a Z axis motor mount I made too narrow. It looks like pic below but with larger centre slot so 20T pulley goes thru. . . . It's 160mm wide and 19mm plate made for Nema 23/24 (60mm) motor.

Just cover postage and it's yours.

[CraftyGeek]

Well I couldn't leave it alone :-)

One quick re-design of the z-axis stepper placement and I can't believe I didn't just go with this all along. Trying to save a few pounds on the z-axis I think was a false economy. This design has the ease of cabling of the previous but with lower z-axis weight as well.

I had a similar thought when I moved mine around as well :-p

[Wobblycogs]

Now put a proper bloody cover over the Z axis and give those bearings and screws a break.

LOL, I've got to leave myself something to regret not designing in from the start!

That stepper motor mount would be really useful, thanks (my back plate is 190mm wide so it would fit perfectly). The stepper mounting plates are one of the bits I wasn't looking forward to making by hand.

[Wobblycogs]

Possibly this is a silly thought but is it worth trying to getting the X and Y axis ball screws machined so that they can be used with a fixed BK bearing on both ends? The price difference of the bearings doesn't seem to be much and it would increase the critical speed nicely. The only problem I can see is that I'd have to be quite accurate with the positioning of bearings.

Any recommendations on stepper motors? I'm currently thinking the 4Nm steppers from CNC4YOU look quite nice.