Xzero Raptor CNC build - linear rail and ballscrew selection

[Mattia]

The only slight draw back is lower acceleration, a thinner lighter screw will accelerate quicker with less power required. Depending on what motors you fit this will be hardly noticeable for the most part unless you are doing lots of point to point moves or short moves like in 3D jobs.

Bigger isn't always better or can be called over kill, because all it's doing is crippling the performance and costing extra. It adds nothing to the machine but weight and money.!

If it was me I'd be fitting 2020.!

I'd also be looking to stiffen up the gantry. Although the Aluminium cross plate may look strong because it's a thick piece of aluminium it's actually not because it's just a flat and unbraced so at that width it will vibrate when cutting, this vibration will transfer into the spindle so will show in the cut quality.
Also don't be fooled into thinking the rails will stiffen it up because they won't and don't. What it needs is a perpendicular brace across the back to make it like "T" on it's side.!

Thanks for the tips! Is there any real downside to a pitch of 10mm vs 20 or 25? If I’ve understood it right, it means less torque if I’m using servos at a given speed, vs running higher rotations and getting more power at the cost of lower top speeds. My assumption was that unwound not be hitting top speeds (in terms of motor rotations) with either solution. I was looking at these motors for all three axes:

https://www.sorotec.de/shop/JMC-Serv...ml?language=en

Running the lot off an EdingCNC board.

I had seen cross braces for the gantry i. Other builds, will see about adding one, thanks! It can double as a mounting spot for the energy chain as well. Any suggestions as to dimensions? Intuitively I would prefer something like 20mm thick 100mm wide solid bar, drilled and tapped every 50-60mm, to a piece of extrusion. Or is something thicker or wider a wiser choice?

[JAZZCNC]

Thanks for the tips! Is there any real downside to a pitch of 10mm vs 20 or 25? If I’ve understood it right, it means less torque if I’m using servos at a given speed, vs running higher rotations and getting more power at the cost of lower top speeds. My assumption was that unwound not be hitting top speeds (in terms of motor rotations) with either solution. I was looking at these motors for all three axes:

https://www.sorotec.de/shop/JMC-Serv...ml?language=en

Ok well when I said 2020 I probably should have given you more info to why and how I'd use them, also I didn't know the motors you where using so didn't want to go too far with it. But with you using Servo's then it's even more important, esp those motors so I'll explain more.

I would use a larger pitch mostly so I could put a ratio(2:1) on the screw to reduce the rotation speed, this lowers any chance of whip on longer screws it also increases the torque, thou this is offset slightly by lower torque of higher pitch. A 20mm pitch with 2:1 ratio will give you the same Resolution and speed as a 10mm pitch but half's the screw rotation speed.

This will become more important to you because your using 3000Rpm motors which is way too fast for a long ballscrew and the fact your thinking to use 25mm which have a lot more inertia it becomes even more important.

Also I don't think those motors are powerful enough to handle a 25mm ballscrew with direct drive, or even 20mm for that matter. They are only rated 0.57nm, I've looked at the manual and I can't see any where the peak rating. Thou Often it's 200% of the rated value for a few seconds which means at best you'll only have just over 1Nm for a few seconds to accelerate and de-accelerate the axis which isn't enough for a heavy gantry changing directions at higher feeds.

However, with only 36V I don't think they will be the most powerful things in the world so I doubt they will give you high peak rating for any usable length of time. If they had decent Peak ratings I'm sure they would have stated them, even if just as a marketing tool.
Now If they where 200V 180W or 200W Servos then they would just about be ok, but even still with a heavy gantry and 25mm screws direct drive it would a close thing.!

If it was me and you really wanted servo's then I'd go with proper 400W servo's. 200w would work but you can get 400w for nearly same money.

I had seen cross braces for the gantry i. Other builds, will see about adding one, thanks! It can double as a mounting spot for the energy chain as well. Any suggestions as to dimensions? Intuitively I would prefer something like 20mm thick 100mm wide solid bar, drilled and tapped every 50-60mm, to a piece of extrusion. Or is something thicker or wider a wiser choice?

Just a piece of 20mm x 100mm like you suggested would be good. I wouldn't bother with the extrusion.