[Al_The_Man]

I had been working on the assumption that a faster pitch is best for a CNC router because that is what I read here before buying my screws but I just read that a corse pitch reduces the "resolution". Is this correct?

It is called the Least Input Increment.
See Post #35 here http://www.cnczone.com/forums/servo-...ne-closed.html
With steppers it depends on the steps/distance.
Al.

[CaptainVee]

I wrote what I think is right because of the second part of your post.

[ger21]

"Holding Torque" is the torque when the motors are not spinning.
What you really need is the torque at max speed.

I keep meaning to read up more on why metal cutting machines use much larger stepper (or servo) motors

The simple answer is that's a general assumption. A properly machine will have a motor that provides the required torque to meet the performance goals of the machine, plus a certain amount of headroom so the motor won't stall or lose position. This may be 50% more than the minimum required torque.
A big router will have bigger motors than a small milling machine. It all depends on the specific machine.

[ger21]

So an increase in dia, and/or a decrease in pitch will result in less effort required.

But an increase in diameter increases inertia, which can require more effort to get it turning.

[Goemon]

But an increase in diameter increases inertia, which can require more effort to get it turning.

Do you think I should buy a larger motor for my long axis then (the one that has the larger diameter screw)? I currently have the 381oz "low inductance" motors that many here start with.

looking at the specs for these motors, they seem to have a decent amount of torque and peak torque for the job but i'm not really sure how much torque is optimal for this purpose. My inclination is to wait and see how well these motors cope before deciding to upgrade or not but.... if I am going to need to invest in new motor mounts and motor couplings plus redesigning the axis to make them fit, it would be easier to do that now if you think I'm likely to need more juice?

If I can do what I need with the 381oz motors then I would prefer to wait until I am ready to upgrade to a decent servo set-up.

[ger21]

I would get the machine running, and then see if what you have works.

[Goemon]

I would get the machine running, and then see if what you have works.

I think that's fair. If the goal is "to make it the best it could possibly be" then I have no doubt that I could spend forever upgrading components - something I have no desire to do. It's time to finish this...

I'm not far off now (I think). My Z and X ball screw assemblies arrived today and, for the most part, I am happy with what I bought. The parts all move well and, by chance, they fit my existing motor shaft couplers but there is something I don't understand on the NSK parts for the X axis.

My (THK) Z axis ball screw comes with two pillow blocks with bearings that fit neatly inside but the (NSK) X axis ball screw seems to have bearings at one end that don't fit inside the pillow block:




The pillow block is loose and I can't push either of the two bearings into the block or remove the black collar at the end (I removed the set-screws but it seems to be stuck).

Before I get my heat gun and wd40 out to try and force the bearings into the pillow block, Is this a problem you guys have seen before? Am I right in assuming that those two bearings are meant to be be inside the block?

I looked all over the pillow block for set screws or equivalent but there were only two screws and a broken plate of some kind which did nothing to make it easier to insert the bearings. This is the broken plate I removed from the sides:




It is going to be a huge issue if I can't push the block and bearings further up because as it stands, I don't have the 30" of travel I need. I didn't realize that the double nut was over 5" long. If the two bearings go inside the block then I have just about enough travel.