Eyeballs and comments sought for noob build

[Tom J]

Loads of luvverly advice, thanks!

Is the direct drive on the z axis such an issue? Should I make that belt drive as well?

Is there a disadvantage of using two Y motors? Sure, they can get out of sync, but surely two homing switches/sensors should take care of that between jobs?

I was not sure about that. My thinking was that by using two Y motors, I could save some weight, and the two motors and lead screws would compensate for the added stiffness the connecting plate would provide. Is this incorrect?

belt transmission gives you extra flexibility, you can adjust gear ratio means=feed, easier do deal with resonance if any occurs, allows to mount motor in two position (up side down and shaft up).
Z axis takes most vibration as is driving spindle up and down, so those shaky shaky gets to the motor and disturb in high speed. My first machine was driven by coupling - cheap Chinese, than with plastic insert, odiham finally end up with 1:1 pulley.

Y drive, if your power supply can handle biggest nema 23 3Nm motor without extra voltage than one motor should be ok and will wait only few hundreds grams more than 1.9Nm. Advantage of having one motor and two ballscrew is lack of need for squaring the gantry (one motor less, 2 sensor less)
Motor have to be powerful enough so they do not loos steps, if you loose steps you loose your job, material, time.

Gantry - more braces make it stiffer - joining them under bed will increase the weight but benefit you gaining by stiffer, more accurate machine are far more important.
I hope somebody else will give you some inside, I only build 3 machines and even on last one I would make something different, now I designed another one will post it soon.

Good luck with the build

[danilius]

Thanks for that. I'm a little concerned that a belt that long will introduce other issues, so will see what to do about that. Will attempt to alter the z axis for a belt drive. I don't suppose it should be too difficult.

belt transmission gives you extra flexibility, you can adjust gear ratio means=feed, easier do deal with resonance if any occurs, allows to mount motor in two position (up side down and shaft up).
Z axis takes most vibration as is driving spindle up and down, so those shaky shaky gets to the motor and disturb in high speed. My first machine was driven by coupling - cheap Chinese, than with plastic insert, odiham finally end up with 1:1 pulley.

Y drive, if your power supply can handle biggest nema 23 3Nm motor without extra voltage than one motor should be ok and will wait only few hundreds grams more than 1.9Nm. Advantage of having one motor and two ballscrew is lack of need for squaring the gantry (one motor less, 2 sensor less)
Motor have to be powerful enough so they do not loos steps, if you loose steps you loose your job, material, time.

Gantry - more braces make it stiffer - joining them under bed will increase the weight but benefit you gaining by stiffer, more accurate machine are far more important.
I hope somebody else will give you some inside, I only build 3 machines and even on last one I would make something different, now I designed another one will post it soon.

Good luck with the build

[Tom J]

Thanks for that. I'm a little concerned that a belt that long will introduce other issues, so will see what to do about that. Will attempt to alter the z axis for a belt drive. I don't suppose it should be too difficult.

use good quality gates HDT 15mm braided one - there will be flex which shouldn't give you error bigger than 0.02mm (I referring here to my steel machine which was 115kg)

[danilius]

Food for thought. Thanks! Time to get back to drawing :-)

use good quality gates HDT 15mm braided one - there will be flex which shouldn't give you error bigger than 0.02mm (I referring here to my steel machine which was 115kg)

[paulus.v]

Hi,

Connecting the gantry at the bottom will give little benefits but, by moving the legs far apart, the base will be a lot weaker.

Why would you put the X rails "hanging"? Only for dust/swarf protection? The side plates extension for guide blocks will deflect a lot and put pressure on the rails/blocks trying to twist them. I don't think it's worth it.

The gantry side plates are beefy but only when looking from one direction. If you cut out one third longitudinally and bolt it perpendicular you will have more rigidity in the Y direction without any loss or weight gain. And you can connect to your t-slot profile overhang.

[danilius]

OK, I think I have understood all this correctly. So, I'll move the rails up top, and stiffen up the gantry walls.

[danilius]

So, I have made some changes. I wasn't convinced that the extrusion on the gantry was going to be rigid, so that has been dropped in favour of some solid lumps of metal. It is also much shorter, and the rails have been moved up to the top.





What I'm wondering is if there is an optimum distance between carriages for the gantry.



I dont have any worksop equipment beyond the basic tools, so don't want to drill into the extrusions or anything, but I'm getting a bit lathered about the hseer size of the machine, given that it's only going to have a work area of 600 x 900. Currently the overall dimensions are roughly 1400mm x 940mm. I can trim a small amount off the length, but is there any way of getting this more compact?