Importance of placing ball screw between the linear rails vs above?

[genixia]

Just cut them to length with an angle grinder. Also send pics when you have it together. Can't wait to see it.

Abrasive blade in a chop saw. Make sure the saw is plugged into a gfci, cut it outside somewhere some rusty water isn't going to be problematic, and use a hose to keep the rail cool. You want to avoid thermal stress. A belt grinder will clean up the cut if needed. Don't forget to clean, dry and oil the rail when done.

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[Goemon]

Just cut them to length with an angle grinder. Also send pics when you have it together. Can't wait to see it.

The angle grinder won't help on this one. I was measuring all the relavent dimensions and the barrel on the nut is 50mm which wouldn't fit under the stage even if I removed the entire flange. Not sure why it's so much bigger than other people's nuts. I have another 25mm ball screw and the nut on that only has a 40mm barrel.

Misumi actually sells height adjustment risers for linear rails so I guess I'm not the only one with this issue. I might have been tempted to buy some of their machine parts if their website wasn't so frustrating.

I'll definately post some pics when it is finished. I have been resisting the temptation up until now as I wanted to make sure it all works first.

[Goemon]

This "K2" CNC router has the ball screw on top of the gantry. For some reason, that makes me feel better about doing it too:

https://www.ebay.com/itm/K2-CNC-Rout...IAAOSwo4pYT3Ut

[ger21]

The top isn't the "best" location, but it should work fine.
If it were an issue, it would be because of a lack of rigidty in other areas.

[Goemon]

The top isn't the "best" location, but it should work fine.
If it were an issue, it would be because of a lack of rigidty in other areas.

Rigidity is one thing I (hopefully) won't have to worry about with this build. I think is just about as stiff as it possibly could be without changing the size. The gantry and base are really solid and it has 25mm rails on all axis (plus 25mm ball screws).

If it did turn out to be a problem then I was thinking that I would have a few options though. E.g. I could add a second ball screw below the stage and run it as a dual motor set-up like people use on moving gantry machines. I kinda wanted to avoid using two motors for one axis because I wanted to use the extra one for a 4th axis (at some point) but it's not a big deal. I plan on upgrading my electronics and motors anyway.

Or, I could go back to adding risers between the bearing blocks and the stage and move the ball screw back to a central position. Once the machine is up and running, I can make myself one of those U-shape stages you see on high-end actuators to allow more clearance. I wish I could just buy parts like that now.

Hopefully none of that will be necessary as I have gotten used to the idea of putting the screw up top.