Easy Q: Is 25" travel ballscrew enough for 24" bed?

[NC_jimbo]

Obviously I'm a newbie and I have an opportunity to pick up a 25" travel ballscrew. Am I thinking right that if the thing has 25" of true travel than that should be good enough for a 24" desired working area. I'm thinking 24" of travel + 1/4" each side for optical limit switch + 1/4" each side for a little spare.

[phomann]

Originally Posted by NC_jimbo Obviously I'm a newbie and I have an opportunity to pick up a 25" travel ballscrew. Am I thinking right that if the thing has 25" of true travel than that should be good enough for a 24" desired working area. I'm thinking 24" of travel + 1/4" each side for optical limit switch + 1/4" each side for a little spare.

It is unlikely to be long enough. You need to take into account the width of the gantry or whatever the ballscrew is driving.

If it is a router gantry, say 3" wide, you will loose a couple of inches there. then there is the Z-axis, with a router attached, there is an inch or 2, assuming you have the z-axis off centre.

I'd suggest your usuable travel is more like 18", maybe 20"

Cheers,

Peter.

[NC_jimbo]

Oops, I screwed up, I meant to say that this is for the Y axis. Mentioning bed in the title was all wrong. I want to be able to move the router free and clear 24" in the Y direction.

[phomann]

Originally Posted by NC_jimbo Oops, I screwed up, I meant to say that this is for the Y axis. Mentioning bed in the title was all wrong. I want to be able to move the router free and clear 24" in the Y direction.

Hi,

The Y axis will still have the same problem. The Z-axis will be 3-4" wide, so you will loose this.

Cheers,

Peter.

[aspenelm]

Uh, 25" of travel is 25" of travel. Don't see the problem. You won't loose any of it unless you design it in a way that interferes with full travel.

Edit: when you make your gantry, usually the desired travel + the width of the y truck assembly will determine width of gantry. If the overall length of the ballscrew is not long enough, you can move the ballscrew support bearing to the inboard side of the gantry upright. You should be able to get full travel. (Also assuming the 25" of travel means you've accounted for the length of the ballscrew nut)

[juzwuz]

Hmmm...I'm pretty new at this too but I think aspenelm is right. If your ballscrew has 25 inches of travel, you just need to design your machine to not interfere with that travel. It might mean that your ballscrew won't span the width of your machine. The usable travel on linear slides on the other hand needs to account for how wide you want to space the trucks/carriages for rigidity. Just make sure your ballscrew has 25 inches of travel (thread length minus length of ballnut) rather than just 25 inches of thread.

Edit: That's funny, aspenelm just edited his post while I was writing this one. They basically say the same thing! Back to real work for me....

[NC_jimbo]

Uh, 25" of travel is 25" of travel.

Sure looked like that when I drew it on paper. Just wanted to make sure there were no gotchas.

In reality I guess in all 3 axis's travel=travel, the big question is always how much EXTRA RAIL LENGTH is needed over the travel length which is obviously a big variable from design to design.

[holbieone]

you should always have extra travel in the screw so limit switches can be reached with out running out of thread

24" needed, 25" available ,1" extra should work just fine

[phomann]

Originally Posted by aspenelm Uh, 25" of travel is 25" of travel. Don't see the problem. You won't loose any of it unless you design it in a way that interferes with full travel. Edit: when you make your gantry, usually the desired travel + the width of the y truck assembly will determine width of gantry. If the overall length of the ballscrew is not long enough, you can move the ballscrew support bearing to the inboard side of the gantry upright. You should be able to get full travel. (Also assuming the 25" of travel means you've accounted for the length of the ballscrew nut)

Yep, you are correct. For whatever reason I was confusing the length of ballscrews with the length of linear bearings. I guess I wanted to answer a question that wasn't asked.

Peter.