On to machine #3

[elogicca]

Well time to build a new machine, construction will be 2x3 1/8 wall rect steel tube.

drives will be ball screws, on abba linear rails powered by servos overall working envelope will be around 68"x32"

[elogicca]

Well got around to drawing up the gantry, probably going to do the z assembly in aluminum....

What do you guys think so far?

[erikkate]

Looks good. However,
It's quite different from the way that I would construct it.
I would make an U-formed table, with on top, the linear slides, so that the gantry wouldn't have to be that high. This dramatically increases ridgity!
More like this (set-up of the high beams with low gantry).

[elogicca]

But then i would have to try and sync two servo's for the x drive as the distance is too far for a belt drive...

[elogicca]

Well new design

Z will still be direct drive ball screw

x & y will be a 3 to 1 reduction using 495oz steppers

Rack and pinion 24t 14.5 deg

somewhere around 5x9 travel

so dual steppers on the x and single on the y

the y beam is 2x6 1/4" steel
the x beams are 2x4 1/4" steel

their thick so i can have them pre machined

[erikkate]

Wow, looks good (better!)!!
I think you won't be dissapointed with the change of plans. This adds lot of ridgity. Big span on the y-axis though!

[cbass]

Originally Posted by erikkate Big span on the y-axis though!

My thoughts exactly.

I would have the gantry traverse the shorter distance, unless you absolutely need wide access to the table...

Carlo

[elogicca]

the y blocks are spaced 10" apart, with rack on each side, this way i only need 1 9' rackand beam shouldn't be any swag... gonna redesign the table base using angle iron instead, this way i can drill it and screw up through my mdf base...

I prefer the 9' open space easier to slide stuff in and out... thats gonna be one hefty y beam, i'm going to get my beams faced also

[elogicca]

Do you guys think 495oz steppers will be strong enough for this unit using rack and pinion & linear rails?? or should i just go with 850os servo's??

[elogicca]

Ok so i will be driving the x axis with a 850oz servo with 500cpr encoder and a 3 to 1 reduction, i will be running a 1/2" drive shaft accross the gantry so i can use 1 motor, the shaft will also act as a pivot point for tensioning the pinion against the rack, the right side will have the motor mounted, not sure yet if i will mount it on my gear reduction or an extra steel bracket from the gantry for weight reasons....

[Greolt]

Just a couple of thoughts. Not criticisms.

1/2" shaft won't do the trick. Not torsionaly stiff enough over that length.

Try to get the shaft mounted as low as you can on the gantry.

It is desirable to have the pivot point as close to the same plane as the racks as possible.

Certainly don't go above 45 degrees. Less is better. Zero is ideal, though you can't do that in this case.

Keep it up, Greg

[elogicca]

Originally Posted by Greolt Just a couple of thoughts. Not criticisms. only want to build it once, thats why i'm posting 1/2" shaft won't do the trick. Not torsionaly stiff enough over that length.

was thinking of using 1/2" cold rolled or maybee drill rod if it comes in that size, there is a bearing on the back gantry supporting it every 18"

Try to get the shaft mounted as low as you can on the gantry. It is desirable to have the pivot point as close to the same plane as the racks as possible. Certainly don't go above 45 degrees. Less is better. Zero is ideal, though you can't do that in this case. Keep it up, Greg

I think i can drop it another inch, I will be spring loading the drive but am wondering what may happen on direction change...

I'm figuring this may be a better solution than trying to tune 2 servo's