ok, first attempt using sketchup 8

[JAZZCNC]

I would of also thought with the end plates it would be more than up to do the job i require.

Yes Dean it will be more than up to cutting wood.! . . . . There are issue's which arn't Ideal like easy setup of parallel rails like Jonathan touched upon. . . But if like I said with carefull selection of material they will be very close and then It's not difficult to manipulate them parallel with filling/grinding and spacers/shims.
My experinece with Cheap chinese round rail is that it's not straight or consistant in dimesions along it's length, just as the bearings mounting surfaces are rarely level, flat or true so shimming is nearly always required to fine tune. . . BUT AGAIN . . . It's down to intended use and for machineing wood then the tolerences are much lower and forgiving so can be tolerated.
If you want to wear belt & braces (excuse the PUN!!) and just add some bracing along it's length.!!


Regards that Pic you posted I'm pritty I've seen that before and it was actually built to cut stone.?? . . . . But don't quote on that!!. . . . But I've certainly seen one built the same that was cutting stone and it actually came up for sale on Ebay.

[deannos]

Regards that Pic you posted I'm pritty I've seen that before and it was actually built to cut stone.?? . . . . But don't quote on that!!. . . . But I've certainly seen one built the same that was cutting stone and it actually came up for sale on Ebay.

Jazz,
I found this on cnczone and reading his posts i think you are correct and it was used for cutting stone, he was in Indonesia. If i chose the earlier option of 2 box sections sandwiched between plate, would it be ok to use 10mm plate and use 20mm on the Z axis only. Just want to weight up all the options at the moment.

Just out of interest, i'm looking at using 1605 and 2005 ball screws, belts and pulleys if possible. I had a go at the weekend cutting the infamous Aztec/Mayan calendar, approx 12" size, after 3 hours i had cut less than a 1/5th. How much faster roughly would using ball screws make a difference.

[Jonathan]

20mm is a good size plate for the Z-axis.

The efficiency of ballscrews is roughly twice that of ACME screws, so it will be significantly faster. For the Aztec calender acceleration is much more important as it's lots of tiny moves. The bearing nut thingy you're using will make the difference slightly less. The main advantage is 5mm pitch versus 2mm pitch - the kinetic energy in the screw is significantly less if it's rotating 2.5 times slower.
The most accurate comparison you're going to get is comparing with my machine, as I sold you the screw. I got 6m/min with the screw your using and 42:13 pulleys on Y. I ran it at less than that with smaller pulleys as that was too close to the critical speed of the screw (see my build log for actual values). With 42:14 (I think) and a 10mm pitch ballscrew I got 60m/min. That's much more than you'll ever need so I've left it on close to 1:1 to get better resolution and acceleration.

[deannos]

20mm is a good size plate for the Z-axis.

The efficiency of ballscrews is roughly twice that of ACME screws, so it will be significantly faster. For the Aztec calender acceleration is much more important as it's lots of tiny moves. The bearing nut thingy you're using will make the difference slightly less. The main advantage is 5mm pitch versus 2mm pitch - the kinetic energy in the screw is significantly less if it's rotating 2.5 times slower.
The most accurate comparison you're going to get is comparing with my machine, as I sold you the screw. I got 6m/min with the screw your using and 42:13 pulleys on Y. I ran it at less than that with smaller pulleys as that was too close to the critical speed of the screw (see my build log for actual values). With 42:14 (I think) and a 10mm pitch ballscrew I got 60m/min. That's much more than you'll ever need so I've left it on close to 1:1 to get better resolution and acceleration.

Ok thanks Jonathan,

What is your thinking on using 10mm plate on the Y gantry, or would it be better using 20mm because of the length