Seeking design feedback before I start

[the__extreme]

I truly value the experiences, expertise and viewpoints offered by so many members of the site, so I'd like to ask for some feedback on a working design before I get into the build.

For reference, the tube on the table is 1", the table itself is about 48"x44" and the gantry is just over 48" wide (which makes sense if the table is 44"). The Y and Z axis will use a new bearing system I'm working with - it uses hex rails and roller bearings, instead of tube. I like it because it increases the bearing contact area, and by orienting the hex correctly, makes for easy surface drilling, and should be quite stable (kind of like a larger V-groove setup). As for the three stepper motors on the front...I haven't decided if I can get away with one in the middle or not. It seemed to work well for Joe, Andy (Lionclaw), and others.

I welcome ALL feedback, and if anyone would like additional images or clarifications, just ask!

- Shawn

[Oldmanandhistoy]

Hi,

Just a quick question for now; what materials are you using for the machine frame excluding rails and where if more than one?

I like your design for rails but have you seen ger21’s design here http://www.cnczone.com/forums/showthread.php?t=34044 this is an excellent design in my opinion and definitely worth considering. Some of the points he makes like the loading of the bearings are fundamental to a good design. I am just finishing up my new machine and if he had started the thread a week or two earlier I would have defiantly used his design for my X axis (Z and Y axes use linear rails). Just trying to be helpful not dis’ing your design.

John

[the__extreme]

Thanks John, I just checked out the page. Very interesting. I have to run out for a while to make some couplers, but when I get back, I'll post my revision to Ger's design. Keep a lookout!

I'll also post my materials, etc, when I return.

Thanks again!

PS - Saw you posted a comment recently on flex in some excessively long X rails used in someone' design, and got a poor response. I totally agreed with you, and sent a link to some simple deflection calculations to back up your (and my) claim.

[Oldmanandhistoy]

I saw your post .

I am just on my way back out to my workshop to complete my wiring but will be back later.

John

[Kipper]

Hi, Is the hex bar ground/precision? Nice drawings btw

[the__extreme]

Originally Posted by Oldmanandhistoy Hi, Just a quick question for now; what materials are you using for the machine frame excluding rails and where if more than one? I like your design for rails but have you seen ger21’s design here http://www.cnczone.com/forums/showthread.php?t=34044 this is an excellent design in my opinion and definitely worth considering. Some of the points he makes like the loading of the bearings are fundamental to a good design. I am just finishing up my new machine and if he had started the thread a week or two earlier I would have defiantly used his design for my X axis (Z and Y axes use linear rails). Just trying to be helpful not dis’ing your design. John

John,

My intention is the use 1/2" MDF for the frame, for all of it. I designed it to be built from the 4'x4' sheets, since my Home Depot only carries 1/2" in that size. I also designed the table and gantry to be modular, in the sense that the size could be expanded/reduced (in 6" increments) by simply adding/removing one 'section' from each. I may acutally extend the table in the X direction a little so that this machine is able to cut all the pieces necessary to build a 48" long machine - right now it can only cut up to 40". (Also posted a bearing in Ger21's thread you suggested, take a peek)


Kipper,

Its extruded aluminum I got from a local metal supplier. (Yes, I already jumped the gun and bought some, relatively cheap though) I don't know the exact tollerances on it, but its likely the same as any other extruded AL or CR steel, about +/- 0.003" -> 0.005" or so if memory serves correctly. Its pretty cool looking stuff.



- Shawn

[the__extreme]

Originally Posted by Kipper Hi, Is the hex bar ground/precision? Nice drawings btw

Thanks for the drawings compliment also!

[Oldmanandhistoy]

My main concern is with your Z axis; as in the plate you have your spindle mounts fix to. I would turn the moving parts of the Z upside down so that the bearings run to the bottom of the rails so to remove the over hang which would flex quite a lot.

Obviously using ½ “ MDF for torsion box construction will work well but I am not sure it is ideal for the Z axis. Getting good corner joints which will take the forces put upon them from preloading the bearings will be a problem. I don’t think you will get enough rigidity in your Z axis as you have it draw.

John

[the__extreme]

I decided to change some things...namely the Y carriage & Z axis. Took some ideas from a few different places. Let me know what you think!

- Shawn

[eloid]

your Z axis rail is right at the rotational center of the torque..I would suggest make your z longer ..by adding an extra length to the Z movement you gain a lot of stiffness and reduce rotational torque on your z axis.

[eloid]

I like the hex bar set up, can you show a drawing of it closer up? is it riding on a hex rail also?

[the__extreme]

Originally Posted by eloid I like the hex bar set up, can you show a drawing of it closer up? is it riding on a hex rail also?

You're right, it is riding on hex rail. I already picked up some hex, pretty cheap actually - 12' for under $30 (CDN). You might also like some of the alternative bearings posted in this thread:
http://www.cnczone.com/forums/showth...t=34044&page=8
I added one on the last page, simple square tube deisgn. I may use it on my table. The way the table is designed, I can use the 'standard' round tube/angle setup, angle/angle or the square tube/square tube. Once I have the machine set up with one bearing configuration, I might use it to play around with the other configurations, see how they work.

As for the Z axis, I do have room to extend the support arm by about 4", to 12" from 8". You're right, it'll reduce the moment reactions by about 33%, and very easy to do. Thanks for the advice!

- Shawn