Thread: New and in need of wisdom
Steel frame is almost certainly the way to go mainly because it's cheaper if you buy it in the standard 7.5m length. Don't be afraid of welding!
3DSmax, you shouldn't find it too difficult to use CNCToolkit which is a free script for 3DS that creates toolpaths up to 6-axis. It's not the easiest CAM program (if you can call it a program) to use, but I think that's mainly due to how different 3DS is to most CAD programs. Having said that if you only need to to 2.5D milling, then there's no point overcomplicating the process - just use CamBam, one of Vectric's programs or similar.
Here's where I got to before your latest comments came in - also threw some nema23's and a spindle on there just for show and the x axis one will likely go on the corner with a second ballscrew on the other corner linked by belt or chain.
Maybe a silly question, but is the tool chatter etc linked to harmonic resonance in the frame essentially and if so would assymetric mass damping help i.e. attaching weights to the extrusions in irregular places to stop it singing like a tuning fork?
Another configuration for your consideration - I think is what you guys were on about getting the gantry sides "shorter" by putting the Y axis on top of the x axis bearings. I guess the trade off will be the Z axis being longer below the y axis rails?
Will probably move the x axis nema and ballscrew outside of the gantry "legs" so if needed I can support the beams the x axis supported rails are sitting on.
I would re think the Z axis as that's very limiting how you have it designed now.? Look around the site and you'll see much better setups.
I know you want to get value for money on the Z axis screws and slides, but there really is no point lifting the head by much more than the distance from gantry to table. I suggest you could shorten the stroke and make everything neat and tidy.
Moved the rails on the Y axis to the top and bottom of the gantry (thanks Mocha) and I assume that was what you also meant Jazz.
Thanks Robert - I have my eye on a set of ballscrews that are 1050mm, 550mm and 350mm currently (machined), so the frames/axis are kind of sized to match. I might rethink that though when I have the main structure layout set.
This is all extrusion currently, but if its sufficient to cut plate then I'll make some replacements for various bits once its up and running. I'm also a bit concerned about the rigidity of the extrusion couplings (I guess I could add some structural epoxy to help with that also, as it seems to work for Lotus, Jaguar and Aston Martin to name a few ;).
However you do it, as Robin said, with the short distance between the chuck and the bed there is no need to have so much travel. You're much better off spacing the bearing blocks out further on the linear rails (this sacrificing the travel) since this reduces the magnitude of the force on each, leading to higher stiffness.
Yes, that or avoiding symmetry in the frame can help to prevent resonance issues.
Ah thanks Jonathan - that makes sense and gives a lot more clearance under the gantry. Questions though:
I thought having a narrow Y axis rail spacing wasn't desirable due to the leverage that can be applied when under x axis cutting motion? Sorry - I see you already addressed this in your reply....
Also, how do you mount the setpper motor on that design - between the rails on the back of the plate?
@ Jazz - no worries, forums aren't the best medium for communicating or understanding design concepts - shame there isn't a fag packet app built into vbulletin ;) If/when you have time to explain I'd be more than grateful for a longer explanation and I'm happy enough to work in the 3d virtual world (it's cheaper) whilst I learn the concepts.
Given that I've hoovered up many supplier links from various threads on this forum, this build is coming in well under my initial budget, which means I think Option 3 (DIY) from my original post is now looking like my decision thanks, to you guys.
Oh and is there a place for discussing 3D Printing on this forum I haven't seen yet?
Last edited by Washout; 30-07-2012 at 08:51 PM. Reason: Poor eyesight ;)
Here's the latest iteration - changes are:
- Re-structured the Z axis to kind of match what Jonathan showed in his photos and some general tidying up in that area.
- Made the corner posts on the bed taller and moved the x axis ballscrew assembly to the same height as the rails and outboard (did the same on the other side as well to keep a dual ballscrew option open).
Still to do - add in the bearing pillow blocks, which will probably mean some changes to some areas to accomodate and anything else I am missing, once you guys have finished ripping into it