Hi Peter
Originally Posted by
peteeng
Hi Mark - What machine configuration are you thinking about? Peter
It was always going to be moving gantry for a first machine, much though a mill style machine appeals. I have never given any serious thought to a fixed gantry and moving table, should I perhaps think about that, I can see some 'easier' setup than a moving gantry (wild deduction, not proven :nono: )
For moving gantry, and ease of life, I think perhaps (and I'm very open to advice) my best option at this stage is to go back to my original plan of a PrintNC machine, but with tweaks. The advantage of that design is that it is tested and on its perhaps 4th or 5th generation with an active Discord server and loads of help there.
What tweaks? Greater wall thickness for the rectangular box / hollow section, some machining of the box section, maybe selective epoxy granite filling of some sections (and I see a comment from you on that somewhere). I have to see what my friendly machine shop will do in terms of machining and accuracy for what cost.
Twisted box will do me in, but I hope to source straight untwisted lengths with a 5mm wall in say 75x50mm section.Thicker wall, 6, 8 10mm starts to get expensive but I could go there if needed. It would be possible to layer steel plate on the side(s) of box section, but .I suspect I would in any case get screwed by some kind of parallelogram action and not gain much.
There are elements of that design that I don't like, eg rails and ballscrews for gantry movement are exposed, but other elements are really nice, I can 3D print parts then machine them in ally and do a swap. Moving some rails and ballscrews to a more protected location may work for me.
Conventionally a PrintNC is configured with a cheap router or high-speed chinese spindle, but I've been thinking of an unpowered spindle belt-driven by a suitably powered sewing machine motor and VFC for mill-like speeds.
Strangely though where Craig says
"There are things that you will dismiss as unimportant, like flood cooling say, that is years to come that you'll change your mind and it goes to the top of the list or near to it."
this is actually something I have been thinking about, but aware that it ups cost considerably in terms of motors etc. I dont know if it is warranted for a simple low budget machine, but It's not hard to achieve (refers to handy diy youtube vid... ).
What is not touched on in the above is accuracy, I read this:
"
The achieved accuracy with PrintNCs is in the range of 0.1- 0.03 mm. This depends on the machined material, how accurately the machine has been squared and aligned, and how much time you invest into the single part." https://wiki.printnc.info/en/performance
Ha ha and listening to you and Craig/joeaverage, no doubt machine size and ridgidity affects that too. Also machining....
I have some Nema 23 steppers and drivers / power supplies that I acquired second hand, some more calculation / thought is needed if these are good enough. Certainly they will get me running and able to cut wood to start, just to see how the software and machine work, and then do a machine clean and a one time switch to using ally as the material I'm working on and whatever cooling solution I go for. (I do have some servos given to me, but they are huge and will take serious work to mount and seem entirely inappropriate here — maybe later use somewhere else.)
So I don't know if it is fixed in stone but this is one plan... and I still have to work out if this justifies anything better than C7 ballscrews and whatever rail rating is appropriate in conjunction with the ballscrew rating I go with.
Of course this jumps your ply prototype stage, but of course, since thousands of these machines exist, I suspect I can do the jump.
Many unknowns exist, eg the PrintNC folk just jam their machines together, no machining of box section, do some shimming and get them to work, miraculous but the antithesis of some sources I have been reading, eg this high end rail mounting spec:
Any thoughts welcome, please feel free to derail me in any way possible... thanks!