I currently run an 8 x 4 MDF machine. Its a machine built off of a kit from a company called SheetCNC which uses machined 25mm MDF for the frame, angle iron for the rails and chain for the drive. Not the greatest by far but all in all, its worked pretty well for what I needed and once it was tuned it up. I've earnt far more than I paid for the machine kit and its a few years old now so Im looking to upgrade.
It runs a 6mm cutter at 3mm DOC at approx. 2500 - 3000mm/min feed in MDF but there is some visible flex on the Z and noticeable chatter on some machined pieces. In an ideal world I need to be pushing those speeds and doc's. I would be happy with that speed but zero chatter and bang on accuracy to be honest, on that note, its good to 0.5mm
I run a joinery shop and have lots of 18mm and 12mm Baltic Birch Plywood left over so my thinking was to use that, a bit like the Holtzman? type machine but different. The idea will be to keep the table/base (25mm MDF) and chain drive from the old machine to limit costs at the moment. I've got 3 425oz motors running on ST-M5045s, Ill be getting rid of the dual motor (X) and upgrading to 2 single motors on the Y axis, single on the X and single on the Z.
For the main Gantry beam, Im trying to decide which would be better, a 300mm x 100mm torsion box made from 12mm Birch Ply with a 12mm Birch skin
OR
36mm double laminated piece of Birch ply sandwiched between a couple of pieces of 3mm steel plate. Either using screws or through bolts from side to side. What do you think?
Maybe an torsion box built with 18mm Birch Frame with a 3mm steel skin and each side? Would it need to be 3mm or could it be thinner? Steel plate is relatively cheap at 3mm thickness where I am (UK), the Birch Ply is paid for and on the shelf so that's zero cost, I also have a few sheets of 25mm MDF.
The plan is for the Z axis setup to move along the X on 20mm Vevor HGR20 (Ebay) rails, see pic. Im undecided on how I will fix them, kind of depends on the make up of the gantry. Initially I had thought to made a box, laminate/Dado (Like Biggs build) in a couple of sections of 12.7mm thick ally bar onto the box and then fix the rails to this. I could always skim the ally on the current CNC to get it fairly flat and go from there? Ive also got a large double drum sander which I could feed the finished section into it with the ally bar fixed to it and level the ally up this way.
For the sides of the Gantry down to the rails Im thinking of doing something similar to the above or maybe double/triple layer 18mm Birch with a steel skin? My concern on the Y gantry was to eliminate the twisting forces, not something Im too concerned with on the X so it might not even need the steel skin, what do you think? My thinking is to sit it onto SBR25LUU, 25mm supported round rails (CNC4YOU Ltd)
Would it need a set on top and bottom of the base sheet or would a single set on the top work?
What do you all think? Am I way off on these ideas? Is there anything I should be thinking of or builds it would be a good idea to watch? Would aluminium plate be a better option? 3mm Aluminium plate and 3mm steel are fairly close on price, obviously thinner/cheaper is better lol.
For a bit of background, I run a Joinery/Carpentry shop which specialises in bespoke/weird designs. I build everything from small boats to tricks for magicians to props for stage shows. The build I can do, its all the details that I need a couple of pointers with which is where I hope you clever people can help me with. Ideally Im hoping to get rid of any costly mistakes or redesigns before I start lol.
Thanks in advance for taking the time to read this, its very much appreciated!