Thread: New CNC Mill on the horizon
I'd go for epoxy granite over concrete. Concrete moves/warps after it's set and since you're using profile rails any movement in the piece they're mounted to could cause serious problems. If the rail is bent ever so slightly the slide coefficient of friction increases dramatically, so if this happens over a long period of time you probably wont notice until the machine stalls due to the greater power needed to move each slide. By that point some serious wear could have occurred to various parts in the system.
Frame looks appropriately sturdy, but I'd be inclined to add some smaller box section to link the legs. It wont cost much compared to the rest of the frame and could help with resonance, since at the moment you have a large mass supported by legs (rather like a cow which wobbles a lot if you push it!)
Personally I wouldn't go with Epoxy or concrete.!! Sand is cheap the concrete example was to make a point that heavy or dense is good.!
Epoxy is not a good solution either has the heat from the large qty of epoxy could and will warp the steel.!! . . .Plus the cost of epoxy it would be just has cheap to buy plate steel.??
Sands good with me likely hood is I'll need to move the machine at some point so the potential to "drain" some weight would be useful
It's not prohibitive, you just want everything for nothing.John S -
Ok, I think I have decided I am going with the twin ball screws on the X controlled by one motors running a belt drive system for the two drives. As much as i think it might be easier to implement the motors to start with the idea of not having to "tune" the motors to work together appeals greatly.
Been quite a while since I was posting about this but it is still going ahead, albeit "general life" has got in the way as it does with so many projects but I now have a Friend on board so we are splitting the costings 50/50 so we have a realistic budget to work with and hopefully the specs are adding up now. Still got a few questions really.
Here is the current spec:
1200x900 footprint area with approx 1000 x 800 cutting area
80x40x4mm steel box section frame with adjustable bed
Aluminium gantry made from a combination of 20mm/15mm plate either standard 6082 or ecocast for the bearing and guide plates
20mm Profile rail on x,y,z
20/05 on x axis (running 2:1)
16/10 on y axis
16/05 on z axis
250mm cutting depth on z
2.2kw chinese spindle
electronics (just ideas at the moment)
1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt (as suggested by JAZZ) running 20/05 screw on a 2:1 ratio
1 x nema 23 3.1nm running y axis on 16/10 screw
1 x nema 23 3.1nm running y axis on 16/05 screw for better resolution
80v Chinese Drives
Price wise everything has been accounted for in our budget which is great managed to get some really good prices on steel and aluminium. I have a couple of questions which as I know may not be possible to answer without imagery but I thought I would pose them anyway!
The length of the x axis thread is 1200mm would this run with 16/10? or is it better to just stick with the 20/05 to prevent the chance of whipping as I was under the impression thats getting to the limit or even past what it should before it whips?
Running the X off a nema 34 and the y and z off nema 23s, would this pose any sort of problems with setting the machine up? is it better to have 34 all round as I am quite happy to do this as all of the screws are belt driven in some form so adjusting the gear ratio to compensate for slower rpm is not a problem. The machine is still being designed to cut aluminium primarily and then hardwoods
The current weight of the gantry based on calculations of size and weight including aluminium, bolts to assemble, spindle, rails and carraiges, Stepper motors and any other parts that were per the design is in the 65-68kg range.
We are hoping to get started on this in early feb and to have a moving machine by the end of march, thats not a completely finished machine but one that can move, even if we have to push it!
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