Thread: DIY CNC 8x4 mdf build
But we are here not to argue or police each other. Right? The man has a question, trying to make a cheap machine and i am giving suggestions as to how to make it without loosing money in future.
So what aluminum profile exactly you suggest for 1300mm travel that will not bend and what is the price of the beam? How much the gantry +sides will cost ?
Even the cheapest servos are 2 or 3 times the price of stepper motor and drive. Then you have the fact that Servos require high pulse rate to get there full speed and resolution. If not then your using electronic gearing which is wasting resolution of the encoder which you paid for and lessens the advantage of servos.
This then means a good external motion control card with at least 500Khz frequency for typical 2500ppr encoder is needed. Far more than the lower end ones like Pokeys, usbcnc or even Cslabs IP-M can offer. This also then means a quality BOB which can process high pluse rates, lots of the cheaper ones can't do this.
You also have the fact servos are very much more affected by electrical noise and require much higher attention to detail on the wiring side. Quality cables are needed and filtering for power etc and the list goes on and on.!! . . . . This is the TOTAL cost of over building.
Many won't do this and will suffer the price in some form or another. Often it's low speed/accuracy or unrelaibilty.!
Profile I DO USE for machine this size is 120 x 80 or 160 x 80 and arranged in "L" shape and can tell you now it doesn't bend even in Heavy use. Yes like anything it will bend if enough force is applied but still it's more than strong enough for any wood router or even one that's cutting aluminium.
It's also nearly 1/3 the weight of 200 x 100 x 5 RHS and not nearly has resonant. Initial Cost is more than steel but the time saving and less treatment required balances this out in the end.
Gantry sides etc are irrelavant even a steel machine will need these if designed that way.!
Also just to clear things up I'm not trying to stop you having an opinion. I'm putting my opion across and saying that what your promoting with your "Must use Steel to be strong" opinion isn't exactly true or even correct if not properly implemented and follwed up with correct components through out the machine. This you don't seem to mention often when preaching use steel.?
So I say what I do for the sake of those who see your posts and hopefully don't go blindly into something they haven't been made aware of by the preacher.!!
Welcome to the forum, I would suggest adding some corner bracing and beefing those legs up or you may just find your frame on the floor after a short while. Having read the others comments using the dreaded "m" stuff is a no no, but if you sheet material Baltic birch ply is much stronger but 4 -5 times the cost and won't swell up as much. The guys on here will help with the other stuff but not happy to help with the "m" stuff. m has it uses like the burner to keep you warm in the workshop.
Last edited by longy; 17-02-2016 at 05:52 PM.
My very first machine used plywood for most of the construction. It worked in that it moved around according to the g-code it was being given, and it did cut thin wood. Like you I built it out of stuff I had lying around to see if this hobby was for me. I actually just wanted to cnc cut a few bits for my model aircraft instead of by hand, and if you were careful this was possible.
However, it did go a bit oval on the circles and you could actually see it twisting a bit when cutting and changing direction. So in the end I stripped it down, chucked the wood out, sold the unsupported 20mm rails on ebay and kept all the 'good bits' for the next machine. These were the 16mm ballscrews and the 3Nm low inductance stepper motors. The following machine used more metal bits and was an improved design all round. As you can see in my signature it went on from there as you reach the limits of each machine and build a better one.
The negative tone on here is not meant maliciously - most guys on here have been there and done that and just can't recommend starting with wood / MDF. Especially when you see problems even when using all metal machines. In the end these machines fly around with lots of vibration over long periods of time and if they are not robust they can let you down just when you need them or be a pain to keep maintained / true.
As has been mentioned if you can buy some quality running gear you can keep them for the inevitable next machine once you realise just how much you can do with these new toys. Any metal you can add this MDF base will be a big help. For example metal parts for the gantry, and box section down the sides to mount the V-bearing plates to.
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