Thread: Some design questions
Again building on what Jazz has said above, depending on what your cutting and width/length of the machine you could also look at rack and pinion set up. There are some pretty good sources these days for both and I have seen a few sources for helical which has some serious benefit in resolution over standard R&P set up. I have seen one set up in the US that has an inverted rack under the table, but the designer pointed out that crude still can get on the pinion without proper shielding.
As far as the MD machine, sell it on ebay as a whole unit. I sold mine to someone who wanted to do some poking around and testing and for what he wanted with the care to keep it completely flat it does what he wants. Anyone wanting to get very into serious CNC activity I would strongly NOT suggest any of MD's smaller line as I have yet to see any product that will not end up twisting itself or otherwise creating misalignment just from running. That is my experience and opinion. -MichaelLife is Live it
CAD software VIACAD Pro v9 (Beta testing x64) Also Aspire v8
CAM Software Aspire v8, PhotoVCarve, CamBam
Machine: Custom built see build log: http://www.mycncuk.com/threads/3661-...Second-machine
Work with Solid Surfaces, Acrylics, Woods, Foamboard.
Thanks for the comments Jazz, but I don't agree with the bit about the motors, they are certainly strong enough to rip the threads out of delrin and jam the whole axis. I am considering belt drives with a 2:1 reduction, so this would double the torque and halve the speed, but the leadscrews will have a bigger pitch anyway.
Flying in the face of advice, I have got the rails and screws I need sorted out from Chai. I have ordered longer than I will need (based on space considerations in my studio) , machined only on the driven end, as I will turn the floating ends of the ballscrews to the final dimensions. I am going with supported rails and probably a similar design to the MD machine (i.e. a gantry), but beefed up a lot. I can't get my head around Sketchup, so my design may be modelled in foamboard (cos I've got 15 A3 sheets of it) after the initial fag-packet drawings. Who knows, it may be rigid enough to run with it ....
I have been looking around the web for design ideas to evaluate and in my travels I found the V-slot system at www.robocutters.co.uk . Intriguing (!), but I would have misgivings about accuracy and rigidity. However, it seems a good idea for 3D printers, that need speed, don't have to handle cutting forces, or move a heavy spindle around, but for CNC milling, I can't have any faith that it would be strong enough or that the timing belt and pulley positioning system wouldn't stretch.
At some time in the future I may build a 3D printer using the Astrosyns and the Digiplan drivers I have, but I am trying to get projects completed, not take on any more new ones.
Anyway chaps, Grandson #2 is about to be born, so I will be away for a few days.
As a bit of a PS, I will be using the old machine to build the new, and then it goes on eBay, but without the current PC and the controller my be repackaged, but still a plug and play system.
Last edited by cropwell; 29-01-2014 at 11:23 AM.
Don't worry about timing belts stretching because other than initial settling in they don't if correctly tensioned and good quality belts.
The fate of the MD machine was decided when the Z-axis linear bearings dropped out during a cut and I realised how basically cheap the design was to use profile end caps to retain the bearings. If they had been a press fit, then maybe OK. But I have got the bug and want better.....
The machine will be sold as a package without PC as I want to build a new controller with 4 drivers and I can't get a matching driver for the existing 3 Tonman PD2064M's. I will repackage the BoB and drivers as there are 'features' on the kit that would be best taken off. So I am going to have to find out more about motors and drivers.
BUT has it happened the person who I was fixing it for had bought a BOB thinking it was Dead which it wasn't it had just blown the fuse so he's got a spare I'll ask him if he want's to sell it.! . . . . . He's on this forum so he may well contact you anyway.!
Last edited by JAZZCNC; 08-06-2014 at 10:05 AM.
Yes the fuse had blown, but after replacing it the device won't spin the motors.
Yes I am interested in buying !
sent him an email thou he may not want to sell if they are a little flaky.?
The BoB worked fine until I squirted 5v up it's Estop.
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