Long time lurker, first time poster.
I have need for a desktop type CNC router. My original thoughts of a chinese 3040 or similar have been dispelled quite early on from reading this forum. As i can't find an alternative within my budget it leaves no option but to build one. . I would much appreciate any input from experienced CNC'ers to help me on my journey and sense check some of my decisions (il need it) before i buy anything.
So starting from what i want out of the machine.
1. Machine mostly hard and soft plastics for small prototypes. flat Carbon sheet. (Small amounts of alloy but not a priority)
2. Relatively good accuracy (0.2mm)
3. Run continually for a few hours for small batch production
4. Tool to learn more about home/DIY CNC without costing a fortune.
My budget for the build is around £700-1000. Building it is a learning experience for hopefully building a much larger and more capable machine in the future.
After doing some reading i have decided a fixed gantry machine ticks a lot of the boxes for what i require (stiffness/small work area). Cutting speed range - up 150IPM (2500mm/mim for us metric devotees) should cover most applications.
Machine foorprint: (footprint around 500mm x 600mm)
Cutting evelope: (around 300mm x 400mm x 70-100mm)
Rail: Supported Rail on x,Y,Z (for cost reasons)
Spindle: water cooled 1.5kw or 2.2kw (possibly overkill but cant find an alternative that could be useful int he future)
Steppers/Controllers/BOB:Not my strong point but from using a few references and motor calc spreadsheet from the link below It looks like my selection "should" work. Although im not totally convinced as i can't find the torque/step graph to find the torque at top cutting speed.
Control: Mach3 with some form of Cam software (suggestions?) still doing research.motorcalcs
Currently undecided on construction. I have access to chopsaw/arc welder and small workshop. I am not confident i can make a welded assembly accurately enough so i am thinking a hybrid alloy plate/extrusion and laser cut steel mostly bolted together to allow room for adjust ability (see images). This is possibly not rigid enough. concerned with gantry stiffness (from twisting caused by Z load). Second do this would be the flex in the gantry from side loads.
Also some feedback on the z axis would be appreciated (should this be reversed to give more height for parts).
Thanks in advance, Shaun!
Alloy plate base (20mm), 10mm Steel plate sides, 80x40 extrusions. (Missing right side components in images).
Well seen has your talking IPM then I'll guess you have been looking around the Zone too much.!!
Your on the right track with Fixed gantry and while I'm not a fan of those round type rails they fit your budget. Personaly I'd spend that bit more and buy Profiled rails but they'll do the job.
Where you start to leave the track is with 5mm pitch screws. Go for 10mm they will give far better performance and flexibilty and still have more than enough resolution for what you want. 2500mm is way too slow for most soft material and you'll want double that for some. 10mm will do every thing you need.
Next is the electronics. DONT buy that Kit it's cheap rubbish. I also don't believe the Spec they are queting because 1.8mh on 4 wire motor this size is unusual. The drives are Ripp offs Leadshine Analog drives. Analog drives are dinosaurs and history, Digital drives are so much better and don't cost fortune. Look for Leadshine DM556 these are great drives for not lot of money.
With motors Don't pay too much attention to the Chinese torque graphs because they are unrealistic jokes and mean very little in real world. The mains things to look for are low inductance and ideally can be wired Bi-polar parallel.
Also Voltage you want about 44Vdc with 50V drive rather than 36v. Steppers get there speed for volts and too some degree higher torque.
Regards the Z axis then really only you can answer whether you have enough clearence or not. No point having loads of clearence if not using because it weakens the machine. It would be easy enough to raise clearence and to little degree stiffen up by having rails on front plate.
Design wise your close and will be strong little machine but don't cripple it with low spec electronics.
Thanks for your feedback! You are most definitely correct on the IPM! With CNC having a steep learning curve iv found myself dabbling in the yank knowledge bases also.
I would love to use profile rails but they are out of my budget for this build. I though about a hybrid with using them on the z (as you suggested) or Y but cant think of any justification for doing so. They would possible be let down by the other rails accuracy anyway. I will keep an eye out and if i see some going cheap this could be an option.
Thanks for the suggestion on 10mm pitch screws. I though i had my bases covered for material so i will do some more research on cutting speeds/feeds for softer material. What would be the down side to going from 5mm to 10mm? I can't think of any but possibly cost?
Stepper/drives: I did say this wasnt my strong point! I will do some research into the digital drives which you have suggested. Can these be run from a similar Break out board? My plan just now it to run this through a parallel port (with the knowledge this is not best practice but may be the only option for my budget).
Much thanks! i will continue working on the model and update soon!
Well first have you priced profiled linear rails from china yet.? You may get surprise.!
5mm or 10mm pitch makes no difference to price they cost the same. There would be more down side to using 5mm than 10mm.?
Smaller pitch would give you higher resolution but this comes at the cost of speed and to some degree torque. Higher pitch will give you half the resolution but twice the speed.
Now the main difference lies in torque or more importantly more torque where it's needed which is while cutting. The higher pitch means for the same speed the 10mm will allow motors to spin at half the speed of 5mm. Now because steppers lose torque as rpm increases the available torque from motor is higher because spinning half the rpm but the cutting speed is the same. The main loss is in resolution but even with 10mm pitch you'll still have more than enough resolution for 99.99% of work you'll do.
5mm pitch does provide more mechanical torque than 10mm but still it's motor rpm where it's needed most and 5mm will mean the motors while cutting are spinning near there speed curve threshold where torque drops away fast which isn't good. 10mm will surve you much better and give more flexibilty.
Regards Digital drives then yes they work just the same. If you want to see how shitty analog drives can cripple machines and people not even realise it and also the difference digital drives make then I recently posted a video showing it. Can't remember the post but do search and I'm sure you'll find it.
Last edited by JAZZCNC; 27-02-2016 at 01:50 AM.
After some research the 10mm ballscrews look like a wise choice (thanks Jazz), Linear rails are still looking like they are out of budget. With my current spec i am floating around the £950 mark which is very near the top end of my budget.
If i can maintain (or reduce this slightly) i would be happy. I am considering a steel box section frame which should reduce the cost (but most likely be less accurate because of my questionable welding skills).
Turning my attention back to the electrical elements and taking you feedback into account jazz i'm looking at the following main elements.
2A (Series) 4A (Parallel) /
8 Wire / 1.8Nm Holding Torque / Double shaft
It would be good to get some feedback on this combination. My understanding is the DM542 is a lesser version of the DM556 you suggested Jazz. Do i need the additional "buffer" of the DM556?
Also the power supply is rated to 12.5A is this suitable for running the steppers at peak with enough of a buffer.
I am still working on the hardware design and will post up some images soon.
Regards drives they are still good drives so yes they will be ok.
PSU wouldn't be my first choice but will work. First choice would be to build toroidal supply which is much better suited to CNC and more relaible. Wouldn't cost much more money.
Few pence cheaper but same...
I know is old post, but worth to show better prices.
Cheaper and stronger motors uk supplier £96 for 3:
Drivers £93.77 for 3 - 5.6A peak 4A RMS
Power supply £19.88 48V 8.3A
few quid saving + quick delivery.
Got all of them and they ok, PSU seems underpower but for for 3A motors is ok.
Last edited by Tom J; 29-07-2016 at 06:56 PM.
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