Another picture got finished counter boring the X axiz end plates with a bit of luck I will get them bolted on to the frame today.
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Another picture got finished counter boring the X axiz end plates with a bit of luck I will get them bolted on to the frame today.
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Yes I though about buy a chop saw. But it would take money away from my CNC budget. I don't mind taking three days to cut a part of aluminium as I can only work for short periods anyway.Quote:
Originally Posted by martin54
The next question That I have is about stepper motors and drivers. What is the advantages to having separate drivers for the stepper motors to having all drivers on one board?
I think I will buy the four separate drivers but wanted to check before sending a order.
Now I will buy nema23 motors but what holding torque should I buy 3.1Nm. or will 2.2Nm work just as well, with the RM1605 ball screws I have. Now I know That it would be better "faster" to drive it with belts and pulleys to change the ratio but at this time it will have to be direct drive. I can change it at a later date if I don't like it.
I will be cutting Balsa and ply 98% of the time but I will require the CNC to cut 3mm aluminium and some hard wood now and again.
I have been reading builds on the forum but it seems that most talk about speed but why? I would be happy as long as it does a good accurate job, if it takes a bit longer to cut I don't mind.
For every material there is an optimal speed (feedrate) at which to cut it and a minimum speed. Optimal is hard to define - it could mean the speed which obtains the best tool life, the highest material removal rate or numerous other factors. The reason we're concerned with maximising the feedrate is if it is too low, you wont be able to cut some materials. Again, weather you can or cannot cut a material with a particular machine is hard to define - for example you could cut aluminium really slowly with a file, but that doesn't really count. For example, since plastics exhibit poor thermal conductivity, they need to be cut with a (relatively) high chipload, to reduce the heat generated by the cutting. Since the spindles we use generally operate best at high speed, this necessitates using a high feedrate to cut plastics otherwise at best the tool life will be poor and at worst it simply wont work. There are ways round this (e.g. using tools with less flutes, use a different lower speed spindl), but in general it's a much better option to choose a drive system which will meet the requirements you expect from these materials.Quote:
Originally Posted by Bush Flyer
Even if you don't end up needing the high speed available, the fact the machine is capable of it is advantageous since the machine will be more reliable at lower speeds - e.g you can pretty much guarantee if you've chosen motors/drivers which will move the machine at 10m/min they will never stall or have problems at 5m/min.
In princible there's nothing wrong with having several drivers integrated into one board, so long as they're reliable and suitably rated. The problem is in reality none of them will output enough current/voltage for what you need, so trying to get one to work will not be reliable. Just forget them and please don't post more pictures of TB6560 drivers ;)
You can try Irving's motor calculation spreadsheet (just search that on the forum) to work out which motors would be best. I'd advise using the common 3Nm motors with a 75V power supply. The difference in price between this and other options isn't that great, and it's the best performance you can get without spending a lot more money. I think CNC4You is currently the cheapest place to get the motors and eBay/aliexpress for the drivers.
I have just done a member search on ebay but aliexpress have not been trading in the last 12 month
But I will take your advice and order 3.1Nm stepper and four separate drivers.
Jonathan has pretty much said it all but just to add that when I first started I said exactly the same thing "don't care if it cuts slow, just want it accurate."
I have since learnt (and stil learning) that cutting slow is counter productive to accuracy and if you take two small a cut then the cutting edge will skate over and work harden the surface making it harder for the following cutting edge to make the next cut, this then causes the tool to deflect and accuracy goes out the window.
It seems odd but there becomes a point when the cutting force increases as the chip thickness decreases. This is because if the radial depth of cut is small it produces a large shear angle so the cutter sees a large area to cut.
Accuracy is more dependant on the correct material removal rate so you need speed and power.
I seems you have to learn how to build a good machine and then learn how to use it:toot:
Jonathan also mentioned aiming for a higher design speed to give headroom on the constant cutting speed but this head room is not wasted as you can have fast rapids when moving between cuts (subject to mass/inertia limitations of course) cut at 5m/min move at 10m/min
They are not that expensive & although it would have been another expense which might then mean the overal build took a bit longer it would have been a useful addition for cutting wood & aluminium to size prior to machining in the future. Why take 3 days to cut something when you can do it relatively quickly & then spend the rest of the time doing something else which is more productive.Quote:
Originally Posted by Bush Flyer
Have you been to or do you go to your local Pain management centre? If you don't then it might well be something worth looking into. They will be able to help you in all sorts of ways, not with just being able to do a bit of work but pretty much every aspect of life.
By aliexpress I didn't mean the eBay seller, I was referring to the website:Quote:
Originally Posted by Bush Flyer
Cheap CNC! Wantai 4 PCS Stepper Motor Driver DQ860MA 80V 7.8A 256micro CNC Router Mill Cut Engraving Grind Foam Embroidery-in Motor Driver from Industry & Business on Aliexpress.com
True, but it's worth noting that a high rapid speed (up to a point) doesn't make much difference to the overall job time compared to a lower speed - 5m/min vs 10m/min is a good example. Often you'll find even doubling the rapid speed will only reduce the overall time by a few percent. This is because in general the machine is moving much slower and in many directions with a finite acceleration. The acceleration often limits how fast the machine will go, since every time it moves to a different position, or changes direction, at least one axis has to accelerate (or decelerate) and the speed is often limited by this. One good example is detailed engraving - the individual moves are very short, so each axis is almost constantly accelerating (and decelerating) whilst cutting, and in addition the rapid moves will generally be short so the machine may not get up to the full rapid speed, hence the speed is likely to be limited by the available acceleration.Quote:
Originally Posted by Ross77
Similarly, if the G-code is well written then the proportion of rapid moves will be quite small (clearly there are exceptions). Suppose the rapid moves comprise 10% of the total time taken for the job. Here, doubling the rapid speed will only take 5% off the overall job time.
Clearly there are exceptions - if the rapid speed is limiting how fast you can cut, then having more speed (so long as the acceleration is sufficient to use it) will decrease the machining time noticeably. An example of this is surfacing an MDF bed, where cutting at 10m/min would be perfectly reasonable (I do it)...but then how often do you need to surface the bed?
Often it's a compromise between maximising speed and acelleration, since increasing either requires more power and the motors only deliver a finite amount of power. With pulleys you can adjust the ratio to optimise for better speed or acceleration, but in the end you still need motors with enough power - hence my suggestion to get the 3.1Nm motors as their power output is plenty and they're better priced than virtually all other realistic options.
Jonathan thanks for the update in finding that site, I have now placed a order for drivers and have also bought the 3.1Nm stepper motors that you advised, That was a good saving in cost. Thanks.
Been a while since I did any work to my CNC router as I was in Hospital again for a few days and the wife has band me from the garage. But I did get some wiring done, but have a lot more to do, I'm waiting on a E stop switch and more wire.
So just some photo's where I stand at this time. I hope to get going again in the next couple of weeks.
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I am managing to get back to the garage for a hour here and there still real sore. I have finished the control box for my cnc but I still have some wiring to Finnish on the limit switches.
I also got some more of the cnc assembled, the next job is to build a table that will house the computer the controller and the cnc router all in one. Then fit a new wall plug in the garage and a bracket to the wall for the monitor.
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Love the model aircraft. Router looks good too. G.
Looks like you are nearly ready to start cutting. Just got a couple of concerns with the power supply. Firstly I can't see in the photos how you are going to cut the power with the e-stop. Also you may have problems with noise bundling all of your signal and power cables together. Anyway, looking really good.
Regards, Ian.
Ian's correct here.! . . The worst thing you can do is use un-sheilded cable and tie signal and power cables together like you have here.!!Quote:
Originally Posted by irgonomics
Things may appear to work ok just jogging around etc but the potential for problems increases big time while cutting with noise getting on the signal wires causing all sorts of strange things to happen.? . . . .Everything from sudden limit or E-stops trips to sending phantom signals to motors causing them to either go in wrong direction or increase steps etc.
Honestly Complete nightmare tracking down where it's coming from so anything to minimise the better and you've done everything to maximise with those cable ties and unsheilded cable on signal wires.!
Other than that looks Good and happy cutting.!
There was nothing in the instructions from cnc4you about shielding, I now need help, do you shield just the wires to the stepper motor, or do you shield the stepper motor wires from the limit switch wiring.
What a mess there is over £70 of wiring there including the plugs.
And here was me thing I was smart keeping all the wiring neat and tidy, Now how do I fix this. Do I let the wires loose is this good enough just leave them loose in a cable track or can you get screening to fit around the cable on the out side of the insulation on the power wiring and of course you need to earth shielding do you earth the shield at one end or both.( On google search I found some mesh but was £30 for 5 metres and you get Tin-Plated Copper Foil Shielding Tape from 3M its about the same price what would you use or is there something better?) Will I have to rewire the inside of the control box or is it just the wiring to the stepper motors and the limit switch's?
On another search I found Guitar Pickup copper foil tape would this work and do I shield each of the four wires from the stepper motor separate?
For the cost of that Mesh you could buy some CY cable and be done with the problem?
Ok well first before you start ripping it apart just do some better cable management.
Separate the signal wires from the Power wires and run power cables together.
Don't cable tie the signal wires together just run along side each other lose.
Shielded cable is the proper way and should really be used and like Swarf says just buy CY cable if you do.
You'll find it here cheap enough and just use 4 core 0.5mm or 0.75mm. CY Cable
Only ground one end at the control box and make sure your control box uses star grounding. IE all grounds to same spot.
But it doesn't always follow that because you haven't used shielded cable you'll have problems it could work fine but you are much more open to interference and corruption of data signals without it. . . . I suggest you try machine and if any strange happenings like Z axis lifting/dropping or false limit or E-stop signals then you'll be getting noise on the lines.
Regards which wires to sheild then it's motors and limit cables, any cables that send signals. Following on from above, if you have trouble with noise then chances are it will be the limit cables that cause it because they tend to be the longest run, effectively acting has a big antenna sending and receiving signals. Similar applies to the Stepper cables because they are long.
Main thing is to keep power cables away from signal cables and shield any signal cables. This esp applies to spindle cables if your using a VFD which are very noisy things.
Note he just means one end of the cable and not both. On the other hand you may get away with it and it all work fine? i did on my first one and that was a can a of worms. Saying that set it up right first time and you will have less problems to sort out later (spending hours guessing what the problem is).Quote:
Shielded cable is the proper way and should really be used and like Swarf says just buy CY cable if you do.
You'll find it here cheap enough and just use 4 core 0.5mm or 0.75mm. CY Cable
Only ground the ends at the control box and make sure your control box uses star grounding. IE all grounds to same spot.
Bloody nice job by the way and a credit to the build so far. You have worked very hard ;-)
Ye I did and corrected it now has wasn't clear was it. .Quote:
Originally Posted by Swarfing
Ye and I'll second that has well.!!Quote:
Originally Posted by Swarfing
Thanks for the help, I have had a look at that CY Cable, I wish I had found that before I had started the wiring, Never mind I will separate the wiring to see if I get away with it . But first I will have to make new bench for the machine then I will be able to try it too to see how it works, But in the end I will slowly change the wiring to this CY Cable starting with the limit switches.
My thanks again Mike.
Well it's been a while since I posted a update. I have done some cable management and separating the wiring, Also I have made a table for the CNC to be bolted down on and also store the controller and computer underneath the CNC Router. I Bought a new monitor and mounted it on the wall above the CNC. I loaded in Mach 3 and now there life. I Quickly made up a spring pen holder and it drew it's first picture I am so chuffed. I got the computer from a friend that he had windows XP on it that had never been used since 2005. I was going to use the same computer to run the Mach 3 program and the CAM program, but find it's not practical. I will have to build another computer to run the Cam program like Artcam express as my laptop crashes when trying to run Artcam express and I also tried Vectric cut2D but the Graphics card in the laptop could not handle the program. It's some thing that I did not budget for. I have a case and some other parts already so it should not be to bad. All that I am waiting for now is some cable tracking from china and some single and double flute bits and I can try some cutting. There is some parts I will improve like replacing the wiring but for now it's running.
My original budget that I worked out was for £1200 so I said it would cost a Total of £1500 when finished But I made some changes as I was building it so now the cost when finished including a second computer will be nearer the £2250 mark, it's so easy to get carried away, I built this to so that it would cut parts for my RC models but I have already started think about building a laser CNC, this has turned out to be another hobby on it's own.:adoration:
Well I now have Artcam express and Mach3 licence bought and its seems to be running well, The only concern is the stepper motors get hot after it has been running for 45 to 50 minutes is this normal the axis all run free so there is no binding in the bearings etc.
Motor case temperature up to 80°C is considered acceptable.Quote:
Originally Posted by Bush Flyer
That's Fine its below that I measured the two X axis motors at 71 degrees the Y axis was 68 degrees and the Z was not worth measuring, so all good will just test again after I have a long cutting job to do.
Thanks Mike.