Let The Fun Begain, New build on the Table.

[Bush Flyer]

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.

[Bush Flyer]

Bit late now but a chop saw would have been a good investment for you if you have problems using a hacksaw.
With the right blade you could have cut all the aluminium both plate & profile yourself which would have made things a bit easier, plus it would also be handy for cutting aluminium to size before machining it once the router is up & running.

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.

[Bush Flyer]

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.

[Jonathan]

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.
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.

[Bush Flyer]

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.

[Ross77]

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


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

[martin54]

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.

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.
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.

[Jonathan]

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.

By aliexpress I didn't mean the eBay seller, I was referring to the website:
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

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

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.
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.

[Bush Flyer]

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.

[Bush Flyer]

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.