Wobblycogs CNC Mk1

[JAZZCNC]

The highest it seems reliable at with 3Nm motors is 12m/min (so about the same as Jazz's but with substantially smaller motors),

Not much difference really because I have single motor turning 2 screws and you have 2 motors, plus 34's are stronger and will hold more torque higher up the curve.!!

Don't see the point of going to all the expense and trouble of implementing a rotating nut design and all it's complexity's when the standard setup will still allow everything he needs anyway.? The extra expense of components and having someone (Namely You) machine the rotating nut assembly cancels out extra cost of 34's etc for what is affectively wasted speed has he'll never cut at those speeds and Rapids are only usefull in quite limited circumstances.!

If speed is required then yes I'd take the rotating nut assembly route has it clearly will allow higher feeds but if cutting below 7mtr/min which most materials are then why go to all the trouble.??

[Jonathan]

If speed is required then yes I'd take the rotating nut assembly route has it clearly will allow higher feeds but if cutting below 7mtr/min which most materials are then why go to all the trouble.??

I agree - clearly the only reason to do it is if it works out cheaper or if you especially need the higher speed and (perhaps more importantly) acceleration. Personally I would do it even if the cost is slightly greater since the factor of safety will be much greater, so you will have a more stable system. Perhaps ask Chai for the price separately for two RM1610-1800mm and RM2510-1800mm so we can compare the relative cost more precisely?

[Wobblycogs]

Thanks Jazz that's spot on what I needed and really helpful, I think I'm just starting to see how the multitude of factors play off against each other.

I suspect the speeds in that table are a bit low because I went for supported-supported and was quite conservative with the limit.

I'll have to get the calculator out and see what the financial damage is if I stick at 1800 on X :-). Whether I build it 1500 or 1800 I've got to get a load of stuff out of the workshop so I'm tempted to stay with 1800. I've also got a project in mind that would need more than I think I could reasonably do on 1500 (lol, two bad excuses)

I realized today that my frame design makes mounting the screw bearings really awkward so it might be back to the drawing board for that. My aim of getting the mechanical side of things done by the end of the year is looking wildly optimistic already

[WandrinAndy]

I reckon it's inside trading wilfy. Lol

[njhussey]

It's through work and we buy quite a lot of steel so I guess get half decent prices...hadn't really thought about it ;)

[wilfy]

argh i need to find a local supplier for my steel... i really need to get a length of 50x25 for less than £25

[Wobblycogs]

Funnily enough I asked Chai that exact question yesterday but he didn't include prices in his reply, just the drawings I asked for. I suspect something got lost in translation so I've tried again.

In the spreadsheet is the screw length the total length including the machined ends or just the portion between the bearings? If it's just the threaded portion between the bearings then I may be able to get away with 1600mm which puts me (just) into RM1610 + 23's category by the looks of it.

What I'm thinking is if I place the nut towards the front of the gantry and keep the rails at 1800mm then the gantry is free to move beyond the end of the ballscrew - yep, that's clear as mud so there's a couple of pictures attached showing what I mean. I've not seen any builds like this so I'm guessing it must be a bad idea but it looks like a simple way to keep the length of the ballscrew sensible and not lose any cutting length.

[Wobblycogs]

So I've got some prices from Chai for the different bearing sizes:

2 * RM1610 @ 1800mm with 2 ballnuts = $130 Air shipping $76 Total $206 (£128)
2 * RM2510 @ 1800mm with 2 ballnuts = $142 Air shipping $97 Total $239 (£149)

Total price works out like this:

2510+34 Setup
Ballscrews: £149
Steppers (86HS115-4208): £160
Drivers (CW-8060): £126
Total: £435

1610+24 Setup
Ballscrews: £128
Steppers (60BYGH401-03): £78
Drivers (CW-5045): £87
Total: £293

Difference: £142 extra for larger screws.

However, from what I've read and what's been said here I'd be better off driving the steppers in the 1610 example on 70V which would mean using the CW-8060 drivers. That reduces the difference to £103. Note: I've not researched the best drivers, I just picked the ones CNC4YOU had.

[JAZZCNC]

Me I'd be spending £100 extra safe in the knowledge you won't have any issues with whip or resonance. Match it to drives linked below and you'll have a very stable system capable of decent cutting speeds.

These Digital drives are the ones you want they knock the spots off those cheap CW-8060 analogue drives which can't compare in performance.
Leadshine AM882 Digital Stepper Drive 80VDC 0.1A - 8.2A With Protection Function | eBay

If you really want the best in performance and accuracy from a stepper/drive combo and can run to it then these are the ultimate.
Leadshine 300W 3-phase Hybrid Servo Drives Set HBS86H Drive + 86HS40-EC Motor | eBay

[Jonathan]

You can get good drivers which are much cheaper (£36.20) than those, for instance:
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

You may get customs fees, but even if it's the full 20% it's still nowhere near the price of buying in England. I've bought quite a few of them and can confirm that they are good drivers. Since they are 80V you could use the same ones for both size motors, so this makes the price difference just the difference between ballscrews and steppers, which going by your numbers is £103.

The Nema 34 motors especially would benefit from better drivers, particularly higher voltage ones. Some more options, not nesscarily the cheapest, just the first I found:
New Leadshine AM882 Drive 80VDC 0.1A - 8.2 | eBay
2MA2278 CNC Stepper Driver For Nema34,Nema42,Nema51 Stepper Motors 7.8A 110/220V | eBay

If I had to use Nema 34 motors then I would use the 220V drivers since the high voltage will significantly increase the torque you get from the Nema 34 motors in the higher speed region, but they do cost almost 3 times as much as the first drivers I linked to...