Wobblycogs CNC Mk1

[wilfy]

Wobbly.....steel prices for you

50 x 50 x 4mm box - £23.77 Each (7.6mtrs)

50 x 25 x 3 box - £13.25 Each (7.6mtrs)

50 x 5 flat - £6.99 Each (6.4mtrs)

VAT will (unfortunately) be on top of these prices. Anyway, once you've finished tweaking your design let me know and I'll firm up the prices :D

where the frig did u get them prices?

[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

[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]

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...

[Jonathan]

Hmm, just read the beginning of this thread again. You're after 1220mm travel on the X-axis but we're discussing buying 1800mm ballscrews, so did you suddenly decide to increase the travel?

300mm is a good width for the gantry, so to get 1220mm travel you could easily use 1550mm(ish) ballscrews. If you're slightly more imaginative with positioning the bearing mounts then you only need the travel plus the length of the ballnut and end-machining, which for RM1610 is 57mm for the ballnut and 76mm for the end machining (including 10mm extra for the pulley). That makes the required length 1220+57+76=1353mm. Call it 1400mm just to 'be safe' and suddenly the motor and ballscrew choice becomes a lot easier as the critical speed is much greater...

On my machine the rails are 2000mm with 2094mm ballscrews and 1700mm travel. The new rails I got are 2200mm, but I'm keeping the travel the same and using the extra 200mm to increase the bearing spacing (among other things!) and using the same ballscrews. This is a similar situation since the frame and rails will be a fair bit longer than the ballscrews.

If you're after more travel then you could get about 1650mm travel with the 1800mm ballscrews.