Thread: New CNC Mill on the horizon
16/10 and 3.1Nm 23's will be much better.
Edit: The only exception is if you want to link the screws with timing belt.? Then you'll need the bigger motors but 16/10 could still be used.?
Also don't use 80VPSU with 80V drive. You need a safety net for back EMF so use 75V psu with 80V drives.
Last edited by JAZZCNC; 16-12-2012 at 10:32 AM.
Noted on the drives voltage that makes sense must be a sunday thing on my part! As ever cheers for the response!
Has sent FVF via email regarding others stuff has well as this but posted for benefit of others and to keep the thread complete without back door dealings so to speak. . .Lol
Seeing your post got me wondering if i'd cocked up on advise but on reading this email again I feel vindicated and relief . .. Lol
To be honest I didn't realise or missed the length was only 1200mm.
Given this then it will be better to use 16/10 has it gives more options. If your wanting to still only use 1 motor linked with belts but nema 23 motor then there's still a possible option.? Thou i've never done it but can't see any problems if only cutting at lower feed rates needed for aluminium.!
Like using the 34's gear it but in reverse so 2:1 (2x turns motor 1x screw) this has the affect of doubling the torque and increasing the resolution at the sacrifice of speed.
To be honest with the price of digital drives dropping significantly and the fact they are soooo much better than Analogue drives in general but esp at handling stalling. Being able to stop all motors when one motor is detected Stalling has meant the racking issues when using twin slaved motors is greatly relieved and with minimal risk of damage if happening at high feed rates.
That said your if your mainly going to cut aluminium then slaved motors is not so much a risk has again the feeds are low so available torque higher. Esp if geared 2:1
Hope this helps
PS: I will post this on the forum for others to see and critique.!!
Agree with jazz about the X-screw - RM2005 wont help. The problem is the pitch is half what you get with RM1610, so you have to spin the screw twice as fast to get a given feedrate. Going from 16mm diameter to 20mm doesn't make the critical speed twice as much (only 25% more) so you actually end up worse.
RM1610, critical speed - 1460rpm => 1460*10=14.6m/min
RM2005, critical speed - 1825rpm => 1825*5=9.1m/min
The feedrate with either screw is plenty, but since 20mm is more expensive and in addition to the above a 20mm screw requires significantly more torque than 16mm, so you only gain stiffness/lifetime which on a router like is completely negligible since the 16mm screw is strong enough and will last for many years.
Jazz & Jonathan
As ever thanks for the informative responses
I follow on the 16 thread thats fine...... so I guess now really its a case of deciding between one motor driving two screws or having them slaved?
Based on the spec what would you guys do if it were you? And will 1 x 23nema 3.1nm running both x axis screws be man enough?!? or is it better to just go down the twin motor route?
Updated spec after current discussions:
1200x900 footprint area with approx 1000 x 800 cutting area
80x40x4mm steel box section frame with adjustable bed
Aluminium gantry made from a combination of 20mm/15mm plate either standard 6082 or ecocast for the bearing and guide plates
20mm Profile rail on x,y,z
**16/10 on x axis (running 2:1)**
16/10 on y axis
16/05 on z axis
250mm cutting depth on z
2.2kw chinese spindle
electronics (just ideas at the moment)
1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt running dual 16/10 screws
1 x nema 23 3.1nm running y axis on 16/10 screw
1 x nema 23 3.1nm running y axis on 16/05 screw for better resolution
80v Leadshine Drives
How is this all sounding? are we on the right track :)
Design wise the gantry design is very similar to the one Jazz has posted on here before with interlocking aluminium plates (copying someones idea is the best form of flattery right? or is that plagiarism :P) anyway it looks an extremely solid design and I tend to make things over engineered so figured this was a good place to start.
With the y axis I was considering a direct drive using a coupler, all the other drives will use a belt to transmit motion, would it better to engineer it so the motors are all belt driven or would this make no odds?
copy and paste mistake yes I mean 1:1!!
I was looking into that possibility and I think I must have guess the dims pretty close as I had exactly the same design issues but I think I can get it in!
after a bit of redrawing last night I had a thought that the fk/ff bearings (which I have just stumbled across) may be a better option for the x axis that the bk/bf ones. I am trying to determine the exact length of the ballscrew I need and cannot tell if the bearings in these units are flush to the back of the mounting plates or they are set in? does anyone have or know a link to some accurate tech specs for these bearings? Because the design of the axis uses a plate either end of the frame to sandwich the x axis ballscrew between two bearing units and I need to know the length of ballscrew I need to order otherwise there will be play or it will be over sized!
Alternatively if I were to machine up my own bearing blocks for the x axis, the floating end is straight forward, what does the fixed end comprise of? angluar contact bearings? sizes?
Nuts & bolts
Water pump for the spindle
Tubing for the water pump
Connectors for the tubing
Accounting for all these sorts of things is adding an easy £200-£300 to my budget (even with making my own cable runs after the machine is built) and then of course before I cut a single thing I'll need a few different router bits so that is another £50.
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