New CNC Mill on the horizon

[JAZZCNC]

Ok, I think I have decided I am going with the twin ball screws on the X controlled by one motors running a belt drive system for the two drives. As much as i think it might be easier to implement the motors to start with the idea of not having to "tune" the motors to work together appeals greatly.

Wise choice and won't regret I know that.!

[fvfdrums]

Right,

Been quite a while since I was posting about this but it is still going ahead, albeit "general life" has got in the way as it does with so many projects but I now have a Friend on board so we are splitting the costings 50/50 so we have a realistic budget to work with and hopefully the specs are adding up now. Still got a few questions really.

Here is the current spec:

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
20/05 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 (as suggested by JAZZ) running 20/05 screw on a 2:1 ratio
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 Chinese Drives

80v PSU

Mach 3

Price wise everything has been accounted for in our budget which is great managed to get some really good prices on steel and aluminium. I have a couple of questions which as I know may not be possible to answer without imagery but I thought I would pose them anyway!

The length of the x axis thread is 1200mm would this run with 16/10? or is it better to just stick with the 20/05 to prevent the chance of whipping as I was under the impression thats getting to the limit or even past what it should before it whips?

Running the X off a nema 34 and the y and z off nema 23s, would this pose any sort of problems with setting the machine up? is it better to have 34 all round as I am quite happy to do this as all of the screws are belt driven in some form so adjusting the gear ratio to compensate for slower rpm is not a problem. The machine is still being designed to cut aluminium primarily and then hardwoods

The current weight of the gantry based on calculations of size and weight including aluminium, bolts to assemble, spindle, rails and carraiges, Stepper motors and any other parts that were per the design is in the 65-68kg range.

We are hoping to get started on this in early feb and to have a moving machine by the end of march, thats not a completely finished machine but one that can move, even if we have to push it!

[JAZZCNC]

1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt (as suggested by JAZZ) running 20/05 screw on a 2:1 ratio
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

Hold on think we may be at cross purpose's here or I've miss under stood you.? I wouldn't have recommended those screws and motors at this size.? Longer yes but not at 1200mm.

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.

[fvfdrums]

Hold on think we may be at cross purpose's here or I've miss under stood you.? I wouldn't have recommended those screws and motors at this size.? Longer yes but not at 1200mm.

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.

My fault I am sure, the x axis will be joined with a timing belt in which case would this still negate the 34 or would the 23 be adequate. but if I can use the 16/10 then thats great!

Noted on the drives voltage that makes sense must be a sunday thing on my part! As ever cheers for the response!

[JAZZCNC]

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
Cheers
Dean.

PS: I will post this on the forum for others to see and critique.!!

[D.C.]

Price wise everything has been accounted for in our budget which is great managed to get some really good prices on steel and aluminium.

I am going through the same design/collect materials phase that you are and I'm building a similar sized 2.2kw spindle, steel frame as you. In your budget did you account for all the 'little things'?

Like:

Control Cable
E-Stop button
Limit switches
Nuts & bolts
Water pump for the spindle
Tubing for the water pump
Connectors for the tubing
Cable runs
Welding supplies
Paint
Etc...

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.

[fvfdrums]

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?

[fvfdrums]

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

75v PSU

Mach 3

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?

[JAZZCNC]

**16/10 on x axis (running 2:1)**

1 x nema 34 7.7nm running 2 x axis ball screws via a timing belt running dual 16/10 screws

This contradicts the other.? If using 10mm pitch you won't need any ratio with 7.7Nm 34 and belt drive 1:1 will be fine.

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?

No don't direct drive keep the belts for resonance reasons even thou your planning using very good drives which handle resonance fantastic. If your copying the gantry I think then I've actually changed the design slightly and the Motor is now on the inside connected to screw with belt. It's very neat and compact. (code for F@#% tight fit.!!)

[PAULRO]

Hi FVFDRUMS, i have been watching this build log because i,m going to build a m/c similar to yours, similar cutting area with similar size tooling(20mm linear guides and 16mm ball screws) .the lengths will be different sizes. i plan to m/c hardwood ( the occasional guitar body) can you let me know where you bought the slides, ball screws and bearing blocks to suit? also is there a download of the specs available so i can incorporate this info in to my dwg.
By the way, how is your build going?