Am I heading in the right direction?....

[Lloyd]

Those links look great! Thank you...

on the design I'm working on, I've now change all rails to square profile type RE your suggestion...

I see what you mean about the epoxy method...

a design I'm trying now (based on a cnc I've seen) is to use 90x60 aluminium profile, heavy duty, which will hold the rail and will be linked to the steel sub-frame at 5 plates along its length - each plate will have 4/6x M10 stubby bolts to allow me to make fine adjustments to the level.

Ive be attached a pic of the design in progress with this system - probably pretty confusing - I'm not using any regular design program, only what I'm used to, illustrator... But with some inspection would give a rough idea of where I'm heading... Anyway, it's certainly not finished, once I'm finalised on the equipment, I will modify the design to suit...

[JAZZCNC]

Eddy is correct with dropping the SBR rails it will let the machine down badly. The Z axis is THE most important part of the machine so if weak it doesn't matter how good the rest of machine is the cut finish will be poor.
Also 300mm Z travel is quite a lot so if your not having a adjustable bed then you will struggle to cut anything hard and thin(<100mm) unless you raise the material to the cutter and reduce Z extension. If not you'll experience bad chatter and poor finish on hard materials and you can forget Aluminium at full 300mm extension.

Regards ballscrews then I wouldn't use 16mm diameter for the long axis because in my experience it's just a bit too long. Now you can get 10mm pitch in 20mm Diameter then your much better using them over 16mm at this length. The difference in performance is neglible and your far less likely to get whip so often can go faster than 16mm screws that whip.!
Use 16mm Dia 5mm pitch for Z axis.
Also I recommend you connect steppers to screw with timing belts and pulleys to help reduce resonance and add some flexabilty with ratios if required.

The gantry you have drawn will need some bracing on the bracket holding the ballnut or much thicker bracket.
To be honest I'm not a fan of the place you have put the ballscrew as it's in the firing line of chips and is fulnerable to damage being high up and exposed.

Electrics then I urge you to go with good digital drives, Esp if building from steel as they handle resonance so much better than anologue drives. Also if planning on using Mach3 then invest in a motion control card. Both these will give you the best machine possible and least hassle along with best performance.

3Nm motors run around 65-70Vdc will be fine but check out the indutance of the motors first, if buying from Zapp or CNC4You then you'll be fine but if from Ebay then they could be High inductance motors which will underperform.
The drives you pick will need to be capable of a higher voltage than 65-70Vdc you'll run motors at with a little safety margin so 80Vdc are the norm.

Toroidal PSU like eddy mentions is best for CNC and you'll need to size so outputs correct Dc voltage running drives at with Amps roughly 70% of total motor amp ratings IE: 4 x 4.2A motors = 16.8A / 70% = 11.76A so output any where around 11-12A will be fine. It's not critical as you'll never get anywhere near pulling the full 11A at one time.

GOLDEN RULE Don't buy anything unless your 110% sure it's correct for your needs.!! . . . . If not then ask on here first.!

[Lloyd]

Thanks Jazz,

Regards ballscrews then I wouldn't use 16mm diameter for the long axis because in my experience it's just a bit too long. Now you can get 10mm pitch in 20mm Diameter then your much better using them over 16mm at this length. The difference in performance is neglible and your far less likely to get whip so often can go faster than 16mm screws that whip.!Use 16mm Dia 5mm pitch for Z axis.
Also I recommend you connect steppers to screw with timing belts and pulleys to help reduce resonance and add some flexabilty with ratios if required.

i was going to use 25mm ball screws for all of them, but I see it would be better with 16mm on the Z... Pulleys idea - I hadn't thought of...

Regarding the gantry sides, I am using 20mm alu as the bracket, I thought this would be plenty rigid enough based on other designs I saw - how would you size it different?

the location of the ball screw - I accept your opinion on this... My thought was because at the max depth I'll be cutting just PU foam, and this is far below the ballscrew it should be ok, and in a simple location build-wise...

Where would you try set it otherwise?

thank you for the heads up on the motors from Zapp

i have heard that Mach 3 can be unreliable - what's the consensus experience with it?

anyway, regarding the hardwear, I'm definitely going for profile rails, circa 25mm, with ballscrews on X and Y of 25mm, and 16 on Z, each with 10/10/5mm pitch respectively.

motors - definitely digital sounds better... Power likely as advised

[JAZZCNC]

Regarding the gantry sides, I am using 20mm alu as the bracket, I thought this would be plenty rigid enough based on other designs I saw - how would you size it different?

20mm is ok-ish but I'd brace it more. Don't under estimate the power of steppers connected to ballscrews. If the cutter jams for any reason but doesn't snap straight away, which does happen with thicker cutters, then something will bend and those plates are directly connected to the screws so are first on the list.! Closely followed by the Z axis front plate( I've seen my front plate bend many times)

the location of the ball screw - I accept your opinion on this... My thought was because at the max depth I'll be cutting just PU foam, and this is far below the ballscrew it should be ok, and in a simple location build-wise...

It's a personal thing and while it's in simple location it's in a vunerable location for getting leant on or against while leaning into machine, crap hitting it etc.

Where would you try set it otherwise?

Tucked in at the sides lower down with some form of cover.

i have heard that Mach 3 can be unreliable - what's the consensus experience with it?

No not at all, yes it as some faults just like others do, inc Linux CNC, but in the main it's IMO the best control for begginers thru to advanced users. There's more support from a massive user base so if you do have any problems there will be someone to help.
The main or most problems with Mach comes from the PC parallel port and people over tuning there motors not the program.
This is why I recommend you invest in a motion control card if using Mach, they allow much smoother and faster performance along with much better reliabilty due to the very stable pulse streams they provide, unlike the parallel port.

anyway, regarding the hardwear, I'm definitely going for profile rails, circa 25mm, with ballscrews on X and Y of 25mm, and 16 on Z, each with 10/10/5mm pitch respectively.

DONT use 25mm ballscrews this is a BIG mistake.? The inertia from 25mm screws is too much for nema 23/4 motors and you'll end up with a very slow under performing machine. Like wise if you go with nema34 Motors then unless you use expensive high voltage drives you'll have underperforming machine due to the slower speed of the motors.

Also you won't need 25mm rails 20mm will be fine, even 15mm would be more than good enough. The main reason why 20mm is prefered is due to bearing size being better suited. Plus the cost differance is nothing. Where as 25mm bearings are just a little too big and then to a lesser degree you have the negative inertia affect and the weight while accelerating/de-accelerating. Loadings wise even 15mm profiled linear bearings can handle the loads you'll need with some to spare.

The combination of 3.1 or 4Nm Nema 23 motors run at 70Vdc connected to 20mm dia 10mm for axis over 1300-1400mm long is well proven if you move away from it you'll regret it when you see a machine that as it. The machine running 25mm screws on 25mm rails with nema 23 motors will struggle perform half as well.!!
At the length your building your even on the border of being able to use 16mm ballscrews for the long axis but 20mm are safer bet in my experience.
I would recommend 20mm for X axis if screw longer than 1400mm, 16mm for Y & Z. 20mm rails all round.

[EddyCurrent]

Regards ballscrews then I wouldn't use 16mm diameter for the long axis because in my experience it's just a bit too long. Now you can get 10mm pitch in 20mm Diameter then your much better using them over 16mm at this length. The difference in performance is neglible and your far less likely to get whip so often can go faster than 16mm screws that whip.!

Yes, sorry about that, I overlooked the length, I was still thinking about my own build.

[JAZZCNC]

Yes, sorry about that, I overlooked the length, I was still thinking about my own build.

Wasn't having ago at you Eddy because he is on the edge of being able to use 16mm just IME 20mm are better at this length and the higher inertia doesn't have a big negative affect compared to if they whip.!

[Lloyd]

DONT use 25mm ballscrews this is a BIG mistake.? The inertia from 25mm screws is too much for nema 23/4 motors and you'll end up with a very slow under performing machine. Like wise if you go with nema34 Motors then unless you use expensive high voltage drives you'll have underperforming machine due to the slower speed of the motors.

I'm considering investing quite some money into the machine - as I'll be using it for some work I do... So I don't mind kitting it out with good quality motors...

that said, it would be good to see anyone's idea of what percentage of your budget you' should allocate to which part of the machine... e.g. 15% on base structure, 35% xyz hard wear 50% on power, control, motors etc....

So you get the best out for your buck..

any takers?

anyway, I'll take your advice regarding the brackets, positioning, and screws, - but this could change should I decide to invest in more expensive digital drivers?

thanks again for the comments

[JAZZCNC]

anyway, I'll take your advice regarding the brackets, positioning, and screws, - but this could change should I decide to invest in more expensive digital drivers?

You don't have to take my advice and by all means go for the larger screws etc but you will regret I guarantee you that.!!

Your doing the classic BIGGER IS BETTER approach and that's a sure fire way to waste money and build an under performing machine. Digital drives won't make any differance if they are sized wrong and mismatched to screws.
Even with the stuff I suggested I recommend you use Digital drives but this as nothing to do with giving more power but more to do with being smoother running and resonance handling capabiltys.

[Lloyd]

You don't have to take my advice and by all means go for the larger screws etc but you will regret I guarantee you that.!!

Your doing the classic BIGGER IS BETTER approach and that's a sure fire way to waste money and build an under performing machine. Digital drives won't make any differance if they are sized wrong and mismatched to screws.
Even with the stuff I suggested I recommend you use Digital drives but this as nothing to do with giving more power but more to do with being smoother running and resonance handling capabiltys.

I understand what you're saying- I have received advice saying I should get large screws on my X,Y and Z and I should get 800w digital drives... But here, collaborative experience dictates otherwise...

as for the bigger is better approach; no, I just want a good solid reliable machine and I'm willing to invest the time and effort in researching the best equipment - you guys seem to know what you're talking about, and I'm just trying to understand the reasoning behind, which for all intents and purposes you've so far done well to justify.

My general philosophy when it comes to building stuff is to keep it simple and functional, I hate things that are over engineered unnecessarily.

So with the machine, I would like to use only the best possible parts for the required cutting area and material.

based on what you've told me (and off the top of my head)

profiled rails are best on all axis.
20mm ball screws on x, 16mm on y and z.
the ball nuts should be reinforced more than I have.
the position should be better placed, to avoid chips and being knocked
i should use digital drives correctly sized and I should not get poor motors with high inductance. (Have to get the maths out for the lads!!!!)
the bed should be adjustable, so when I cut alu, I should be as close to the y gantry as possible.
to help reduce resonance, I should use pullies this will also enable me to adjust ratios...
pitch on the ball screws should be 10mm on x and y and 5mm on z...
And dont waste money - unless I really want to ;)

did I miss anything?

[EddyCurrent]

did I miss anything?

Yes, you mostly just listed the mechanical items.

the PC to machine interface
breakout board / spindle speed control
Emergency stop / limits / homing switch strategies
the rest of the electrical stuff like power supplies, what voltage to use, amps required ?
the spindle and cooling system if water cooled
the variable frequency drive
type of wiring to use
cable drag chain
fan assisted cooling of control panel
software to use, Mach3, Linux, other ?
material and construction of bed surface.

must be something I've missed now ?