My baby 15" x 15" machine

[wilfy]

anyone willing to look this over and let me know if anything is drasticaly wrong?

total width of machine is 800mm so i'm wondering what the chances are of using a single screw??

and also is there any advice on what size motors to use on each axis? as everything is steel am i best just going for 3nm on all??

[Jonathan]

It's hard to give a definitive answer as it depends on so many factors, what you need to cut and how often, how fast, required accuracy, personal preference... etc
It's borderline, you'd probably get away with one screw as the distance between the bearing blocks is fairly small, but if you're going to be cutting metals at all regularly or just generally want to be able to cut at a good material removal rate accurately then get two ball-screws. You certainly wont regret it.

[wilfy]

brilliant thanks for the reply... is there anything else that looks out?? i did wonder if the gantry would need any triangle/cross bracing from top to bottom outer corner?

what i might do to start with is use one screw and then if i find myself cutting or want to start cutting metal on a regular basis i'll upgrade to a second screw.

the chances are if i get the bug i think i'm going to get from this machine i'll end up re-building and making a bigger machine anyway as i originally wanted a 4'x4' machine but cant justify the cost until i can get this machine to prove itself.

thanks again for the input i'll work on locating motors, mounting plates and anything else thats missing, i can also start to work out screw sizes so that i can get a price for my missus from chai

[Jonathan]

I forgot to answer the motor question...

You could use less than 3Nm motors in places without reducing the performance, but 3Nm motors are by far the best price per Nm so it's hardly worth getting anything smaller, especially since the 3Nm motors would be good for the 4'x4' machine if you decide to make it. Currently the cheapest place I know of to get them is here:

Nema23 3.1Nm

Remember to ask Chai to make the end portion of the screw longer (25mm is good) to make it easier to fit and align the pulleys. This will of course mean adding a little to the length of the screws you buy.

The gantry is currently quite tall so it look like it could bend 'backwards' (parallel to X) relatively easily. It would be a good idea to add in some diagonal pieces as you said to combat that.

[wilfy]

that site is now bookmarked than you for that.

i'm happy slapping some diagonal's in that wont be a problem...

i had already thought about the extra length on the end of the screws as i've seen u mention it a few times but thanks again for the reminder.

i'm quite surprised there's not much else to pick at tbh, now i just have to get prices and try get my missus to agree to part with some cash :D

[wilfy]

electronics wise.. is this everything i am likely to need for my machine??
Upgraded Smooth CNC Standard 3 Axis TB6560 Driver +Box & 3Nm Nema 23 Motor & PSU | eBay

would it work out cheaper if i split them down and got the drivers from the place you recommended.. i'm not sue what size drivers to get and what size psu where as the above package seems to have it all included..

[Jonathan]

Nooooo... those are terrible drivers and bad motors!
The TB6560 driver only reliably accepts up to about 24V and you want to drive the motors from a much higher voltage to get the best performance. Ideally around 75V, so three times as much. For example:

Best Selling! Wantai Stepper Motor Driver DQ860MA 80V 7.8A 256Micro CNC Router Mill Cut Laser Engraving Grind Foam-in Motor Driver from Industry & Business on Aliexpress.com

(But shop around, that may not be the cheapest.)

The motors in the listing you linked to have a significantly higher inductance than the CNC4You motors. This will limit the torque you get at higher speeds since a high inductance means the current takes longer to reach the rated value, so at high speeds the current doesn't reach the rated value and hence you get less torque. That is also the reason for using a higher voltage - the current rises faster when a higher voltage is applied.

Edit: Just remembered, I posted a much better explanation here.

[wilfy]

ok without wanting to annoy you i need to ask this for my own peace of mind..

what is wrong with running the motors slower? why cant you cnc at the speeds your equipment can cope with if it ends up being that you buy the cheap crap stuff??

i understand you are looking out for us and dont want us to make mistakes and end up needing to buy the better stuff anyway, and for this i thank you... but i just wanna know why not if it's easy enough to explain it in simple terms.

just from a rough guess i'm looking at around £100 more than i expected to pay for the electronics, so i just basicly wanna be able to justify it..


also i will look in to finding a driver i presume aslong as i get any driver around 80v and 7.8A they will do the job?? any pointers on a PSU?? and is that all i need to buy.. motors,drivers & psu? the kit i linked seemed to have other stuff

[Jonathan]

what is wrong with running the motors slower? why cant you cnc at the speeds your equipment can cope with if it ends up being that you buy the cheap crap stuff??

If it's sufficient to run your machine as efficiently as you need, then there's nothing wrong. It's just hard to know if it will be..
The motors from England and the drivers are cheaper than the kit you just linked to, so I see no reason not to get the better ones. The TB6560 is generally so unreliable I wouldn't even consider it an option as I guarantee you'll only end up getting better drivers a few months after buying that.

For the PSU a 500VA toroidal transformer, 25V(*2) or 50V is the best option, with a rectifier and capacitors.

[JAZZCNC]

Wilfy I have spent many many hours talking and helping new people to DIYCNC on the phone and via email and THE MOST COMMON (by a long way) single mistake they make is buying the wrong drives and PSU. The TB based boards are one of THE easiest ways to waste money and more importantly time, mainly resulting in frustration and disappointment.

To answer the question regards speed and what's the correct drives PSU to buy then the Honest answer is CAN'T ANSWER.!! . . . . .Until more information is known about the machine and what materials your going to machine.?
I help loads of people either on here on via the phone etc and When I ask folks what they want to machine they generally say "Oh nothing too difficult just MDF, wood, plastic and the Occasional bit of Ali" . . ERmmmm is my reply.?
Whats wrong with that you may think.? . . . . Well it mostly boils down to cutting speeds.!

Given the TB based board and 24V has a crude example.!! . . Out of all those materials you'd think the hard ALi would be the challenge.? BUT in reality given the machine frame is strong enough it will be the most suited to the slow TB based board.? Ali only requires low feed rates and the 24V will probably be ok. This is also why lots of small milling machines and lathes use 24V.
But Wood, MDF, plastics etc require high cutting feed rates so in general require the motors spin faster for longer. There are other things that affect feed rate like screw pitch but in general in these softer materials the motors are working faster. To enable this speed you need voltage and 24V (Excuse the pun) just doesn't cut it and available speed is low and therefore feed rates. Too low feed rates wears tooling out very quickly and leaves a poor finish.
Then you have the workload of the drives.! They are constantly MAX'd out and eventually this takes it toll and in the case of the cheap TB based stuff results in either poor performance in form missed steps etc or has often happens they die quickly by frying themselves.

The extra £100 is worth every penny and will enable a very wide range of cutting capability with the least amount of stress.