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[01012f]

Hi all
I'm attempting to build myself a 1200x600 cnc router. I'm making up the plans as I go along, so probably making loads of mistakes. I've so far got the Y rails mounted and built the gantry with rails ready to be fitted. I hope to end up with something that will mostly cut wood but be capable of milling aluminium and possibly adding a 4th axis at a later date.

[01012f]

Hi all

I'm struggling with the linear rails I bought for my project.
How easily should the carriages move on a HGH20 rail?

My 3d printer has 12mm linear rails and the carriages fall freely when the rail is held vertically. I was expecting similar for the HGH20 rails but they just sit there. Even removing the wiper plates there is no roll although they do move with a light tap but then stop immediately. Is this normal?

As a test, I replaced the HGH20 rails with some Sbr16 rails and they work fine, even when I attach my end plates and gantry and my stepper motors easily move it all.

Have I bought the wrong rails? Am I expecting too much of them?

Thanks

[JAZZCNC]

This is quite normal, it's the preload that is holding them. The preload is one of the details which makes them so much better than the others. You don't want loose sloppy rails on your machine and any bearing that slides easily without any effort is basically sloppy.

Don't hesitate to fit them and forget, they will outperform and outlast all the others.

[Neale]

And they move more easily when loaded, surprisingly enough. My carriages seemed a bit sticky when I tested them on the rails as I was building. Then I leant on them and they moved much more smoothly and easily.

[01012f]

Thanks guys
I guess I'm now going to have to source dual lead screws for it, my steppers can't cope with it as it currently is (3:1 reduction & GT2 belt)

[JAZZCNC]

Thanks guys
I guess I'm now going to have to source dual lead screws for it, my steppers can't cope with it as it currently is (3:1 reduction & GT2 belt)

Why would you source new lead screws if the steppers are too small.? You might be throwing good money away on the wrong things.? I suggest you post up the full spec of what you have and a few picks of the machine so we can take a look for you.

[01012f]

Hi JazzCnc

I think I over-spec'd the rails, I could probably get away with smaller rails but I have them now.

I only have 50oz nema17 stepper motors and the way I had it all assembled, the motors can't cope. On each side of the gantry I have a 20 tooth pulley on the stepper driving 60 tooth pulley on a shaft with a 20 tooth pulley on the other end. A GT2 belt runs around 2 idler pulleys to that last 20 tooth pulley. I think my dual y-axis controller board is splitting 1 stepper output rather than having 2 full power outputs. It would probably work as planned if they were full power outputs.

So, my thoughts were to replace the belt drive with lead screws. That should give me a ~10:1 advantage rather than the belts 3:1.
And yes, lead screws are expensive, so I'm first going to test the princliple using m10 studding.

I have some (lack of) progress videos on my youtube channel
(https://www.youtube.com/channel/UC0NnUpU2b8wQNtOSQB5yqzg)

[dazp1976]

Hi JazzCnc

I only have 50oz nema17 stepper motors]

There's your problem.
Even cheap chinese machines that size have at least 425oz nema23.
Steppers are too small.
The rails are prob really good tbf.

Look at other machines that size and see what they have.
I suspect 425oz > DM542/DM556 >48vdc.

[01012f]

Yes, I quickly realised the steppers were too small. I'm not against changing them but only if I really need to (I probably do).
I want to test the lead screws first, then I'll consider the steppers

My controller board has built in stepper drivers (little plug in boards). Nema23 steppers will draw more current than the board is rated for. Is there a way to connect the DM542 type driver to my controller board? ie removing the plug in board and wiring in the DM542 type ?

[dazp1976]

Yes, I quickly realised the steppers were too small. I'm not against changing them but only if I really need to (I probably do).
I want to test the lead screws first, then I'll consider the steppers
My controller board has built in stepper drivers (little plug in boards). Nema23 steppers will draw more current than the board is rated for. Is there a way to connect the DM542 type driver to my controller board? ie removing the plug in board and wiring in the DM542 type ?

At the end of the day you say you want something that will do aluminium and wood.
It will need to be fairly rigid and have some decent drive.
If you try and do it really low budget, try to fudge controls and are willing to cut corners. Then I suggest you abandon it.
It's a far cry away from a £50 3d printer kit.

I'm surprised the steppers moves at all with 3:1 (big pulley stepper > little pulley screw) yes?.
You don't even need that inless you're trying to achieve a possible 15,000mm/min top speed (15m)! (that's based on 5mm screw)
Most machines I see this size are direct driven (no belts) or 2:1. The long base driven by 2 steppers 1+slave.

Direct drive with a stepper of max 1000rpm driven direct gives max 5000mm/min with 5mm pitch screw..
If you want more speed you either get 10mm pitch screws or just buy AC servos with 3000rpm (NOT hybrid stepper type).

I suggest you do more research, look at more images etc and go from there.
I mean to buy a basic Workbee (crap) which aren't great with cutting alum, are £1500 start WITHOUT even a router head.

[RobC]

I would say a proper set of drivers would be a better solution and go with a dedicated controller that you can do much more with. I use a very cheap generic 5 axis bob but then I've had to buy a more expensive UC100 so I can use it and it's worked great now for 4 years but it's dependant on how much money you want to spend on this. I personally would go back to using the Hiwin rails over the round rails after using round rails for years.


Rob

[01012f]

At the end of the day you say you want something that will do aluminium and wood.
It will need to be fairly rigid and have some decent drive.Mainly wood with a bit of aluminium but yes, I get your point


If you try and do it really low budget, try to fudge controls and are willing to cut corners. Then I suggest you abandon it.
It's a far cry away from a £50 3d printer kit.hmm, maybe a misunderstanding.
I'm willing to fudge and cut corners to test if something works, if it does then I do it properly :)


I'm surprised the steppers moves at all with 3:1 (big pulley stepper > little pulley screw) yes?.
no mate, the other way around, little pulley on stepper -> big pulley on shaft, little pulley on other end onto the drive belt. so the stepper will turn 3 times to make the belt pulley turn once.
But as mentioned above, I've already decided to drop that in favour of dual lead screws


Most machines I see this size are direct driven (no belts) or 2:1. The long base driven by 2 steppers 1+slave.that's where I'm headng

I fully accept I'm doing this with no experience but it's getting there, slowly, and i'm learning and having fun. Hopefully I'll end up with something that does what I want but either way, I'll enjoy the journey :)

Thanks for your input 30650

[JAZZCNC]

Hi JazzCnc

I think I over-spec'd the rails, I could probably get away with smaller rails but I have them now.

I only have 50oz nema17 stepper motors and the way I had it all assembled, the motors can't cope. On each side of the gantry I have a 20 tooth pulley on the stepper driving 60 tooth pulley on a shaft with a 20 tooth pulley on the other end. A GT2 belt runs around 2 idler pulleys to that last 20 tooth pulley. I think my dual y-axis controller board is splitting 1 stepper output rather than having 2 full power outputs. It would probably work as planned if they were full power outputs.

So, my thoughts were to replace the belt drive with lead screws. That should give me a ~10:1 advantage rather than the belts 3:1.
And yes, lead screws are expensive, so I'm first going to test the princliple using m10 studding.

I have some (lack of) progress videos on my youtube channel
(https://www.youtube.com/channel/UC0NnUpU2b8wQNtOSQB5yqzg)

Hi, Yes I went to your Youtube after posting what I did and saw what you are planning and what you are working with!

I understand testing the waters with what you have but what you have is just wrong in every department, but I think you get that by now.
My strong suggestion if you are serious about a router worth the effort is to forget all the electronics you have, right down to the PSU.? They will only frustrate the hell out of you and massively underperform.

NEMA 17 motors are ok for a small super lightweight machine ie: 3d printer using thin light belts etc but they just can't handle the inertia of larger lead screws and linear rails that you will need for a router this size. You'll need at least 2Nm Nema 23/24 and ideally 3Nm or more, however, the real key is the voltage you run them at and this requires the drives to match and have a little spare overhead.
This is why I said "right down to the PSU" because for a typical 3Nm stepper you want to be running them with around 50-55Vdc, smaller motors like 2Nm you can get away with a little less at 40-44Vdc. If you run them with less voltage than this you will be compromising performance and it's just not worth doing.

Regards the drives then don't buy Cheap analog drives, they are old tech and run very rough compared to digital drives, there is a night and day difference in performance and smoothness. You also want to leave a 10% margin of safety on the maximum voltage they can handle compared to the voltage you run the motors at.

Lastly the controller.? This is another KEY component to a good machine and especially a router as you need a nice fast and smooth pulse train.
If you want a stable machine and one that performs well then don't use the parallel port (Unless you use LinuxCNC, but that's for another time!) because again it will frustrate the hell out of you and is relatively slow.
I would avoid a USB-based controller because while better than PP they can still be a little flaky depending on which controller you use and the PC it's used on.
An Ethernet-based controller is the only real sensible choice if you want a rock-solid machine that performs great.

In my experience, any trying to cut corners is always regretted and costs more money. I've seen it time and time again and what's crazy is that it doesn't actually cost much more to do it right the first time. It also makes the build go much smoother, far less frustrating, and enjoyable.

Good luck and if you are unsure of what to buy just ask. The golden rule is never Buy before asking or checking if it's right for your application.

[01012f]

Hi Dean

That's a great post, thanks.

I've just has a look at your site, wow, you build some gorgeous machines 30654

After feedback from here, the upgrades include lead screws, nema 23 steppers, decent drivers and a new controller :peaceful: so they'll come as funds allow.

Thanks everyone for the help and suggestions 30654

[Doddy]

Ooof, Just watched your videos - you've receive good advice so far.

One point from me which I don't think is covered from what I've skim-read - please don't connect/disconect steppers with the drivers powered/active. Being an inductive load, and that the stepper windings are under constant excitation you will generate high-voltage spikes on supply interruption to the stepper that can damage your drivers. Not much of an issue if you're replacing that kit, but useful to get into a habit of powering down. The problem gets bigger as the steppers (and drive currents) get bigger.

[01012f]

Time for a long overdue update on my progress.

I followed advice from here and upgraded -
1, all the steppers to 425oz Nema23s from 60oz Nema 17s
2, the stepper drivers to external drivers
3, to a 48v 600w power supply from 12v 750w
4, the y-axis to dual leadscrews from dual belt
That lot is all in and working a treat :thumsup:

I've got limit switches on both ends of each axis
And I've made x-axis and z-axis carriages from 6mm aluminium

I think I'll need to spend time tuning it all in, it's a bit noisy and lumpy in places.

It's all there really. It just now needs tidying up, ie cables in drag chains, a controller board making up, e-stop etc.
Then I need to sort out a waste board and a router/spindle of some sort. The original plan was to use my main router but I've since realised that it doesn't dis-assemble to a mountable form.

It's been fun building it :thumsup:

latest update video https://youtu.be/loWaDqnpO-Y