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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

[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.