CNC machines

[Ned__]

Do you think ill run into the corner rounding issue on 3mm steel Hood? I only use mild steel, never stainless or aluminium. I can't weld them.

I built my table to cut completely submerged, but it turns out, that the torch I have ( Hypertherm T45M ) can't cut completely submerged.

So someday I'll upgrade the plasma unit, down the line, because this action is way too cool -

Apparently cutting submerged presents a danger of blowing up the torch... ? How does that happen?

 

[MattH]

How powerful are the servos you are running Hood?

Dual 400w AC servos with 5:1 planetary gearboxes can drive my gantry at 3000mm/s/s but the overshoot is horrendous.
I had them set to 1400mm/s/s from memory to get the following error down and at that setting the machine was doing a terrible job on 1.5mm MS.
I then gave up and went Laser.

People miss that it's easier to build a CNC plasma for thicker material.

Granted @ned isn't cutting thinner than 3mm but I still think the Nema23 steppers will struggle.
It will cut, but you will have to turn the acceleration down so low to avoid missing steps that the finish will be awful.

 

[Hood]

Do you think ill run into the corner rounding issue on 3mm steel Hood? I only use mild steel, never stainless or aluminium. I cant weld them!

I built my table to cut completely submerged, but it turns out, that the torch I have ( Hypertherm T45M ) can't cut completely submerged.

So someday I'll upgrade the plasma unit, down the line, because this action is way too cool -

Apparently cutting submerged presents a danger of blowing up the torch... ? How does that happen?

It will depend on the plasma as to what is the ideal feedrate, for me I would likely be about 4-5000mm/min but that is 80Amps, if your plasma has less current then it will be a lot slower. Of course you can always lower the current and use finer nozzles which would reduce the required feedrate and thus the corner rounding.

I am not sure about submerged cutting. I know that with the style of torch I have it can cause issues. That is because it is a blowback ignition and from what I understand the submerged cutting will gum up the torch and stop the electrode retracting properly.

How powerful are the servos you are running Hood?

From memory I think they are about 750W but will have a look in a bit and see.

 

[Ned__]

Thanks Hood. That is good news.

Matt my machine is belt drive, and the GT3 pulleys are not available for Nema 34's.
Changing the drive system is too much to think about, right now my only concern is crashing into the finish line.

The nature of what I intend to cut is probably relevant

What do I want to make:

Fires and benches. The fires will sell, I have customers already. The benches are an unknown. It's not really precision engineering that I'll be doing, more sculptural I guess

 

[Hood]

I can't find power specs for the motors but looks like they are about 900w @5500rpm on the Y axis. Specs for X axis says it is 600w @ 6000rpm, Z is 100w @4500rpm.
I have the Y axis through planetary boxes but not sure the reduction, 5:1 rings a bell but...
X axis is through a worm box and I think it is somewhere around 25:1 but again not sure.
Z is 2:1 belt reduction. Z axis I have set to 3m/min velocity and 10,000mm/s/s accel.

 

[ned]

So I made a wooden mockup o the gantry. Ill send the plate off to the guy tomorrow and he can use it to make a drawing and mill it.
Ahh, I sold some tools and bought a second 48V 10 amp power supply for the steppers today also. I needed an extra 8 amps for the new steppers. So a good day.

 

[ned]

The Myplasm controller arrived today. The steppers have cleared customs also, so should arrive soon.

Its teeny!

 

[Ned__]

this is the back of the controller, it's a lovely shade of petrol blue

I bought a Chinese 4x8 machine years ago and dismembered it. The control box, the steel shell, was crappy, so I replaced that shell with a box I found in work and restored.

This is it below, the Chinese electronics in the restored box.

Trying to think will I use an aluminium plate as a backing board for the electronics. Do the power supplies get hot in use?

I imagine the stepper drive cards do, there's a massive heatsink on them.

One 48v 10 amp power supply
Theres another 48v 10 amp power supply on the way

Three stepper drivers (i need to buy another) Leadshine M542-05

One 24v 3 amp power supply

The Myplasm controller

 

[Hood]

The stepper drives will likely get the hottest, I would fit a couple of slow running fans, one pushing and one pulling.

 

[ned]

Cleaning for paint. Big job.

2 hours a night each day after work, I reckon this will take me a week.

 

[Onoff]

Is this cheapo kit any use as the basis for a CNC machine driving a wood router? 40N of torque didn't seem bad spec wise.

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[MattH]

Is this cheapo kit any use as the basis for a CNC machine driving a wood router? 40N of torque didn't seem bad spec wise.

[£40.09 17% OFF]TWO TREES® CNC Shield + UNO R3 Board +4x A4988 Stepper Motor Driver +4x 4401 Stepper Motor Kit for 3D Printer Office Equipment from Computers & Office on banggood

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No.

 

[Ned__]

@Onoff those Nema 17 motors are too small. The most popular sizes for hobby projects using stepper motors are Nema 17, Nema 23 and Nema 34.

For a wood router you need will need Nema 23's, or Nema 34's, because there are forces involved, you are pushing a router through material.

Probably the best way you could go would be to buy an Openbuilds Ox kit that you can build yourself, you might get it done for 500 to 1000. Sometimes they come up second hand, have a look on ebay or gumtree.

Thats deff the easiest, fastest way to go, all the parts will be supplied, as will the instructions, there loads of tutorials online covering every aspect of an Ox cnc, and there are large and active forums that will help with the many questions you will have.

 

[Onoff]

@Onoff those Nema 17 motors are too small. The most popular sizes for hobby projects using stepper motors are Nema 17, Nema 23 and Nema 34.

For a wood router you need will need Nema 23's, or Nema 34's, because there are forces involved, you are pushing a router through material.

Probably the best way you could go would be to buy an Openbuilds Ox kit that you can build yourself, you might get it done for 500 to 1000. Sometimes they come up second hand, have a look on ebay or gumtree.

Thats deff the easiest, fastest way to go, all the parts will be supplied, as will the instructions, there loads of tutorials online covering every aspect of an Ox cnc, and there are large and active forums that will help with the many questions you will have.

Cheers. Why the big cost difference, £500 to 1000?

 

[Ned__]

I'm around 5 - 8 grand into this project, all told.

If you buy a complete kit, 500 to 1000 is cheap and you might actually complete it, unlike me.

I'm the wrong person to be asking for advice, given what a dismal failure it has been for me to this point.

 

[zeppelin builder]

I had the steel yard cut the beams becuse my saw did not have the capacity. The operator I think did a good job, he had a very nice behringer saw.

Looking forward to welding the horizontal sections, the verticals I think I might skip weld. Not sure.

always weld the verts first , that way you can move it on diagonal measurement
add temp bracing on corners then weld the flat bits

 

[Ned__]

@zeppelin builder that is solid advice

 

[Onoff]

My mate turns bespoke wood pieces. He's been on about a CNC router for ages. Questioning him on what he wants to do he's written:

"Basically just burning my logo onto finished work or may be burning a sign I want to be able to exchange the router / spindle with a laser".

From that he wants a dual purpose machine I'm thinking. Any pointers?

 

[Onoff]

When the "first" DIY CNC routers were built I assume they were pretty rudimentary and low accuracy. Would they have used bog standard all thread / studding?

Ref backlash, is that not taken out by the stepper motor(s) not moving?

As you can tell, coming at this with no knowledge whatsoever!

 

[m_c]

My mate turns bespoke wood pieces. He's been on about a CNC router for ages. Questioning him on what he wants to do he's written:

"Basically just burning my logo onto finished work or may be burning a sign I want to be able to exchange the router / spindle with a laser".

From that he wants a dual purpose machine I'm thinking. Any pointers?

Dual machines for router and laser involves compromise and very good design.
Router needs to be quick and strong to avoid flexing when cutting.
Laser needs to be quick and light to get maximum acceleration.

Off course, if you're only fitting a low power laser, then you don't actually need that much speed.

When the "first" DIY CNC routers were built I assume they were pretty rudimentary and low accuracy. Would they have used bog standard all thread / studding?

Ref backlash, is that not taken out by the stepper motor(s) not moving?

As you can tell, coming at this with no knowledge whatsoever!

Threaded rod is still used by those on a very tight budget, but don't expect performance, low backlash, or longevity.
Next step up the price ladder is Acme/trapezoidal rod with delrin nuts. It's a bit better than threaded rod, as it's courser pitch, but it'll still need a reasonable amount of fettling for it to work reliably.
But if it's any kind of serious machine, ballscrews will likely out perform other options.

Backlash compensation is done by moving the motors a set amount rapidly each time cutting direction changes. But it's rarely a good solution for a bad machine.