Determining Maximum Speed on a K40 using a 3d Printer card

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Can someone who is way more educated on lasers than me please advise me what determines the maximum speed i can get out of my machine, is it the steppers, the software, the board or a mixture of any of those.

Currently running a K40 with a soon to be upgraded gantry in the 1 square metre region and at the moment I am using a standard Makerbase MKS 1.3 3d printer card with built in stepper drivers for two Nema 17 steppers ( one with with dual drive) on Windows 10

The gantry is all made and working well using linear rails on 2040 Vslot extrusions, purely linear bearings , no Vslot wheels at all.

Were doing some testing without the C02 laser head on it and we seem to be getting what appears to be a max speed of 400mms more or less, there is a noticeable drop in speed at 200 mms and when you exceed 400mm nothing changes.

To achieve more speed for cutting and for engraving what route would be best to look at, I have seen something that says on a C02 laser that there are maximum speeds of 120 mms for engraving and cutting but I have been using mine at above that and still get good engraving and cuts. ( well I believe that is so) with lightburn of course.

At some point I will probably change over to a more professional direct C02 laser card but I would like to know what I am in for, new steppers, new card, separate stepper drivers or what., the new gantry is very fast on a linear rail 15H bearings as we purchased high quality units as against the cheaper chinese ones that seem to stick etc.

The card is limited to just under two amps I believe on the MKS card so does not require separate drivers for the current steppers I have been told. I just want to know what I should be looking at to push the speed up further. ( apart from a dedicated card possibly)

Thanks for any help.

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Yes :slight_smile:

You can go as fast as the steppers will turn, but your machine mechanicals may not like it.

Probably a better question is ‘how do determine the best speed for a job?’

Go too fast and quality will degrade.

‘K40’ is a general description - my K40 has linear rails and a proper bearing for the X-axis gantry, so it will take a lot more speed than one using the ‘shower door’ nylon wheels.

There’s no hard and fast rule, because every machine is different.

Most of the NEMA17 steppers and drivers in K40s can go faster than the CNC components can handle.

Go too fast and artefacts will start to creep in, you’ll get wobbly lines, the beginning and end of lines will start to be offset, the ends of vectors won’t meet up - worst case, your steppers will start to skip and your origin will move.

How I approach it:

Do a material test to determine the best setting for the job - say you end up with a nice result at 15% at 50mm/sec. You can then double the speed and the power to 30% at 100mm/s, or 60% at 200mm/s and see if the result is still acceptable.

In my experience, running a K40 at ~300mm/s is the upper limit, and will require frequent maintenance - the stresses will cause your bearings to need more frequent adjustment, screws and nuts will start to shake loose, etc.

They aren’t high-tech - they were designed to engrave rubber stamps at ~150-200mm/s and at those speeds, they will run for ages without having to continually fiddle.

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Ok thanks for that, so the answer to my original question is basically the speed is in fact controlled by the steppers , obviously the gantry etc will be a deciding factor as you could end up shaking the machine apart unless you have a machine strong enough to cope and bolted down.

My new gantry is being made from C beam and other heavy gauge extrusions and H15 block linear rails on top as against steel rods and tubular bearings. The fittings are all mounted on 3d nylon printing which seems quite strong over PLA and it seems to do the job nicely, I cant afford to go for CNC milled aluminium so Ive designed then to be 3d printed, they seem strong enough and hope that they will last over time but the beauty is if I notice a fault I can just print off another mount or fitting. also doing it this way allows me to get the mount exactly how i want it.

The laser head will be mounted on 8mm acrylic, high end sealed bearings are being used everywhere that need it and larger than the normal 6mm steel lined rubber drive train is being used.

The gantry will be solid as rock as against the existing piece of “shower curtain” ( very good analogy) there are no Vslot wheels or anything that can upset the travel, its all very high quality rails rather than ali express stuff.

I am also changing the card over to a VMS card as I have seen this work with incredible high quality on a machine running at 600mms and no glitches or missed steps in the finished work at all. the machine was built for the card so to speak with high end extrusions and rails. I just want to make sure before I go down the route where I need to spend the money,

Its not power I am after but a bit more speed and a much larger bed size, I dont cut anything over 8mm , 6mm is my norm anyway, I have no need so not looking to go to 60 or 100 watts, 50 will be plenty big enough.

I never run my existing K40 over 100mms anyway, power is always 6 milliamps and I cut at 5 mms at 32.5% power and engrave at 100mms at 5% power 6 ma on 3 mm, seems to come out fine for me with nice brown edges over charred black ones that i normally see on others work where the power is over the top. I am always conscious the gantry might fly out of the case if I go any quicker than 100mms.

So thank you for your help Bo in answering the question It looks like I will need to beef up the steppers, add some drivers and contact Eric Norton for the specs to look for on his board.

thanks for your detailed response.

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That sounds nice - useless without pics :slight_smile:

Steppers are not really constrained by speed, more by torque - a nema 17 is more than adequate to shift a hundred grams or so at full speed.

But, Nema 17 ain’t Nema 17 - a cheap Chinese stepper will not perform the same as a Longshine hybrid, for example.

If only for packaging’s sake, I wouldn’t look outside Nema 17s for drive - they are small and fast and can certainly shift a lightweight head on the X-axis gantry faster than you will ever need to go.

Maybe, just maybe, if your gantry is hefty, you might want to look to beef up the Y-axis stepper, but as the Y doesn’t need to move anywhere near as much or as fast as the X, I would look at tuning what you’ve got before upgrading.

In order of performance upgrade, you’ve done most of it already - rails being the most important, then controller.

The LX4 uses TMC2209 stepper drivers, which are more than adequate for a small engraver, and you won’t see much improvement with an external stepper driver - because you will run out of performance at the chip/firmware level before you get anywhere near topping out the CNC subsystem.

Of course if you want to do a lot of engraving, rather than cutting, grbl really isn’t the way to go. It can do a decent engraving job, but it’s nowhere near the reliability and performance of a DSP system.

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