Cutting 3mm Acrylic

[pwelbourn]

On the LS3040, is it normal if cutting square 50mm x 50mm , That the size i get left with is 50.7 on the x axis and 50.3 on Y axis , Do my mirrors need aligning to make it so both come out same on each

[Spooky]

Hiya

Mirrors won't make any difference to cut size, the step settings would need adjustment but to be honest on a 3040 0.3 to 0.5 ids pretty good for accuracy. Setting the machine to cut exactly 50mm will cause problems when you switch from inside cuts to outside as the width of the beam also has to be accounted for.

best wishes

Dave

[pwelbourn]

HI Dave what do you mean by switching from oustside cuts to inside cuts, is there a option somewhere ? , is the beam width the kerf

Cheers

[Spooky]

Hiya,

Imagine you are wanting a 50mm square piece, you set the steppers to cut that size and the piece that falls out with be 50mm x 50mm, the hole it leave behind will be 50mm (+kerf) x 50mm (+ kerf) (about 50.5 to 50.8) so all good and you get a 50mm sqaure piece cut out.

With the steppers set like that though if you come to cut a job that requires a 50mm HOLE to be left behind the sizes will be wrong if you set the laser to cut 50 x 50.

Beam width is the spot size the laser produces, that spot is a combination of wavelength of the beam + beam profile + TEM mode.

Kerf size is all the above + burnback (you will always have a line wider than the actual beam as the material either side of the cuts vaporises). I don't know if NewlyDraw has the option to set inside or outside cut, Lasercut does but I rarely use it as many of the jobs I do require both inside and outside cuts on the same sheet.
I tend to have the steppers set to give me a good average between the two to reduce fiddling with stepper counts. so if I set my machine to 50mm square I get a 49.7mm cut out piece and a 50.3mm hole.

Step count for the most part isn't a user setting that many people will want to mess with, it's easy to get it wrong and outside of "user serviceable" adjustment much of the time.

A big industrial laser has all sorts of compensation for inside/outside cutting as well as backlash elimination but home brew lasers rarely do under the £50K mark with machines that have those kind of features being closer to £200,000 and upwards.

best wishes

Dave

[PhillyDee]

I tend to have the steppers set to give me a good average between the two to reduce fiddling with stepper counts. so if I set my machine to 50mm square I get a 49.7mm cut out piece and a 50.3mm hole.

Step count for the most part isn't a user setting that many people will want to mess with, it's easy to get it wrong and outside of "user serviceable" adjustment much of the time.

Just to reiterate especially the second point, it is a finiky setting to play with, and be aware that thermal expansion of the cut parts can also be a factor. I do as spooky says above, and have a balance between, but it can still vary depending on material and kerf at the time. I am not a fan of playing with the stepper values, since it can go horribly wrong with a misplaced decimal or value!

[pwelbourn]

What are the steppers you talk about, where you find this option and also on laser cut where is the option so you can choose inner or outer cut

cheers

[PhillyDee]

Machine Options ->
Worktable

And on that screen you have X Axis and Y Axis, the box has Pulse Unit in it. Adjusting this adjust how far a single pulse on the motor moves the table. Adjust this with caution, and make sure you write down the previous value and any other changed value. You actually have to adjust these when using a rotary axis, which I dislike doing personally.

You then Save (not close) and then you need to download the new parameters to the machine by clicking DownLoad and then Download CFG.

I accept no liability or responsibility if you banjo the machine.

[Spooky]

Ummm I'd seriously recommend NOT messing with steps counts unless you speak to HPC first.

cheers

Dave

[robburge@sky.com]

Hi

I discovered that my machine (3060) cuts over size too. But rather than messing around with steps and stuff why not just adjust your drawings? Here is what I do:

Draw a line ( or two marks apart) of known length as near to the maximum length as you can (on my machine a 500mm line or marks would do fine)

Mark it with your laser on something stable e.g a strip of mdf

Measure the result carefully and note the difference to what's expected.

Scale the dxf drawing down incrementally until the laser marks match your ruler measurement.

On my machine, if I need an exact real-world size, I scale my drawings by 0.987 to get a near-as-dammit result. (Yours would differ). Most of the time, though, its not critical and I don't bother.

Rob