Question about cutting thickness for MDF and also flaming.

[Robert Silvers]

I did 95% power of my RECI Z4 100 watt with 2 inch lens on 1/2 inch thick MDF with focus on the surface.

At 10mm/sec, it went about 9mm though. It was enough so that when I bent the board, it easily sheared on the cut line.

But then I tried cutting out a 10mm circle. I had to go all the way to to 3mm/sec AND I had to focus in the middle of the board. Lots of charring.

Why was it so hard to go 12.7mm when it can so easily go 9.2mm? Does this mean that I need a 4 inch lens? The depth of field is greater so that helps. But the spot size doubles so that hurts. I am not sure which wins in the end.

Question two - I get flaming, and I am concerned the flame will damage the auto focus probe or the aiming laser or the nozzle. My compressor is going, but it is the standard small one, and does not blow much air. Do I want to find a way to hook up a real compressor? How can I adapt a real compressor to that snap in tubing? Should I?

[Dave Sheldrake]

A Z4 isn't going to cut 1/2 inch MDF Rob without charring and very slow speeds.

I run a 180 watt ZX1850 at peak with 12 cfm of air at 40 psi on one of my machines and that doesn't like MDF anything over 9mm.

Laser cutting is a product of the inverse square law and the exponential function when it comes to power Vs thickness.

When a laser cuts it generates 2 by products that make our job a lot harder, free carbon particulates and CO2 gas, both of which do a very good job of blocking 10,600 nm wavelength radiation.

As a basic rule, twice the thickness = 1/4 the speed at the same power or 4 x the power for the same speed.

cheers

Dave

[Robert Silvers]

Thanks. What is my practical thickness limit for acrylic?

[Dave Sheldrake]

@100 watts I would say 10 - 12mm, it will cut more but it will be slow and heat will become a problem. 15-16mm is good for a 150 watt with 20mm being a realistic limit for a 180 watt.

In truth a 1 watt laser will cut 1 meter thick acrylic eventually(weeks not hours), but theory aside the above will still give somewhere near sensible speeds. Every day I hear all sorts of "claims" about what lasers will do but from a business use standpoint lasers don't like thick materials.

The one that always makes me giggle?

"Our 40 watt lasers cuts up to 35mm acrylic" and I'm sure it does but cutting a 20mm diameter circle once a week isn't much use to most businesses ;)

cheers

Dave

[Robert Silvers]

Just tried 1/4 inch MDF at 95% and 10mm/second and it worked well. I will try faster speeds.

I still think I need more air.

[Dave Sheldrake]

Air is essential Rob but needs to be applied carefully to get the full benefit.Co-Axial works well with a 2.5mm exit hole and a 3mm standoff from the job, what you are trying to do is extend the kerf to the nozzle to reduce vortexing and loss of pressure by deflected air. Reducing the air exit hole in the nozzle will reduce the air requirement and give better directed pressure.

Your test speeds on 1/4 mdf will be the norm when the tube settles aback to it's normal range (RECI tubes peak when new for around 6 to 8 weeks) I would counsel a reduction in power and keep the same speed to reduce load on the tube. More power is often less when it comes to thicker material.

I've spent the last 2 years working on nozzles for Chinese lasers and the results are worlds apart when you get it right.

cheers

Dave