Good news / Bad news

Anything to do with air assist, vacuum tables, fume extraction and related...

Re: Good news / Bad news

Postby educa » Mon Dec 26, 2011 9:19 pm

Hi Dirk

This is my first post here on the forum, but I intend to post quite a lot.

I am looking for info to build my own laser cutter just like you guys all do.

The aim is to build a laser which accepts 121x61cm wood plates and acrylic, so its a rather large one. about 4'x2'

Currently I don't know if I'll go for 40 , 60 or 80 watt. The idea is currently to go 60 Watt from cnccoletech.

I found info about your PPI system and will try to understand your exact implementation. I'm also a atmel avr programmer (sometimes also arduino, but if needed I do also plain AVR which is much more powerfull for timing stuff)

If I understand right , then you have found out that the ignition of a laser is a lot more powerfull then the power it puts out in the rest of its burn cycle, so its better to ignite the laser for very short (3ms) pulses and instead of cutting you actually are perforating a row of holes... making the laser work less, provide more power and cut more clearly.

If I calculate right, then when you set a feedrate of 50mm/min at 1200PPI and a pulsewidth of 3ms, then the laser is only burning in about 118 milliseconds per second it is working and the other 882ms it is not burning at all. That means the laser is only on in 13.4% of the time and the rest of the time idle, making it run cooler and in meantime more powerfull ? Am I right with my calculations?

Now can I ask you how many steps has your machine for moving 1 inch in X/Y ? I suppose its the same steprate to ease things?

Also, I can clearly understand that, for example if you have 2000 steps per inch, you can count the steps on X or Y and know exactly how far the head has traveled, but what do you do then with the following example?

1) If X increases by 2000 steps, then the head moved 1 inch

2) If Y increases by 2000 steps, then the head moved 1 inch

3) If X AND Y increase by 2000 steps, then the head moved by 1.4142 inch !!!!!!!!!!!!!!!!!!!!!

Does your system count for that too ?

Kind regards,

Posts: 239
Joined: Thu Dec 22, 2011 9:13 pm

Re: Good news / Bad news

Postby dirktheeng » Mon Dec 26, 2011 9:32 pm

educa wrote:Hi Dirk

This is my first post here on the forum, but I intend to post quite a lot.


Kind regards,



Good to see that you are now on the forum and hoping to join us on what will be a very fun build. To keep this a bit cleaner, let's talk about this on the forum thread about the PPI control entitled: Getting more power and cutting accuracy out of your home built CNC Laser. I'll copy your post as a quote and respond there.
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Joined: Thu Sep 09, 2010 4:49 pm


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