Squeezing a K40 laser engraver, part 1.

So, What do you get when you buy a K40 laser machine?

  1. 200x200mm engraving area.
  2. 300x200mm cutting area.
  3. Rubbish usb controller PLUS usb key, wich will reset itself for no reason sometimes.
  4. Even more shitty cutting software.

While engraving is fine, it is not dependable. You can’t etch and then cut in a reliable way (often, it will have about +-0,5mm drift, if not more) and cutting, due to software, is about the shittiest thing you can throw to anyone’s face. It is somewhat usable, but frankly, I’ve been driven nuts, then insane, by the software. It requires you to learn tons of tricks in aligning two works, it never saves your desired settings for different materials (altough it says it does) and the list goes on and on…

You just bought a cheap (mumble with me) EN-GRA-VER, got it?

So, what do you do (change) after you have extracted the most of the thing “as is”? (wich is not much, by the way)

I’ll make a post on each topic, and link it here when it’s done.

Let’s begin, shall we?

1st. Controller:

Let’s be honest, the controller in the laser is not that bad really. It moves around the stages, quite fast while engraving, it’s silent and it handles the return to home all by itself. However, it all goes down the drain because of the software, but that will be covered in the next topic.

Right now, we will talk about the controller you will use once you realize that a decent software is needed. You’ll also probably go the parallel port route, because it is still very easy to find computers with parallel port at cheapass prices, and you can monitor and troubleshoot it if needed, unlike a USB port, where you needed a decent scope and knowledge of what you’re doing.

So, I had bought a TB6560 CNC board at first, but having to rework the flat cable of the X axis to connect it to the board, just didn’t appeal to me (pure procrastination, not that I can’t do it) so I continued with moshittisoft for a little longer…until one day I found this board that I could throw in directly and would solve all my problems…would it?

I don’t blame it on the board itself, it looks nice and does what it needs to do, however, the drivers (polulu) just don’t cut it. Their current chopping is just AWFUL! and made the motors noisy even at the lowest possible setting. Also, one of the drivers died on me with no apparent reason (remember, direct replacement, I could not do anything wrong).  I’m sorry chris, just change the drivers to something better.

So, I continued some more with the original shittycontroller and moshittysoftware, but it was just a question of time vs insanity until I could no longer endure the lack of precision, repeatability, functionality and more “ity’s” that you can think of. (seriously, if you haven’t tried it, you can’t imagine how bad it is)

Moshidraw-2014r

While on holiday, I decided it was time to do what I had to do and spent a couple of days working on it. For a brief period I changed to the TB6560, and things were…acceptable. Not that it was the best solution, tough.

First, those CNC boards do not have especially good design (overworked 5V regulators, slow speed optocouplers and other things pretty much covered in any google search for “TB6560 board repair”.

My share of mods included the dreadful double inversion of signals through a schmith trigger (7414) to clean up the signal flanks, dealing with reversed microsepping DIP switch configurations and changing the sense resistors to enable “higher” setup current. What I mean is that, at “low currents” other than the max configured by the Rsense, what it does is a very bad chopping, that becomes audible as you configure lower and lower currents (25/50/75%). So, by decreasing the max current by Rsense, you can reduce chopping to a minimum. (can’t remember if more or less resistance, but doesn’t matter, if this post doesn’t convince you to change or NOT to buy that board, I can’t help you further, mainly because I’m a lazy bastard) (grin)

125c - CNC controllersSee what I had to do? (cries)

I had this setup around for about six months, until I decided to finally install the end limits, and after cleaning all the cable mess I had inside the machine, inadvertently trapped and shorted a pair of cables of one motor. When I powered the machine, the blue smoke of chip death welcomed me. So, back at square zero…what was I going to do?

For a while, I thought about buying the same board, because I already knew it, drawbacks and so forth. On the other hand, I considered the following: A suposed update on the TB6560 board, and a complete Module based controller.

125 - CNC controllers

The diference in price was not that much (90$ for the Modules vs 50$ for any of the other boards, including shipping) and after I found (and sort of remembered) that the chinese keep on cycling those two boards (when I bought the blue ones, I remember them being the “new” ones, and the red version was the older) decided for the Modules. Also, I looked up the longsmotor name, and it belongs to a chinese company that makes stepper motors and stepper drivers so…It should be at least as good or bad as the other board was.

So along came the drivers, and I swiftly installed them.

125b - CNC controllersSo neat. ^_^

ATTENTION: Those modules come in different current ranges! If you do, pick up the one with lowest max current (mine was 2A RMS, DM420A) otherwise, the minimum current might be too much for your motors! (just like the TB6560, but unlike that, this one works well at minimum currents).

Oh boy, that was like a dream. Probably you can buy even better, brand name drivers, and they will perform even better than these ones, but since this is a cheapass laser, this driver is so much good than all the other things combined that I could not be more pleased. Current chopping is good at any level, Smothness in microstepping is really good, and it has half current holding switch, so you can drive the motors harder, but let them cool when not in movement, whilist mantaining a suficient holding torque.

Microstepping is (big quote marks) really good, as current control is (no more dreadful less-than-20Khz-chopping). I am so much happy with it, you probably can’t understand, you had to be there. (clenches his lilac)

By the way, this is the motor pinout for the Y axis, in case you want to rework them. I can’t remember if the X axis had the same colors, but you should have a tester around to identify the coils, and advance from there.

  • RED            -> A+
  • BLUE         -> A-
  • YELLOW  -> B+
  • WHITE     -> B-

Next post (whenever that is) in the series:

Software

And why moshisoft programmers should disembowel themselves with a USB connector.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s