• Improved Extraction

    Octavio.Makes04/27/2019 at 05:27 0 comments

    Edit: Fixed the thingiverse page with the STLs!

    This is the written project page for my video on the same topic: 

    This is the K40 laser cutter. The epitome of cheap Chinese manufacturing. Cheap enough to risk it, and just expensive enough to warrant some confidence. It is go-to laser cutter/engraver for makers on a budget, not only for its price but also for the community behind it. Which is very important, considering that its up to you to finish the manufacturing and to protect yourself from accidental fires due to poor wiring.

    My K40!

    The manufactures made quite a few compromises to make a machine this cheap. While some design choices were rather smart, many were, to put it lightly, hasty or desperate. So, it’s very common to see upgrades online that tries to fix these poor choices.

    This video is the start of a series of videos where we will make incremental upgrades to this laser cutter until we have fixed most, if not all, of the common ‘issues’ it came with.

    Among many of the issues common with this machine, I find the extraction system to be very frustrating. It’s probably because they threw a bathroom extractor on the box to be used as a smoke extractor. And since this machine is not exactly a bathroom then is not surprising it severely underperforms. So, I decided to start with here because of that and also because I already had all the parts I needed laying around.

    Let’s start by pointing out the issues of this extraction system first:

    1. The extractor’s fit is too loose: the manufacturers employed a slit-in system that allows us to quickly install and remove the extractor when needed. This, however, cause the fit to be excessively loose. The extractor sucks some air from the sides reducing overall airflow across the bed and allows some smoke to leak into the room.
    2. The extractor is too big: the base plate is unnecessarily big. This blocks access to the tube chamber and require us to unmount every time we want to look at the tube.
    3. The extractor is not powerful enough: this causes the airflow to become slow at the front end of the machine.
    The gap is huge.

    There are a ton of ways we can solve all of these issues and, if that is all we care about, then any solution that fixes the problem is a good solution. But we know that some solutions are better than others. In order to constrain the problem further let’s consider some design aspect that our exhaust system should have in addition of the fixes from before:

    1. Quick mounting and dismounting: the exhaust should be easily installed and removed without compromising the air-tightness
    2. Adjustable speed: this will allow us to regulate the speed to reduce noise production.

    Let’s start by selecting a fan.

    The best way to move air through the flexible duct is an inline blower. This is mainly because flexible ducts create a significant pressure drop that needs to be overcome and inline blowers sustain a bigger static pressure than regular fans. That means that for the same airflow, regular axial fans need more power and generates more noise than an inline blower. For short segments of flex duct, the drop in pressure is rather small and not a deal breaker.

    This is some serious fan power.

    While all of that is true, I went with a 120mm computer fan that the seller claims to be very powerful. According to the seller, this is a 12V 3.9A Axial Fan, capable of up to 252 CFM or 7.16m3/min (airflow at no load),1.41 in h2o or 35.88mm h2o of static pressure, runs at 4800 rpm with tachometer and pwm control and generates 65dBA of noise. It sells for about $20 which is good for this specs. I tested the current draw with my incredibly unscientific power supply, and it registered about 2.71A, which is way out of spec. Don’t be surprise if all of these specs are off. I’m still using this fan mostly because I already had it from university project that I sadly didn’t...

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