Enclosure and extractor fan

Hi,

In case its of any value to others, I thought I'd post my experiences so far with building an enclosure for my MendleMax.



I built the enclosure for several reasons.

1. Smell of ABS in the house was very strong, and I know is not good for the health.
2. I had problems with ABS warping due to it cooling too quickly e.g. if the air temperature in the room was low e.g. 10 deg C, as I had to have the window open because of the smell of ABS
3. Print bed took ages to heat to 115 deg (for ABS) due to convection cooling.


I built the enclosure from wood etc I already had left over from house renovations etc, (apart from the acrylic sheet which I had to buy, and cost $30 (AU) for 2 x as much as I needed).
Consequentially, the appearance of the enclosure isn't as funky as some other's I've seen, where people have used aluminium box section to make a cube, and completely surrounded it in acrylic sheet (aka Plexiglass) - but this would have been a much higher cost option than re-using material I mostly already had.

The sides are 3mm MDF sheet. The frame is approx 20mm square wood (pine). I used some metal picture frame brackets (I already had) to help construct the base.

I was concerned about the temperature inside the enclosure effecting the RAMPS and the mains PSU, so I have mounted them externally.
Well, what I did was bought a large plastic food box, for $4, and cut a rectangle out of the back of the enclosure, and glued the box into the enclosure, so that the electronics and PSU, are physically inside the enclosure, but are divided from the internal temperature, but the plastic box. The back of the box (actually the top of the box), is left open, so that the PSU and RAMPS can get air directly from the room.

The enclosure works well. Without the extractor fan, with just a 25mm hole in the top, the temperature inside the enclosure goes up by around 15 to deg C during a long print, i.e from around 15 deg to around 30 deg C.
I have not measured the temperature with the fan turned on, but I suspect its the same, as (read below) the current extraction system is not very effective.

ABS doesn't warp and the motors don't seem to get excessively hot even without fans. (i.e they are just warm to the touch).

One thing that doesn't work as well as I'd like is the extraction system.

I already had some 25mm flexible electrical conduit (pipe), which is around 4m long - which I decided to use for the extractor duct. And I designed and printed an adapter (see extractor_pipe.jpg), between the fan and the pipe.

However the 40mm fan doesn't push enough air though the conduit to completely suppress the smell of ABS in the room. Its 90% better, but its not perfect.

This problem is partially a combination of the small size of the conduit, the length of the conduit needed to go out the window (4 m) and also the shape of the conduit (its a sort of helical construction, which would impede the flow of air).
However the primary problem is that a 40mm fan is inadequate to push enough air to compensate for the small air gaps I have between the acrylic and the front of the box, and the holes at the back where the electrics wires go though.

So I'm going to replace the 40mm fan with a 80mm fan (I took out of a PC power supply). But I'll also need to design and print a new adapter first.

If I find that even with 80mm fan, I'm getting insufficient air flow, I'm hoping to use a long hose from a vacuum cleaner instead.

Anyway. I hope this info may be useful to anyone else thinking of doing the same thing.


Cheers

Roger

Edited 2 time(s). Last edit at 10/26/2013 07:27PM by rogerclark.

Hi..

Just thinking... Instead of a single 80mm fan, the problem might be "coverage".

You could try 2 x 40mm fan, 1 each side ?

We have a laser that smells pretty bad, that has a 80mm fan, (might even be 100), but it just doesn't cut the mustard, because fumes come out of the side where the fan isn't.

I wonder if 2 x small fans will work better than 1 big one ?

Also, presuming the box isn't air tight, is there somewhere for the air to go in ? If the box is pretty airtight, then it needs a vent at the opposite side to the fan.

cheers

Dave.



having had another look at the pics, looks pretty airtight,.. I reckon you need some small vents down the bottom/front to let the air flow in that will then be extracted with the fumes.

Edited 2 time(s). Last edit at 10/26/2013 07:47PM by DaveS.

Hi Dave,

I've noticed that due inaccuracies in my woodwork, that there are some 1mm gaps at the sides of the acrylic front panel.

I'm contemplating using some window draft excluder, (the stuff that about 1cm side strip of foam rubber with the self adhesive backing, but I'm not sure if it would start to come unstuck when the enclosure gets to 40 deg inside.

I may use some exterior grade, clear, silicon sealant that I have, as its rated for metal roofing, which gets very hot.
I've found from doing home renovation, that silicon sealant doesn't stick to soapy (detergent) covered surfaces, so the trick is to put detergent on the acrylic, then put a bead of silicon sealant down where the gaps are. Close the door (or window etc), then wait a few hours for the silicon to set.
You can then open the window, as most of the time the silicon sealant hasn't stuck to the surface that had detergent on it.

Re: Having 2 x 40mm fans.
I'm not sure this would be enough. I get hardly any draft even if I remove the conduit tube, so I'm pretty sure using a larger fan is going to be necessary.

I need to create a negative pressure so that all of the air gaps have air being drawn in though them, albeit I want to minimise this as it would cause excessive cooling if I'm not carefull

I'm just designing a fan adaptor plate in OpenSCad at the moment, so I'll let you know how I get on with a 80mm fan.

I use these type of fans, may have been my setup, but they never were powerful enough to push much if any air at all though my pipes.

I had to use a squirrel cage style fan and got a little bit better airflow

@nechaus

Just tested a 80mm fan, and it didn't push any air into my 25mm tube. However if I added a 50mm length tube between the fan and the reducer cone shape, I get some air flow.

I probably need to use a centrifugal fan, but don't have one, so I'm going to see if there are any duct shapes e.g. Spiral that may help

Hi Roger..

you're sort of missing the point... you need holes... you DO NOT want an airtight box. (I'm very into air moving, I have a race car, and some things are counter intuitive when it comes to aerodynamics)

Looking at my little 40mm fan on my reprap I use for cooling, I reckon it moves air at about 10cm a second. Put yours in free air.. you'll feel a nice breeze coming off it.

It's a 40mm fan, so it moves 4x10 cm cubed of air a second.

So... Takes it about 25 seconds to move a LITRE of air. That's not bad. That means you can expel a litre of air from your case every 25 seconds.

Now.. unless you are expecting to use it as a vacuum pump.. you need a litre of CLEAN air entering your case every 25 seconds.
So.. what you do is make some holes at the front bottom of the case, to let that litre in. Nice clean air will come in those holes, and exit out of the top.

Try it... put a pencil under the front of the case so that you have a big gap running along the front of the case. Start the fan.. light a match and blow it out so you get some smoke,,.. and move that along that gap.
You'll see the smoke travel, through the case.. and out of the top,.. (actually you'll probably just see it sucked into the case)

anyway...

common mistake.. Holes will make a massive difference to your extraction rate... you need to let air in. I'm pretty sure your 40mm fan will be big enough, if you ventilate the case properly, and consider the air flow it's creating.
Where that air is moving.

cheers

Dave

Hi Dave,

I see what you mean. But I've actually got quite a few holes where air could enter the cabinet, e.g. though the holes I've drilled at the back for the motor wires etc, as well as unintentional gaps between the acrylic sheet and the front of the enclosure.

The problem seems to be that the fans I have are the standard axial ones, which are designed for high flow rate, but don't blow at much pressure.

I was hoping to use existing fans that I already salvaged from PC power supplies etc, but it looks like I need a centrifugal fan that is capable of generating some pressure.

Although I suppose I could print out a centrifugal fan from one of the designs on Thingiverse, I suspect it would be hard attach to my existing fan motors, so I may as well just buy one of the "blower fans" from eBay
e.g. [www.ebay.com.au]

Thanks

Roger

Hi Roger,
Nice cabinet - quite similar to mine except I used some 4.5mm MDF for the carcase. My electronics is located at the rear left with an opening for the connections. A fan on top of the Arduino/ramps case draws air in from outside through an intake manifold.
My cabinet temp gets to around 40C without additional heating - gonna put something in there to raise it higher when I get time. I'm surprised you have such issues with ABS odours - I can barely notice it, if at all (maybe some ABS filament stinks worse than others?).

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Waitaki 3D Printer

Thanks for posting this guys, I'm thinking of making one at some point.

Waitaki, it looks like you made your Mendel frame out of wood as well?

@waitaki

Actually the ABS smell is not that bad even running the small 40mm fan. I've doubled checked and its pushing out more air than I'd realised.
I as hoping for no smell of ABS at all, but I've realised that it mainly smells if I have to open the cabinet just before the print starts, to get rid of excess extruded filament hanging out of the hot end.

I have ordered a small "blower" type fan (from eBay for $1.50), so I'll see if that works any better than a normal axial fan.

Re: Internal temperature.
I double checked yesterday on a small print that took just over an hour, and the internal temperature was still around 30deg (which is similar to when I wasn't using the fan, and just had a 25mm dia hole in the top of the cabinet.

I guess it depends on the temperature of the incoming air. Its been relatively cold here recently, so with the window open, the room with the printer in it is only at around 15 degrees C.

I was going to fit a mains powered lamp inside the cabinet, so that I can see how the print is getting on, so I could put a 100W filament bulb in the socket instead of a low energy 22W. This would add 100W of heat to the inside of the cabinet, which would definitely increase the internal temperature. If that wasn't enough there are those "heat lamps" that are intended for use in bathrooms, which I believe are higher powered and give off mainly IR radiation i.e heat. But I'm not sure that having that much heat on the motors etc is a good thing ;-)

Re: side thickness.

I happened to have 3mm left over from another project and it seems to be thick enough, as I have strengthening sections of wood down each edge. You could probably achieve the same result with 4 or 5mm plywood, and probably only need some of those plastic joiner blocks at the corner (which you could print yourself).



Cheers

Roger

If you do decide to seal up the box, there are tapes made for that purpose. They are a bit ugly, but quite cheap. One of them is gray in color and was originally designed for duct work .....

Maybe try insulation foam to attempt to get it more air tight, then add another hose for air intake.

You could add a fan blowing air in too help, in conjunction with the fan blowing out the exhaust hose.

Thanks guys.


The box is pretty air tight apart from the front acrylic sheet and the back where I have drilled holes for the wires.

I painted it inside and out (with normal house paint), and this sealed up any small gaps between the sides.

I have "duct tape" (both the stuff with fabric and the real duct tape which doesn't have fabric in it), but if anything, I think that stick on draft excluder (for windows and doors) would be the best solution to air gaps around the acrylic sheet.

But overall, I've realised that I don't have much of a problem with this after all ;-)

NormandC Wrote:
-------------------------------------------------------
> Thanks for posting this guys, I'm thinking of
> making one at some point.
>
> Waitaki, it looks like you made your Mendel frame
> out of wood as well?


Yes, it's 18mm MDF frame and solid 18mm MDF base - I like robustness!

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Waitaki 3D Printer

@Waitaki

I used an 18mm plywood base, just because I had some wood left over from another project. And you are right, it makes it very robust. I actually screwed by MendelMax down onto the base board.

Computer fans have major issues with back pressure. Their air flow drops off quickly as you restrict things with a pipe or something similar. Blowers are designed differently and they handle the back pressure much better.