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How to build a custom metal shroud

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vbbartlett

Registered
Joined
Apr 24, 2002
Location
Denver
There have been questions about working with sheet metal to create a shroud, so I said I would write a little [edit:long] how-to/tips for creating a shroud.

Please note that this is directed toward how to create a shroud, it is not designed to give you the best design. Although I will describe how to create different styles of shrouds, I have no experience with the efficiency of these designs. With that disclaimer lets get to it.

The first step is to have a heater core and fans. For instance the shroud that I last made was for the 77 b'ville and I wanted to use 3-92mm fans. When choosing the fan sizes I often refer to this site for help and information about airflow, fan speed and noise. Remember that the purpose of a shroud is to help direct efficient airflow through the heater core. But efficient airflow also has to consider the noise generated by the fans. One of the nice properties of water cooling is the fact that the machine should be quieter than it was originally... And just like a water flow through water blocks, the more air that is moved throught the heater core the more effective the heater core will be. So if you are only considering performance of the heater core, choose large fans that are capable of moving massive amount of air.

Anyway once you have selected the heater core and have considered how much air flow you want, you should next determine how the shroud will attack to the heater core and how and where it will attach inside/outside the case. This decision will drasticallly effect the design you will create.

For the purposes of this discussion I will consider the venturi style since it is actually the most difficult to measure and design. Most other designs use the basics of this style with simplier measurements and angles. Second I want to attache the shroud to the top of the case, which will mean that I will also end up doing a case mod.

Next I needed to determine whether the fans should be mounted on the inside or the outside of the shroud. I do not know whether this has any effect on the cooling effect of the shroud, other than to say that the distance between the fans and the heater core should be at least 1" apart min.

Lets take a brief moment to discuss this. One of the reasons for a shroud is to move the fan away from the core because the center of the fan has a dead spot. ie not air moves through that area. And if the fan is directly mounted to the heater core there is an area directly under the fan that has stagnant air and is not being cooled. This will decreate the permormance of any heater core.

So by determine whether you will mount the fans inside the shroud or outside, you will be able to determine the approximate height that you will create the shroud. In my case I want the shroud on the top of my case and the fans located inside much like this case design.

DESIGN
Now for the good stuff, designing the shroud. This is probably the most difficult part of the whole process. If you get any of the angles wrong it won't fit together properly and you have waste time and energy and a couple bucks. But here are some tips and tricks to making the venturi shroud.

Tip 1: Allow for 1/8-1/4 " at each bending point because each corner will not be a precise corner, it will actually be rounded. If you do not allow for this, your shrouds will not be the correct height or width.

First step is to measure the "mouth" of the shroud. The mouth of the shroud is where it will attach to the heater core. Usually you will want this to be only the actual heater core size and not the entire heater. However in my case I am designing a bit more complex of a shroud.

For my heater core and shroud the mouth will be 5 3/4" (added 1/8" to the actual size since this shroud will have sides) x 12 1/2"

Next determine the size of the throat, this is usually where the fans attach and is the smaller than the mouth of the shroud. In my case the throat will be 3 3/4 (actual 92 is 3.62") by 11"(actual dist is 10.87") This size will leave just enough room to fit the fans inside after I have bent the sheet metal.

Ok simple so far right? next you have to decide whether you want a symetrical look or something that is non symectrical. In my case I wanted the front/sides to have the same slope while the back had a much steeper slope. Where you place the throat will determine if it is symetrical or not. As in the Mouth & Throat design you will notice that I have an 1" around the front & sides while the back only has 1/2". This will produce a steeper slope on the shroud. The closer the throat is to the mouth the steeper the sides will be. Make sense? if the mouth and throat are the same size you basically have a rectangle...

Now take the lines one the mouth and extend them as shown in the pic. Now you determine the height of the shroud. In my case I want to put the fans on the inside and want at least 1" clearance. So I chose 2" high, a nice even number. Now based on this you figure out how long each side will be. For those that have been through geometry this should be obvious, a² + b² = c² (eq. distances of each side of a 90º triagle).

So in this case I have a 1" distance from the throat to the mouth and 2" high so i get 1²+2² = 5 thus c = sqrt(5)= 2.23 ˜ 2 1/4" (always round up) this is for the front and sides. The back is slightly different, .5²+2² = 4.25² = 2.062 ˜ 2 1/16. Using these values, measure away from each side the correct distance and draw a line parallel with that side. pic

Well if you are thinking ok where is the hard part? well that was it! Doing it this way makes use of geometry without involving any calc/trig/angles. So basically you draw lines from the corners of the throat to the intersection points of each side and mouth line. See the pic for specifics.
With Fans.
Final Design.

So now we have the basic design of the shroud. For my shroud I wanted sides, so I extend all the sides. I will explain all the extra lines later. But before the shroud design is complete, we need to decide how we are going to attach the sides of the shroud together. For myself, i have a friend that allows me to use his mig welder, So I can simply cut the edges EXACT and the stitch them together with the welder. however many of you probably don't have access to one and since they are ... kinda... expensive you may way to look into other alternatives. I have seen dual gas torches and welding sticks for a minimal cost. Sticks were $3 and the torches were $30ish at Home depot. I haven't seen the welding sticks anywhere else though and haven't actually used them so I don't know how well they will work. The other two alternatives are as easy and cheap. The first and strongest is to rivel the sides together. This provides a strong connection between each side however bending and aligning the peices are sometimes difficult. I will talk about riveting in a few moments. The third is simply jb weld or epoxy. This is probably the weakest of joints but is proably the easiest of the last two options to get correct. This simply involves roughing up the inside of the metal, firly taping the outside and fillng the joint with jb weld(epoxy) and letting it set up. However you do have to be careful as I have had the jb wel pop off the metal (of course i welded the corner and was using the jb as filler and didn't rough up the metal, and i was pounding on that edge with a hammer... :) )

Ok back to welding, Im working with 26 ga. plate metal so I can weld it together but I have to be VERY careful as it is EXTREMELY easy to blow holes in the corners you are welding. I have discovered that I can only stitch outside corners. Any inside welding just causes holes. Another note is that welding Aluminum is very difficult and should be taken into consideration when you decide how to put the shroud together. I would buy or use scrap aluminum to test welding on before you ever try it on your shroud.

Now rivetting, here are a couple tips/tricks to getting a good corner.

Tip 2: find the correct length rivets first!
Tip 3: make shallow tabs (pic)
design with a tab.
Tip 4: make these bends as precise as posible and usually first. putting them in a vice and pounding with a hammer will prevent the round corners and will help with creating a nice corner.
Tip 5: tape the corner together and then drill the hole into a scrap wood block drilling from the inside.
Tip 6: rivet from the outside as this will create a nice look to the end product

Ok so back to our design, now you need to select a piece of metal big enough for the design and transfer the design to the metal. The easiest way I found was simply redraw the entire thing again. I usually try to either center it in the piece of metal as Im going to use the entire sheet, or put as many edges on the factory edges to limit the number of cuts.

So now you should have your design layed out on sheet of plate metal(in my case) Now to begin cutting. I use a pair of metal sheers to cut the striaght cuts and a dremel and cutoff wheel for the angle cuts. Although this took a bit longer and I went through several cutoff wheels in the process, I had a much nicer and more precise cut in the end. If you use the metal sheers try never to "finish" the cut, alway stop the cut before the end of the sheers as it leaves a nasty bend in the metal. If you do end up finishing a cut, place the metal on the floor (cement) and pounding it flat with a hammer. When cutting with metal sheers always make sure to bend the scrap side of the cut away fromt he sheers to help keep the sheers from binding and twisting.

Bending the metal:
You will need a small strong flat edge. I used an old paint brush stirrer and although it wasn't as strong as I would have liked, it did work. You will also need some sort of C clamps, the larger the better, and something salid and flat such as a small 2x4. Placing the straight edge on the inside of the bend directly on the line that will be bent, clamp it in place tightly. now take the 2x4 or what ever you have come up with and place it on the back side of the metal opposite of where the straight edge is and press firmly bending the metal to the approximate angle you want. If you have a large vise, the more power to you as it will make this process a bit easier. If you place the metal in the vice and use the jaws of the vice as your straight edge you should be able to obtain a nicer and sharper corner. (more precision!) Now take a hammer and tap right next to the bend. This will help flaten the bend out and make it less rounded. With 26 ga, I was also able to use my thumb and a lot of pressure to sharpen the corner. Hopefully some one knows what I am talking about here and can get you some pictures to make this part clearer.

Ok now that you have a shroud you are looking at it thinking, hmmm should there be holes in the throat??? Answer is ... no, the reason for this is that bending the metal is much easier when you are dealing with a solid sheet. if you cut the holes for the fans earlier, it will make bending the metal that much harder.

Base on your design and available tools glue/weld/rivot the shroud together. Try to leave as little or not gap in each corner being attached. if there is any gap i would suggest filling it with jb weld or silicone. The more air tight the shroud the better the performance!

Now you should have a reasonable looking shroud minus some fan holes... To create a nice looking hole I would suggest actually drilling the holes for the fans first. Using these holes I take a standard fan gril and using the outside ring mark out the size of the hole to be cut. Cutting a round hole in metal is on par with swimming up stream and making progress... so unless you can find a corner cutting sheer that will cut a tight enough circle, i go back to the dremel this time using a router bit made for metal. It is a "FUN" job but it is the only way I have been able to come up with to cut the holes in the metal

Tip 7: When ever using a dremel and sheet metal use safety glasses and EAR PLUGS.

I have proably killed my hearing because I didn't use ear plugs.

So we are getting closer, now we need to mount the shroud to the heater. When mounting the shroud to the heater core, either use a foam and silicone to seal it. (Oh make sure that the fans are attached and it is painted if you desire)

To mount the shroud and heater core you can use long bolts as described in this tutorial or as in my case i used the heater cores own ends to secure the core in place.

For those that want to mound the shroud directly to the case there are several ways. If you take a design like mine, and bend flaps out along the bottom edge of the shroud you can rivet or (screw rivet the shroud directly to the case. simple easy and cheap. For mine, Im simply cutting a rectangle in the top of my case and setting the shroude in it. The shroud will be held up by the front and back of the shroud which have been bent in to provide ledges for the shroud to sit on.

...

more to come
 
This is a bump so people can see this thread without having to change the display options of the forum.

I used this guide to make my shrouds, and they work nicely. Good job vbbartlett.
 
Why not?

It may not be a sticky, but atleast here people will be able to see it without having to search. It seems sticky worthy to me, as it is pretty complete.
 
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