Cutting Foam

One of the drawbacks of our hobby is the large amount of instruments that we have to carry with us in each observing session: lenses, scope finders, cameras, cables, laptops, laser, filters and so on. And the problem is that it is not unusual to forget one of those objects at home, or even worse, at our observation site and then loose it.

To avoid this kind of situations many of us have created some suitcases in which we organize every astronomical gadget we have. In particular we have bought some good quality suitcases at  Berwall (german online shop).

Once we got our suitcase we have to accomodate every instrument on it. There are several way to do that, but one of the best that we have found is to cut a high density foam and thus adapt every single gadget on it:

But... how do we cut that foam with the shapes of our instruments? That is what we are going to explain in the following.

Ingredients for one suitcase:

• Piece of foam that we want to cut: We have used a high density foam which can usually be bought in any mattress shop. Usually you have to specify the exact dimensions you need and they will prepare it for you.
• A workbench: We will need some free space to work in a confortable way. The foam has to sommthly slide over our working space, so we have used a plywood piece to achieve a smoother slide.
• A nail: We will hammer it to the workbench and we will tie an electrical wire and the hot wire to it.
• A spring: We bought it in a hardware store. It allows the hot wire to be tight even when it gets hot and dilates.
• Hot wire: The foam will get cut with a hot wire. We have tried different possibilities according o different suggestions found on the Internet: The wire from a resistor, the wire from the brake of a bicicle... but in the end, the best option is to use a Nichrome wire because it remains quite strong even at high temperatures. This wires are quite expensive, but you can get one at a very reasonable price buying a bad quality hairdryer in a Chinese bazar (5 €). The resistors that this devices usually use are made of this kind of wires.
• A Crochet needle: This kind of needles have a small hook that can be used to drill the foam and to pull the hot wire through the foam and attach it to the nail in the workbench.
• A laptop power supply: To get the hot wire hot we will make some electrical power go through it. We have used a laptop power supply to do it. Our power supply allow us to adjust the output voltage which was useful to obtain the exact temperature that we needed. However, the final temperature of the hot wire depends not only in the voltage of the power supply but also of the wire lenght and section. So, some previous testing is needed prior to the actual cutting.
• A pair of electrical wires: To connect the power supply to the hot wire we used a pair of standar electrical cables. This cables must not be very slim to avoid them heating.
• Paper: We will use it to draw some templates that we will use to guide the cutting wire. The paper should be hard enough (maybe card is better) as it may help you to make the cut accurately.
• Pencil: To draw the templates.
• Scissors: To cut the templates.
• Pins: To fix the templates to the foam as we cut.

General Scheme of our "cutting device"

This is a generic scheme of our cutting device. It is not difficult to set up, but maybe the most difficult thing to do is to adjust the hot wire length and the voltage of the power supply in order to get the wire hot enough but not so hot. In our case, around 50cm of wire and a voltage of 18V allow us to produce an accurate cut on the foam. Take into account that a very hot wire may make the foam to "rejoin" once they are cutted. Of course, if the wire gets red-hot (it has happened to us several times) it will probably break and you'll have to replace it.

Steps to cut the foam:

• Place all your instruments over the foam and arrange them to use the most of the space you have to store gadgets. It is interesting to leave at least 1cm between every object to really protect them and avoid that a knock or sudden move of the suitcase damages them. This point is not as simple as it looks as there are always dozens of elements to be stored in the suitcase. It is also interesting to think about future gadgets that we are planning to buy and leave some empty space for them. It is also convenient to carefully think about the placement of each instrument and take care of the 3 dimensions that we have. For example, it is usual nicer to the sight to place lenses in an horizontal way, whilst putting them in a vertical way will allow us to save lots of space.
• Draw the outline of each instrument in the paper sheets. You have to draw the templates as accurately as possible to avoid looseness once the foam is cutted.
• We cut the templates. Make sure you don't leave any burrs as later on the hot wire can get stucked in them. In the photo you can see Zerjillo cutting the template for a SW ED 80.

• We spear the templates with the pins into the foam (each one in its place). We have to be careful to put the pins as vertical as possible to avoid the hot wire getting stuck with them. It is interesting to use many pins per template as having only a few pins may make the template to move or blend during the cutting. To save time we usually prepare more than one template at each time:

• We use the crochet needle to drill the foam. We will spear it from the bottom side (not the template one but the opposite) and we pierce the foam completely (it may be more or less difficult depending on the foam thickness). We will try that the tip of the needle (the hook) arises just below one of the templates but very near to the border of it. If we miss the exit point, we remove the needle and start again this step.
• We hook the hot wire to the needle (the power supply must be unplugged at this point!) and we pull the needle out making the hot wire go through the foam. We will hook the hot wire to the nail in the workbench. The hot wire must be tense enough and as vertical as possible.
• We plug the power supply. Inmediately the wire will get hot (be careful not to touch it) and it will begin to cut the foam. We must then move the foam slowly following the template edge as accurately as possible. One important remark: the hot wire will have more inertia than one could initially think. That means that, specially at hard turns, the wire will continue its movement in its previous direction. Thus, it is important to move the foam slowly. In the photo you can see Antonio cutting some pieces of foam:

• Once we hav finished one template we unplug the powre supply, the hot wire will get cold and we will remove it using the crochet needle. We can then remove the cutted foam piece... and we can fit our instrument on the hole. We should not get annoyed if the bottom part of the hole is much more irregular than the upper part of it. It is normal and it happens because the hot wire is not always completely vertical and because we are moving the foam just looking at the upper side of it. In any case, this much more irregular cut is not usually visible and will not greatelly affect to the tightness of our pieces in the foam:

• A final step is tu cut a layer of the removed foam piece that we will insert into the hole to avoid our gadget getting too deep in the foam. In this last step we usually have to measure the thickness of this layer and cut it using the hot wire, which is usually easier because the piece of foam is much more easier to control.

And we just have to repeat this process for each template we have in order to prepare our foam for each one of our instruments.