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Cal Kit inserts
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Hi group,
Much have and can be said about the dreadful inserts used in most expensive calibration kits that I've come across, but rarely anything positive. In case you haven't seen it, just look for used calibration kits at ebay. I don't know the specification of this material, but it don't last much longer than the warranty period. If you always use your cal kit regularly, you have time to notice any degradation and can react. If the kit is staying in the shelf for extended periods, you may not be so lucky. What alternatives do we have? Sometimes I visit old historical museums and find many interesting things sometimes also with a travel transport box, usually with nice colored velvet(?) fabric surrounding the precious piece of nobility history. How about this? Maybe supported by wood, for instance balsam wood, easy to carve and form to your liking and avoiding anything spelled plastics. Microfiber clothes looks tempting, but may be in the same class and risky to use? Maybe even a business idea for some entrepreneur with self respect. At least I would be prepared to pay. Any thoughts / flames ? |
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Hi Bo,
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You might find this thread useful: . A lot of the foam in cal kits tends to be polyurethane foam, which experiences long-term degradation in a way that results in corrosive goo. There's an interesting paper from the British Museum discussing how it corroded old metallic tokens (). There are a number of alternatives for replacement. Polyethylene foam is one choice and seems to last a long time. But, it's not soft like polyurethane foam. There's also neoprene foam, which is somewhere between polyurethane and polyethylene foam in terms of softness. It's a bit denser than polyurethane and takes more pressure to compress, but it works pretty well for many applications where polyurethane was used. These choices seem to be safe from the corrosive degradation, though I don't think this is known for sure, so it's probably best to check up on it every once in a while. And, for cal kits, use dust caps over the mating surfaces to protect it in case the foam degrades. All foam will degrade eventually, I've heard. The important thing is to avoid using a foam that turns corrosive. Matt On Sun, Dec 31, 2023 at 4:54?AM Bo in Finland <bfredr@...> wrote:
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I had a nice 3.5 mm cal kit which suffered from foam deterioration. A friend with a 3D printer designed a very nice and clever insert that will probably outlast the wood box.
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Probably the best solution available, IF you can come up with design and the printer. From Tom Holmes, N8ZM On Dec 31, 2023, at 12:35 PM, Matt Huszagh <huszaghmatt@...> wrote: |
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How about 3D printing the support, then surrounding it with foam as cushioning? ? (furniture seat covering foam seems reasonable). Foam never touches parts.
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Harvey On 12/31/2023 5:59 PM, Robert G8RPI via groups.io wrote:
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What I liked ot use is polyethelyene foam such as this on ebay:??? I find that it is very easy to cut, robust, and I believe that you can sometimes find it an ESD resistant pink.? It's not completely free, but not terribly expensive either.? I use this and cigar boxes to make custom boxes for my cal kits that I put together from odds and ends on epay.? Perhaps not the most brilliant solution, but it works for me.
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Thanks for several useful suggestions!
3D printing I did not think about as I lack a good friend with a printer and haven't so far created anything. I have at least 5 different kits including one from the groups admin. I've seen at the local library that they have 3D printers, so I could check if I can print there. Fairly hard, yes, but with soft fabrics in between, it should be doable with enough shock protection and leaving a gap to the box, again filled with soft fabric, should be safe for a small lab without the need for silk gloves even if accidentally dropped at the floor. The wooden box may be damaged though. Much bigger risk in a big hectic lab with many engineers with different discipline sharing the tools. Yes, the parts should never touch any kind of foam and preferably always have the dust caps on, at least when stored, so we need an extra compartment for all dust caps. I'm surprised the big companies still only offer polyurethane. I bought one such set for the company where I worked some years ago at a fairly high price. Yes, I read the abstract, so we are not alone with this problem. I've also seen destroyed loudspeakers and earphones using polyurethane foam internally. The worst part is that it corrodes the expensive objects we try to protect. The black polyethylene foam looks similar to what was used for ESD protection of various IC's and even this black foam fell apart to small particles although I never saw any meltings or corrosion issues. However, I may be wrong about what material was used for the earlier days of ESD protection. These were not meant to be stored for long, just for transport and short time storage. |
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I use the black closed cell poly foam for making up my field kits and have had no issues over the years with degradation or deterioration of the items placed in it.? I have several military test equipment in kits that are on the order of 20 years or more old and the poly foam is still lively and shows no signs of giving up.? For making up kits it is easy to work with using standard kitchen knives or such works to form the features in it.? Cavities are made by using separate layers of foam by cutting out the features in the top one(s) and installing a solid sheet below them as is the way that custom case manufacturers do.? A touch of cooler hot glue between layers creates a solid insert (deft use of cooler hot glue prevents melting the foam when assembling the layers) ? When making my own foam inserts I use a company (Club Cases) who provides the foam cut to order.? Prices are not necessarily cheap but I order large sheets which reduces the per unit cost significantly.? Most case vendors will not offer buyer specified sizes but these people will. ? It is cheaper to order the cases from other vendors such as Newark Electronics who now handles the Duratool line of equipment and waterproof transit cases once handled by the now gone MCM Electronics (MCM was absorbed by Newark and was part of the same corporate conglomerate ¨C Farnell).? The cases are brought in directly from China and are basically the same products that the big case vendors offer but without the price gouging markups. ? I have had only one instance with contents damage involving a foam insert case for my Bird wattmeter elements.? I ordered a custom transit case offered by a seller that contained a large number of positions for the assortment of elements I use.? It contained the normal closed cell poly foam inserts.? Upon receipt I placed all of the elements in the case and set it on the shelf.? I came back some weeks later to use the elements and when opening the case I found that all of them had signs of corrosion.? It turned out that the problem was not from the ploy foam but, instead from the adhesive the seller used to secure the foam inserts into the case. ? Greg |
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