DIY Dewar neck tube core/lid

[Skiller1nc]

Recently purchased a dewer with a 4.5" mouth so that I can cryo larger blades. However, it didn't come with the neck tube core. Being that really all it is, is a foam tube I decided a cylindrical paper mold and great stuff foam could work. I haven't tested it yet but what do yall think, seems like a good solution? the fit is tight but not air-tight. think the welding supply store will fill it?

In the image below, it can sit further inserted so the blue lid can close

Here it is in all its glory

 

[Thom Moss]

Think I have the same dewar, 34HC. my foam cap insert is not at all air tight and not even sure it should be. mine came with the six sample holders also that hang on the rim of the opening and definitely not an air tight fit. So might be a design/safety reason to not have a tight fit.

video from my Instagram for an example. https://www.instagram.com/p/BoUUcoNBJAI/?utm_medium=copy_link

 

[Skiller1nc]

Think I have the same dewar, 34HC. my foam cap insert is not at all air tight and not even sure it should be. mine came with the six sample holders also that hang on the rim of the opening and definitely not an air tight fit. So might be a design/safety reason to not have a tight fit.

Yeah, I have taken that into consideration, the foam leaks more than enough to let the pressure out, ie it won't build up and shoot the foam out the top but it's still a good seal.

 

[Ken H>]

For sure you don't want any pressure to build, as the N2 evaporates it has to have a place to escape. My plug has small channels down the side. That's not only to allow vapors to escape, but also a place for the straw rods to be positioned. Of course for HT'ing the straws are not an issue.

 

[Stacy E. Apelt - Bladesmith]

Cut a few grooves with a hack saw down the sides.