How large of a thread can the original refill hole support

[Osage]

to drc023,

I somewhat respectfully disagree that one can rely on the thread itelf to seal.
A straight helical machine thread is not ment as a seal---maybe something like a spirial type pipe thread would work---but even then--in any kind of pressure application---the pipe thread is usually aided in sealing with some sort of pipe dope or teflon tape---to fill any gaps.

However, in a non pressure application---or in an application where the pressure involved is less than an inch of hydralic head ink pressure--just the thread alone may be enough to get a decent enough seal to work in practice. But one must remember--that the thread can wear over a number of uses--and even a tiny amount of air leakage over the long time a cartridge remains in the printer could cause some ink to leak out the cartridge.---which is why I advocate a gasket--with a O-ring being ideal to complete that air tight seal.

But its still a testable hypothesis---drill and tap a thread through plastic similar
to an ink cartridge---that is the only air outlet in some sort of pipe--put some air presure behind it from a pump---and I predict it will leak--add a o-ring gasket held tight by the screw head bottom, and I predict it will hold considerable pressure. Such a device could be easily made with a bit of plastic pipe and a few
pipe caps.--drill into one pipe cap with a threaded screw--and the other to hold a
tire valve---hook up even a hand pump-- Hold it under water to watch the bubbles.

 

[kudos]

No they do not have the tabs but they fit the hole perfectly!

 

[drc023]

to drc023,

I somewhat respectfully disagree that one can rely on the thread itelf to seal.
A straight helical machine thread is not ment as a seal---maybe something like a spirial type pipe thread would work---but even then--in any kind of pressure application---the pipe thread is usually aided in sealing with some sort of pipe dope or teflon tape---to fill any gaps.

However, in a non pressure application---or in an application where the pressure involved is less than an inch of hydralic head ink pressure--just the thread alone may be enough to get a decent enough seal to work in practice. But one must remember--that the thread can wear over a number of uses--and even a tiny amount of air leakage over the long time a cartridge remains in the printer could cause some ink to leak out the cartridge.---which is why I advocate a gasket--with a O-ring being ideal to complete that air tight seal.

But its still a testable hypothesis---drill and tap a thread through plastic similar
to an ink cartridge---that is the only air outlet in some sort of pipe--put some air presure behind it from a pump---and I predict it will leak--add a o-ring gasket held tight by the screw head bottom, and I predict it will hold considerable pressure. Such a device could be easily made with a bit of plastic pipe and a few
pipe caps.--drill into one pipe cap with a threaded screw--and the other to hold a
tire valve---hook up even a hand pump-- Hold it under water to watch the bubbles.

Unless you've actually tried using the nylon screws that I use, there is no way for you to know if the threads seal or not. However, I have used both black steel cap head screws (which rusted) and nylon screws and neither has leaked on the well over 100 cartridges I've done. The threads which I tap in the cartridge surface itself in combination with the nylon screw provides ample sealing surface area to prevent leakage. If the screw was a very loose fit I agree it would tend to have an air leak problem, but that isn't the case with the nylon screws. The fit is so tight I have to use a screwdriver to run the screw down anywhere further than the first couple of threads.

As to wear over a period of time, that could be a problem if there is a considerable amount of removal and replacement which could possibly wear down the thread surfaces, but how many cycles would be involved? Far more than the lifespan of the sponges. As I recall, most refillers recommend only using a tank for around a dozen or less refills since the holding power of the sponge tends to lessen over time. Unless the tanks are flushed and rejuvenated with Grandad's method, they will need to be discarded well before thread wear could be a problem.

Why would I want to apply an extreme amount of pressure to test the sealing capacity of the nylon screws? The testing method you suggest is more like a pipe bomb than a plastic ink tank with no internal pressure. A more realistic leakage test would be to test an empty tank which has been converted to use the screws. A seal with tape or a finger over the vent opening is necessary. Attach a piece of flexible vinyl hose to the outlet and apply a bit of air pressure. If the cartridge is a new unfilled virgin tank or has been flushed of all ink, you could also try to inflate it as you would with a balloon. P.S. I have performed pressure tests on the tanks and there was no leakage.

Where you may be confused about the sealing capabilities of using the nylon screws is the location of the threaded hole. If it is done on an area other than the original fill opening, there is only a single thin plastic layer to work with which is only a thread or two in depth. Instead, I remove the original plug from the tank and use that opening to thread. In order to hold the original sealing plug the opening extends about .25" or so into the tank and as a result there is far more threads to work with than on the other areas of the tank.

Once again I'll state that we tend to obsess over the merits of one refill technique over another. Note that the HobbiColors tanks have smaller screws and coarser threads and they don't use o-rings for sealing. So far, no one has reported a leakage problem with those tanks. Also note that I use and recommend the use of o-rings as added insurance to prevent leakage. While it's true the nylon threads alone have been sufficient to prevent leakage, it's also true that for a couple of cents an o-ring provides an added margin of safety. The o-rings are insurance. While I don't plan on croaking any time soon, getting sick, having a wreck or watching my house burn down, I still carry life, health, auto and home owners insurance.

 

[hpnetserver]

Osage, If the screw is tightened the screw is compressed against the thread. If both the screw and the tank are metal there is a chance the screw will not perfectly match the thread then it may leak. But if the screw is of nylon materal and the tank is plastic the combination will be more likely to provide a good seal. DRC apparently is very experienced. I only have a small number of Hobbicolor tanks. But I agree with him. I never experienced any leaking problem. I am pretty amazed that such a simple doubtful sealing method with a cheap nylon screw actually works and works very well. There is no doubt, it is not the only method that will work. The original method is simply a small plug to plug up the small hole. It is as simple as that.

 

[Osage]

I may be over concerned---but in the case of a hobbicolor cartridge--the final seal is accomplisd by both the screw thread and the screw thread bottoming out the top of the cartridge--nylon is a far better gasket material than steel.--and the hobbicolor cartridges can probably be relied on as having dead square threads.

And drc023 best says it---that 2 cent o-ring is the excellent insurance policy--because any that leaks past the thread is going to be stopped by the o-ring. Period.

Which is why I have decided in my miniscule mind that the stainless steel screw and o-ring is better than a rubber plug. Although a nylon screw and an o-ring will do equally well.

Given that these are materials are locally available, super cheap, infinitely reusable, its the way I have decided to go. But like everything else, you pays your money and takes your chances.

 

[hpnetserver]

Using stainless screw with an o-ring has an advantage that the screw will last much longer than a nylon screw. But a numer of refillings later the thread on the cartridge may be worn out by the metal screw. At least it may wear out faster. Only actual experience will tell if this is true. On the other hand nylon screw may be worn out faster. It is a much weaker material.