As Andy points out there are times when you do things differently for specific reasons and that looks to be the case with the Macdev situation (it also was when I was doing a version of the Freestyle valve system with the tip o-ring on the center shaft that always wanted to come off). Sometimes you are constrained in the space/location and it causes different decisions. I haven't found a perfect science to it, but have found my method is usually a good starting point for most of the things I design.
I pretty much always rely on extrusion to seal the o-rings with the lower durometer o-rings, and it seems to work well for the low forces and low frictions we find in many paintball situations.
Can't say I have looked at the book for a very long time. Much of the standard industrial methods they specify just simply doesn't work for paintball. Much of what I do comes from years of doing it and some amazing conversations with someone I consider to be a pneumatics Guru, Mike Woods (of Nova, SuperNova, Assault etc. fame)
I've had many o-rings that ended up with a little too large a groove diameter and too thin a groove cross sections such that they leaked, and simply putting the parts back on the lathe and opening them up got everything to seal up perfectly.
That's called indexing. You need to specify the parts that need to align and give an angular tolerance. Some machine shops will hate you for it, others won't care. It can be a HUGE PITA to get right after you take into account tolerances and finishes. Try not to make it overly critical if you can.
Ever so many citizens of this republic think they ought to believe that the Universe is a monarchy, and therefore they are always at odds with the republic. -Alan Watts
I work for the company building the Paragon
So, here I am again trying to learn from those of you with much more experience.
If you had a dimension on a dynamic seal that fell right in between 2 oring sizes how would you handle it? Stretch and the smaller size or just make the gland deeper and go up a size?
I usually look for a metric size in the middle, increase the bore if possible to properly fit the larger size, or stretch the smaller size ( in that order of preference). Unless im trying to prevent blowout like mentioned in the MacDev or freestyle variant mentioned where stretching gives an advantage other than fit.
In the event of needing to go with the stretched option, do you reduce the gland depth? Running a .075" depth worked fantastic when I could control the bore and not stretch the oring, but since the bore is dictated in my case I need to stretch to get the right fitment. I am not sure a whether a floating type gland is still appropriate or if I'd go with a traditional bore squeeze gland spec.
Depends on the amount of stretch and the elasticity remaining after stretching. The smaller the percentage of stretch the more elasticity remains available for a semi-floating seal to work. If you stretch the equivalent of several sizes like the clone the more you want crush.
One of the more useful things found in the parker guide, and of the few that pertains directly to us, is a chasrt that compares percentage stretch to percent loss of cross section. You can work that backwards to determine gland diameter based on you chosen o-ring, bore diameter, and desired squeeze.
I actually designed that into a spreadsheet, then I started this thread. Now I have the "Simonized" oring gland spec table.
I suppose I could run a metric, but I just hate them unless absolutely needed. It limits the material selection.
You have to registar, but I've used this in the past: http://www.tss.trelleborg.com/global...alculator.html
In the instance where I need to rely on crush, what % do you guys like for low friction and an adequate seal?
Are you talking about having an internal groove, with an o-ring sat in it, and a shaft running on the ID of the seal? But where the shaft is a smaller diameter than the ID of the seal, so you reduce the ID of the internal groove to place crush on the o-ring to bring it down to the shaft size you are running through it? Is that the scenario you are asking about?
Jack