right! 218.24mm
Problem is buying from the US takes longer times and higher shipping costs. More, i cannot buy from the US as a professional due to some odd fiscal reasonsā¦i would get some problems on the fiscal side, go figureā¦
Anyways, using a standard o-ring would mean to lose the power of freely designing a shape for the pocket without caring for the o-ring groove length. I know about some people getting companies to make o-rings to their specs, but iām out of that since it requires higher production volumes then what i need.
In the meantime, i ordered some shore 60 silicone cord, 2.5mm and 3mm as you suggested earlier, but i wonāt get it before 7 to 10 days.
Iāll stop flooding this topic and wait till i have some consistent result.
Thanks for your support guys 
By āUsing a sealantā you mean to bond the cover to the piece? If that is the case, it would make me lose the ability to disassemble the thing for future inspection.
You could also use sealant (silicone or similar) to form your own āringā by gluing it into the base groove, and using a separator film (cling wrap or similar) to avoid it bonding to the top piece. This mill make a removable top piece with a fixed seal on the base part.
Basically fill the base cavity with sealant, add a separator film or agent to top piece, assemble with almost no pressure (maintaining approx 1mm separation between base/top part and let it cure. Remove top part and separator, reapply top piece and secure it to its desired firmness.
You could also make the slot for the O-ring to a different circumference, tailored to available sizes, both in length and in thickness.
Just another 2cents worth 
Have you considered making a gasket instead. You can buy a sheet cut it to shape. Best method would be to use drag knife cutter. You can buy or make your own. But I think you could probable rout it with the right end mill and some practiceā¦ Cork makes a good gasket and cuts well.
Sure, i really appreciate it, thanks!
Yep i thought about making the seal by filling in the groove like a mold, but i see some problems with this. Hereās what i mean: (by the way, i have NO experience with silicone, so these are just my ideas and could be totally wrong!)
Basically, a seal is created when the o-ring is pushing against the top piece. At the same time, i canāt let any space stay in the middle after securing the top to the bottom piece, the two pieces must look like they were bonded, so the o-ring should be a little bit taller than the groove, just enough to squeeze when pushed down, fill the groove width and go flush with the top of the groove. The cured silicone wonāt push upwards because it wonāt be taller than the groove after curing and thus would not be squashed down by the top piece like an o-ring, and would also have zero space to squeeze and fill the width of the groove.
I donāt know how to 1) have the silicone cure 0.5mm/1mm taller than the groove height 2) have the silicone not fill the whole groove width when poured, so to have some free space for the silicone to squeeze when actually securing the top piece.
Again, these are just my ideas, i may be wrong!
Yes indeed! but iām looking for a very high quality cut, and iām not that skilledā¦my hand cut would simply look bad. I also thought about milling a sheet of some rubber, but i fear the x-carve and the router arenāt the best tools for such a job, as you also said, the best tool would be a knife cutter. I fear an end mill would rip the sheet apart.
The silicone (or similar media/sealants) need to be oversized, that is why I mentioned leaving say a 1mm gap between the parts for the curing stage. Once cured you can attach the top piece firmly, the 1mm oversized (in height) silicone will allow a proper squeeze/achieve seal
You mean that while curing, the silicone will raise 1 mm above the top of the groove by itself? or that i should put a 1mm routed mask to allow for a taller height?
And how would you go about leaving free space in the width of the groove so to allow for some squash? When pouring the liquid silicone, it will fill the entire width of the groove, and when attaching the top firmly, the silicone will not have room for squeezing.
Silicone wont increase in size, however it is solid enough to not flow much in its uncured state.
So using 1mm spacers for the curing stage sound easy enough.
Silicone do not flow much uncured so making it undersized for your gasket groove seem easy enough (in my head 
)
but that would require 2 more pieces:
- a 1mm thick routed mask to ensure a slightly taller silicone mold
- a 0.5mm (or whatever) spacer running all along one of groove internal sides
and then i should find a way to firmly secure the spacer to the groove side before pouring.
sounds pretty messy
I think either cutting a gasket from a rubber sheet or using a silicone/nitrile cord with larger values than what i tested to make a cut-to-size o-ring is the way to go!
No, and in order to achieve 0.1mm accuracy one need to address the mechanic side of things aswell.
But it is not our project nor us that need convincing
I have offered a simplified approach that may or may not appeal to OP
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We were talking about the rubber sheet for making gaskets, not about the acrylic to be milled.
The material variance has already been discussed and yes, thatās a major issue. Iām already looking for a quality acrylic reseller.
And thatās what weāre trying to do here, mostly on earlier postsā¦other than finding alternative solutions.
Anyways, iām going to test for microsteps config on the g-shield in a day or two, and post here my results in the hope it will be informative for future readers.
For the record Andrea I am not telling you are āwrongā or anything like that, it is your project and you have your goals for it. I have no saying on that
However, micro stepping is not something that will give you an increase in accuracy / position consistency. Also, as long as steps per mm is 10 or higher you have 0.1mm there already. Micro stepping mainly smooth out the machine (less motor noise being a very noticeable effect) and will also have an impact on torque.
Is the spindle within 0.1mm?
Is the tool deflection within 0.1mm?
Are the materials of your machine immune to humidity and thermal expansion / contraction within 0.1mm?
Are the drive belts 100% rigid, with less than 0.1mm flex?
Backlash account for how much?
Getting your system as good as it can become is a fair goal, maybe (I hope/wish!) you can get very close
I disagree however trying to get the system within 0.1mm is the better approach, in order to get a seal working - thats all
Is the 0.1mm material/machine accuracy a personal goal or an application requirement?
Is there a reason for the square configuration of the slot? Have you considered using a ball mill for a more circular shape so that you donāt have to worry about the āsquashedā shape of your seal. it looks like you arr trying to put a round seal in a square hole.
Indeed! I see your point guys, and i totally agree! Thanks to your tips in this discussion i realized i will VERY hardly achieve that level of accuracy. In fact, i donāt have the right tools and/or the expertise to measure if the tool deflection is within 0.1mm, or to measure your other (good!) points.
Thatās why the discussion went off-topic and we started discussing on different designs rather than achieving that level of precision, so i also agree with this
So testing with different designs/approaches is the way to go for me, as you all are suggesting. I ordered a different cord for making o-rings (silicone shore 60) and even a neoprene sheet for making gaskets. Iāll also try with different groove profiles! Also surfacing and/or buying the proper material to work with is mandatory.
I just want to test with different microstep settings because of this early post
which, in short, says that lower level of microstepping might turn into a liiiiitle bit of extra accuracy in some cases.
But thatās maybe the last chance i can take on the mechanical side of things really, other than actually measuring the travel distance on the z-axis and set the proper steps/mm (and thatās mandatory in my case).
So yep, iām good to go for now iāll post here in a couple of days my next trials and errors, just for completeness.
Thank you all so far!
If you want to have some idea of the depth of your slots you might purchase some dowel pins and drift keys that fit your slot. Measure the size of the key/pin and insert into the slot, measure off the face of the unit and the height of the of the pin and subtract one from the other. It would be better if you had access to some precision J blocks and/or guage pins, In fact you can buy just the sizes you need without buying a complete set. getting some of the ones that are minus the tolerances and the maximum tolerances (GO/NO GO) would be the must cost effective way to go. Of course it will help a great deal if you have a outside micrometer (a must anyway) that covers up to one inch(metric equivalent). You cannot expect to do any kind of precision work without the basics to do the job!