Image has wrong dimensions

[0PandaDEV]

So I'm trying to make a 10" rack reference model in Fusion360 and used the image from The 10" Mini Rack Standard section. But it turns out that the image has inconsistencies regarding the hole center to opposite hole center.

For a 10" rack, the most outer distance from the outer edge of one rail to the other, it is 254mm [10"]. The inner distance from the inner point to the other inner point of the rails is 222.25mm [8.75"] which means one rail has to be 15.875mm [0.625"] wide. Now it incorrectly says the center of one mounting hole to the exact opposite side is 236.525 mm [9.312"] but this can not be correct because then 7.9375 mm * 2 + 236.525 mm should equal 254 mm [10"] but it's 252.4mm.

I noticed the same error for the 19" version, which is also being displayed there.

So what I'm really trying to get is what exactly are the right measurements for a 10" rack.

[0PandaDEV]

So I did some research and found a few people pointing this out #29 (comment) #29 (comment) I think we might have to redo that SVG sketch and make a "real standard"

[0PandaDEV]

The more research I do, the less sense this sketch makes IBM says 19" holes have a 6.75mm spacing to the unit and 15.9 to each other this could also just be rounded numbers though but then again there are dimensions where even they specify a tolerance of .8mm or .75mm.

I think the 10" rack should be a standard with rounded numbers and then the "to be mounted" components should have the tolerance since 3D printing is not 100% accurate by making use of rectangular holes.

[Chobok0]

Funnily enough, I just ran into the same inconsistencies when modeling a new minirack from scratch in FreeCAD.

Typically I've been modeling mounted components based on the inner rail-to-rail width 8.75in (222.25mm), ignoring the hole-to-hole measurement on wiki. I model things at 222mm max because I typically use 0.25mm tolerances in my models anyway. With this, the width of rails matches the hole height 0.625in, and between outer rail edges we do get 10in (254mm), so I'm inclined to believe that the measurement for hole-to-hole width on wiki is incorrect.

Gets even more annoying when you start comparing DeskPi RackMate inner rail-to-rail widths, which is either 8.34in (211.836mm) for most models or 8.74in (221.996mm) on their TL1, so now I'm a bit worried about compatibility for my models since it's more than a 10mm difference from the smaller RackMate width to my modeled mounts. I use about a 10mm slot on holes so hole-to-hole width shouldn't be an issue for me, but the inner rail-to-rail width is really confusing me.

It all feels like a game of rounding error telephone to me. I just want nice, clean measurements that are relatively easy to remember. I started modeling a new minirack because I wanted a perfect 10in wide by 10in deep rack, and of course rack depths are an oddity in itself, but at least a lot more forgiving to deal with.

[Chobok0]

Further down the rabbit hole, found a link to openminilab from the minilab subreddit, and stumbled upon their source for 10-inch rack dimensions. What interested me is this quote from their source:

Interesting to note is that the 10" rack, to a certain degree, follows the nesting paradigm of computer form factors: the rack opening on a 10" rack is exactly 5U wide (44.45mm x 5 = 222.25mm). Given a rack offers matching horizontal mounting rails, it is possible to mount 5 1U 19" modules vertically in a 12U tall 10" rack.

Honestly to me this solidifies the inner rail-to-rail width as 8.75in (222.25mm), making the hole-to-hole center spacing 238.13mm. But, I guess this is the "de jure" standard, but the "de facto" is still probably going to be DeskPi's 8.34in (211.836mm) since they seem to be the popular minilab rack brand right now. It's as @geerlingguy edited onto the main site:

Allowing for extra tolerance, mini rack gear should fit within around 210mm (8.45”) of horizontal space, and mounting holes should be able to accomodate a few mm of width to either side.

[0PandaDEV]

I propose this as a corrected spec, I can also provide it as an SVG if needed. This could also be changed to have all rack mounts fit within 220mm which would give a bit more tolerance.