Flat mounted GPU?

[Grimfox]

Hi I'm new,

I'm working on my first custom case project where I'm planning to use a PCI-express extension cable to mount the GPU in a parallel (perhaps co-planar is more accurate) orientation to the motherboard. Currently the only thing holding the GPU in place is(are) the screw(s) on the PCI slot plate and the tab on the slotplate. The case is going to be vertically mounted (IO at the top) and subject to some movement and shaking. I'd like to come up with a flexible mechanism to hold the GPU in place securely. By flexible I only mean that if I switch GPUs later I don't have to drill new holes or redesign my base plate, not that it needs to bend.

Currently I'm thinking about using some slotted holes to give myself the flexibility and then using a pair of rubber washers between a pair of flat washers and a screw to "pinch" the edge of the board. If none of that made sense see hardware order below.

-screw
-lock washer
-back plate
-standoff
-flat washer
-rubber washer
-GPU
-rubber washer
-flat washer
-nut/screw

I figure I should use 2-3 on the edge opposite the PCI connector 1-2 on the connector side and 1, maybe two if there is room, on the edge opposite the pci slot.

Do you think that will work? Or is there a simpler option out there that I'm not aware of? Or am I crazy and need to re-evaluate my life choices? I was planning to use 1mm steel for the back plate (mobo and gpu plus some odds and ends mounted to this) Or would aluminum be fine? I can adjust my design fairly easily right now to accommodate a different thickness of whatever. I'd like to keep the thing as light as possible as I'll be moving it around a lot.

Let me know what you guys think.

Relevant build notes: Based on a m-ITX Z170 mobo. Using Sketchup for design, but might switch to FreeCad due to broader export capabilities that I'd need to have to get the thing built.

 

[alex1577]

You could also make a simple bracket for the pcie extension. Most extensions that use short pcbs for the gpu side have holes for screws. Additionally you could put a wide screw at the fork on the end of the pcie bracket for more strength

 

[jeshikat]

Or is there a simpler option out there that I'm not aware of?

Couldn't you just cut two blocks of foam to size and sandwich the card in there?

I was planning to use 1mm steel for the back plate (mobo and gpu plus some odds and ends mounted to this) Or would aluminum be fine?

1mm steel is good, 1mm aluminum may be enough depending on the design but you may want slightly thicker.

Using Sketchup for design, but might switch to FreeCad due to broader export capabilities that I'd need to have to get the thing built.

SketchUp is good for rough layout but I'd definitely recommend switching to something more powerful later on. Most manufacturers will just politely (or not so politely) tell you they need a proper CAD file to work with, or they'll have to charge you extra for an engineer to rebuild the model in their CAD software.

*shameless self-promotion* You may check out this build log I'm writing you haven't already where I cover much of this: https://smallformfactor.net/forum/threads/stx160-0-the-most-powerful-atx-unit-in-the-world.934

 

[Grimfox]

https://www.amazon.com/dp/B01CEIEWU4/?tag=theminutiae-20

This is the riser I was planning on using, but it looks like I missed that ship, which is unfortunate because that one looks really slick compared to the grey ribbon and blue tape ones that are flooding the market. It does have mounting holes, so I'll have to find one or find something else (recommendations?) and measure it out.

I hadn't thought of big foam blocks...but it is and "option."

What thickness of aluminum would you use to achieve a similar stiffness and would the weight saving be worth the switch? I know that is hard to deduce given the lack of details. At this point I think the mobo tray and maybe some pieces of the body would be metal while everything else would be plexiglass or some sort of plastic. I found a company that will do plastic enclosures for all sorts of electronics so hopefully that will help me keep the weight down.

Sketchup would probably work if I paid for the pro version but that's like 700USD so... nope. I think I might use Sketchup to export STL files then import those to Freecad to export to something useful. There's a lot of capability in Freecad but I'm still learning it.

 

[jeshikat]

You may review the other options here: https://smallformfactor.net/forum/threads/flexible-pcie-risers.873/

1.5mm-2mm aluminum would be comparable to 1mm steel. All other dimensions equal, even 2mm aluminum is lighter than 1mm steel.

The Pro version of SketchUp still can't easily export to useful formats. That said, if you need a .SKP converted to .STEP or .IGES, PM me and I can convert it.

 

[Grimfox]

I've transitioned to freeCAD. It's a different experience. I just about lost my marbles yesterday because it wasn't letting me use the edges of some existing geometry to constrain a new sketch (2d drawing) but I figured it out, I hadn't fully constrained that initial geometry.

I do have one question about the CPU mounting cutout in the back of the MOBO tray. I found a sizing guideline in this forum but I've not found anything that would give me an idea about where to place that hole. So any thoughts on that would be helpful. Or if I need to start a new thread as I've drifted from my original topic too much.

On the GPU note. The seller of the original PCI-E extender put some more back up for sale, so I managed to snag one of those. It looks really similar in construction to the thermaltake extenders. I'll have to test it out this weekend (if I remember) and make sure it doesn't have the same quality issues that I see from the thermaltake reviews.

 

[jeshikat]

I found a sizing guideline in this forum but I've not found anything that would give me an idea about where to place that hole.

Mobo specs have the needed dimensions: http://formfactors.org/formfactor.asp

 

[Grimfox]

I didn't find anything specifying the location of the CPU on the Motherboard. However, after looking at the Corsair air 240 it seems like just leave it all open is their plan. The 240 seems to have tabs that stick out for the mounting pins and that's about it the rest of the space behind the mobo is open. I looked at a range of mobo's too. Older mITX mobos have the CPU all over the place while newer mobos tend to have it towards the top of the board and centered. So that's about where I put the opening. Now I need to figure out how to copy the flanges to each edge of that opening whilst still keeping them linked to the same root sketch, not critical but if I need to change their shape or size I have to do it 4 times.

 

[jeshikat]

Ah sorry, I was thinking of the IO shield cutout.

 

[Necere]

I try to make the CPU cutout on the motherboard tray pretty much as large as possible. The only real boundaries are the PCI slot(s) and the rear I/O ports. The RAM will usually be at the front of the board, and can be considered another boundary, but some server boards do have it at the top edge running front-to-back.

 

[Grimfox]

I shot an e-mail over to protocase asking about bend radii and it's relationship to cutouts relative to their capabilities. They didn't really give me good answers (which is fine I've not given them any money yet and was asking for free engineering help) but they suggested I switch from .081 to .063 aluminum because it increased their ease of manufacture. I tried to do that but found my model to be inadequate to the task. So I'm going to start over. Whomp Whomp

 

[jeshikat]

I shot an e-mail over to protocase asking about bend radii and it's relationship to cutouts relative to their capabilities.

What question did you have?

 

[Grimfox]

Behind the CPU I'd like to include a cut out with flanges around the edges for some added stability. Since those flanges are coming from the cutout space I know I need to leave out some material at corners to accommodate the bend/tooling and also the flange overlap. The trouble is I'm not sure how much to leave out.

My second question also relates to bends. Should my final design include those bend radii or is that something I just need to be aware of as I go about my design?

My questions from the e-mail. Their response said to leave a .12" gap and that the flanges needed to be at least 7mm. Which now that I've thought about it, is a better answer than my first thought. I just needed to read it a few more times.

 

[jeshikat]

Yup, that basically answers your question.

That said, I don't think the edges of the CPU backplate cutout necessarily need to be reinforced if you're working with 1.6mm aluminum depending on the design. Once the motherboard is attached that should stiffen up the mobo tray.

And I would include the bend radiuses in the model to ensure the engineer knows how you intend for the parts to be formed.