BigPoser

Hi All,


I have a steel gravel build coming up and I'm going to go 1x Di2 and am wondering what size hole is needed for the wire grommets. Since it's 1x I'll need to have one hole on the DT and one on the CS. I have read that it needs to be 7mm x 8mm in size. I would also assume that it would behoove me to re-enforce the hole as well. With that being said, it has me wondering if the grommet would fit since it would be a bit thicker with the extra material.


Anyone ever done this that could lend a few tips?


Thanks in advance.


Brandon

Canaboo

What material are you using? I have made the holes for a bamboo frame by using carbon as the base. The grommets were slightly oval in shape so I just drilled small hole and finessed the fit with a chainsaw sharpening file.

I'm not sure that doubling up with most materials will work very well. The groove in the grommet is not very wide.

BigPoser

Sorry I should've mentioned that it'll be steel.

Canaboo

Is this going to be a modified frame or are you starting from scratch? Reinforcing the area seems to be a good idea. I would think if the initial hole in the frame is a hair larger and then the overlaid piece has the actual proper sized hole then the issue of double thick ness becomes moot.

https://bikerumor.com/wp-content/uplo...ed-frame-2.jpg

BigPoser

Yup, that's what I was thinking. Thanks for the pic.

Marcus_Ti

There are two sizes of Di2 grommet. The 7x8 you already mentioned, and a 6mm circular.

https://www.competitivecyclist.com/s...a-di2-grommets

BigPoser

Does is matter which to use? I've not used them so I'm clueless.

Canaboo

Depends on the hole in the frame.

Marcus_Ti

Only matters if you find a 6mm circular hole easier to cleanly drill than an ovular 7x8mm one.

BigPoser

I'd think it would be easier to fish the wire through the larger hole. Maybe I'll use the 6mm for the entry and the 7x8 for the exit.

Andrew R Stewart 

I'm no electronic system expert but I do wonder if the 7x8 oval hole is to allow for either a wire or a cable w/ casing to be used. Andy

Canaboo

The actual hole in the grommet is still small, regardless of the dimensions.

unterhausen

I wonder if Andy is right. Trek has had bikes with cables and grommets, just as one example. But they had their own grommets made, not sure they even bother buying from Shimano

Andrew R Stewart 

My comment about the grommet size differences was not focused on it's ID but the OD/shape. For a mechanical cable and casing to fit through the frame's hole and do so at a "working" angle means a somewhat oval hole (in the frame) is usually needed. The cable/casing won't bend without binding if the hole is only as large as the casing is in diameter. But a electric wire can bend rather tightly and be able to enter the frame at about a 90* angle with no function suffering.

So a frame made for either mechanical or electric shifting likely has an oval port. Frames made specific for e shifting only need a round hole. The electrical system grommets are made in a couple of shapes to allow for this choice. Andy (who is waiting for the side bar of whether designing a frame for only one type of option is a best choice)

BigPoser

Thank all. I put the 6mm hole on the DT and the larger 7x8mm hole on the CS. The 6mm wasn't big enough to fish out the wire. Working well now.