installing a cable guide underneath the BB-- where's the screw hole?
 

Hi,

I just received a new steel frame that I am building up. I assume I need to install a cable guide underneath the BB. However there is a large diameter drain hole in the middle of the BB (~ 10 - 15 mm) but no screw hole for the cable guide. What should I do?

I have an 107mm IRD BB I want to install. I think it is just a standard square taper cartridge BB (it requires the Park BBT-22 tool to install). The BB shell was not chased or faced, and I don't have the tools for that. Should I go to my LBS and have that done? Or once I figure out the cable guide solution, should I just install the BB into the BB shell as is?

10-15mm is larger than I would expect to see for a drain hole. Typically that single hole is where you would screw in the cable guide and it is much smaller. You can often get away with using an adhesive for the cable guide and the tension from the cables themselves will help to hold it in place as well.

You don't usually neeeed to chase and face the bottom bracket shell. If the bottom bracket can thread in without much force from the tool then it is surely fine and chasing shouldn't be needed. Facing often isn't needed either. If you want to be very precise then go for it but otherwise it isn't usually necessary.

Ok, I measured the hole. It is either 7 or 8 mm, and it is not threaded. I have what I think is a 5mm screw for the cable guide and it is way too small. I measured the width of the screw and it looks like 4mm to me, and the head slots perfectly into the cable guide.

Is it a bad idea to mount the cable guide directly over that hole with some double stick tape?

I used double-sided tape to fit a cable guide. (didn't have a screw of the correct size handy).
I made a small hole in the tape over the drain hole, but never got around to putting a screw in. It's still there and hasn't caused any problem.
Now that I think about it...I won't be putting a screw in there. It's my wet weather bike and I think it will drain better.

+1 I would go with the double sided tape and open up a drain hole where the screw would normally be inserted (as long as it lines up with the existing hole in the frame, if not, just drill a hole in the cable guide to line up with the frame).

A lot of the cheaper cable guides have a split post that fits into that hole and then the screw acts like a wedge when inserted and tightened( like a picture hanger for drywall), that may be what it takes.I know Shimano makes them also. If you have a cheap frame laying around check the cable guide on it it may be what you need.

Double side tape or super glue will keep the bb cable guide in place just fine and the cable tension will further retain it. You don't need the anchor screw.

Sorry, I'm not following that. By 'open up a drain hole' do you mean drill a hole? Secondly, I have no idea where the (guide?) screw would normally be inserted.

No, he means cut a hole in the double sided tape where it covers the existing drain hole.