Did anyone do that before? I have an 1980 trek 700, and it have these ugly plastic brake cable holders on the top tube. If I drill the top tube, would that compromise structural integrity. What other alternatives do I have?

Edit
This is actually model 412.

^^This is not a Trek.

yeah but how are you going to fish it through? I have never had an internally routed bike, but I imagine there is some sort of channel to guide the cable into the holes?

No, there is usually no channel, you just have to fish it through with string and vacuum cleaner, or some other trick. I was also thinking about adding glue-on cable guides, but I don't have them, and internal routing looks much smoother.

Internal routing is a pain in the ass to work with...but it does look pretty cool.

1) run a steel brake cable down the hole
2) grab brake cable with magnet
3) run housing over cable
4) replace steel cable with stainless
done.

many of the bikes that have internal routing have a tube braze into the frame to guide
the cables, I've got 1 bike with internal routing and never had to fish cable out when
I've changed them.

Not sure that I'd want to do that (drill top tube) you might want to wait until someone
like Unterhausen or John D Thompson post (both framebuilders).

Yup most internal routing arrangements have a small tube inside to guide the cable. My gios has simple slots in the TT to pass the entire housing, but they are reinforced at the periphery. And a tight rubber grommet.

I've seen some Mieles and Miyatas with simpler non-reinforced slots w. a grommet. Not sure if it's a good idea in terms of keeping structural integrity. I think I heard somewhere that they sometimes failed. So a DIY hole is probably a bad idea.

BTW the OP's picture is of the type with a tube within the TT I think.

I have had bikes with the channel and without. You don't really need it. It's just a little time consuming fishing the cable/housing through. All you need to do is drill a couple of holes but they have to be ovaled out so the cable can enter/exit at an angle. I don't think there will be structural problems. There will be rust issues around the bare metal though.

I was thinking to drill the hole and than use a metal rod to bend it out like this:

Than I'll prime it and touch it up with paint, after it dries I'll spray some oil based metal protector inside the top tube.

looks like a Klein Palamino frame

The tubbing is Ishwata 022, if that makes any difference. By the way, how is it compared to Reynolds 531, is it above or below?

it's the same
(really, the differences are NOT as significant as the build quality and the geometry of the FRAME)
Technically the alloy composition is slightly different: one is manganese-molybdenum steel, one is chromium-molybdenum steel (guess).
You are treading in dangerous waters when you start punching holes in tubes without prior experience: if it's a beater frame: fine, knock-self-out.
If it's something of value (to you or others) why not leave it be and get a frame that already has the internal routing you desire...they are out there.

Yeah, trying to bend the hole to look like this sounds like a bad idea.

Agree with the previous two posts--it's nuts to drill holes in a sound frame. It's very unlikely that you'll come up with a satisfactory-looking job, and it will weaken the frame. There's no up-side to it. PUT DOWN THAT DRILL!

....or, drill away.

I'm thinking that this is one of those things where asking how and whether to do it proves that you lack the experience and background to do it.

I wouldn't want to see this done by anyone but a framebuilder or at least veteran frame hacker. Too easy to have that exit would land square on the wrong part of the taper and create a major stress point.

Frame part suppliers do sell bungs and fitments to do this job nicely.

I've slept on the idea, and came up with same conclusion. It's a touring frame, so any unnecessary holes will weaken the frame, and that's not good. I will go with glue-on cable guides instead. Thanks for your input!

Glue on? Why not get some clamps like these?

https://www.velo-orange.com/diacocahocl.html

Well, to my taste, they look semi ugly, on this bike. I want it to look more modern I guess. Currently there are some plastic wrap-around guides, and they look cheap. Also I have found some brown cables, that should look good with brooks seat, and leather bar tape. So it would be better not to hide those inside the frame.

I salute you for choosing to leave the frame intact. The world will be a slightly better place for it.

glue on the guides on the bottom of the top tube

The absolute best way to get sweat and rain inside your frame is internal cable routing. Just perfect for that unaware inside-out rust job. Do it!

Internal routing done properly will not equate to rust/corrosion inside the frame, see older Merckx frames, more notable all Klein frames.

I would address the moisture problem with this thing.

But it might be more hassle to do it, so I will be installing some glue-on cable guides.
On the other hand, internal routing does look pretty sweet.

moisture problem -- solved