I want to attach a pump holder to my aluminium frame. Can I drill holes in it ? I would then use blind rivets with some glue for waterproofing to attach the holder.
Is there a place on the frame where this would be better?
I know this question, but it is for carbon frames.
Do not do that. Although the question you referenced is about carbon fiber, the answer mostly applies. Aluminium alloys used in bicycle frames are quite fragile. Drilling may easily start cracks that will then spread under stress. Even if it does not happen, you weaken the frame unpredictably. Not only the warranty is gone, but you just don't know if it will fail catastrophically or not. And professional metal defectoscopy is too expensive for bike frames. (Yes, expensive X-ray machines are not just for carbon fiber even if some say so).
It is easy to use the bottle-holder screw holes. Many pumps come with these brackets as already mentioned by @Renaud. If your frame does not come with bottle mount holes, you can use other solutions based on velcro straps or something similar.
You can drill the frame in some locations, though it might not be the best answer. Numerous aluminium bikes from big manufacturers use rivnuts to secure the bottle cages, even and especially on the lightest models with the thinnest tubes. Frames can be modified to take Di2 internal routing. Advice can be had directly from manufacturers where it is safe to drill when you are in the trade.
There are some caveats. You should drill nearer the middle sections of the tube where forces are lowest; note where bottle cage locations are on standard frames. (Middle of downtube, lower on underside of downtube, middle of seat tube). The hole must be very clean/round.
If you drill the seat tube, you will probably interfere with the function of the seat post. You will obviously lose any warranty that may or may not apply to your frame.
It's possible to buy clamp-on adapters that take a bottle cage bolt from eg DMR and Problem Solvers in common frame tube sizes. Zefal make a very good velcro/rubber pair of pump holders that go anywhere called the Doodad. Others may be available. It is not always necessary to get the power tools out to solve the problem.
drilling seems totally unnecessary. you can use braces or even zip ties for that.
when you go to do DIY mods always consider the many options available of fixing/attaching things and choose(or test first) the ones which does not damage the original parts. because one day you have and idea, then other idea, then you want to make changes, iterate on the invents, and if you start drilling and cutting and even soldering(solder does thermally affect the pieces) the piece will end up broking or becoming unusable.
and also when you cut, drill, damage the original parts they loose value and may become unable to resell later when you no longer use or want to change for other model completely
If this is just to make a traditional-style pump peg, you can do that without drilling. Just buy a pump peg, use a half-round file to profile it to the tube you're putting it on, take the frame down to bare aluminum in that spot with sandpaper and epoxy it on.
