Tapping threads in frame

[Bikeshrink]

I've rebuilt a Raleigh Sprite and would like to add a rack from my mountain bike. I'd also like to add a bottle cage. The Sprite doesn't have any threaded holes (Braze-On's?). Can I drill a hole in the frame, tap threads into it and be good to go?

Thanks in advance.

[xerxes]

Short answer, no.

The frame is very thin, lightweight steel frames may be as little a 0.3mm thick in places, but even heavier plain guage tubes will only be a millimetre or so thick, so they're just not thick enough for a thread. In addition, it would create a weak point which may lead to cracking.

If you look at bottle bosses and rack mounts on a bike that has them they are a forged or machined fitting that is brazed into or onto the frame to provide the depth necessary for a thread and to reinforce the hole, in the case of bottle bosses.

You can get some racks that are designed to be used with frames without braze-ons, some fit over the rear axle and attach to the brake bridge, or you can use P clips with a standard rack, something like this: http://www.flickr.com/photos/zzpza/3563163067/

You can also get bottle cage clips: http://www.nordicgroup.us/cageboss/

[jr14]

xerxes is correct. If if wasn't designed into the frame, isn't going to work. Drilling and tapping into the frame will create stress risers, and any abnormal stress may cause a failure in the frame.

That said, you do have an option. Rivnuts. Rivnuts are similar to pop-rivets, but they leave a threaded hole behind.

http://www.aimfasteners.com/about_rivnut.html

This link will tell you all you all you'll ever need to know about riv-nuts.

Good luck.

[GeorgeET]

10-4 to what xerxes says. Lots of wrap around fastener type components available. No need to drill.

The drilled frames are reinforced behind the hole.

Not sure where you are but here in USA the wrap around clamp type components are usually found in dept stores . That are used on the less expensive bicycles.

[Bikeshrink]

Yikes!

First, thanks for all your responses. I have to confess I jumped the gun! I read from a different site where someone had drilled holes and used sheet metal screws and I thought "that sounds simple enough" and jumped in with both feet, drilled 2 - 1/8" holes on the tube running from the crank to the fork and one on each of the tubes running from the derailleur to the seat post. Everything has mounted up very nicely.

Hopefully I haven't screwed things up royally (pardon the pun). If I have, what do I need to watch for and is there any remedy?

I promise this time I'll wait for your response before taking any action.

[xerxes]

I guess you'll just have to keep an eye on them. The chances are it will be fine, it's just not something I would do. But if you do see any cracking around the holes, stop using the bike and either get the frame repaired or replace it. If you get it repaired, you could have proper braze-ons fitted in the holes you've made, although I doubt repairing it would really be an economical option.

I'm not sure about using Rivnuts either, I know that bosses etc. are riveted to aluminum frames, but they have much thicker tube walls and are generally larger diameter to, so the section where the rivet is fitted would be nearer to flat. In a small diameter thin steel tube the Rivnut may partially flatten or deform the tube where it's fitted and create a weak point where the tube is no longer round.

[jr14]

(08-09-2010, 12:02 AM)xerxes Wrote:  In a small diameter thin steel tube the Rivnut may partially flatten or deform the tube where it's fitted and create a weak point where the tube is no longer round.

No more so than drilling.

No, seriously, custom framebuilders have been using rivnuts for a long time with no adverse effects. Is it better than brazing or welding a boss? No. But there are plenty of people who have done it with no problems.

Just don't do it on a downhill bike. They encounter SLIGHTLY higher forces than cruisers.

But since the damage is done, watch for cracks, and prepare yourself for a catastrophic failure. That's more likely than a small crack becoming big.

[Bikeshrink]

(08-09-2010, 06:38 AM)jr14 Wrote:  

(08-09-2010, 12:02 AM)xerxes Wrote:  In a small diameter thin steel tube the Rivnut may partially flatten or deform the tube where it's fitted and create a weak point where the tube is no longer round.

No more so than drilling.

No, seriously, custom framebuilders have been using rivnuts for a long time with no adverse effects. Is it better than brazing or welding a boss? No. But there are plenty of people who have done it with no problems.

Just don't do it on a downhill bike. They encounter SLIGHTLY higher forces than cruisers.

But since the damage is done, watch for cracks, and prepare yourself for a catastrophic failure. That's more likely than a small crack becoming big.

Thanks for all the feedback.

Is it safe to ride?

The bike in question is my daily ride to work bike. This week we plan to go vacationing and do some rides up by the north shore of Lake Superior so I guess I'll keep my fingers crossed.

I have another frame from a Raleigh Triumph that I used as a parts bike for the sprite and if needed I can always switch frames.