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drill/tap in frames
On Sun, 08 Jul 2018 01:08:28 +0200, Emanuel Berg
wrote: Jeff Liebermann wrote: The tubing is probably too thin for threading the hole. You need at least 3 full threads wall thickness tubing to keep the mounting screw from stripping the threads out of the hole. For an M5x0.8, that's 0.8 mm per thread. So, the minimum tubing wall thickness would be 2.4mm. However, since the tubing on your bicycle is probably around 0.5mm wall thickness, the tubing wall will never be thick enough to support threading. To get more threads to grip is one reason why builders use braze on bosses for mount points. I keep hearing this, Then, it doesn't hurt to repeat it a few more times until you become a believer. Please repeat a few hundred times: "Thin wall tubing should not be threaded" but it isn't the case for my bikes which have chainguards. These have three stays, and of those, two are mounted on the bike frame with M5 screws. Threaded hole, no nut on the other side! How thick is the tubing at the 3 stays? Are you sure that there isn't a Rivnut, PEM nut, or other threaded insert in the stays? Then the chainguard is mounted on the stays, likewise with M5s, threaded holes (only here sometimes there are nuts as well). How do you install a nut when the ends of the stays are all welded shut? There's no sane way to install a nut inside the stays. Hopefully, your machine does not have an M5 fastener going though both sides of the stays, and secured by a Nyloc nut? Overtighten and you'll crush the stays. The stays are about 1mm. How thick the frame tube wall is I don't know, but I can take a discarded frame and cut it with an angle grinder to find out, God willing. The stays are likely to be double butted, with different thicknesses at the ends, compared to the middle of the tube. If you don't mind drilling a tiny hole in your scrap bicycle frame, you can easily measure the thickness. 1. Drill a very small hole in one side of the tube. If you plan to ride this bike again, drill on side of the tube that will drain water. 2. Make a straight pin that is long enough to go through the hole and hit the opposite side while having a little stick out of the hole. 3. Measure the length of the pin accurately with calipers. Flatten the ends if necessary. 4. Using the same caliper as above, measure between the projecting pin end, and the far end of the tubing. 5. Subtract the length of the pin from the above measurement and you have the wall thickness. 6. Plug the drill hole so water doesn't enter. This ain't to say that rivnuts ain't a good idea, of course. Make sure you use steel Rivnuts on a steel frame. Never mind. It's a dumb idea. An M5 Rivnut is going to require a 7.0 mm (+0.1/-0 mm) hole. That's going to seriously weaken the stays. If you notch the hole to prevent rotation of the Rivnut, you also get a stress riser. Don't do it. BTW, do you by them online? I don't think they are in our HW stores... (which is common with the stuff you guys mention: durometer, soft jaw pliers, etc.) Actually, I steal them from former employers and companies where I consult. Same with other consumables, such as pop rivets, office supplies, electronic parts, etc. I'm still using parts that I stole perhaps 30 years ago. I bought my durometer on eBay. I've never seen one in a retail automotive parts sto https://www.ebay.com/itm/322919230951 My soft jaw pliers came with an ITT Cannon circular connector kit. I have three with different tubing diameters. https://www.google.com/search?q=cannon+connector+pliers&tbm=isch However, they're quite expensive from Cannon, so I would get something cheaper: https://www.google.com/search?q=soft+jaw+pliers&tbm=isch Someone sells plastic covers that slide over the jaws to convert channel locks into soft jaw pliers. Avoid. They don't work very well. 147 hardware stores in Stockholm: https://www.yelp.com/search?cflt=hardware&find_loc=Stockholm -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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