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drill/tap in frames

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Old July 8th 18, 01:35 AM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 2,989
Default drill/tap in frames

On Sun, 08 Jul 2018 01:08:28 +0200, Emanuel Berg

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
My soft jaw pliers came with an ITT Cannon circular connector kit. I
have three with different tubing diameters.
However, they're quite expensive from Cannon, so I would get something
Someone sells plastic covers that slide over the jaws to convert
channel locks into soft jaw pliers. Avoid. They don't work very

147 hardware stores in Stockholm:

Jeff Liebermann
150 Felker St #D
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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