View Single Post
  #17  
Old July 9th 18, 08:44 AM posted to rec.bicycles.tech
John B. Slocomb
external usenet poster
 
Posts: 805
Default drill/tap in frames

On Sun, 8 Jul 2018 09:10:49 -0700, sms
wrote:

On 7/7/2018 4:08 PM, 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.



It depends a lot on what the tube set is design for. A top tier road
bike (steel) will likely have tubes in the 0.5 - 1 mm thickness range.
Spirit - a top of the line triple butted frame set with oversized
tubes will be (top tube) 31mm O.D., and wall thickness of 0.5 - 0.38 -
0.5mm.

Steel frames traditionally use a small threaded boss soldered on where
the screw is required and other materials often use a "Rivnut", which
before anyone starts to disparage them should understand that they
were originally designed to provide blind holes in aircraft structure
and used literally by the millions. Successfully :-)






I keep hearing this, 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!

Then the chainguard is mounted on the stays,
likewise with M5s, threaded holes (only here
sometimes there are nuts as well).

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 normal engaged thread length depends on the diameter of the bolt
and the "standard" (strength) For example, an M5 screw (grade 6h/6g)
will have a minimum stressed (threaded)area some 4.0103 mm long.
This is usually felt to be a sufficient thread engagement to provide
some 100% of shank strength. There are innumerable tables available
giving the required data.

This ain't to say that rivnuts ain't a good
idea, of course.

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.)


In my area you can by them over the counter at a fastener company
(http://olander.com/). Probably few, if any, hardware stores carry them.

--
Cheers,

John B.


Ads
 

Home - Home - Home - Home - Home