Monday, April 10, 2017

This is Why You Make Prototypes Before Starting Production Line

It only took a few turns under load for steel bolts to strip the threads in 1/8" aluminum.  I guess that C-channel is going to be steel.  I'm not thrilled at the idea of tapping 1/4"-20 holes in steel but the Tapmatic should make it tolerable.  Steel also improves stiffness of the structure.

Hmmm.  Steel channel doesn't seem available except with radiused interiors.  Right angle interiors?  Nope.  Perhaps use aluminum bolts?

Or would using 1/4" or 1/2" thick aluminum solve the problem?


  1. Often a good idea to use thread inserts in Al.

  2. Thicker aluminum, or "Nut Rivets" which are like gigantic pop-rivets with the inside threaded. (They CAN spin though if the hole is oversize or the crimp isn't tight enough).

    The aluminum with sharp angles though is typically a soft alloy for "Architectural" uses. i.e. decorative. Stronger materials will have radiused corners.

  3. Available through Amazon is an assortment of steel gizmos called "rivet nuts." They're threaded steel "sleeves," in several different threads from 10-24 through 5/16-18 (probably other sizes as well, but Amazon doesn't seem to carry them). They are straight knurled sleeves with a flange on the outer face; drill proper size hole, thread rivet nut on the crimping tool, insert rivet nut to full depth (flange-to-surface contact), operate crimping tool until rivet nut is tight. You'll need the correct length rivet nut for the material into which you are placing it because the exterior of the rivet nut is knurled for secure gripping when installed.

    I've had very good results using them in sheet metal (.045" - .110"). Pro Tip: Practice on scrap with with several first. Installing them correctly is very definitely a learned skill and drilling an improperly installed one out is a #$@!. Also, getting the hole diameter they go into exactly correct is important. Tight is better than snug, very tight is better than tight, so drill size and technique count.

  4. 1/2 inch would give you more threads to engage and distribute the load. Have you considered something like a Riv-nut. Just asking, not sure really how this all goes together and whether you would have the clearance.

  5. Typically, you want the threaded part to be at least one screw diameter thick, to get sufficient holding strength. A finer thread can allow this to be slightly thinner. A finer thread is normally recommended when threading into aluminium, to give it more surface engagement.

    You could consider using a threaded steel insert in the part, especially if it will be used for adjustment purposes. You really don't want to have screws working in bare aluminium if it can be avoided, especially thin sections. Shoot for double the screw diameter in that case. Consider going for the tightest hole you can run a tap into, when using alum. 60-70% thread engagement is ok for steel, but marginal for alum, especially if it is a working screw. The tap form can be a variable with hole size. Try not to change this after determining hole dimension. This can also be affected by the type of aluminium you are using.