Re: Tap Driver?
 

This statement is very misleading when viewed by anyone without an understanding of what you're talking about.

For starters, the best way to avoid galling is by using two different materials, preferably with a large difference in hardness (though mating two materials that generate oxide layers like Titanium and Aluminum can cause problems). The lower the roughness of the thread the better as well (ie: form taps perform better than cut taps).

Avoiding stainless fasteners is a general rule of thumb for us.

We have tapped thousands of holes in aluminum that receive steel fasteners with absolutely no problems, as I'm sure the majority of FRC teams have.

Re: Tap Driver?
 

Likewise our team has had no issue with tapped 8020 and the standard kit frame bolts (same as 8020 bolts minus black oxide coating)

Re: Tap Driver?
 

What you're saying might be true in some cases, but not all. Consider any automobile with an aluminum engine. I have yet to see an aluminum engine with thread inserts as a feature, and the automotive world is one of the most cost-aware industries. I have used thread inserts for repair work where someone grossly over-torqued a fastener and sheared out all of the threads on a 20+ year old engine. They work great for that.

Helicoils require a tapped hole to start with, so you're not saving any time there. Sure you can replace the threads when they wear, but we're talking about an FRC robot that needs to last a few months, not an industrial machine or welding fixture that will undergo thousands of torque-down cycles.

I'm not terribly familiar with PEM products, but at first glance it looks like installation requires access to the back side of the sheet, which is not always possible. Riv-Nuts might be an acceptable alternative solution if their protrusion is not a problem. They still run the risk of failure without proper installation. It's awfully hard to improperly install a nylock nut by comparison.

What I'm driving at is this: the best is the enemy of good enough, especially in FRC where labor costs are 0 and where its much easier and cheaper to purchase and store a tap and die set instead of a press. Especially when one brings this equipment to competition.

Re: Tap Driver?
 

I can see what I said can be misleading. I need to better define what I mean instead of making a general statement aimed at the rookie user who doesn't know much about using threaded inserts vs tapping.

There are lots of ways to join two pieces together but the end result wanted is a cost effective method. I understand in the context of building robots running a tap and screw to join two pieces will work to get it done but we try to teach sound engineering principles to the the kids. Sorry if people misunderstand what I'm trying to say. In a polite manner just ask a question to clarify what I mean.

If the material is thin guage aluminum sheet it would be better to use a threaded insert to make a better thread. Rivnuts or Pem fasteners in thin wall aluminum tube is almost always a better choice. If tapping was wanted another way to get the needed threads per inch to create a strong thread would be to extrude the hole. Yet another way to join would be to use a self tapping screw and skip the tap.

The effects of galling in an aluminum thread is something people don't quite understand. That was my point in my response. If you used an aluminum screw with an unfinished aluminum thread good luck in trying to get the screw to come out. With time/pressure it will weld together.

If you use a steel screw with a aluminum thread it would work but again screw size and number of threads needed to make a stong thread should be considered. Think insert hardware. Lot's of diffrent kinds of hardware to get the job done. My point is if you used a 1/4 -20 tap in ...060 alum 5052-h32 it's not going to be a good thread. The tap will fail if any presure is applied.

The use of stainless steel inserts in aluminum is standard practice for aluminum parts that get anodized and the hardware is inserted before plating. If steel hardware was inserted before plating the plating on the hardware would be etched off and the hardware would turn black and rust. If the aluminum part was alodined or painted then steel hardware would be cost effective in lieu of stainless hardware.

Roll taps vs cut taps is another area lots of users forget to consider. What is better for the type of material threading.

And don't get me going on loc tight vs lock washers.

Getting back to the original question the Bosch tapping gun is the bomb. We have one and it works out great.

Re: Tap Driver?
 

That makes a lot more sense, I was struggling to see the logic if someone was dealing with thick aluminum plate or in my teams case 8020 where we can tap several inches if we desired/had the tap to do it.

One thing about the aluminum and aluminum welding together, that requires neither to have a oxide layer plus enough thermal energy for their crystal lattices to join.