This may not be the right forum for this type of question but I didn't know where else to go. My question is about the aluminium frame I'm building, it is made out of 3D printed joints and aluminium extrusions. I wanted to connect these two different types of components using threads in the aluminium and regular M3 bolts. I drilled the holes with a quality 2.5mm drill bit and made the thread with a cheap Chinese 3mm tap bit. When I screw in the bolt I cannot get it tight enough because it destroys the thread when I apply only a little bit of force when it is completely in. I also tried to directly screw in the M3 bolt in the 2.5mm drilled hole, this creates the thread but I get the same weak thread. Is my material too soft or am I doing something else wrong? My aluminium is EN AW-6060 T66 grade quality. Thank you.
6061 aluminum is tougher and threads will last longer. BUT, the industry always uses "pressed in nuts" for threads that will be used over and over. Google that and look at the images for suggestions.
This may not be the right forum for this type of question but I didn't know where else to go. My question is about the aluminium frame I'm building, it is made out of 3D printed joints and aluminium extrusions. I wanted to connect these two different types of components using threads in the aluminium and regular M3 bolts. I drilled the holes with a quality 2.5mm drill bit and made the thread with a cheap Chinese 3mm tap bit. When I screw in the bolt I cannot get it tight enough because it destroys the thread when I apply only a little bit of force when it is completely in. I also tried to directly screw in the M3 bolt in the 2.5mm drilled hole, this creates the thread but I get the same weak thread. Is my material too soft or am I doing something else wrong? My aluminium is EN AW-6060 T66 grade quality. Thank you.
Getting a decent thread in aluminium is an art form but not impossible.
Must have a good quality tap and usually a taper tap to begin with and a new sharp drill bit.
Must use some form of cutting lube such as (best) aluminium tap magic for both drilling and tapping.
Must turn in 1/2 turn then back 1/3 turn to break of swarth.
Must use some form of guide to stop the tap wobbling around during the tapping process.
Must withdraw tap and blow out debri on a regular basis while tapping if hole is blind.
Thank you very much for all the responses, I think I'll try self-tapping screws first as it seems like the easiest solution. My material is 2mm thick so there are enough threads and the thread pitch is the same on both the screw and the tap but I think the threads are simply too fine for the soft material. If none of this works out I'll consider rivet nuts but that would require some design changes and redoing a lot of already finished work. Thanks again all!
One other option for you. DO NOT drill holes for the threads. Make the hole with a punch of some type so the aluminum is deformed and then tap the threads. Much more surface for the threads.
Since the rule of thumb for materials like steel is material thickness = bolt OD - so it was not going to work - just not enough material for strength in the threads - so pick one of the other suggestions above.
I have had good results in Aluminum using thread inserts so the insert grabbed a larger diameter of material - but I have not tried that method for 3mm bolts
first off, thread cutting taps are a no-no for softer materals. you use a thread forming tap. it shapes the metal and work hardens at the same time. MUCH stronger threads.
second there is an H number on taps. an H3 is a very sloppy thread it leaves a larger center hole and the threads engage only about 60% so 40% is not supported.
an H2 is a smaller clearance and has more support on the threads. this is the most desired for common use.
an H1 is harder to find and leaves a smaller and tighter hole. but, you have to get good screws, not the mass produced ones that are every bit as sloppy as the tap.
in addition, you need to get coated or clad fasteners. stainless and aluminum do not mix, they WILL react with each other and over time will destroy the aluminum.
a nutsert or rivnut will allow you to remove and replace screws as needed.
as others noted, not all metals are hard enough to work.
when cutting aluminum, you should let it sit for a day to anodize. the oxygen on the fresh aluminum creates a sort of skin. over a day the thickness of this skin increases to the point it stops the oxidation.
when cutting aluminum in a shop, the freshly exposed aluminum is so soft it can gum up the cutter tools. on a lathe or mill, you use a cutting fluid to eliminate the gummy adhesion of the aluminum.
Interestingly the oxidation is so fast on exposed aluminum, a simple skin forms instantly, before the part or cutter make a revolution. The depth increases rapidly and if you were not educated in the natural anodizing, you would never know about it.
lastly, the amount of force created by a screw is huge. your simple wrist turn might put 100 pounds of force on the threads. so be VERY careful with how much pressure you use.
saildude:
Since the rule of thumb for materials like steel is material thickness = bolt OD - so it was not going to work - just not enough material for strength in the threads - so pick one of the other suggestions above.
I have had good results in Aluminum using thread inserts so the insert grabbed a larger diameter of material - but I have not tried that method for 3mm bolts
good point. # of threads engaged is important as well.
aluminum should be 1.5 or 2x bolt OD
for sheet metals, there are lots of options for fasteners.
Rivnuts are just that, nuts. they also make threaded posts so you use a regular nut on the post.
dave-in-nj:
first off, thread cutting taps are a no-no for softer materals. you use a thread forming tap. it shapes the metal and work hardens at the same time. MUCH stronger threads.
second there is an H number on taps. an H3 is a very sloppy thread it leaves a larger center hole and the threads engage only about 60% so 40% is not supported.
an H2 is a smaller clearance and has more support on the threads. this is the most desired for common use.
an H1 is harder to find and leaves a smaller and tighter hole. but, you have to get good screws, not the mass produced ones that are every bit as sloppy as the tap.
in addition, you need to get coated or clad fasteners. stainless and aluminum do not mix, they WILL react with each other and over time will destroy the aluminum.
a nutsert or rivnut will allow you to remove and replace screws as needed.
as others noted, not all metals are hard enough to work.
when cutting aluminum, you should let it sit for a day to anodize. the oxygen on the fresh aluminum creates a sort of skin. over a day the thickness of this skin increases to the point it stops the oxidation.
when cutting aluminum in a shop, the freshly exposed aluminum is so soft it can gum up the cutter tools. on a lathe or mill, you use a cutting fluid to eliminate the gummy adhesion of the aluminum.
Interestingly the oxidation is so fast on exposed aluminum, a simple skin forms instantly, before the part or cutter make a revolution. The depth increases rapidly and if you were not educated in the natural anodizing, you would never know about it.
lastly, the amount of force created by a screw is huge. your simple wrist turn might put 100 pounds of force on the threads. so be VERY careful with how much pressure you use.
