I would look into a tap and die set rather than trying to under drill
Just load the tap into a cordless drill (or drill press if you have access to a reversible one).
Hi. I found nothing with google, so I ask here: which is the right diameter for holes in a steel plate, so that the screws exactly fit in? I'm not sure, but for M3 screws (self-tapping M3), a hole in steel with 2.7mm diameter shall be ok, is this true? With a soft material such as wood, it doesnt matter much. You drill a hole, and almost any screw finds its way in. But steel is not that soft, the holes must not be too tight, nor too loose. So i don't want to make a mistake at this point.(What I got to know so far: M3 screws are allegedlynot 3mm in diameter but 2.9mm. The recommended core drill hole for M3 is given with 2.5mm. But AFAIK this refers more to soft materials, such as wood, not to steel. I guess that would be too tight for steel. Someone proposed me 2.7mm for steel. But not entirely sure.)
beast, these are the non drilling self tappers I was refering to. Technically they will drill, but they are meant for very soft metals like tin duct work for the HVAC in your house or similar materials.Show Image(http://www.use-enco.com/ProductImages/8790769-23.jpg)
Eszett, I personally wouldn't use self tappers. They are a pain if you have to remove and reinstall them multiple times. Plus, they don't like stainless. I am speaking from experience there. If you are using stainless, tap the holes by hand. Judging by your questions, I am assuming you don't have a lot of metal fabrication experience. In this is the case, I would def hand tap, and make sure you use cutting fluid. Don't do this in the house, as most have a very noticeable odor, and will stain about any thing non metal it comes in contact with.
Unless you have access to a mill with good speed control, you are just going to break taps. They aren't going to be that expensive in those sizes, but they are extremely hard and difficult to remove without destroying the rest of the threads and the hole. Also, the grade of stainless makes a large difference as well. Most stainless steels are difficult to work with, personally I feel 304 is the most difficult to drill and tap due to it being relatively soft, gummy, and likes to stick to the bit. Though, 316 isn't to bad to work with.
Melvang, alright tap better by hand then ... You are right I have zero experience.
Would it be possible to leave the top and bottom plate holes unthreaded, and just the holes of the middle layer (acryl) to be threaded? Would that fix the whole case enough? In order from top down:
– top plate with 3.0 mm screw holes, M3 screws just slip through.
– acryl middle layer with 2.6 mm screw holes, M3 screws tap by itself.
– bottom plate with 3.0 mm screw holes, M3 screws just slip through.
– finally, nuts to fix bottom plate with screws.
Just load the tap into a cordless drill (or drill press if you have access to a reversible one).
And if you do use a cordless drill be very careful because the taps can break easily, especially in something like steel. And if you break a tap off inside the hole you're gonna have a bad time.
Personally I would try to use a hand tap unless you have monk like precision. With a sharp tap most stainless alloys should be able to be hand tapped.
Do you guys really think a hand drill is a bad idea in something as thin as plate steel? I was trying to save him from having to purchase a tap wrench.
Thanks for the recommendations. Well, I have a 2.5~2.6mm hole in a 1,5mm plate, that means the hole is wider than deep. In this case to tap a thread correctly perpendicular ist not that easy. I think about better visiting a local machine shop for this.
Thanks for the recommendations. Well, I have a 2.5~2.6mm hole in a 1,5mm plate, that means the hole is wider than deep. In this case to tap a thread correctly perpendicular ist not that easy. I think about better visiting a local machine shop for this.
In high school I was on a robotics team. We built robots. It was cool. They taught us how to tap holes. If my dumbass could tap a hole when I was in high school, I have faith you can do it too.
Melvang, alright tap better by hand then ... You are right I have zero experience.
Would it be possible to leave the top and bottom plate holes unthreaded, and just the holes of the middle layer (acryl) to be threaded? Would that fix the whole case enough? Or, perhaps, this method, in order from layering top down?:
– top plate with 3.0 mm screw holes, M3 screws just slip through.
– acryl middle layer with 2.6 mm screw holes, M3 screws tap by itself.
– bottom plate with 3.0 mm screw holes, M3 screws just slip through.
– finally, nuts to fix bottom plate with screws.
I did not use a cutting fluid as Melvang suggested, but he is one of the pros here when it comes to machining. I was tapping all my layers together, so I lined them all up by putting skewers through all the holes and then clamped everything together and tapped it. I was very careful to clean my tap often...
@Melvang Thanks for the recommendations! I understand, that it doesn't make sense to tap all layers, since this construction will have zero tolerance to misalignment. What I do not understand ist, why you don't recommend to tap the middle layer only? What is wrong with that?The only way this would work is if you had a very thick middle layer that both sides could screw into otherwise it would not hold all the layers together.
If you are only going to tap one layer, I would just tap the bottom layer and screw everything to it and just have screw heads on the top. Am I making any sense?
Every layer needs something to hold it in place. The top layer should be held in place by the screw cap. The bottom layer is held in place by the threads. And the middle layer is held in place by the top and bottom layers.