screw holes in steel?

[Eszett]

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.)

[neverused]

I would look into a tap and die set rather than trying to under drill

[njbair]

I would look into a tap and die set rather than trying to under drill

Absolutely. Or rather than a set, if you only need the M3 you can find individual taps for sale as well. Just load the tap into a cordless drill (or drill press if you have access to a reversible one). And use some lubricant, especially if you're doing a lot of holes. Tap Magic is really good lube, even if it smells like a zombie ate a skunk and pooped it out onto a dead fish.

[jbondeson]

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.

[The_Beast]

If you're in a pinch and can't reference a chart, I've had decent luck with going slightly bigger than the cress of the fastener (in other words, measure the small diameter inside the thread, and pick a drill bit slightly bigger). But again, my main area of work has been wood, not metal.

In your case, you're using self tapping screws, so I wouldn't lose too much sleep if you don't have exactly the right drill size.

[swill]

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.)

I found the same reference that The_Beast linked and ended up cutting my brass case with 2.5mm holes and then tapped them to M3.  It works perfectly...

Note:  I usually prefer my spiral taps for acrylic because they work great for soft material.  I found them to be harder to work with on brass (steel would also be the same) because of how hard the material is, so I preferred using my standard straight edge taps for the brass.

[Eszett]

Thanks, swill, I have to think about that ... I'm not sure yet whether I should use a tap or self tapping screws. But in either way, I have to pre drill holes, right? And 2.5mm are the right number for both methods, taps and self tapping screws?

[Melvang]

If you are using self tapping screws, all the ones I have used were self drilling.  Meaning they drill their own hole.  If they are sheet metal screws, with a coarse thread like a wood screw, then those won't work in steel.  At least not self tapping, especially stainless.

[The_Beast]

Like Melvang said, most self tapping screws (infact, I've never seen a self tapping that didn't) have a tip that acts like a drill.



But pre-drilling might not be a bad idea, since the screw may slide before the drill part of the screw starts actually starts cutting a hole.

[Eszett]

@The_Beast @Melvang And what is the standard method of "Do-it-yourself" keyboard makers? Tapping screws or tapping? Hand tapping or tapping with a drilling machine?

[Melvang]

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.



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.

[The_Beast]

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

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.

However, if you rotate that screw just a bit, I'm sure there is a relieve cut, not quite as drastic as my picture, but one that still allows it to drill a starter.

Anyways, I second Melvang, self tapping screws are meant for production runs of something that doesn't get taken apart very often or at all. I'd fully trust his advice with stainless grades, my limited metal working knowledge pales in comparison to his. You can still use a mill/drill press to make sure the tap is perpendicular to the surface being tapped, hat should make tapping a bit easier.



Also make sure you break the chip being formed but reversing the tap a half/quarter turn for every one to two turns forward you do. Slows things down, but it ups your chances of not breaking a tap (not fun at all).

[Eszett]

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.

[swill]

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.

If you are going to put nuts, then there is no point in tapping IMO.  I tapped my case so I could avoid nuts completely.

I also second The_Beast's suggestion to reverse the rotation of the tap for a 1/2 turn every turn or so to stop the tap from getting saturated.  When I did mine, I even removed the tap completely a couple times when I got to the bottom 3mm plate to clean the tap.  These taps are small and it didn't feel right (too much resistance) and I didn't want to break the tap, so I was very careful.  It pays to be careful... 

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...

[neverused]

Another alternative would be sex bolts aka Chicago screws, that may be a viable option

[Snowdog993]

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.

Definitely a hand tap for a project like that.

[njbair]

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.

[Snowdog993]

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.

You can use a hand drill to make the initial hole, but definitely use a tap wrench to make the threads.

[Eszett]

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.

[CPTBadAss]

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.

[njbair]

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.

Is that where you built your avatar?

[The_Beast]

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.

If I'm understanding this right, it doesn't really make sense to tap the middle plate. I would just use the nut to secure the case together. The threaded middle part doesn't really add anything other than maybe slightly easier case assembly. I would tap just the top OR the bottom plate and have clearance holes (slip through) on the other 2 plates. Or even easier, just use bolts and nuts to secure the layers together.

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...

Tapping all the layers may lead to problems if the threads some how get out of alignment in the future. Like my suggestion above, I would have only tapped one of the layers and used the head of the screw and the thread to smoosh the entire assembly together.


Also remember to buy the right tap for the type of hole you're drilling. If it's a blind hole (one that doesn't go all the way through the plate) buy a bottom tap. However, if it's a through hole, buy a taper tap. They are a million times easier to get the thread forming started.

[Eszett]

@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?

[swill]

@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.

To me, tapping the middle layer is pretty pointless because you would then still have screw heads on the bottom, so how is this different from using normal holes and nuts on the bottom?

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?

[njbair]

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.

[Eszett]

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.

Agreed to both of you. However, I thought about tapping the middle layer only, and having screws on both sides of the sandwhich, top plate and bottom plate. By this I have no ugly screw tips (or nuts) showing.