Self Tapping Screws

[RunnerDuck]

I am having a hard time trying to get the self tapping screws I bought to drive into the square steel tube of my frame. I thought they would work as they seemed to work for a friend of mine but I can not get them to "drill" into the steel to get the threads to catch.

I've been trying to predrill the holes but even getting a bit into the steel seems to be difficult. I'm even using a carbide bit and cutting fluid and it still takes forever.

I'm going to use them to screw the floor to the frame.

Here are the screws I'm trying to use.

Screws001.jpg (107.78 KiB) Viewed 1952 times

Any suggestions on what I might be doing wrong?

[scooter bob]

From the picture it looks like the wings below the thread will create a hole larger than the thread. I would try another type without wings.

[MtnDon]

Aren't common carbide bits usually designed for drilling masonry / concrete and do a poor job on steel or even wood? But I do understand there are others that are made for drilling hardened steel with cutting oil. I guess it depends which bit type you are trying.

A good, sharp ordinary hardware store steel bit should drill any steel I've seen used for a frame. Sharp, is the key.


Scooter bob, the wings are there to drill a large enough hole through the wood that is to be attached to the metal member. They are designed to snap off when they hit the steel. The idea is to drill a clearance size hole through the wood in order to snug down properly. Those things do work very well on normal mild steel, in my experience.

[H.A.]

M

[Shadow Catcher]

Depending on the steel and how it was rolled it may have been surface hardened, I would find a high speed steel drill bit (harder) and give it a try. There are also differences in quality of self tapping screws.

[RunnerDuck]

Thanks for the comments. The tubing I'm using is 2" X 2" X .120" steel. There should be nothing special about it.

I'm using a hammer drill after trying a regular drill but it turns pretty fast, perhaps that's the problem. I might be work hardening the tubing.

It does seem odd that new machine grade drill bits won't drill though it without a huge amount of pressure. Even the carbide drill bit has a lot of trouble with it.

Seems very strange but I really need to figure it out before I try and set 30 screws around the edge of my floor!

[MtnDon]

I'm using a hammer drill after trying a regular drill but it turns pretty fast, perhaps that's the problem.

... not in hammer mode though?

That 2x2 x 0.120 steel.... probably 'normal' mild steel? That should drill easy.

I've used literally thousands of self drilling screws in working with metal framed buildings. Every once in a while I run into a screw that just does not want to cut into the steel. Probably some manufacturing defect... Have you tried more than one screw? Have any new, unused drill bits to try. I normally use variable speed 1/2" capacity drills with moderate speed (in low gear).

Granted the steel building frames are not .120" thick steel. However I used screws as pictured for the floor in out cargo trailer conversion and only had one or two stubborn ones. That has 0.093 frame thickness (I think).

[Vedette]

Okay Ken
Just grasping for straws here. And I don't want you to take this wrong.
But, is your drill set on the right rotation direction.
Brian

[Jrst67]

I've run self tappers through 1/4" wall tubing. It's slow going but they will go through. Could it be you are trying to drill through the seam? Still shouldn't matter but it could make it more difficult.

[vegask]

Those really look like self tapping concrete screws to me. Self tapping metal ones are much more coarse of a thread and do not have wings. They have a groove and the "tapping" portion of the screw is a smaller diameter than the threaded part of the screw.

[RunnerDuck]

All great comments and Brian, no offense taken, any suggestion is a good one but in this case I did check the rotation and it's correct

MntDon, why not a hammer drill or impact drill? It seems like that would help break the surface. And yes I've tried many different screws with no luck.I also used a brand new carbide bit right out of the package.

Something strange going on.

[MtnDon]

Nothing wrong with the screws as to intended purpose. link page As was stated before the wings serve as cutters to make a hole for the screw through the wood.


Hammer drills are designed to make drilling concrete and masonry easier. The impact breaks up the sand, stone that is cemented together. Article

Common carbide bits that we buy at the hardware store or home improvement center are usually the type that are meant to drill masonry / concrete. Link to sample of bit Those use carbide that is actually quite dull; the edges not sharp. Carbide is used for it hardness. There are carbide bits that are designed to drill metal, mostly meant for hardened steel. But where I live you don't find them at home centers. Some of them look the same as a standard high speed steel bit, others are different. Tube steel like you have is not likely to be hardened so should not need a carbide bit for steel.

Bits that are meant for drilling steel have a sharp cutting edge, 118 degrees for a wood design and 135 for metal, though they can be interchanged. They work by slicing into the steel / metal as the bit rotates. It is a pure cutting or slicing action. If used in a hammer drill the hammering would dull or chip that edge the same as taking a chisel and smashing it into steel. The sharp edge of the tip should rotate smoothly and cut into the steel removing a spiral of metal, or at least smaller chips. The tips of the self drilling screws work the same way. Self drilling screws are designed to drill a hole one time unlike a drill bit. Using hammer action drilling with one of them probably flattens the cutting edge within a couple of blows.

You also mentioned an impact driver; not the same thing as a hammer drill. Whereas a hammer drill actually pounds the bit forward into the material being drilled at the same time the bit is rotated, an impact driver applies the impacts to the bit in a rotary motion. No forward hammering. Impact drivers are great at driving long wood screws. I must admit I've never used mine to drive a self drilling screw. It should work as the motion is all rotary. The danger might be in overdriving and compressing / tearing the wood unless the driver has a clutch.

[RunnerDuck]

Problem Solved!

Thanks everyone for your fine input and education, it really is appreciated.

Have you ever heard the term: "The right tool for the right job"? Well that along with "Using the right tool correctly" solved my problem, sort of.

I know now that I was running my drill way too fast and work hardening the steel. Also I believe that the bits I had were not up to the task.

I went to Fastenall this morning to see if they had any better screws and they didn't have what I wanted in stock. But they did have some nice "HSS 135[DEG] Split Point Black & Gold Finish Jobber Drill" bits. I found a drill in my collection that ran at a nice slow speed. I applied tap fluid and in no time drilled eight holes. I added a little tap fluid to the screw and zipped it right in.

I did try putting in a screw without predrilling and while I do think it will work it was just easier to predrill the hole.

I'm a happy guy and am moving on

[blentz]

I used the same screws on a gate awile back, worked fine. There may be another problem. Depending on the grade and if the steel is heat treated. On my trailer I just drilled completely through the frame and used nylock nuts