Countersink M2-M2.5 screws not able to tighten the frames 4

[BreadboardPerson]

Hi, I assembled some frames using M2-M2.5 countersink screws but I noticed that due to the countersink shape, it seems that these screws are not able to mount the frames as tightly as those flat head bolt screws. I mean I could still slide the frames around after tightening up the countersink screws. Is this a common problem with countersink screws or just my specific case? I have tried both aluminum frames and 3D printed frames but I got the same issue.

 

[SnTMan]

BreadboardPerson, lots not known here, but: In a properly designed and manufactured assembly counter sunk screws should tighten it up as well as any head style. Although I'm not sure I'd count on such small screws to generate much clamping force.

I'd guess you've got some other kind of problem(s).

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[ctopher]

Is the angle of the c-sink correct?

ctopher, CSWP
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[3DDave]

Often the cone of the countersink is too deep (particularly if the part is thin,) allowing the screw to fit through the countersink and clamp on the mating part, not the item being retained. You can tell by dropping into the hole and seeing if any part of the countersink screw head sticks through.

 

[Tmoose]

Sometimes it is helpful to coat one of the c'sink surfaces with black or blue permanent marker. Either the screw head or the C'sunk hole. Not both.

After tightening, and disassembling the transfer of the marker to the uncoated surface and marks in the coated surface should help make it clear what is touching and what is not.

My Holokrome catalog only has dimensions for flat head screw screws down to 3 mm.

There are some here -

https://www.mcmaster.com/screws/fla...etric-alloy-steel-hex-drive-flat-head-screws/

 

[mfgenggear]

possibility the tapped thread length is not deep enough

 

[hydtools]

What 3DDave said. Also it is all but impossible to have all c'sk screws in a pattern to all seat well unless each hole is match drilled in place.

Ted

 

[mfgenggear]

Or the length of thread on screws are bottoming out prior to seating of c'sink head

 

[RRiver]

There are some other issues not yet mentioned:

1. Improper drill size for the material. The standard suggested drill isn't always right for the materials.

2. The use of the wrong type of tap. Did your tap have enough lead taper for the material? Did the tap pull up or pucker the mating surface? Bottoming taps should usually be a second tap used. Bottoming taps used in holes that weren't bottom drilled often creates problems.

3. Tap thread tolerance. Did your tap thread tolerance match the fastener thread tolerance? Are the threads properly meshing?

 

[rb1957]

use glue.

another day in paradise, or is paradise one day closer ?

 

[IRstuff]

or VHB

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[Jboggs]

All of the above comments are a good summary of why I avoid using flat head screws at all if any other options are available. When you think about it, the whole reason that clearance holes are larger then the screws that go through them is that usually the precise location of the tapped holes is somewhat inaccurate. The size of the clearance hole allows the final screw position to align with the tapped hole and still hold the untapped piece tightly. BUT... cone-shaped countersinks create a very specific centerline location for the screw. In order to function properly the screw must have contact all around the countersink. The centerline of the countersink and the centerline of the tapped hole are NEVER in perfect alignment, which means you are always inducing some lateral load on the screw. It also means that the contact force of the screw on the countersink hole will vary widely around its circumference. If those screws are in a pattern, once one screw in the pattern is tightened all the others will be slightly off position. We're talking thousandths of an inch here, but it might as well be feet. That misalignment can also cause the screws to gall up in the hole, making their removal very difficult. Experienced machinists will tell you that the most common type of screw to have to drill out are flat heads. Bottom line? Find another way. If the presence of bolt heads is a problem use counterbored holes, or maybe use button head screws.

 

[mfgenggear]

Well said Jboggs

 

[kjoiner]

If you are working with material thinner than the head of the screw, you can sometimes get flat head screws with undercut heads.

Kyle

 

[Tmoose]

I think I saw BreadboardPerson walk by the window earlier today ( June 2 ) but did not stop in to say HI .

I'm wondering what he found out about screw head contact, bottoming etc and etc for his screws, installed in his frames.

thanks,

Dan T