Cutting a screw while minimizing the damaging effect of vibration

Question

I need to cut some screws (from M3 to M4) coming out of a LCD screen. What technique would you use to avoid damaging the device with vibration?

I was thinking of using a Dremel cutting wheel. Sawing by hand or cutting it with a pincer/tenaille would need some file work after, and thus cause more vibration.

The screws have been placed to repair the device (a cheap fix), but they come out of it. They are too long, and I need to cut them just at the bolt limit. For some reason, it's not possible to remove them before cutting them.

Answer 1

The Dremel style tool with an abrasive cutting disc is your best option. These come in a couple different sizes and durability options.

Dremel disks

I go for the smaller, heavy duty disks. These are usually the darker color ones, like the one pictured. The red ones tend to be the "light duty" style and will tend to crack just installing them. The dark ones can crack when installing, but not as easily.

Using the smaller diameter disc will help prevent vibration and other problems, just take it slow and with deliberation. Just like with almost any power tool, you don't want to start the motor with the disk touching the material, and approaching the material slowly will help prevent any vibrations due to the shock of touching the spinning wheel.

These disks can also be used to file off any burrs as well as just generally rounding off the exposed end of the screw. Doing this will help fix the threads so the screw will be able to be removed, eventually. These disks are also thin and easily maneuverable. Being thin will help prevent vibration.

Also, there's likely a speed setting that'll help prevent vibration. Too high of speed and you won't be able to keep the disk on the screw, causing vibration. Too slow and all you'll be doing is vibrating the device.

The large diameter disks are nice, but they are 2-3 times thicker and much harder to control in tight spaces, as well as with small parts. They are great for larger cutting things, but as tiny a screw as you're talking about, it' not appropriate.

Hand tools

A hand saw would need very fine teeth to prevent vibrating, and you won't be able to control it as easy as the Dremel tool. The thing with a hand saw is that you sacrifice speed for control. You can have all kinds of control, but it's going to take you at least 10 times as long to cut through the piece.

Also, you'll still need to file off the burr and fix the threads. Using a hand file has the same problems as the Dremel and the hand saw. Too fast and you create vibration, too slow and all you're doing is vibrating the material. Too fast and you lose control, too slow and you're just vibrating the material.

Answer 2

You did not tell what "sensitive device" means. Is it mechanical? Electronic? Mixed? Anything else?

If vibration is so dangerous, I see very few options:

• just do nothing - assuming that the extra length does not impair the use;
• use pliers; if you use gradual force (paired with press-release cycles), you should be able to do it without any relevant vibration; if you use force, there will be some kind of good shock when the screw is actually cut;
• cut it chemically; it might take a longer time, but there will be no vibrations at all; apply some small amount of acid at the point of "cutting"; brush the rust; repeat until finished;

Depending of the material the screw is made of, other substances might work also, besides acids.

Answer 3

You can minimize vibration by increasing the MASS of the device by clamping the device to something very heavy such as a large table (where it can be seen, examined, modified, etc.) or something more portable such as a bar-bell weight plate so that it can be moved around while working on it.

Then, the finest tooth dremel cutting wheel can be used. The vibration will be damped proportional to the amount of MASS increase. A 25Kg plate is more effective than a 10Kg one.

IMPORTANT: This repair can only be used ONCE because after you cut the head off a screw fastener you cannot make any further adjustments. You cannot tighten it further or remove it without drilling out the screw and using an extractor.

I strongly recommend you take the device out of operation and use headless set screws to replace the longer screws you dislike for aesthetic reasons.