Stubborn screws: Milling out screw heads, recommendations for milling cutters

Andreas Thaler

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Stuck screws, secured with adhesive, that I can't loosen with solvent or heat have put one or two of my projects at risk.

Because if a screw doesn't come loose, you can't go any further, e.g. dismantling a lens bayonet.

To make progress, I tried using a screw extractor and a drill, but that was almost unsuccessful.

But I can continue with a tungsten carbide milling cutter on the Dremel.

I mill off the screw head that holds two parts together. The rest of the screw can be unscrewed comfortably with the Nejisaurus pliers (see below). This way, the thread is retained.

I work with the egg-shaped tungsten carbide milling cutter from Dremel:

9911 Cutting & Carving Bits | Dremel

Dremel 9911 1/8 In. (3.2 mm) Tungsten Carbide Carving Bit
www.dremel.com

I'm very happy with it, it works through metal like it's butter, and the shape is also suitable for my purpose.

It is just a bit too big for my application and this usually causes damage around the spot I am working.



The two adjacent screws were milled out with the tungsten carbide cutter on the Dremel causing some damage to the tripod plate.

With the PZ-57 (Nejisaurus) pliers I removed the stuck remainders of both screws.

See

Post in thread 'Nikon F4 aperture lever issue: Removal of the mirror box, cleaning, lubrication, assembly'
https://www.photrio.com/forum/threa...ning-lubrication-assembly.205740/post-2781482


Do you have any recommendations for smaller tungsten carbide milling cutters?
 
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Ian C

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If you use a HANDHELD high-RPM grinder, it won’t be possible to precisely control the tool path. Some damage to the surrounding area is almost inevitable. Used in a handheld grinder, brittle carbide tools are especially likely to shatter due to vibration or if the cutter digs in to one side of the work.

If you can obtain the use of a small milling machine and have a way to hold the workpiece safely and securely, the screw head can be milled away precisely without damaging the part. This allows feeding the spinning tool into the stuck screw head in tiny increments that makes the process controllable and prevents damage to the workpiece and cutter.

For such occasional work, it isn’t practical to buy a milling machine. But you might be able to get the services of a small machine shop for such tasks. The amount of setup and machining time for such tasks is quite small and should be relatively cheap. You might get this done for free if you could submit it to a vocational school that trains student machinists. Many high schools and junior colleges have such programs.

For the task of milling off a screw head, you might need to drill a small center hole to clear away the central material slightly deeper than the depth of the screw head. Then mill away the head with an end-cutting milling cutter (plunge cutter). There are many sizes of small diameter carbide milling cutters available in catalogs of milling machine cutters. These are available via Internet from industrial suppliers. [This won't work properly in a handheld grinder.]

For example,

https://www.google.com/search?q=sma...AAGBYYHhgKmAMAkgcEMTguNKAHp30&sclient=gws-wiz
 

Dan Daniel

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An approach I have used on small brass screws that are not under 'high' load is to drill out the screw with a drill smaller than the body of the screw. Then dig out the wall of brass against the threads of the main body. Chase the threads with a tap. A cutter like in your dremel is a good way to make a starting hole. Hand-held center bit, really. If you do set up in a mill or drill press and can get good clamping, a center drill bit could be useful to create the start hole for drilling out.

Victor Machinery Exchange Inc. - Search Results

Search results from Victor Machinery
www.victornet.com

Now this kind of stuff is fine for side panels and holding parts that aren't much force. If the threads end up a little deformed or trimmed back a touch, everything will be fine. And the screw being brass means that the metal left in the threads will deform and be removable with a pick and such. I've seen people drill out a 10mm bolt on an engine block and chisel the remaining tube out by collapsing to the center. They plan on chasing the threads to clean out the metal and reshape the threads. A lens mounting flange is subject to gravity and jolts from walking/motion, and hand pressure, so you want to keep thread reduction or damage to a minimum, of course. But still, this isn't a rocket or car suspension- the forces are pretty small.

By the way, if you get a similar cutter but with a 3mm head, not 6mm, it's easier to do tight-in work. Like bit #SG-41 in the top group (expand picture, upper right column)
https://www.victornet.com/alphabetic/Carbide-Burrs-1-8-quot-Shank/37.html
Or here, pointed tree SG-44 is my choice because the head is 1/8" (3mm) like the shaft-

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
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Andreas Thaler

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To try it out, I ordered the not-cheapest tungsten carbide cutters from China, diameter 0.5 mm, on Amazon.

I'm excited to see how I get on with them.
 

mshchem

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Looks like you did a good job in a very tight spot! I always think of some exotic dental drill when confronted with these things. I would have buggered it up.

So did you use thread locker during reassembly?
 
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Andreas Thaler

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mshchem said:
Looks like you did a good job in a very tight spot! I always think of some exotic dental drill when confronted with these things. I would have buggered it up.

So did you use thread locker during reassembly?
Click to expand...

Thank you!

I should steal the drill bits next time I go to the dentist ...

I didn't secure the screws with glue. Who knows if I'll have to open the F4 again one day.

I'll practice with the egg-shaped cutter from Dremel. That should help you get even small screw heads out cleanly.
 

Laurent

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I tend to rely on standard Hss bits, rotated by hand in a hand-chuck (not sure if this is the right name, basically a shaft with a small chuck at one end, you roll it between filters. )

When the head is gone, it is generally easy to extract the part, then work on removing what remains of the screw.

Sometimes there'll be a small part of it that protrudes ans you can gran with pliers.

If not I try to drill the screw completely, as close to the diameter as possible so that I can tape the home gently to remove all screw remains. Works surpringly well, even is the screw is steel and the hole is in some tender alloy. The tap is roller between two fingers, that should be enough torque if you drilled big enough.

When you know the original diameter it isbeasier as it gives you the right but and tap sizes.
 

koraks

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@Andreas Thaler you've got that drill press you purchased a little earlier. Why not use it? It's a matter of clamping the workpiece at the proper angle and then use the dremel with a suitable bit. Otherwise you're going to end up machining away part of your thumb one of these days...
 
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Andreas Thaler

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So far I have failed at setting up the drill stand

The egg-shaped Dremel cutter cannot be placed vertically on all screw heads, as this causes bouncing. I imagine that if it is placed vertically at an angle it would be too inflexible on the stand.

But I will clamp the camera to be worked on in the Dremel vice. It has gentle plastic jaws and is very stable.

Guide the cutter with a well-supported hand and magnifying glasses over safety glasses.
 

Laurent

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A regular bit works surprisingly well in most cases. As it is designed to only cut from the front, it tends to go down only, and not cut sideways. At least this is the case for philips/JIS heads, where the head tends to guide the bit to the center of the screw.
 
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Andreas Thaler

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I have probably collected all the miniature cutters from Dremel, but I can only make progress on all the screws with the ones made of tungsten carbide.

The egg-shaped one is the only one that suits me in terms of its shape.

I am really looking forward to the 0.5 mm tungsten carbide cutters from China.
 
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Andreas Thaler

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My experiments with various tungsten carbide cutters (Dremel) on the Dremel 4250 on the drill stand of the manufacturer:






The steel of the screw heads on the bayonet of my training Nikon F4 is removed well, but none of the cutter shapes cuts the screw head completely off.

Perhaps the 0.5 mm tungsten carbide cutters will help to rework this.
 

Dan Daniel

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Essential Guide to Choosing the Best Center Drill

Master the art of precision machining with our essential guide on selecting the best center drill, covering types, sizes, angles, and usage tips.
www.cnccookbook.com

Countersinks - All About - Machinist Guides

Learn all about countersinks including what they are and how they compare to other similar types of features including multiple examples.
www.machinistguides.com

A different approach rather than grinding away the whole head is to drill in the center at the diameter of the screw or slightly larger. Eventually the head will be separated as a collar, not fully ground away. Same effect, less exterior damage.

Locate a source for machining supplies in Europe. In the US, there are places Like Victor, McMaster Carr. Not sure what is similar. Search for 'end mills, center drills' and see what suppliers show up and which ones will handle small orders? Assorted bits and cutters are in the $5-20 US range give or take.
 
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Laurent

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at the risk of repeating myself, a regular bit, smaller than the screw's head, give good results. Then one has to find a way for getting rid if the screw's shaft
 

tom williams

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Andreas - that's a tough job to do cleanly with the tools at hand: pliers and a moto-tool. Dremel makes a stand for the moto-tool, making it into a kind-of drill press - but it's very loose (sorry to admit that I bought one) and I think inadequate for precise work.

I thought Laurent and Dan Daniel made good suggestions, but hard to execute without at least a sturdy benchtop drill press. Ian C makes good points. I'm assuming you want to improve on the work shown in the photograph, as well as to find a more effective approach.

You can buy a decent, small, benchtop drill press - of the kind you might see in an electronics shop - for about what you'd pay for a couple of visits to your local machinist. I have one of these, and with it I can knock down a pan- or button-head screw head with an end mill, and follow with a center bit to establish a starting point for boring the screw shaft with a drill bit. Since I have appropriate end mills, I prefer to make the first bore with an end mill, which may obviate the center bit operation. For countersunk screws, post #15 applies to get to the top of the screw shank.

Starting with an end mill/drill bit that I'm sure is smaller than the screw shank, I can bore through the screw body. Following with successively larger drill bits, I can hollow the screw shaft out precisely, until the shell of the screw will spin out, or I can collapse the shell into the bore and pull the debris out, a la Dan Daniels' post #4.

I had access to a full-on machine shop to start with, and accumulated tools and bits of all kinds over the years, so the approach I describe seems simple and accessible to me, and it's consistent with my goals for a tidy repair. If you don't already have the tools, I fully endorse Rube Goldberg rules (being a regular user). But, I think you can field the setup I described for less than $200, in used parts. I paid $75 for a good benchtop drill press (used, and a bargain), and I think that the market for used bits is very buyer-friendly. A good vise, suitable for your drill press or substitute, makes a difference.
 
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Andreas Thaler

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Thank you, Tom
 
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Andreas Thaler

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From my side, thank you for all the information and suggestions!

So far, I've had the best results with the egg-shaped tungsten carbide cutter on the Dremel, which I use freehand.

But from what I've read here, there are much better solutions.

My limit is that I don't want to buy any equipment other than the Dremel because I work on the move. If I had a workshop, it would be easier, but I work in our kitchen.

With the Dremel cutter, the screw head can be milled out in a cone shape down to the screw shaft. If I sacrifice some of the material around it, see photo, I can remove the screw head.

I want to try this second step with the 0.5 mm tungsten carbide cutters from China. If I can work more finely here than with the Dremel cutter, it should work.


I grew up in my father's wood carving and carpentry workshop. As a talented craftsman and artist, he worked in many fields, so I know professional tools. Here, of course, I'm in the amateur range.
 

tom williams

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Andreas, it will be interesting to hear how you manage - you have some significant constraints. I'm sure I would break that tiny bit, or have it spin off across the workpiece. Good luck!
 
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Andreas Thaler

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tom williams said:
Andreas, it will be interesting to hear how you manage - you have some significant constraints. I'm sure I would break that tiny bit, or have it spin off across the workpiece. Good luck!
Click to expand...

Thanks!

If that doesn't work, I'll stick with the „Dremel egg“ and use the 0.5 mm cutter to work on soldering points. Maybe I can remove old solder with that.

I've come across soldering points on the Nikon F4 that I couldn't melt with the soldering tip despite adding flux.

Or other delicate work.

Tools are never superfluous
 

koraks

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Drilling PCB's (RF4 material) and sometimes softer metals such as aluminium. Forget about anything harder; I tried using them on copper once and that was a total failure; this was with the larger and much more sturdy 3mm bits.

You'll destroy at least a handful of these figuring out how to use them with a Dremel without breaking them on soft and thin materials. Anything hard or thick simply isn't going to work. The Dremel's torque simply snaps the bit instantly.
 
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