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

dxqcanada

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Unimat DB/SL's can sell for up to $1000 ... way overpriced but it has become vintage ... yeah, so better investigate something new for less.
I also have a Unimat DB200, but I was lucky enough to have it gifted to me ... awesome lathe/mill for my camera repair work.
 

Laurent

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Andreas Thaler said:
Confirmed today

Post in thread 'Stubborn screws: Milling out screw heads, recommendations for milling cutters'
https://www.photrio.com/forum/threa...tions-for-milling-cutters.205826/post-2783854
Click to expand...

I had a chat with my son about this. He's a very good machinist, and his first thought confirmed one of my doubts: the "cutting speed" (not sure how the french terms translate in english. This is the actual speed of the cutting edge in the matter to be cut) for stainless steel is around 15m/s (he comments "according to Dormer, and they tend to be thugs") which gives a rotating speed of more or less 2000rpm for a 2mm bit, and this is quite slow for a Dremel or similar tool.

That may explain why HSS may have hard times cutting stainless steel on a Dremel or other small rotating tools.

Regular steel is machined at around twice that speed, which would give 4000rpm, closer to the Dermel range.
 
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Andreas Thaler

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Dremel recommends for the here shown HSS cutters 15 to 25,000 rpm. It worked well with 20,000 rpm.

The cutters will probably be put under a lot of strain, but I have enough replacements to experiment with the drive working best.
 
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koraks

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Laurent said:
his is the actual speed of the cutting edge in the matter to be cut) for stainless steel is around 15m/s
Click to expand...

15 meters per minute (not second) sounds right. The circumference of a 2mm bit is around 6mm. 15000/6 = 2500rpm, which is close to the 2000rpm your son suggested.
See here: https://en.wikipedia.org/wiki/Speeds_and_feeds

Andreas Thaler said:
It worked well with 20,000 rpm.
Click to expand...

You removed material at 20krpm. I wouldn't say it worked "well". You got away with it - with the inevitable wear & tear and risk of damage to tools and workpiece.

A Dremel isn't a proper machine tool. It's an allround device made for odd jobs around the house.
 

Laurent

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sorry, yes, meters per minute...
 
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Andreas Thaler

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It worked, try to look at things positively from my point of view.

I will continue to experiment with the speeds, once one cutter is used up, the next one comes.

The Dremel meets my requirements, what else could it do better.
 

DREW WILEY

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You don't find dentists using Dremel tools except in third world countries; nor are fossil bones removed form their matrix using hobby tools like these. There are far better options both air driven and electric for those who need and can afford them. Dremel tools are ubiquitous and quite affordable, but need to be used with a steady hand or some kind of support frame, and one must be conscious of the correct RPM for the application. That applies to all drills and grinders as well.

You also need to keep in mind that if a bit or cutter breaks at very high speeds of rotation, the fragments can fly off at dangerous speed almost like a bullet. That fact applies to every category of fast rotation, including routers, die grinders, hobby tools, and saw blades. Ideally wear a full face visor and not just safety glasses.
 
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Andreas Thaler

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I will tell you about the next screw that I had to remove with force.

But I will also further work on being able to remove the problem screws - in my case the ones that were secured with adhesive. Heat, solvent, that worked well in some cases.
 

DREW WILEY

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Andreas - Fisch made many of the best high-speed drill bits, along with screwdriver tips. But I distributed them through the much more inclusive Festool label. Over the years I was also given a huge assortment of samples for personal use, including carbide items. We had the biggest selection of some of these brands in the US, and the highest sales, at least under my tenure. A lot of it came from Europe.
 
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Andreas Thaler

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My father had a milling machine in his wood carving and carpentry workshop. Big, green, heavy, as high as a table. For working on beams and boards. A monster.

There were three five-centimeter-long knives in the milling head that you could clamp in. One time one of them came loose and got stuck in the wall opposite.
 

DREW WILEY

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I didn't sell that much heavy equipment, but sold at lot of portable equipment to the cabinet shops and furniture factories. One down the street had a planer that would do four sides at a time, and cost around $250,000. In our own shop there was some awfully big woodworking equipment too, running on 440Volt 3-phase. Before I retired I made it a point to replace some of that with safer more modern gear.

Jointer accidents were common at the furniture factories. I don't know why they didn't use power feeders routinely. The foreman at one of them had to sign paperwork with his little finger, because all he had left on both hands were a little finger apiece. I've seen piece of carbide fly off shapers and embed themselves two inches deep in wooden beams on the opposite side of the room. Typically the wrong rake angle to the tip for the kind of material involved, or else too high an RPM.
 
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Andreas Thaler

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BobUK said:
Any chance of a photograph of the "special pliers" ?

I am very curious as to what they are.
Click to expand...

Sure, I am sorry!

PZ-57 | ENGINEER INC.-Global

How to remove stripped and damaged screws? 5-inch Screw Removal Pliers for electronic components, PCB, mobile phone, game console, etc. 120mm small-sized body and ESD-safe handles. PZ-57 NEJI-SAURUS
www.engineertools-jp.com
 
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Andreas Thaler

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Today freehand with the Dremel:









See

Nikon F4: Mission Aperture Lever - two ways to fix the aperture problem

{Moderator note 12 Jan 25: five threads on the F4/F4S aperture lever repair have been merged into the present thread. You may encounter one or two dead links to 'other' threads. The posts they pointed to, are now all part of this thread, which mostly still follows the journey in a logical and...
www.photrio.com
 
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Andreas Thaler

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Drilling and milling exercises

Today I continued practicing drilling and milling screw heads made of steel.

Participants were:



A nameless SLR for practicing with steel cross-head screws in the bayonet ring.



  1. HSS cutter
  2. Diamond cutters
  3. Tungsten carbide cutters
  4. HSS cobalt drills

The cutters (Dremel) were used on the Dremel 4250 with 25,000 rpm.

The drills (right-handed, Bosch) were inserted in the cordless screwdriver Bosch GSR 12V-15 (max. 1,300 rpm) and used with cooling lubricant.


HSS cutter





Although it has the perfect shape for the job, it is not designed for milling steel.

The cutter obviously overheated and the cutting edges on the front became blunt.


Diamond cutters



The cutter with the conical tip removed steel well. It allows you to work in a controlled manner and is suitable for milling small volumes.

The smaller ball-head cutter had a weak grip and is better suited for engraving.


Tungsten carbide cutters



These cutters cut through steel like it was butter. But they are too big for the job and therefore remove material around the screw head. They also tend to bounce off when they are placed.


HSS cobalt drills



They cleanly remove the upper part of the screw head, leaving the surrounding area intact. But they do not separate the screw head from the thread.


Results



I had worked on the screw at nine o'clock with the drill and then with a tungsten carbide cutter, which slipped when I started to use it. But the screw head is completely removed.

I first worked on the screw at eleven o'clock with the drill too and then with the spherical tungsten carbide cutter. The cutter was too big for that.




But it also shows impressively on the bayonet ring what it can do with steel.




I worked on the screw head at seven o'clock, first with the drills (from small to large) and then with the diamond cutter. The screw head is off, a satisfactory result.

All other screws fell victim to various combinations of cutters and drills and I have not documented them here.


Conclusion
  • The HSS cobalt drill bit enables a large part of the screw head to be removed precisely.
  • The remaining work is done with the diamond cutter.
  • The rest of the screw can be unscrewed with the Neji-Saurus (Engineer PZ-57 pliers); there must be a protrusion for this.

+++

All information provided without guarantee and use at your own risk.
 
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Reginald S

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1) HSS is an old german term which means "Schnellarbeiterstahl".
This has nothing to do with speed. It's just tells about the quality of the steel, which is good enough for milling or drilling smooth steel, brass and aluminium.

2) Your link shows a "Formfräser", in this case a kind of arrowhead shaping angles and triangles.
Concerning it's small diameter it has to rotate fast (high speed) as seen in the description of this product.
 
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