Does a low speed, high torque rotary tool exist?

[ASICMaestro]

I was reverse engineering a PCB recently and was using a rotary tool to remove the mask and it was really hard because it was so aggressive( with a round grinding stone). It's not the first time I've wondered this. Anyone feel me, are there options. It would be extremely useful for opening a via during trace repair too, especially in a press made for holding a Dremel, I break way too many bits doing this.

[tooki]

A regular drill is a low-speed, high-torque device. But I really don’t think you want high torque!

Sounds to me like the problem is technique: you want a light touch, and the right bits. I’ve never heard of using a grinding stone for any kind of PCB work. The usual is a small burr or round mill. And a light touch, did I mention that?

As for breaking drill bits in vias: the LAST THING you want is lower speed and higher torque!!! You need high speed, low torque, and very high rigidity. If you are using the Dremel-brand drill stand, there’s your problem: it uses plastic for all the important parts, resulting in an imprecise thing that flexes too much to use for fine drilling. You want a precision metal stand, like what Proxxon offers for its tools. (And those tools have lower run-out (eccentricity) than Dremel’s.) And you need to make sure the board does not shift AT ALL while drilling.

And did I mention a light touch? (I mention this because everything you describe hints to me at too much pressure being used, both in grinding and drilling.)

[jpanhalt]

A direct answer to your question (high torque, high speed) is something industrial, like a Dumore hand grinder (attachment).  They can be quite expensive.  The spindle is mounted in ball bearing and has very little runout.  There is quite a difference in feel when using something like that to grind instead of a Dremel.

But, as others have said, that is not what you need for removing resist.  For very small areas (a few mm square), I might use a small burr, but generally, I use a fiberglass scratch pen.  It does not risk cutting through the thin copper of the PCB (Capture2).

[2N3055]

I was reverse engineering a PCB recently and was using a rotary tool to remove the mask and it was really hard because it was so aggressive( with a round grinding stone). It's not the first time I've wondered this. Anyone feel me, are there options. It would be extremely useful for opening a via during trace repair too, especially in a press made for holding a Dremel, I break way too many bits doing this.

You need to try to use small (3-5mm) diamond burr...


My mistake, I didn't understand it is only mask to be removed. For mask definitely something like brush that will not remove metal...

[BrianHG]

A dremel with a steel brush bit and a delicate touch will remove the solder mask.

https://www.amazon.ca/Brushes-Rocaris-Wheels-Accessories-Dremel/dp/B07PKS819T

[DiTBho]

micro-sandblaster, sand + compressed air? 

[helius]

The PACE Minichine and Microchine are low-speed, high-torque rotary tools for removing resist, grinding FR-4, and polishing tarnished pins. They have been developed by PACE since the 1960s. The MC-65 provides a speed range of 2500 to 10000 rpm, and a minimum torque of 14 N.mm. The proprietary probe brake makes it possible to remove resist without damaging the underlying copper trace.

There are other rotary tools that provide low speed and high torque, including the Minimo tools from Minitor. Their lowest speed motor uses gear reduction for a speed range of 660 to 6600 rpm, and a maximum torque of 98 N.mm.

[tooki]

Do you know how that compares to Dremel and Proxxon tools? Neither of those specify torque.

(They do, however, specify vibration and noise, and Proxxon is far superior to Dremel in those. The Proxxon IBS/E has less than 1/5 as much vibration than the Dremel 3000, and less than 1/7 as much as the Dremel 4300! It is also quieter, though the Dremels admittedly have more power.)

Regardless, without the (super nifty) automatic brake of the Pace, I still maintain that high torque isn’t a desirable feature for this application. It’s too easy to grind right through a track.

[helius]

I think it should be possible to calculate torque from other specs, since torque is effectively the power per angular rotation. Torque is at maximum at the lowest speed and becomes zero at the highest speed, but that doesn't mean that grinding at a tool's lowest speed will be the most effective. There is a balance between torque and speed that yields the fastest material removal. One other benefit of a lower speed, higher torque tool is easier control while still maintaining the same level of power (in other words, the same rate of abrasion to the workpiece).

Another important criteria for rotary tools is the runout or total indicator displacement at the tip. A runout of less than 0.2 mm will feel precise and be able to make small openings, but with higher runout the tool becomes more of a blunt instrument.

[thm_w]

The PACE Minichine and Microchine are low-speed, high-torque rotary tools for removing resist, grinding FR-4, and polishing tarnished pins. They have been developed by PACE since the 1960s. The MC-65 provides a speed range of 2500 to 10000 rpm, and a minimum torque of 14 N.mm. The proprietary probe brake makes it possible to remove resist without damaging the underlying copper trace.

There are other rotary tools that provide low speed and high torque, including the Minimo tools from Minitor. Their lowest speed motor uses gear reduction for a speed range of 660 to 6600 rpm, and a maximum torque of 98 N.mm.

Microchine is super interesting, always thought of a dremel with proper speed feedback so it wouldn't bog down. $500 + whatever the base unit is though (doesn't even say on their website).

There are some reasonably priced minimo units: https://www.ebay.com/itm/303945300954
But its a brushed motor and has no mention of speed feedback.

Brushless one for $800: https://www.saeshin.us/product/oz-elite-high-quality-50000-rpm-slim-brushless-micro-motor-handpiece-set/

[David Hess]

I wonder if an old style electric drafting eraser would work.  They had different erase materials and the ones for ink were quite abrasive.

[shabaz]

I have a Dremel-like tool that is geared down, but completely useless for the task of removing surfaces off a PCB. It's way too aggressive a tool.

A felt wheel (not the completely flappy ones, but the ones which hold their disc shape) on a normal (high-speed) Dremel or Proxxon tool plus polishing compound will easily strip off the green part of a PCB, down to shiny copper, if this is what's required for reverse-engineering.

If one needs to go deeper.. I needed to remove the surfaces off a couple of vehicle ECU boards once (actually needed to go down one layer of copper to the inner-layer, not for reverse-engineering, but to repair some traces). Low-cost hobby-grade milling machine was great for that (provided the board is definitely clamped fully flush).

[Arts]

You want torque at low speed? You need this:

https://www.walter.com/products/-/producttradename/power-tools/finishing/dialspeed-straight-grinder-6145?setLocale=true

[jpanhalt]

Re-reading the original post, perhaps ASICMaestro wants to remove all of the resist to better see the tracks.

An epoxy remover may work.  Those usually contained methylene chloride and other organic solvents in the past.  More recently, it seems they include N-methyl 2-pyrrolidone (2MP) and another solvent, such as butoxyethanol (butyl Cellosolve, ethylene glycol monobutyl ether), e.g., epoxy grout remover by Rustoleum (https://www.rustoleum.com/MSDS/ENGLISH/EPOREMQT6.pdf ).