0.6–6.5 mm 400 W 220 V Mini Die Grinder. Or just a rotary tool.

Many DIYers probably often find themselves needing a rotary tool for their projects. I use a small homemade drill, but I've often seen others use a Dremel or one of its clones. It looked convenient, but I wanted something more powerful with a standard chuck. I spotted something similar in a well-known store and managed to get one for review.
Well, let's take a look at the outside and poke around inside a little to see whether it's worth it.

As I mentioned above, I was specifically interested in a version with a standard chuck, since that seemed more versatile in terms of accessories. Of course, you can't attach a flexible shaft to it like you can to a Dremel, but I didn't need one for my purposes.

I'm no expert on power tools, but I hope more experienced folks will correct me if I get something wrong.

So, I received this box. It was packed in a plastic bag, with the contents wrapped in polyethylene foam. No complaints about the packaging; everything arrived safe and sound.
The only thing was a fairly strong, distinctive smell of plastic and grease—those in the know will understand.


Specifications
Supply voltage — 220 V, 50 Hz
Power — 400 W
Rotational speed — 0-26000 rpm (in reality, the speed control doesn't start at zero)
Accessory shank diameter — 0.6–6.5 mm (definitely up to 7 mm)
Power cord length — 1.9 m
Weight without cord — 843 g; with cord — 982 g

The whole kit is very simple and consists of:
1. The rotary tool (or grinder, whichever you prefer)
2. Chuck key
3. Manual
4. Plug adapter for European sockets.


The manual is almost entirely in Chinese. What's interesting is that the cover shows the rotary tool as it actually is, while the manual itself depicts a tool with a different chuck and a different design. That said, it doesn't matter at all, since hardly anyone reads manuals anyway.


The little key is small, but it grips the chuck well. If you have trouble tightening or loosening the chuck, the problem may be less with the key and more with the design itself—but more on that later.


The adapter. Oh, that's a whole story in itself. It simply doesn't fit our sockets.
Never mind grounded sockets—they're obviously recessed. It doesn't even fit sockets that aren't very recessed, so overall it's useless.
It's better to just replace the plug. Faster and more reliable.


And here's the rotary tool itself. The color seems to be modeled after either Hilti or Milwaukee—hard to tell. But it looks good; it doesn't feel like some no-name brand.
It's about 250–260 mm long.


Since this kind of tool is usually held in your hand, its weight matters quite a bit.
Brands stand out not just for their power or weight, but more for the balance between weight, size, and power. But since I have nothing to compare it with, I'll just weigh it.
The first photo shows the weight without the cord; the second shows it with the cord.


There was some confusion about the name. The store page says Liyuan, but the one I received says Boli. Neither name means anything to me. It looks exactly like the one on the store page, maybe even better (there are no signs of rust on the chuck key).
The specs are also a bit confusing. The power rating is the same, but the maximum speed is different. The store page says 33,000 rpm, while the box and the nameplate say 26,000.
For some reason, I trust the latter more.


The front section is metal, and the chuck is recessed, which may make tightening and loosening it a little awkward. Though you may get used to it; perhaps it's also because the chuck is small.
The front section dimensions (for mounting in a stand) are: 38mm diameter, with a 16mm-long straight section.


Although the chuck is marked for a maximum of 6.5mm, I had no trouble clamping a 7mm drill bit, and there was still room to spare. So I think the actual capacity is around 7.4–7.5mm. I just didn't have a drill bit of that size, and an 8mm bit wouldn't fit in the chuck.


The power switch is at the back. It's a standard switch, nothing special.
I'm used to having the switch at the front, where you can operate it with one hand.
That won't work here: you'll always be holding it with one hand and switching it off with the other.


The speed control is also at the back.
The markings show 6 positions, but in reality it turns in small clicks, giving about 27 positions in total. The first 26 feed power through the speed controller, while the last, stiffer position supplies power directly, bypassing the controller. The clicks are crisp and easy to feel.


A quick word about the power cord. The plug is self-explanatory: flat pins, red color :)
I'll definitely cut it off and replace it with one that fits our outlets, though the plug itself is decent.
While waiting for this tool, I was almost 100% sure it would come with a “plastic” power cord. I have a drill like that at home—awful. I even got a decent cord from a locally made drill ready to swap in.
But when it arrived, I was surprised: the cord is quite flexible and about 1.9m long, so I'll only replace the plug.


And of course, next comes the teardown. We need to know what we're working with.

Now let's move on from theory to practice.
But first, I'll tell you a little about the issues and shortcomings I found (there are always some—even Hilti tools have their flaws).

Heat
It does get hot. At first, the front section got quite hot after just a couple of minutes of use, reaching about 50-55 degrees in around 2 minutes.
During disassembly, I found a small piece of rubber wedged between the front section and the front bearing. After removing it, the heating decreased slightly (or at least it seemed that way to me); apparently, the front bearing had been sitting a little crooked.
But modifying the cooling system made a much bigger difference

The front section was what heated up; the chuck stayed cool and only warmed up after I switched the tool off, as heat began to transfer from the front section through the bearing and shaft.

Vibration, runout, and noise
Strangely enough, I didn't notice much vibration. It was slightly worse at low speeds and slightly better at high speeds.
After I took it apart, the vibration decreased and was almost gone. I don't know what caused the change—whether it was simply taking it apart and putting it back together, or removing a small piece of rubber. Hard to say, but there was a difference.
The runout of a drill bit installed in the chuck was about 0.2 mm with an 80 mm overhang, which is quite acceptable for a threaded chuck. I used a 6.5 mm drill bit for the measurement. To improve accuracy and account for any curvature in the bit itself, I rotated it in the chuck several times and repeated the measurement. To be honest, I estimated the 0.2 by eye, but since I often work with thin wire, I can judge it fairly accurately. It was under 0.25 mm, but clearly more than 0.15.
The noise only becomes noticeable at settings 5–6. Below that, it isn't uncomfortable, and you can work for a long time. Most of the noise comes from the fan impeller running at high speed, and it's very hard to do anything about it.

Ergonomics
It sits quite comfortably in the hand. The slot in the front of the housing (intended for locking the shaft) faces downward, as does the cable.
It's probably a decent copy of a tool from one of the well-known brands, since the ergonomics are fine. But keep in mind that if you have small hands, I don't think it will be comfortable to use, as it's still fairly large. The diameter of the section I hold is 54 mm.
By the way, speaking of ergonomics and cooling, here's another reason why the ventilation slots need some work.
With this grip, at least one of the air intakes near the brushes is blocked, which isn't good.
While running, most of the air is blown downward near the front. The airflow toward the accessory is not very strong.


A few quick tests.
First, I checked how much power the tool draws at no load.
I took measurements at four power dial settings: 1, 3, 6, and max.
The readings are in the photo.


Next, I decided to try cutting something with it. By the way, be careful: there's no guard, and the power and speed are quite substantial.
For a test, I grabbed an anchor bolt and started cutting it with a cutoff wheel (they were included in one of my recent reviews). It was comfortable to work at power setting 2 or higher. At setting 1, the speed dropped significantly under load.
I also measured the power draw as I went, but taking photos wasn't very convenient, so I'll just write down the readings.
At dial setting 2, the power reached 120–130 W; at setting 3, 150–180 W (sometimes up to 200 W); and at max, it reached 280–310 W.
But I was afraid to put too much pressure on the small wheel, so I couldn't load the tool fully. It still had some headroom.
I didn't time it precisely, but it took about 30 seconds to cut almost all the way through. I was playing around with the speeds, though, so the result isn't exact. Still, it cut pretty well.


That's probably all I have to say for now. I couldn't measure the speed. I tried using an oscilloscope, a coil, and a couple of nuts attached to a grinding bit, but it didn't work. I don't have any small magnets :( If anyone has a way to measure it, I'd be glad to hear it.
I thought about measuring it from the current ripple when the windings switch, but I'm not sure that would work.

In the end, where there's a will, there's a way; seek and you shall find.
I measured the rotational speed. I won't describe the whole process; I'll just say I used a phototransistor, an old motherboard battery, a marker, and an oscilloscope.
Here are the results.
Speed 1: period 4.5 ms, frequency 222 Hz, speed 13,300 rpm
Speed 3: period 3.5 ms, frequency 285 Hz, speed 17,000 rpm
Speed 6: period 2.9 ms, frequency 344 Hz, speed 20,700 rpm
Max speed: period 2.5 ms, frequency 400 Hz, speed 24,000 rpm


And this is my small collection of bench tools. I also have a really tiny drill, but I don't use it, and it's lying somewhere far away. All the tools are powered by the same power supply. The electric screwdriver has a reverse function, so it has two buttons.


Summary.
Pros.
Good build quality, both inside and out, although not without a few flaws.
The chuck centering is good enough to get a 4 out of 5.
The body is sturdy and comfortable to hold.
Plenty of power for fairly demanding jobs.
The chuck accepts accessories with shank diameters from 0.6 to 6.5 (7) mm—that's actually why I bought it.
Soft, long power cord.

Cons.
The ventilation holes need some cleanup due to casting flaws.
A small piece of rubber got caught near the front bearing during assembly (though this may be an isolated case).
It gets quite hot, in my opinion.
The switch isn't in the most ergonomic position (in my personal opinion).
No spare brushes included.

My take: It's nice to hold, and not just to hold but to work with, too. But because it gets hot, I wouldn't recommend using it for extended periods; you'll need to take breaks to let it cool down. There's plenty of power. I can slow the chuck down by hand at the lowest setting, but I tried sanding with a felt disc and it worked fine. Still, I wanted to switch it to setting two, since the lowest setting is really very low.
After I got this rotary tool, I spotted a similar one from ROYCE on the market. It cost about the same and looked different only in color, but the build felt a little worse. I won't compare them, since I haven't tried using it.

I hope you enjoyed the review. If you have any questions or suggestions for tests, I'll be happy to answer.


The product was provided by the store for review.