Disc Grinder Restoration and Conversion - 110V to 20V by Rewinding

Disc Grinder MG-125J
AC 100V 50/60Hz 8A
125 mm x 16 mm x 22 mm. 4300 m/min.
Power in 780W
Power out 480W
MITACHI
Tokyo Japan
I bought this tool from Japan recycle store without testing. When I use it, it does not seem to work well, because some bearings are broken. By replacing those broken bearing, this tool will work normal. But I want it runs with battery instead. As a result, I can do it.
Video sections
00:33 before restore testing
00:59 disc grinder blade removal
01:18 disc grinder disassembly
03:28 broken bolt removal
07:48 armature disassembly
10:04 commutator bar install
10:25 DC rewinding diagram 18V
10:29 DC armature rewinding
16:40 permanent magnet install
16:56 motor testing
17:26 carbon replacing
20:14 battery adapter mount
22:54 painting
24:48 battery disc grinder assembly
31:15 battery disc grinder grinding test
I hope you find this video useful and enjoy it!
Furthermore, I am happy to receive feedback, suggestions to improve myself.
!!! I'm sorry for the mistake if I did in this video !!!
Thank you very much for choosing to watch my video!
Have a nice day
Gear Show

[@jlinkels]

NO high speed playback, NO music, WITH natural tool and workshop audio, THANK YOU!

[@Tomaszs9999]

Widzę że nie tylko mnie to denerwuje

[@ЕкатеринаСинякова-х6б]

@@Tomaszs9999 ,

[@ЕкатеринаСинякова-х6б]

@@Tomaszs9999 ,

[@albeiroperez1917]

Buen trabajo mi muchacho y muchos éxitos 🙏👍

[@joaquimoliveira1577]

​@@ЕкатеринаСинякова-х6б😊

[@johngassmann9581]

My man is over here hand winding the armature. What an absolute mad lad!

[@e8182461]

哈哈，馬達那邊忘了包紙，白弄了！ 又重拆掉，就是喜歡看有翻車的時候，讚！

[@istefanswanepoel1876]

When he first started the grinder. It sounded like most Hondas in our neighbourhood

[@gerardconway4927]

What a fantastic job

[@esqueue]

Great video. Love your skills. Unfortunately, it seems too slow for what we use. Just takes way too long to cut that little bolt, much less an 8-inch pipe.

[@Zignas1]

4700 rpm in not enough for grinder. But with some additions it can suitable as polishing machine, so good job anyway 👍

[@walterricardomartinez5185]

Excelente trabajo. Será q acá en bs as alla un bobinador de bobinas ?

[@TEMHblU_PblUAPb]

А можно было просто почистить коллектор и поменять подшипники 😏😁👍🏻

[@orhanozdemir5565]

Very good

[@5280EvoMR]

If you'd use the correct size drill bits for those taps you'd get some actual threads instead of relying on lock tite as an epoxy

[@spedracer55]

this wont cut out due to high load perfect

[@JDLarge]

Sorry brother, you couldn’t hear me yelling at the screen telling you “Don’t forget the insulating paper!!!” That sucked but I bet you’ll never forget that again. It’s how we learn my friend, some lessons are easier than others… Sweet restoration overall, I did enjoy watching. Thanks for taking us along and owning up to your mistake. Honesty is the best policy and with that you’ve made a sub out of me! 👍🏼👍🏼 from this guy!

[@ItsBoyRed]

@@tomgreen4409 The metal is very sharp at the ends so it cuts the enamal wireing making a short, its not heavyduty insulation.

[@mobuildsstuff]

The motor could work if you got lucky while laying the coil and didnt scratch any insulation, but the vibration from running ac through a coil rubs enough enamel of to short the coil

[@Troyvidihoo]

Yeah that was surprising,I almost think he did it on purpose to show is that important step because this obviously isnt his first motor rewind! Either way it was awesome he included that, if it was truly a mistake I think most guys would have edited that out and not mentioned it!

[@PaganWizard]

@@Troyvidihoo I completely agree.

[@محمدباقرجعفرجعفر]

ما سر علاقة المغناطيس بالكهرباء

[@koreanature]

Wow, My best friend, Thank you for your hard work in making the video. I enjoyed the good video. Have a happy day.

[@gear_show]

Thank you so much, my friend. I'm so glad you enjoyed this video.

[@LambeauLeeeper]

Hes my best friend not yours.

[@QuockhanhPham20]

Around 5000rpm that wasn't too bad it still enough for grind and very safety because the speed was't too big Keep it up i love your video

[@gear_show]

Yes I will, thank you for the feedback!

[@1misticointolerante]

Jamás evitas poner aislantes..... Te equivocaste está vez......????? O fue para demostración..????

[@gear_show]

Vi que esta armadura ya tiene aislamiento, pero el orificio de la pila es angosto para la nueva bobina.

[@yasha1279]

First thing I thought was "hmmm. No insulation paper. Well, he's the expert." Well, great restoration as always!

[@gear_show]

I saw this armature has insulation inside, but the armature stack hole is narrow for new coil.

[@LISnoname]

@@gear_show а почему на коллекторе не припаяны провода, почему не использовали щетки нужного формата, зачем оставили пружины в качестве токопрвода, пружины же быстро потеряют свои характеристики????

[@intel386DX]

​​@@LISnonameI wondered the same. Why he did not solder the wires to the collector

[@DiodeGoneWild]

The brushes had braided copper wires going to them for a reason. A very good reason, especially at a low voltage / high current.

[@lemagreengreen]

Have to say I was surprised and pleased to see you rebuild the armature, never seen anyone do that.

[@aquakey9834]

its prob because min wage where u're from is way over 50cts/hr...theres a whole industry of workers who rebuild armature n other consumable parts for a living, just nt in your part of the world.

[@Mmouse_]

You see it a lot in places like India, something we'd just throw away and get a new one, they strip and rebuild, rewinding isn't hard it's just time consuming and fiddly. I once got a quote to have a 3 phase electromagnet rewound, the company wanted £700 to do it, a new one was £250.

[@mobuildsstuff]

@@aquakey9834 Not necessarily. I worked for a company in Germany which specialized in rewinding industrial motors for automated factories and heavy duty mining equipment. If you just need a standard 3p Motor its usually not worth the time, but old and specialized motors/generators are still beeing used all over different industries.

[@joaosantos3229]

@@aquakey9834 ppppp

[@omprakashjhangdi3514]

@@Mmouse_ g

[@2OO_OK]

That came out looking great!. The no load rpm is influenced by the strength of the permanent magnets. A stronger magnet results in more back emf and slower motor speed for a given input voltage. You could use 2 batteries in series. The original on off switch was designed for AC. You can protect it with a flyback diode for DC use. Well Done!

[@xenoxaos1]

The switch it likely fine. The AC rating is typically higher than DC because most of the time it's not going to make contact at the peak of the sine wave. Without measuring the inductance of the coils, I can't determine the peak current of the the motor at start/stall. The battery probably has over current protection though. A flyback diode as well as a 30ish volt zener diode would have been good though. Not to protect the switch, but the battery. The battery should have diodes protecting the MOSFETs, but not necessarily guaranteed. The switch does disconnect the battery from the motor so the back EMF won't be a problem until the battery decides it's dead and turns off. Then the switch would still be on and the motor connected to the battery and could send high voltage spikes back to the battery. Using more turns of a thinner wire would have reduced the spindle speed and gave it more torque. I'm assuming that he did the math as number of turns at 100V and divided by 5 to get to what it could be at 20V.

[@themoemechanic]

0:45 *motor is sparking like crazy and sounds like literal explosions* "It does not work well" I laughed pretty hard.

[@re-fix9678]

👍👍😘

[@gear_show]

👌👌👌 thanks

[@christophergrabon1294]

Mad respect for you winding that copper!! You’re awesome.

[@gear_show]

Thank you!

[@vladislavzepesch953]

Это не реставрация, это уничтожение старого инструмента.

[@gear_show]

Мне очень жаль это слышать...

[@vladislavzepesch953]

@@gear_show это же ушм из 50-х, их осталось мало. А вот сама идея и ее исполнение действительно крутые!

[@TrafficBuster]

Hi there you're videos are very good and one thing you should not check the leakeage current using line tester because line tester cant detect voltage bellow 80v better you use Multimeter...work safely...Electricity is very dangerous and life is very important...

[@gear_show]

Absolutely right, thank you so much for the tip.

[@htn1986]

These are the kind of things they need to teach in school. Amazing video, thank you sharing!

[@mdraju4574]

😅😅❤😅

[@Bender13]

Unfortunately we’re a throw away society now. Doesn’t work….throw it out and buy a new one.

[@artvinli6873]

Türkiye'den selamlar...

[@gear_show]

Gearshow'den selamlar...

[@alanerickson3075]

I can definitely feel my blood pressure go down every time I watch one of your videos, it's always very relaxing to watch someone doing something right.

[@gear_show]

I'm so glad it helps you. Thank you so much for sharing!

[@thirumoorthy893]

@@gear_show Ni

[@anmolsidhu2770]

@@gear_show L

[@utggjhtghi1943]

In

[@ایران-م5ذ]

@@gear_show۸۲۸حح ححح۸حح۸۸۷۸۲۲۲۲۲۲۲۲۲۲۲۲۲۲۲۲ح۸۸۸ح۸ححح۸ح۸ح۸۸۸ح

[@Maranello12374]

Дружище ,👍.. Все твои видио смотрю.. Браво...Ты по ходу уже все перечинил и уже не знаешь что переделать..,😉...Браво так держать.

[@gear_show]

Да я сделаю. Я рада, что вам понравилось это видео, большое спасибо😉!

[@Restoredt]

FULL RESTORATION VIDEO: Diesel Engines For Large Capacity Pumps // Repair Water Pump Diesel Engine kzbin.info/www/bejne/h5-9lK1-oL91kM0

[@georgegeorge899]

So...! You're the guy that showed me what's wrong with my JBL Xtreme... My battery had a swollen module... so I discarded the whole battery... I'm using the speaker without the battery because it's always staying in one place... 👍 Keep up the work !!!

[@creativeashok3469]

Converter a 220 volt hammer drill to a 20 volt cordless drill

[@gear_show]

Okay, it is the same 100v to 20v hammer drill I did in my previous project.

[@creativeashok3469]

@@gear_show yes i watch all previous video's but can you use a 775 motor in it

[@Gerard_Hugo]

What a challenge! I never saw someone modifying an AC motor into a DC motor. Well done!

[@jzrgrmm]

Those motors are called universal motors, they natively run on both AC and DC. Most corded power tools have them. I've seen people build 120/240v DC power banks to supply power tools on remote sites, and they work just fine.

[@arisusnto3314]

@@jzrgrmm ttjtjjtjtjjjjjtjtjutjjtjjtjt8pppjppp7p

[@arisusnto3314]

@@jzrgrmm higl

[@jacksvacssafety2620]

5:30 I'm no smart man but I know something is wrong when I see it

[@gear_show]

The armature bearing is broken, that cause the armature doesn't stay in the center.

[@jacksvacssafety2620]

@@gear_show yeah, the whole cage that holds the bearings in just shredded, had that happen on a Sharp Twin Energy vacuum and it ruined the whole motor.

[@alexpadovano8172]

Gear Show is the real deal. He's the only person in the KZbin restoration game who actually rebuilds motors and fabricates battery packs. Also, I went out and bought a Makita 7.2v cordless impact screwdriver after seeing you use it so frequently.

[@gear_show]

I get more confident after seeing your comment, thank you for the comment.

[@alexpadovano8172]

Please keep it up! Seriously great stuff!

[@boofe7206]

check out 'my mechanics'

[@JeremyMitts]

Magnet wire is so expensive. Pretty sure a new 20v cordless would have been less money than the wire, bearings, paint, and 18v battery connector. Even if you calculate $0/hour labor...

[@m0sh1994]

Thank for this video, i asked you to do this modification in old angel grainder video by rewinding the armture and finally i see this video, it's very satisfying work👍 No noise, no lot of vibration, good grip and weigh balancing👌 I was excited for every minute in this video 😁 Keep going... 👏

[@gear_show]

Yes, I remembered you ask me to do it. Anyway, I'm so glad you like it, thank you!

[@АлександрАнтонов-щ1в]

А смысл ? Где брать 20 вольт ? Таскать с этим набалдашником ? И на сколько хватит батареи ?

[@CyberPick]

I can't believe so much work, so complex, so skilful and finally it's working. For me it's art. Congratulations :)

[@MM2009]

4800 rpm not enough, will wear the disc lacking speed and momentum, waste of time. 33:00 perfect example, might be good for something else though.

[@zoisbasis7791]

I recently was given a Makita impact driver. It's in a bad shape, no battery or charger. Can't find the courage to restore it. Hope I will manage it. Love your job. Great, relaxing & educational. Thanks from Greece🇬🇷🇬🇷🇬🇷. Keep up 👍👍👍

[@guillermoocsasgamarra4327]

Da .mucha ayuda y efectiva graçias

[@TheBandit343]

Балбес пендосовский. В курсе что можно поменять диск без ключа?

[@mobuildsstuff]

Its really nice to see someone rewinding their motors. Dont let these old skills become rusty and forgotten

[@zloiprigorshnia8083]

если уж переделывай на акб то надо ставить бесщеточный а не вот это все городить и оборотов будет нормально и мощность

[@gear_show]

Хорошо, большое спасибо за советы, я сделаю это со своим будущим проектом.

[@pachecoCardososilva]

Parabéns seus vídeos são os melhores, eu estava esperando faz tempo por esse vídeo.

[@gear_show]

Muito obrigado! Estou tão feliz que você gosta deste vídeo.

[@Eric1SanDiego1]

Diagram at 10:26 showing the Armature, Commutator, Carbon Brush, and Magnets. Me: "Whoa, something just flew WAY over my head"

[@gear_show]

I try to make it easy to understand. Will you understand it?

[@Eric1SanDiego1]

@@gear_show Unfortunately no, I have no idea how motors work. But your video was extremely entertaining and thorough!

[@edgar7472]

Great job on the grinder,looks an sounds amazing,thanks for this videos sir.👍👍

[@nikolaos9906]

Two big mistakes first the insulation paper and you didn't solder the contacts on the rotor with solder. Whether it was all worth it with so much work and material I am questionable

[@alan-tl5dv]

Parabéns pelo seu trabalho muito bom continue assim ótimas ferramentas japonesas abraço aqui do Brasil 👍🏻🇧🇷

[@gear_show]

Muito obrigado! Estou tão feliz que o vídeo pop-up no feed do Brasil.

[@ahmedkhedr2754]

How to calculate the number of turns and cross-sectional area of the wire To operate on direct current

[@Kokosha3110]

Молодец! Супер мастер! С удовольствием смотрю твои видео без перемотки ! Мозг и руки золотые! Спасибо за твои ролики, Большого успеха тебе во всем!

[@ВадимКупер-ч2у]

он убил рабочую ушм, сделав из неё уродца! что в этом видео хорошего???

[@serfer5877]

@@ВадимКупер-ч2у рабочую?

[@DoCRabbittttt]

@@ВадимКупер-ч2у У нее якорь закорочен был, а учитывая год выпуска и марку, сделал приличный хендмейт ради интереса. Так что самоделка ни разу не хуйня.

[@ВадимКупер-ч2у]

@@DoCRabbittttt ротор и статор перематываются. а это просто уродства винтажной вещи. было бы лучше если бы он распечатал собственный корпус, это был бы хэндмейд.

[@tutturu-]

@@ВадимКупер-ч2у У неё корпус металлический и она в любой момент может начать хуярить током, если использовать от сети. Кто пользовался советскими дрелями - тот знает, как это "весело". Так что нормально переделал, вопрос только к снизившимся оборотам.

[@ihasolak]

Mitachi, is that a bootleg brand of Hitachi?

[@gear_show]

I'm not sure about this too.

[@AbhishekKumar-cj6xi]

Great work. I am a DIY enthusiast and seeing your work and the ideas you implemented when you face any problem. Gives me inspiration. Keep it up good sir.

[@ricardolizarraga7755]

Muy buen trabajo pero perdió la mitad de la revoluciones con la conversión

[@edeforelle664]

Excellent work! Seems to be well balanced and the weight of 4Kg is still light!

[@gear_show]

Thank you very much! It is lighter than my previous drill (5 kg).

[@АйнурАляров-й8х]

Привет коллега ремонт класс здоровья тебе и твоим близким я подписан на твой канал поставил лайк больше ремонтов коллега

[@youtubed.4264]

Impeccable work, congratulations !!!! 👍🏻👍🏻👍🏻👍🏻🔝

[@davidepiccini9254]

Love you wow

[@gear_show]

Thank you!

[@Yaman-D-Chhaya]

2 words!! Simply awesome Great build brother God bless you and keep the good work going 👍👍👌👌

[@Val-yq6ym]

Please ensure the disks to be used on that grinder are adequate to the new RPM

[@johanrynjah8241]

That was a daring attempt and a successful one as well. At first I thought you're going to replace the armature with a RS-775 motor or a higher rated DC motor. The motor you converted I think its torque and RPM is equivalent to a heavy duty motorbike starter motor. It's a great accomplishment surrounded with perfection. Greetings from India.

[@Rudy97]

By the amount it seemed to bog down when cutting I think it's 500-600w. Very cool but a bit slow.

[@SokolFeniks]

And what, the wires at anchor do not need to be soldered or just bent the ends and that's it?

[@ezequielsilva2709]

Bom trabalho, adaptação muito bem feita 👏👏

[@gear_show]

Muito obrigado!

[@rolandolievanoagudelo.5112]

Maravillosa restauración maestro 👍

[@rickburch4447]

Lets see you change it back to 120 volt.

[@arturlend2297]

Patrzenie jak przerabiasz i dajesz drugie życie elektronarzędziom, to przyjemność. Szkoda że ja tego nie potrafię. Dobra robota jak zwykle. Brawo Ty 😎

[@gear_show]

Jestem bardzo zmotywowany po przeczytaniu twojego komentarza, bardzo dziękuję!

[@hasansalibeyli]

@@gear_show uhdsjej

[@masterQ20]

Thanks for sharing. God bless you 🙏

[@gear_show]

Same to you!

[@mattbanks3517]

This is the best made angle grinder i've ever seen. SO strong simple and servicable. Love the fact you can use a wrench on the hub.

[@swedishpsychopath8795]

It is spinning the wrong direction, it goes half the rated speed AND the battery will overheat / be destroyed due to no BMS.

[@mattbanks3517]

@@swedishpsychopath8795 to be clear i was talking about how it was built originally, but i like the fact that the man rewound the motor instead of replacing it, it's cool and creative and solid. Also, my AC enihell grinder spins twice as fast as the same model and disc size but battery powered. He should add a bms tho.

[@koaasst]

@@swedishpsychopath8795 most batteries havs bms built in the pack, not sure about these chinese ones, but probably. i have a bin full of starter motors, but i thought the duty cycle was so low using in a tool wasnt worth the effort.

[@jelajahmania]

Replace Disc Grinder with chain saw 1 meter

[@valmirramos4195]

Excelente trabalho GearShow! Gratidão

[@gear_show]

Muito obrigado!

[@MRBROWNMUNDE]

Best video sirrrrrrr........

[@gear_show]

Thank you!

[@bricoda]

Great job, always inspired by you, thank you

[@gear_show]

Thank you! I'm glad to hear that.

[@james10739]

That motor winding seemed a lot less bad than I would have thought but that was a lot thicker wire than what was there before

[@markdunford3181]

Great job. Your work is so neat and beautifully crafted. Thank you

[@gear_show]

Thank you so much!

[@barthanes1]

A very elegant solution. The weight of the batteries counterbalances some of the weight of the grinder.

[@gear_show]

Absolutely right, I feel it is easy to use, even it weighs 4 kg. Thank you very much!

[@andybelka]

Очень впечатляет Ваша работа! Продолжайте в том же духе!

[@АлександрЛюфт-б1ъ]

Чё тебя впечатляет? Как человек из старой болгарки сделал мусор?

[@ВОИНДОБРА-у1о]

@@АлександрЛюфт-б1ъ изначально было 9.000 оборотов. Когла сделал то стало 4,700 оборотов. Ну да слабоватенько

[@Zignas1]

@@ВОИНДОБРА-у1о Согласен, оборотов маловато. Но, с небольшой доработкой ее можно использовать как полировальную машину - для этого оборотов как раз хватает.

[@ailtonsantos9731]

Muito bom parabéns..

[@mustaphagaci8046]

Tout est bon . Mais ya aucune sécurité ni pour moteur ni pour batterie

[@andersonbicalhodesouza3588]

Você sim é um profissional 👍

[@domingolucena3218]

Lo que pocos se dieron cuenta que que no tiene fuera, al desvastar no ubiera quedado al rojo vivo el tornillo y eso no debería de suceder lo mismo con el disco de corte se calentó la varilla por que no tiene nada de fuerza y corta muy lento lo que quiere de cir que no asentaba el disco y eso daba tiempo al calentamiento fuera de eso buen trabajo pero inservible

[@bigmesstest230]

What is the reason for the glue

[@gear_show]

The glue keeps the coil wire stay in place while high speed rotation.

[@bigmesstest230]

@@gear_show ok that makes more since it is a special glue and what grease do you use

[@marcelolaudadio.5908]

Muy buen trabajo, felicitaciones ! Has medido la corriente sobre los 19 volts ?

[@staskarpov3396]

Люблю смотреть ваши видео. Хотел бы стать вашим учеником. Так классно у вас всё получается. приятно смотреть.

[@gear_show]

Я мало что знаю об этом, это просто мое исследование и тестирование. Я так рада, что тебе это нравится.

[@staskarpov3396]

Напрасно вы говорите что это просто. Я же вижу какой у вас профессиональный инструмент. Вы как Хирург, который делает сложные операции.

[@АндрейНикитенко-ф4с]

Brilliant work done. Really interesting video.

[@Eric1SanDiego1]

In hopes that I'm not _completely_ ignorant about electricity, doesn't the modification mean that the specs on the old label are now technically incorrect? Regardless, I'm glad you affixed the label again, that's always a nice touch.

[@gear_show]

I want to keep it as original, new modify tool can measure next time.

[@autumn5592]

Yes, since he rewound the motor, pretty much all it's specs are different now. The label is meaningless (for information) now.

[@BASF111]

Очень интересно, очень умело. Спасибо за вашу работу и ваши ролики!)

[@gear_show]

Пожалуйста, большое спасибо за просмотр!

[@Alechkohashmelaii]

you'hw needed to use that angle grinder with DeWalt flaxvolt battery 60v /9ah and after that show us a relly show...

[@mohammadmojaveri8609]

❤❤❤

[@gear_show]

Thanks ❤❤❤

[@The_Seal77]

what electric screwdriver are you using?

[@CrookedSkew]

Thank you for another wonderful video maestro. Some feedback - it would be good if you put more subtitles in, like why you appeared to "quench" that heated bolt in oil. Thank you!

[@hamzefarahani5295]

عالی بود دوست داشتم هنر شما رو

[@litvye4636]

That's a nice idea, the weight distribution can be in the midle of the grinder

[@gear_show]

Thank you!

[@warwikdallas]

Классно, как всегда. Но, вроде, не хватает оборотов на диске.

[@Kostoprav_ai_covers]

раза эдак в два)) но автор честно это показал за что ему респект) и мощи явно не хватает)

[@ja_nic_ja_muzikant]

Hi, this grinder looks pretty rough on the outside but is still looking great on the inside (I mean that there's pretty much no rust, the screws came out looking almost like brand new). I'm wondering how many projects/videos have you scrapped due to bad state of the thing you were working on?

[@hlaokaboutfightiganimalstun]

Very very thank you Sir.

[@nourddinenourddine1107]

عمل جيد

[@gear_show]

شكرًا لك!

[@kwestionariusz1]

Love your work greetings from Poland.👍 Keep recording.

[@gear_show]

Yes, I will do. Thank you so much! I'm glad you love my work.

[@fahedq825]

👍👍👍👍👍

[@gear_show]

Thanks

[@MarcioCostacantor]

Estou aqui Prestigiando seu trabalho, vamos sempre juntos somar e fortalecer. Márcio Costa O Canhotinho do forró

[@ananiid8700]

А как насчет балансировки якоря

[@sniphalos]

4000 rpm 😂😂😂😭😭 you probably joking it's wasted time to nothing in such RPM you only wasting grinding disc nothing more in normal tool rpm 8000-11000 what's there's in your created toy 4000?😂😂😂😅😂😅