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Old 16-04-2020, 12:29 PM
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Unhappy My new lathe

Because my home-made lathe was not good enough for larger pieces and harder materials (plastic was OK, but that was about all), last Friday I decided to invest in "real" machine...

It arrived today, and it is quite a piece of iron.. and actually bigger than I anticipated or hoped for.

Unfortunately, it worked (erratically) only couple of seconds.. and then the motor stopped.

I didn't smell any smoke, but it is likely the faulty control board.

Now I have to through the hassle of servicing or returning the whole thing... which is not easy considering 65kg of weight.
Anyway..
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Last edited by bojan; 16-04-2020 at 01:15 PM.
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Old 16-04-2020, 01:08 PM
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Have you checked the safety cut outs on the chuck guard, gear end cover etc? Maybe a sticky or incorrectly adjusted one.

Michael.
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Old 16-04-2020, 01:17 PM
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Everything checked.. Head rotates freely by hand.

Motor was turning quite erratically for couple of seconds and that was it.
Pity, the machine seems to be mechanically quite good.
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Old 16-04-2020, 01:40 PM
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Nice little lathe, I have an old Hercus they were made in South Australia a lot of them are the lathes that were in high schools, my one was out of Blackwood high my 9 year old told me that's where the hip hop band the hill top hoods went to school lol, anyway my wife says the only thing I seem to make with my lathe is more things for my lathe hope you enjoy
Simon
Actually was just looking at the lathe you made its pretty neat just wondering how you managed to drill through what looks like vernier gauge with the heads cut off? that must have been tougher than a cat's head
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Old 16-04-2020, 03:38 PM
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Quote:
Originally Posted by bojan View Post
Now I have to through the hassle of servicing or returning the whole thing... which is not easy considering 65kg of weight.
Anyway..
At least you don't have the same model as me - mine's 280kg!
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Old 16-04-2020, 09:18 PM
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Quote:
Originally Posted by bojan View Post
Everything checked.. Head rotates freely by hand.

Motor was turning quite erratically for couple of seconds and that was it.
Pity, the machine seems to be mechanically quite good.
Sorry to hear of your problem Bojan. Capacitors?

Best
JA
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Old 17-04-2020, 05:09 AM
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Sorry to hear of your problem Bojan. Capacitors?

Best
JA

I had a look at the control board.. nothing obvious.

It seems the output driver of motor controller is single FET (or SCR), on heatsinks (next to coil must be Graetz rectifier). On the attached image, red and black are mains (left of the PCB), red, green, black bundle (next to the adjusting pots) is speed control pot on the front plate, DC motor wires are blue and white (in the middle).
The supplier wants me to provide demonstrating video of the problem, to come up with solution (which will be replacement of the controller board (my preference) or the replacement (more likely) of the whole machine)
I think I made mistake with supplier.. but no one else had that particular model, and form mechanical point of view this machine is exactly what I wanted.
If supplier becomes difficult or the whole situation gets too complicated, I may attempt to repair controller board myself, it seems it is very simple circuit, probably just PWM driver and SCR or FET output stage (motor is DC, no visible marks on it.. I will try to connect it to 12V just to see if is operational).
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Last edited by bojan; 17-04-2020 at 09:18 AM.
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Old 17-04-2020, 12:02 PM
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I connected 12V to motor - and it works (couple of rev/sec).
So- no doubts, it is faulty controller board.
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Old 17-04-2020, 12:27 PM
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Originally Posted by Symon View Post
... just wondering how you managed to drill through what looks like vernier gauge with the heads cut off? that must have been tougher than a cat's head
One pair of calipers (now on standing drill cross vice) was really hardened and not easy to drill.
Another one (currently on that home-made lathe) was made of "white brass", so easy to work with. I would like to get some more, but when I ask vendors about material they swear their products are made of "best quality stainless steel"...
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Old 17-04-2020, 01:00 PM
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Thanks for the reply it actually made me smile hope you get sorted soon
Simon
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Old 17-04-2020, 01:27 PM
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I just couldn't resist...
Some pretty nasty hand-soldering here.. machine soldering is OK.
I found cold joint on "A-" motor faston tab, I re-soldered it but still no joy. It must be FET or it's associated driver or both.
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Old 17-04-2020, 01:51 PM
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Are they using solder to increase the current capacity of the tracks?
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Old 17-04-2020, 02:50 PM
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Are they using solder to increase the current capacity of the tracks?
Yes... not very good idea, but it works.
Also, there is no proper ground for the rest of electronics, because they used Graetz rectifier directly on mains.. so the "GND" is actually live every 10ms.
Very unsafe practice, actually it is illegal (in Europe definitely, here in Oz most likely).
That also means it is very tricky to debug this circuit as is, to do that isolation transformer is needed (or test gear should float... ).
Or, separate external supply voltages for motor and for driver electronics must be applied.
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Old 17-04-2020, 04:47 PM
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I have been out of electronics work so long my brain is bubbling trying to work it out. Ignoring the volts drop of the diodes (Insignificant) is that essentially about a 240VDC circuit but essentially a balanced circuit with no ground reference as such, the neg rail around -120V with reference to "ground" (The MEN grounded neutral in this instance) and VCC of +120VDC?
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Old 17-04-2020, 07:46 PM
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Quote:
Originally Posted by The_bluester View Post
... is that essentially about a 240VDC circuit but essentially a balanced circuit with no ground reference as such, the neg rail around -120V with reference to "ground" (The MEN grounded neutral in this instance) and VCC of +120VDC?

Not quite..

DC voltage between "+" and "-" lines is 340V (240*SQRT(2)).
If neutral is at GND potential (it never is), then "+ " oscillates between 0V and +340V, and "-" oscillates between "0" and -340V with frequency of 50Hz.

This could be deadly.
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Old 17-04-2020, 09:17 PM
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Quote:
Originally Posted by bojan View Post
Yes... not very good idea, but it works.
Also, there is no proper ground for the rest of electronics, because they used Graetz rectifier directly on mains.. so the "GND" is actually live every 10ms.
Very unsafe practice, actually it is illegal (in Europe definitely, here in Oz most likely).
That also means it is very tricky to debug this circuit as is, to do that isolation transformer is needed (or test gear should float... ).
Or, separate external supply voltages for motor and for driver electronics must be applied.

Hello Bojan,


Test that kit with RCD!! I bought (for work) a SMD de-soldering kit. The heat-gun keep tripping the RCD till I reduced the heat on the 3rd unit below spec. The mica insulator with fiberglass reinforcement burned thru and keep tripping the RCD. These items from China should not pass testing, and sold without modifications for safety! Check yours before using it!





Mick
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Old 18-04-2020, 08:12 AM
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Well, this is end of my road. I applied the external power (12V) to controller board, in parallel to existing 240V->12V supply regulator.
LED marked with black arrow is supposed to be ON.

HT66F018 (A/D Flash MCU with EEPROM) is PWM generator, and it is dead, there is no output activity from it.
I need another controller board....

The good thing about all this is, there are DC motor controllers on the market (I can even make my own with Arduino), for couple of $$ and better/safer than original one.
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Old 19-04-2020, 02:37 PM
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I think this circuit may be good enough for the purpose..
It doesn't have overload protection (like chinese deign) but it is simple and low cost.
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Old 19-04-2020, 06:08 PM
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Great news
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Old 22-04-2020, 12:44 PM
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Not counting you repairing that Lathe, I used the Metal working Lathe at the Tweed Heads Men's shed -- am learning to use a lathe -- to make a couple of adaptors to use Weightlifting weights as counterweights on my Skywatcher EQ6 -- it came without Counterweights or a tripod, but cost only $200 with an Argo Navis, etc. plus I gave him a Marklin train set that I would have been willing to sell for just $200.

So what I am saying, is once the Corona Virus is over, your local men's shed may also have a Lathe. Only $50 a year and $5 a week for coffee and a raffle ticket at our one.

Bojan already has his Lathe, but others may be interested in this. Good luck in getting yours going Bojan. Sn some small ones that I would love, but no money.
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