Member postings for David Joyce 6

Hi guys. I got a new osaki mini mill which is essentially a sieg X2. I have it a couple days, used it twice and the third time it wouldn't start up. I checked the fuse and it was blown which was strange because it was working fine the day before. I put a new fuse in but this time the fuse exploded in the fuse holder, glass dust everywhere and destroyed the fuse holder.

I check for shorts and checked the motor but couldn't find a problem. The control board is the XMT2335, I took it out and looked for burn marks or blown caps but couldn't find anything obvious.

The mill states the face mill capacity is 30mm and I put an ER32 collet chuck in which is larger than 30mm so I wonder if that was too taxing for the power components in the board. I only used the mill for twenty mins or so cutting slots in 1.5mm thick steel tubing, I took full depth cuts but only took light passes each time. The motor was only warm afterwards not hot.

I had the same problem with my mini lathe and it turned out to be the motor windings burning out but that caused the motor to get very hot and smoke to come out. I had nothing like that with the mill. I think its a short and I am guessing its the mosfets or something but I have no clue really. I have limited knowledge of electronics. I measured the resistance between the live and neutral at the plug and its 0 ohms. Thats a straight short circuit isn't it?

The motor is 230 volt dc permanent magnet brushed 350 watt but I think its fine. Im replacing the bust fuse holder with a panel mount push reset circuit breaker but that doesn't solve the issue causing the blown fuses. I would love to get it fixed cheap rather than paying £142 for a replacement board. Very frustrating but just my luck. Any ideas are welcome

Sorry guys for the late Update but I have confirmed the short in the motor. Did the 180 degree test on the commutator and got an average of 30 ohms on most of the contacts then it dropped to 20 ohms then went right down to 9 ohms on one or two of them so I have ordered a rotor for my motor.

The circuit was then tested with the bulb method and I confirmed that the circuit is operating correctly, no issues. The bulb got brighter as I turned up the pot and duller as I turned it down . It turns off when the pot clicks to zero.

So thats good news for me it spares me the extra £50 cost for a new circuit so its just the motor. Have to wait a couple weeks for delivery but I don't mind that.

Edited By Neil Wyatt on 05/09/2020 16:02:29

***UPDATE*** So the motor definitely has a short. I will do the bulb test later today when I get back and I will find out if I need to buy a new circuit too 😒

I found the parts I need its for my exact model the only down side is waiting 2 weeks to a month for delivery but I guess thats the price you pay. I had to order a bulb on ebay especially for this test as all my bulbs are smart bulbs so I just have to wait for that before I do the test. I will keep you updated.

Edited By Neil Wyatt on 29/08/2020 21:51:49

oh ok thanks for the tip. I will have a look for some of those

Oh thats good. Thanks

No I am using dcmt070204 inserts for steel. Yes I feel like it is just the motor because the control circuit is rated for 6 amps and is protected by a 5 amp quick blow fuse (F5AL250V) which blew so I am hoping that did its job and protected the circuit.

reason I use indexable carbide tools is because I do not have a grinder and have no experience grinding my own tools. It just seemed more economical for me and was working fine up to this point. I felt like the problem was more to do with the 2 inch thick 200mm stock of hard steel I was turning which was too much for me to expect of my baby lathe.

Yes I was taking light cuts. The EN19T steel was harder than the previous stock I machined and that usually machined very nicely with nice strings coming off. This time the lathe really struggled, slowing down.

I only have a 100 watt old style bulb. Will that be ok to use for the test or should I try to find a 60 watt. The control circuit is £50 . A whole new control box is £135 and the brand new motor is £100 but only £60 for just the rotor which is the part I need. I guess the 300 - 400 you are quoting is for professional repair? I can do it myself if I get the parts so it will be much cheaper that way

Edited By JasonB on 27/08/2020 16:11:39

Thanks guys. Yes I did read about the bulb test but I heard 100 watt bulb. I guess the wattage doesn't really matter so long as its not more than 400 😄. I will keep you updated as things progress. First port of call is motor commutator test with ohm meter to look for internal shorts then the bulb test to see if controls are ok.

I just remembered a few days before that the speed control was getting a bit weird. The lathe would rev up by itself for no apparent reason and one time when I turned the pot to off the lathe turned on by itself and revved up full speed. I think that indicates a Problem with the pot but it may have been a bit of swarf, as I said the control box is damaged so its possible some got in there.

Hi guys, thanks for the replies. I dont think it will be that expensive, new 400 watt motor is £100 but I found just the rotor  for £60 so thats not too bad. I think its looking like its the motor but I have to wait until friday to get my multimeter back and check for sure. The question now is whether or not the control circuit is affected, if it is I did find a replacement for around £50 which is not too bad unless this happens again and it becomes a regular expense 😖. The Ammeter in the motor line is a great idea so I think I will do that. Amadeal have a replacement control box but its the one with the space in the top for digital speed read out which my lathe does not have so I guess I could buy that and use an ammerter in there instead.

Edited By JasonB on 27/08/2020 16:11:21

Hi guys I need some help. I have one of those chinese mini lathes CJ0618 model 300 mm with 400 watt motor. I have had it for over a year now and when it came it had sustained some damage to the control box and change gear cover. It was just the plastic shell that was broke so got replacement gear cover but the control box was broken where the bolts attach so I had to improvise a strap to hold it to the lathe. There is a slight gap where swarf could get in so that might be the problem.

Anyway lately the motor has been overheating and smoke came out a few times but yesterday I was turning a piece of 50 mm EN19T steel ( I know, I know its too much for this little lathe to handle). This is the biggest piece of stock I have turned to I took it easy at around 1100 to 1300 rpm on the high setting (knob turned about half way), so because the motor was heating up I would turn up the speed after each cut to try cool it but each cut was slowing down the spindle, I use indexable carbide tips and taking cuts of between .075mm to 0.1mm ( 3 to 4 increments).

So then yesterday after a cut I turned up the speed to try cool down the lathe and I heard a pop and saw a flash coming from the commutator end of the motor. Lathe stopped and the fuse in the control box was blown. The pop sounded more like a match stick being ignited. I took the control box apart and there appears to be no obvious damage, no black marks or blown components. I took the motor out and had a look, no obvious black burn out marks but I have not looked at it with multimeter yet as I left that at my friends house. The motor did have blobs of black stuff in there kind of looked like burned plastic blobs but felt very light and crispy. Other than that there are no obvious signs.

I changed the brushes in the motor and put a new fuse in. The machine turns on with no prob but as soon as I turn the potentiometer the fuse blows again.

So I guess I want to know what to do next. Am I right in assuming the motor has an internal short from the windings insulation melting? Is there a test I can do to find out if its the motor or the control circuit? Bear in mind there was no swarf in the control box but I could use a new one to prevent that happening in the future.

Thanks for your patience and sorry for such a long question.