# Chinese 7x Lathe Safety Issue



## Cogsy (Dec 15, 2012)

Last night I was happily turning away on my Chinese mini-lathe and I needed to do a quick check of the part. 

I spun the speed control to zero and the workpiece stopped, but I left the direction switch in 'forward'. Then I grabbed the bottom of the spindle with my left hand, just to rotate the piece a little, so I could see what I needed to. I've done similar things a hundred times before.

This time, the spindle had an uncommanded high speed start up, the chuck grabbed my hand and rotated a half turn before it stopped again. It wasn't a slow spin-up like when you turn the speed control - it made a 'thump' noise like it started at something ridiculous like 700+ RPM. If it hadn't stopped itself so quickly, I believe I'd have been off to the local hospital for repairs.

Obviously my lathe has a fault with something, but I'd be very hesitant to go anywhere near the spindle/chuck or workpiece on one of these lathes, without at least turning the direction switch to 'off' and I'll be pressing the e-stop as well.


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## Herbiev (Dec 15, 2012)

Hi Cogsy. I would bring this to the attention of the manufacturer. A recall might be in order before a serious injury occurs


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## Cogsy (Dec 15, 2012)

I'm embarrassed to say that I did suspect something like this could happen as my lathe has been doing a few 'funny' things, so I have contacted the seller, who in turn contacted the manufacturer.

Their response was to say that the PC board may be faulty, but as it is out of their 30 DAY warranty, they just offered to sell me a new board... I'll be contacting the relevant authority on Monday and seeing if I can legally return the thing and get my money back, but at least report the safety issue so nobody gets injured. I'll also never deal with supposedly 'reputable' seller again, as they are just completely ignoring my emails now.

I should have taken extra care but I literally only wanted to advance the chuck 30 degrees and I thought it'd be ok. Now I know better.


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## skyline1 (Dec 16, 2012)

Hi Cogsy,

Sounds like a controller fault to me, but some of the cheaper ones are very sensitive to mains spikes and the like, if you have any high current switching nearby that might be the cause. I once had a 1.5Kw three phase industrial one that kept glitching like you describe when someone turned a nearby fluorescent light on. I traced it to poor wiring in the end, some idiot had run the speed control pot wires in an unshielded cable in the same conduit as the lightswitch so every time you turned the light on the induced voltage would cause the drive to "kick". Any thyristor drive can have this problem but more expensive ones. are better protected. Big ones have a mechanical interlock relay or contactor to prevent this sort of thing from happening.

But a 30 Day warranty on an important and safety critical component is stupid. It is unfortunately rather typical of Chinese companies, they are not all bad, there is some good stuff coming out of china, but they do have a "throwaway and buy new improved" philosophy. After sales support with some is non existent.

I do think you have a valid safety concern though. I don't know about consumer laws in Oz but in Europe they would take a pretty dim view of of it.

This is why manuals nowadays are at least 50% safety warnings and very little by way of operating instructions. It's much cheaper to print pages and pages of safety Warnings than design the thing right in the first place.

Regards Mark


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## MuellerNick (Dec 16, 2012)

Even a mini lathe should have a chuck guard. And if that one is opened, there should be no way to start the spindle.
I always open the guard at both my lathes when measuring etc. I could throw the spindle switch with my hip on the manual lathe, and I repeat that habbit of opening the guard on the CNC-lathe.

There are morons on this planet, that remove that safety feature 


Nick


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## Cogsy (Dec 16, 2012)

It does have a chuck guard, and I have left it installed, but... I reached under the chuck. My guard only goes over the top. I admit I was doing something very foolish and bad practice, but it still shouldn't have started on it's own.

It's been occasionally fluctuating it's speed on the fly as well. I'd hate to have it go from 80 RPM to 1000 RPM while I'm threading to a shoulder. I expect the crash would be nasty.

I don't know much about electronics, but my shed is separate from the house and the only things I run when the lathe is on is a light and small radio. Thanks for the help though.


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## gus (Dec 16, 2012)

Cogsy said:


> Last night I was happily turning away on my Chinese mini-lathe and I needed to do a quick check of the part.
> 
> I spun the speed control to zero and the workpiece stopped, but I left the direction switch in 'forward'. Then I grabbed the bottom of the spindle with my left hand, just to rotate the piece a little, so I could see what I needed to. I've done similar things a hundred times before.
> 
> ...



Hi Cogsy,

Am glad you were not hurt. This is bad PR for the supplier and manufacturer.
It is up to both to restore our faith in their product.

Gus


Gus.


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## gus (Dec 16, 2012)

Hi Cogsy,

Please post foto of lathe plus a close up shot of the controls. I have to alert a mate of mine in USA.I bought him a Chinese Mini Lathe.


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## Tin Falcon (Dec 16, 2012)

> I spun the speed control to zero and the workpiece stopped, but I left the direction switch in 'forward'. Then I grabbed the bottom of the spindle with my left hand, just to rotate the piece a little, so I could see what I needed to. I've done similar things a hundred times before.



I may be playing devils advocate here but the speed control is a speed control not an on off switch . It does not cut power to the motor. turn the machine off before working on it. Do not blame the lathe for operator head space errors. 
You are the operator . you are the one with the brains. 
Good safety practice is important.  sometimes we can break the rules a hundred times and be OK. 101 and all H*** breaks loose. 
And yes I am very glad to here you are not hurt. 

SAFETY IS YOUR RESPONSIBILITY 
That said,there may be some fault in the circuitry in that the speed of the motor should have been slow not stopped.  These boards are notorious for minor failures do to cold solder joints. You may want to remove the board examine with a magnifying glass  and re-flow the solder if needed. I would expect these boards are dip soldered at the factory. IMHO QC is not that great in Many of the Chinese factories. 

In your case it sounds like some energy was stored in a capacitor then cut loose. 


Tin


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## SmithDoor (Dec 16, 2012)

Tin Falcon is right
If this was my lathe I would put a swicth with a guard. *SAFETY FIRST *
I have had I lot of machine tools in my life I did not go to the MFG I just fix it. 

Dave


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## Rocketcaver (Dec 16, 2012)

My mini lathe will often start up again after I turn it "off" with the speed control.  Early on I developed the habit of always hitting the "E-STOP" every single time after turning it "off".


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## Cogsy (Dec 16, 2012)

I appreciate what you guys are saying, and I definitely did the wrong thing by grabbing the chuck at all, but I know it's not right to be supplying a lathe that can randomly start off or massively change speeds by itself.

The speed control knob stops the spindle turning long before it hits it's zero mark, so I have just been relying on that when I go to take a measurement or check something (I know now not to do that again), but the way this thing is changing speeds and the suddeness and violence that it started spinning on me is a concern. I hardly know anything about electronics and I don't want to fiddle with something, not be able to fix it and then get accused by the supplier of causing the issue in the first place.

So just to clarify, when you guys stop the lathe to take a measurement, etc, you just turn off the direction control or do you power the lathe off entirely?


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## Anko (Dec 16, 2012)

my mini-mill does the same thing, when I pull the speed control knob totally off, it pull a switch that makes "click" that supposedly turn off the machine, but with a little rotarion by hand of the spindle, its start to rotate at very low speed...

I have gotten used to this fact, but I have found that the rotation after the off is very sensitive to te position of the speed control knob, the more close is the knob to the "click", the machine will not start rotating, but if y pass the "click" when I rotate the knob to tur it off, it will hapend.

Thats my experience, hope to help

Saludos


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## hacklordsniper (Dec 16, 2012)

i never heard about 30 day warranty, this is illegal in most parts of the world.

When i want to check my piece i turn the speed pot to minimum, put direction switch in neutral, stop the lathe off on start switch and turn off main switch which completely kills the power. This way im 100 % sure nothing bad can happen.

Im not a machinist but i spent last few years repairing/building high power switching supplies and some high current motor drivers and i can give you an advice:

Never, ever trust any electronics especially ones on Chinese machines. Always use a double pole switch to switch off electricity before doing anything on it.


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## Tin Falcon (Dec 16, 2012)

> So just to clarify, when you guys stop the lathe to take a measurement, etc, you just turn off the direction control or do you power the lathe off entirely?


I have had mine open and had to replace switches  so know how things work. 
if you put the direction switch in the middle you are turning power off to the motor. The power board still has power to it. . if you turn off the main power switch you discontent power to the board.  to be safe turn off both.
In practice I just put the direction switch to the middle. knock on wood I have never had it start unexpected.

I say again turn the machine OFF before putting your hands or measuring tools near the chuck or work.  You were not turning the machine OFF!! that is not the MACHINES fault.  

The mini mill has a on off switch built into the speed control I usualy engage the e-stop to keep it from starting. 
Tin


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## hacklordsniper (Dec 16, 2012)

Here is an accident with my lathe, i just remembered i have a picture:

I was making a cut off with a carbide insert trying to cut a piece of hardened steel. It went fine until the index "digged in" the material jamming the lathe. Immediately i punched the safety switch which fell apart and lathe was still powered.

I replaced the switch with good quality one, but luckily this time the worst thing that could happen is that i would break the insert. Luckily i was not in situation that the chuck was chewing my fingers.


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## MuellerNick (Dec 16, 2012)

> but the way this thing is changing speeds and the suddeness and violence that it started spinning on me is a concern.



That is right, it should not happen.

I already described how I switch off my lathe while measuring etc. The reason why I use the chuck guard is, that, while bending over the lathe to measure, I might easily touch the lever (sitting on the saddle) that turns the spindle on.
I could even accidentally switch it on and close the chuck guard ... but nothing will happen. The chuck guard has to be closed BEFORE you can switch on the spindle. I verified that, it is a safety requirement.

It doesn't make much sense to switch off all switches on your lathe, unplug it and cut the mains to your house after calling the power plant to switch off the nuclear reactor. You just have to use a safe procedure that you can not accidentally turn the spindle on.


Nick


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## skyline1 (Dec 16, 2012)

hacklordsniper said:


> i never heard about 30 day warranty, this is illegal in most parts of the world.
> 
> When i want to check my piece i turn the speed pot to minimum, put direction switch in neutral, stop the lathe off on start switch and turn off main switch which completely kills the power. This way im 100 % sure nothing bad can happen.
> 
> ...



Sound advice, I too have worked on big machine drives, (Biggest was a 1MW 4 Quadrant, impressive noise changing direction !).

We were always taught never to rely on semiconductor devices for Isolation always a physical switch or contactor, (preferably both).

That having been said it sounds like the controller board is faulty, it should not be starting and changing speed of it's own accord. another possible cause is the speed control potentiometer itself, unfortunately the only way to test it is with an Ohmeter. 

It may be a one off, but could equally be a generic problem and I am surprised the manufacturers are not taking more notice, (they should be).

Regards Mark


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## bret4 (Dec 16, 2012)

I used to have one of these lathes. Sometimes when I would turn off the spindle using the speed control switch it would run a little after the switch was off. I opened up the speed controler and made some adjustments to some of the pots inside and never had that problem again. I couldn't tell you just what pots I adjusted but for these lathes I doesn't hurt to go over these adjustments once in a while. If you do this be really careful not to short anything out and don't get zapped. Take it slow and you should be able to stop the run on problem. Like others said, it's best to turn the main switch off when touching the spindle. Lucky it didn't happen with the key in the chuck.


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## Herbiev (Dec 16, 2012)

Cogsy. You are doing the right thing reporting this to the Consumer Affairs authority. There could be dozens of these faulty machines floating around and it is just a matter of time before a serious injury happens. I would definitely ask about the legality of a 30 day warranty also. One year is the norm in Oz


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## Tin Falcon (Dec 16, 2012)

Guys what part of turn the machine OFF don't you understand. the speed control is not a power switch. This is operator error!! not a design flaw. :wall:
Tin


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## MuellerNick (Dec 16, 2012)

> This is operator error!! not a design flaw.



That's like saying it is OK for a car's engine running in idle to suddenly rev up (with a automatic transmission in D, that would be fun).
It is both.


Nick


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## Tin Falcon (Dec 16, 2012)

Nick when one parks the car the AT lever is placed in park and the ignition switch is turned off. One does not leave the engine running and leave the car in drive and walk off. that is what cogs is doing. 
Tin


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## MuellerNick (Dec 16, 2012)

> One does not leave the engine running and leave the car in drive and walk off. that is what cogs is doing.



Hah! That even did my landlord with his Claas 7040 telescopic lift. Until we heard some strange noise outside. But we could not open my door because the Claas blocked it, breaking some pallets on its way. It *very* slowly starts to creep forward when the engine is running and not in neutral.

There are two mis-behavious you have to look at separately and that are BOTH unacceptable:
The lathe suddenly starting to rev up.
cogs doing a unsafe procedure (no need to keep on bashing him, he already learned his lesson).


Nick


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## Tin Falcon (Dec 16, 2012)

OK we agree that the lathe should have been shut off and it was not. 

As far as the lathe starting on its own IMHO sounds like there was a bit of energy stored in the circuit board. the operator turned the motor enough so the brushes engaged, the energy was momentarily discharged . The pulse suddenly turned the spindle 1/4 turn. 

I can not discount the possability there is a problem with the control board. these boards do have issues from time to time. there is no way to know if the board is defective without testing or examination. I therefore canot confirm or deny a problem with the circuit board.
Tin


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## starnovice (Dec 16, 2012)

Personally, I have to go with Tim on this one.  I have one of these lathes and would not think of working around the chuck without turning the toggle switch off but I don't see the need to turn off the power switch for routine measurements and tool changes.  I would power it down completely before I swapped out material or changed the chuck.

Mine is an older one that has the toggle switch from forward-neutral-reverse and does not have an E-Stop.  Real easy to go from forward to reverse by mistake. 

Having said that, I really don't need some company to protect me from myself if I use the machine as advertised.

Pat


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## kf2qd (Dec 16, 2012)

My 7x10 has a toggle switch and a potentiometer. When the speed pot is turned all the way down the spindle will still turn slowly. So I put the toggle switch in the moddle - OFF position when I want the spindle to stop.

My MiniMill has a potentiometer with a switch at the low speed position. Mine also has a toggle wswitch that I added. It has 2 positions - Forward and Reverse.

I would never assume that low speed on the minimill is STOP. Poweris still fully applied to the speed control and there is no guarrantee that the spindle won't turn. Low Speed IS NOT  spindle stop. It is just Spindle LOW SPEED. 

Just the same as low throttle on a car, truck or fork lift is not the same as engine off.

I would say this was a case of operator error, and to blame that on the manufacturer is the reason it is so expensive in this hobby... Someone else is to blame for my error. And to tell the truth, I really don't want to get to the point where someone else gets to make all the descoisions what SAFE means. Because then we will all be less safe because safety really depends on the operator using some common sense, and most of the so-called safety ideas are just trying to compensate for a total lack of common sense and without some sense from the operator there is no way anything can be made safe.


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## Jeff-in-PA (Dec 16, 2012)

Tin Falcon said:


> Guys what part of turn the machine OFF don't you understand. the speed control is not a power switch. This is operator error!! not a design flaw. :wall:
> Tin


 

 I'm with Tin on this one.  It's a machine, it doesn't care if flesh is in the way when it starts or impacts something. * YOU are the safety device on the machine*. It's up to you to be responsible for your own safety ( I do agree if it truly is an electronic problem, the manufacturer must address that ).

 I've been a machinist for about 35 years and when it comes down to it, I am responsible for my own safety.


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## Cogsy (Dec 17, 2012)

Whoa, this has turned into quite a debate!

Just to clarify, I was at fault for touching the chuck when I did, no doubt, absolutely. 

However, the machine has got some sort of fault with regards to the occasional speed fluctuations (and it's jumps of several hundred RPM) while running and I believe it should be covered by a warranty longer than 30 days. This thing cost me $750 + shipping and then tooling as well, so I would expect more than a couple months of hobby use.

The best thing to come out of this though, is I have now learned a valuable saftey lesson, and it didn't cost me any blood.


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## Tin Falcon (Dec 17, 2012)

1) Cogs thank you for sharing you lesson  so others are not tempted to make the same procedural error. 
2) We can now all see the importance of electrical isolation when adjusting maintaining machines two or thee points if needed. direction switch center position. power switch off . Unplug or power off power strip. 
3) thanks to all for keeping this thread civil and above board, respectful and to the point. 
4) You are right the machine should last for more than 30 days. 
5) you are right there should not be major unprompted fluctuations in rpm. 
6) I do hear and  feel your frustration. 
7) lets move forward and help solve the problem of unpredictable card function
8) Again I am glad you were not injured . I apologize if I added to the emotional pain . My intention was not to bash you only to point out the procedural error. 

Tin


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## gus (Dec 17, 2012)

Gus worked for 7 years in a Chinese factory with dud ISO Certification. I told the boss and we had a hot argument but he finally admitted so as practically every Chinese factory does to bluff consumers. 
For 4 years I worked with the QA and got quality up to mark. Three years down the line, old problems resurfaced. I gave up and left.
There are many factories in China with DUD ISOs.One good look at the framed up Certification will show. International ISO Certification Companies are mutually cross audited and accredited by other ISO Companies to be credible. This is not so in China. Quality is compromised.

A bad speed control board would have been picked and replaced by a Japanese Supplier and Corrective Actions taken followed by Preventive Actions plus a note of concern/apology to end user.Apparently not so in China. 

Vee belt driven or gear driven lathes has on/off switch to isolate power supply and accidental self starting is prevented. Variable speed control lathes are best to rely on the on/off switch to isolate power supply and accidental self starting prevented. Same applies to electronic on/off switches.Took me a long time to accept soft starters. I would turn off and lock up isolators before working bare hands on starters.It is my life and I only have one life.


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## mwilkes (Dec 17, 2012)

Thanks for that, Gus. I swear I'll never buy a Chinese machine. Cheap things come with a price tag, as they say. By buying a Chinese machine I'd be implicitly supporting poor working practice and exploiting people. 

...plus I'd end up with a machine totally covered in packing grease....


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## hacklordsniper (Dec 17, 2012)

MuellerNick said:


> That is right, it should not happen.
> 
> It doesn't make much sense to switch off all switches on your lathe, unplug it and cut the mains to your house after calling the power plant to switch off the nuclear reactor. You just have to use a safe procedure that you can not accidentally turn the spindle on.
> 
> ...



Im guessing this criticism was aimed at my post. My procedure lasts exactly 3 seconds, timed and proven on video just for this topic. This way i cut off power to the motor, engage turn direction to "neutral" and turn off the main switch witch completly cuts off power.

Is 3 seconds needed to turn off the machine worthy of my fingers, hand or something else? I think not. Accidents don't happen to "other" people, they can happen anytime to anyone. 

I like to play it safe.

Here is a video showing what i think is a safe procedure before manipulating the work in lathe.

http://www.youtube.com/watch?v=wV0Z2f1R2oA&feature=youtu.be


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## skyline1 (Dec 17, 2012)

gus said:


> There are many factories in China with DUD ISOs.One good look at the framed up Certification will show. International ISO Certification Companies are mutually cross audited and accredited by other ISO Companies to be credible. This is not so in China. Quality is compromised.
> 
> A bad speed control board would have been picked and replaced by a Japanese Supplier and Corrective Actions taken followed by Preventive Actions plus a note of concern/apology to end user.Apparently not so in China.



Gus you've been reading ISO9000 again, this is exactly how it should work and does in most parts of the world, but not it seems in China. Indeed much of their certification is bogus. It really screws up traceability (another ISO requirement). They do tend to pay lip service to Q.A. I have seen quite a few potentially lethal bits of Chinese "electronics", which carried all the certification required, but had never actually been tested, if they had they would have failed.

Regards Mark


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## gus (Dec 17, 2012)

Hi Mwilkes,

Bought a 7x Sieg in the US for a friend.He spent a week cleaning up the superduper,messy gunky rust preventive !!!!. Glad I bought on the net thru LMS.Lathe arrived in good condition and good quality as LMS has their own on-site QC. Items bought from LMS were up my expectation.

Spent s$2500 in 2004 to buy a Japanese Sakai 360 , 150mm swing over 360mm between centre.
Above is actually a watch maker's lathe. Had some regrets paying too much but now it worth every cent. Will take very light cuts and gives the precision and finishing. Tapping Fluid is very good for surface finish. 

Came with conventional step pulley drive. A bit inconvenient to change speed so I left at 500 rpm.A robust on/off/forward/reverse switch ensures no accident self start. I still have my all fingers plus nails.

Bye now.Off to finish up the W.I.P. QCTPost now on my thread. This my second QCTP with cam lock.


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## Cogsy (Dec 18, 2012)

Tin Falcon said:


> My intention was not to bash you only to point out the procedural error.


 
No worries, no offense taken.

I would like to explain my actions a little bit though, not to justify them, just so you know how I managed to make such a 'simple' error.

My speed control knob needs to be turned a reasonable distance before the motor starts to 'hum' then turn, so I assumed it was cutting the power when fully turned off. I assumed it worked somewhat like my variable speed hand drills - they have a switch for forward/reverse but not 'off'. I think nothing about grasping the chuck on one of them, as long as the speed control is at zero. (Now that I type it, I wonder if I'm wrong in that as well...) 

Anyhow, that's how I arrived at my incorrect conclusion. With zero training, it was actually an easy assumption to arrive at. I'm going to really take a careful note of all the actions I do in my shed, just to make sure there's no other potential hazards that I'm exposing myself to without thinking about it.

One last item of interest - when it happened, it was far from the first time I've moved the chuck in exactly the same manner, it's just the first time I had an issue doing so. What this tells me is that just because you've gotten away with a hazardous operation in the past, doesn't mean you will always get away with it.

Stay safe everyone!


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## Tin Falcon (Dec 18, 2012)

Cogs I must also admit that the manuals for the mini lathes  are were marginal at best. If you have not already done so download and read http://littlemachineshop.com/Info/MiniLatheUsersGuide.pdf
35 pages of good info written in real English. 
Tin


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## hacklordsniper (Dec 18, 2012)

Tin Falcon said:


> Cogs I must also admit that the manuals for the mini lathes  are were marginal at best. If you have not already done so download and read http://littlemachineshop.com/Info/MiniLatheUsersGuide.pdf
> 35 pages of good info written in real English.
> Tin



Nice one to read. I wonder how Chinese manufacturers translate user manuals, even google translate cant be that bad.


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## Ken I (Dec 18, 2012)

As stated in earlier posts - never rely on a daisy chain of semiconductor devices always switch off.

Its possible your circuit is open circut (on the potentiometer) = flat out - then a momentary loss of contact on a cheap Chinese pot will cause the problem.

I wouldn't trust my safety to any pot - let alone a Chinese one.

I used to have a shop lecturer who would say "are you really going to trust your life to just one switch !" that's a thought that's been implanted and has served me well for several decades of work on industrial equipment without serious mishap.

Ken


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## gramps51 (Dec 18, 2012)

After reading through this whole thread I learned two things: cogsy was lucky and his lathe is faulty. I had one of these things and because of lousy quality I sold it and bought a REAL lathe, a South Bend 9A. 50 years older and 150% better. My opinion only of course based on ownership and use.

Mike


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## neilw20 (Dec 18, 2012)

You turned to pot to stopped.
The electronics says speed command = 0.
You rotate the shaft, now speed is not zero. Back emf from the motor rotation is sensed by the electronics. You rotated it backwards.
Electronics makes a poor attempt to return to zero speed from a negative speed.

The supplied  instructions (if any) if followed are probably OK, but in a practical world, they are not followed and are useless.
You need a safety relay in the circuit, which is no doubt not in the design. I have replaced electronics cards destroyed by the on-off-reverse switch breaking current to the motor.
Disconnecting the motor connection directly, while running, will eventually lead to failure of the electronics, when a high current is opened by a switch.
Return to zero speed, then switch to stopped once rotation has ceased.
Ideally, when stopped, the power from the whole circuit needs to be removed, but now the issue of turning on can lead to high current surges to the filter capacitor destroying something in the input rectifier/switch circuit when power is reapplied repeatedly.
The circuit design is no doubt cr4p.
A circuit needs to sense the stopped condition, then disconnect the motor or disable the drive circuitry.
For startup, the motor needs to be connected before any current is applied.  -- The drive circuitry is enabled after the motor is reconnected by a relay. It can be a secondary contact on the relay.
For any safety circuit to rely on crappy electronics to ensure no power is applied is a recipe for disaster. USE A RELAY.


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