Cj18a mini lathe

[Steve LangParticipant @stevelang11304]

Hi,

I have a CJ18A 14 x 12 mini lathe that has started running fast and slow and now only runs at 100 revs per minute,

I have fitted a new reverse switch and also a potentiometer,

Has anyone any ideas on what's wrong here, I have done some basic multimeter tests,

Thanks

[Steve LangParticipant @stevelang11304]

Slow turning

[John HaineParticipant @johnhaine32865]

The speed controllers in these lathes are a disgrace, they seem to give endless trouble. Best thing to do is fit an alternative industrial dc motor controller such as a Sprint or KBE one IMHO. People do spends a lot of time troubleshooting them but it's polishing the proverbial.

[Steve LangParticipant @stevelang11304]

Thankyou so much, will look into it.

[Steve LangParticipant @stevelang11304]

I don't really know much about wiring another board in, but see this on on line, looks simple, would this speed controller work, please

[Steve LangParticipant @stevelang11304]

[Ron LadenParticipant @ronladen17547]

See what Steve..? there is no link..?

[Ron LadenParticipant @ronladen17547]

Got it now

[Steve LangParticipant @stevelang11304]

Thanks, do you think this board would work?

[Brian GParticipant @briang]

This thread suggests that the motor runs on 180V, so I don't think this controller would work.

Minilathe/Mill motors

Brian G

[Steve LangParticipant @stevelang11304]

0r this Ron,

[Steve LangParticipant @stevelang11304]

[Steve LangParticipant @stevelang11304]

My dc motor is 550w, but I think this might work, any thoughts please?

[Anthony KnightsParticipant @anthonyknights16741]

I have used the item shown in the last two posts, to successfully run the motor on a Clarke mini lathe (CL300).

[Steve LangParticipant @stevelang11304]

Thanks Anthony,

Sorry just to be clear, so are you saying that the speed controller in my last two posts might work please

[Steve LangParticipant @stevelang11304]

Hi again,

I have 5 of these diodes on the board which I have de soldered, if I set my multimeter to 200k ohms 3 of the go to zero, but 2 of them stay on 1 on the meter, can anyone tell me if any or all are faulty please,

[Steve LangParticipant @stevelang11304]

[Steve LangParticipant @stevelang11304]

I put the two multimeter probes on the outer pins

[SillyOldDufferModerator @sillyoldduffer]

Apologies if what follows is overly negative, it's partly personal opinion! Even though I have the test gear and a long running interest in electronics, I don't enjoy diagnosing especially without a circuit diagram! Faced with this problem, I'd do a few simple checks, and if the answer wasn't fairly obvious, I'd flash the cash and replace the board.

Too late now, but dealing with faulty electronics, it's best not to rush into taking stuff apart. Diagnosing electronics isn't as simple as fixing a mechanical mechanism where how it works and what's wrong can often be sussed just by looking and poking at the parts. Unless a faulty electronic component is actually smoking, it's not obvious what's wrong. Now there are two problems: the original fault, plus new issues resulting from the board having been removed and bits de-soldered.

The initial symptoms suggest a faulty potentiometer. These contain a carbon track along which a wiper arm rotates. They're prone to wear and vulnerable to dirt. Made-down-to-price equipment usually contain ordinary consumer pots, which aren't made for constant use in a dirty workshop, rather than the much more expensive sealed units available: it's cheaper to replace 4 or 5 ordinary pots than to fit a fancy one once.

Intermittent pots can often be restored by squirting switch cleaner from an aerosol can inside through a gap in the casing; I use Servisol, other brands available. Otherwise, replace the potentiometer with one of the same ohm value, type linear.

Running at low speed after a new potentiometer was fitted suggests the pot is the wrong ohms value or was wired incorrectly, such that the control voltage wasn't getting from the pot to the board. A multimeter set to measure about 12V would confirm the pot is working correctly and the control voltage is reaching the board.

Only after that would I look deeper, and the device Steve has removed is a suspect. As I don't know the board in question, to be sure of what the 3-legged beastie is, I would have to look on the web for a data sheet matching its part number. Could a bipolar transistor, FET, SCR, or a Triac; it matters – how they measure on a multimeter varies.

With luck one of better motivated and qualified motor experts will be more positive than me. If not, my list of preferred alternatives, in order of easiness:

• Replace the existing board with a new one – Amadeal seem to stock them, about £100. Advantage is it fits straight into the existing lathe and the reversing, NVR, pot and safety interlock switches all just work.
• Replace the board with an external unit of the second type pictured. The example illustrated would work, but even the 500W version is a shade underpowered compared with the motor. Won't deliver full power during normal cutting and might go pop if the motor overloads due to a stall. An unknown here – some power supplies are designed to protect themselves against all manner of abuse, others just emit smoke. No hint in the blurb as to how clever the unit pictured is, but a number of reviews say they've been successfully used on mini-lathes. Big advantage cost – £25. Disadvantage, more installation work compared with a new board, but not rocket science.
• Replace motor and board with an industrial Sewing Machine motor and controller. This option is proving ever more popular – power and reliability at reasonable cost. Disadvantage: everything is different, so more installation work.

The lathe is fixable, but probably not by basic multi-meter methods.

Dave

[Steve LangParticipant @stevelang11304]

Hi thanks for the detailed info,

I am loathed to buy another board from Armadale as after research I have found they often blow, then I down the same route,

Again thanks I will have a think,

[Anthony KnightsParticipant @anthonyknights16741]

The motor on my Clarke CL300 lathe is a 180volt DC permanent magnet brushed motor, rated at 350(chinese) watts.The control unit shown is rated at 500 (chinese) watts and works fine on my lathe. There is an internal adjustment for the output voltage. I fitted the pcb in the original lathe control box. While this voids any warrentry, for £20, I thought it was worth the risk. This is only a temporary measure as I already have a 3phase half horse power motor with inverter which I am in the process of fitting now. Keeping the lathe running with this cheap control box enables me to make the bits necessary for the conversion. Interestingly, the 1/2 HP motor is physically twice the size of the DC motor and they are both in the 350watt range (1hp=746 watts). It must be the difference between Chinese and British watts.

[Ron LadenParticipant @ronladen17547]

I could be wrong but I suspect that the Chinese watts quoted are input watts and not output watts. Its all a bit of a finger in the air situation with a lot of the figures quoted on Chinese kit. I have some Chinese 24volt 150 watt motors in one of my 5 inch locos with an unloaded RPM figure quoted at 2750 rpm but an unloaded bench test showed them to be closer to 4000 rpm.

Edited By Ron Laden on 02/05/2022 14:32:13

[Steve LangParticipant @stevelang11304]

Yes I agree, I'm going off buying a Chinese lather again,

[Ron LadenParticipant @ronladen17547]

Steve although it can be difficult to track down the true figures and how and where it has been measured on Chinese machines and equipment it doesnt mean that they are all bad. Once you have sorted the unfortunate motor drive failure on yours I,m sure you will find that you can produce some nice work on it if you havnt already.

My mini lathe was also the CJ18a and I was maybe lucky in that mine never suffered any electrical problems. I did break the plastic drive gears in the head when I stalled the machine on parting some steel but other than that it worked well and was reliable. I did do a couple of mods to mine which did improve it and made it a bit more user friendly and I would probably still have the lathe but I needed something with a bigger capacity so moved up to a bit larger machine but still Chinese and 24 years old so that must say something…

Edited By Ron Laden on 02/05/2022 19:16:07

[Steve LangParticipant @stevelang11304]

Yes you are probably right, I am toying with buying the other control unit that I posted pictures of, would you be able to tell me if this takes the place of my existing boards,

There looks like there are 6 simple connections on the rear,

Thanks again

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