|John Rudd||13/09/2017 11:12:49|
|927 forum posts|
Basically there are three different species of variable speed drive train for mills/lathes.
The basic pm motor with its troublesome brushes, usually accompanied by a thyristor based speed controller, of Chinese origin or the slightly more reliable KB controller from the States. This drivetrain is probably the cheapest entry level....for smallish mills and lathes, although my lathe had a 1.5kw dc motor fitted!
Then we are on to brushless motors, multiphase with Hall devices for feedback, using a dedicated control board. More expensive than the dc motor, but more powerful for just about the same physical size, can be found on numeroys Sieg machines
Finally, the usual industry standard 3 phase motor with a vfd, using a larger motor, generally found on bigger lathes..
|larry Phelan||13/09/2017 11:29:00|
|286 forum posts|
Like Duncan,I thought it was a bit odd to hear of an AC induction motor with a controller.
Both my lathe and my mill have simple induction motors [Chinese],as has my bandsaw. Touch wood,none of them have given any trouble [so far !! ] Must be going about 12/14 years now.
Would it be possible to simply change the motor type? Wishful thinking perhaps !.
1788 forum posts
I didn't miss your point.
The remark you chose to quote was an extension of my personal opinion in addition to my reply to you.. (and as it seems sort of ish backed up by JS in the next post)
Technology moves forward to address issues and problems. Soon brushed DC motors on machine tools will be a distant memory. e.g. In the same way drum brakes are no longer fitted to cars.
Having said all that Jason has had 2 brushed motor machines that have operated flawlessly for quite a number of years now and still to the best of my knowledge still are. (think he replaced brushes on his lathe once) And he probably uses his machines more in a month than most of us do in a whole year. Add to that he builds quite large models so it's not as if he is 'babying' them.
|1858 forum posts|
Looking for anything unusual that might explain your problem, the statement that the mill is fitted with a single phase AC Induction motor is odd. Can you confirm that please? If true, it means the motor and control board on your mill are unusual, which may be a clue. Are you able to post a photograph of the motor? (And if you incorrectly think it's an AC motor, you won't have checked the brushes...)
Secondly, I don't see how a dodgy capacitor and/or centrifugal switch explain your symptoms. Perhaps an expert will comment, but I associate both with failure to start, or in the case of a jammed switch, overheating. That doesn't seem to fit with a motor that starts, initially loses 200rpm, and then runs at a maximum of 10rpm.
It's too early to blame the motor because it's Chinese. Possibly you've been caught by counterfeit motors, or cheap nasty clones, but don't underestimate Chinese industry - they've been able to make decent motors for donkey's years. It would be useful to know what you use the mill for and how much work it does in an average week. (There's a big difference between a couple of hours per week gently milling Aluminium, and 24x7 piecework on Stainless!) Can you think of anything odd about your workshop or household - for instance, do the house lights ever fail.
Don't be too disheartened: the worst that can happen is you replace the motor with a 3-phase type and a VFD. Spending the dosh will be painful, but the improvement acceptable.
Edited By SillyOldDuffer on 13/09/2017 11:48:02
|John Coates||13/09/2017 12:16:03|
550 forum posts
You bugger! Almost spilled my tea and coughed and spluttered over my keyboard after reading that!
|not done it yet||13/09/2017 12:24:20|
|998 forum posts|
brushed DC motors on machine tools will be a distant memory.
Not so. There are still many machines on the market, aimed at first time buyers, generally. Often those that are in the market, but unaware of the deficiencies of some machines, particularly the motor/controller combinations.
1788 forum posts
I didn't say there wasn't. I meant their days were numbered.
Unless of course they have a revival like the Bay City Rollers did.
|not done it yet||13/09/2017 14:12:47|
|998 forum posts|
I meant their days were numbered.
You may well have done, but there are lots of them out there, and will be for several years - unless their horrible, not fit for purpose motors/control boards are replaced, before being offered for sale, or these cheap under-designed machines are scrapped.
In the meantime, there will be a lot of unsuspecting buyers (perhaps as JS suggests, or maybe new starters that just don't have the funds for a bright shiny new machine). Ethics, really - whether you support the unsuspecting innocent buyer or the possibly unscrupulous seller pushing off his rubbish machine to an unsuspecting buyer.
I rest my case. It does not, and will not, affect me. I would be very wary of buying second hand chinese and would even avoid new chinese at that end of the market.
But please don't quote me and then include dealers or distributors in your apparent reply to my quoted post. I did not mention them at all.
|Michael Gilligan||13/09/2017 14:56:50|
|9930 forum posts|
'not done it yet'
As a disinterested [not unininterested] observer of this thread ... may I ask a favour ?
When you are quoting others, could you please do so in the conventional manner [i.e. by using the Quote button and thereby including the timestamp etc. of the source posting] instead of just pasting an emboldened phrase taken from some prior post. ... Extracts are fine, but the timestamp identifies the source.
It's a small thing, but it does make it easier to follow the thread.
1788 forum posts
I wouldn't know.? - As to date I don't own any far eastern machinery.
|Graeme W||13/09/2017 17:12:35|
921 forum posts
For those of you who may be interested, the 'nominal supply voltage in the UK is now harmonised with Europe and is quoted as 230V +10% -6% which means the voltage you measure in your property on a single phase supply can be anywhere between 216v and 253v and still be within permissible limits. My supply normally sits around 242V but I have seen it drop to 235 at peak load times, we are however quite close to the sub station so variation is usually small.
|1858 forum posts|
Deeply offended by that I am. To be clear I 'm not only tight arsed and deep pocketed, I have short arms as well. When first married my wife and I shared something truly beautiful. But then she spent it.
|David Standing 1||13/09/2017 19:11:09|
|442 forum posts|
Stop that right now
|Neil Wyatt||13/09/2017 20:07:48|
10999 forum posts
Keep up at the back Duncan! This has been on the website for three years:
I'd stress that I blew my motor by trying to take extended cuts at 6 11/2" diameter in cast iron at 60rpm. No one told me that could overheat a mini-lathe...
The board blew in response to a long thread of swarf snaking into the control box, a bit of an unlikely event, but mine was a 1998 machine and 'modern' ones have a rubber gasket blocking the hole.
Personally I don't think the brushed DC motors with the second generation boards have anything wrong with them IF you understand that they must not be allowed to overheat.
The new brushless motors are more pricey, but better as they have more intelligent controllers and really can't be sdescribed as 'horrible' in any way.
|Mark Lawson 1||13/09/2017 22:07:21|
18 forum posts
Brushless motors were not an option at the time I bought my mill regardless of how deep my pockets, I don’t have to justify anything to you least of all what I spend.
Hi Silly old duffer, my mill is used a few times per month; it’s used mainly for alloy and occasionally a bit of brass I build 1/6 scale RC tanks mainly from kit and either modify parts or scratch build them, I never mill steel or stainless the largest tool I use is a 13mm end mill but mainly 6,8 and 10mm with a .5mm cut.
If I’m going to be spending £300 on replacement motor and board then I’m going to be buying brushless as opposed to these motors.
Edited By Mark Lawson 1 on 13/09/2017 22:09:26
|Mark Lawson 1||13/09/2017 22:18:11|
18 forum posts
This is what I’m working on at the moment
|Ian S C||14/09/2017 10:27:58|
6351 forum posts
That is a DC motor with brushes. At 5200 rpm its no induction motor on 50 HZ.
A web site that I had a look at said that Chester removed the Chinese control board , and replaced them with boards made in USA.
Tony Durkin, Sales engineer at Chester Machine Tools has a forum on line where you can ask questions, and forward ideas.
Ian S C
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