732 forum posts
Well I seem to have done it again
This time was drilling a 22mm hole using low speed and all of a sudden the main RCD tripped. Reset it and switch the mill on, nothing. Replaced both fuses in the mill as both had blown. Once replaced the motor fired up but sounded like it was sparking/arcing and would only turn at 250rpm no matter where the pot was turned to so I suspect the motor is broken, just wondering what test I can do before ringing Warco tomorrow?
Also just wondering how much a replacement motor may cost?
Edited By petro1head on 17/02/2020 17:38:37
732 forum posts
Well, the specification does say maximum drilling capacity 16mm, sorry New motor price depends whether it is the old DC brush motor or one of the newer brushless variety.
Edited By Journeyman on 17/02/2020 18:29:40
17296 forum posts
If you keep breaking it I would be looking at a new operator rather than motor or at least treat it as a hobby machine and don't expect it to cut like an industrial one
|3165 forum posts|
I dio not think I have ever drilled a 22mm hole and I have a Bridgeport (amongst other machines).
Much easier to start with what size drills easy and open up by boring (better accuracy as well).
3575 forum posts
Anything above 16mm should be bored on a hobby unit
|not done it yet||17/02/2020 23:54:55|
|4164 forum posts|
My lathe has a one horse power motor. I was drilling a 22mm hole last week, over 50mm deep. ~6mm pilot and in aluminium. But not even using back gear. No problem whatsoever.
I don’t have any short drills to do that on the mill (my large drills are tanged).
Seems like those motors don’t cut the mustard when the going gets tough.
|Martin W||18/02/2020 01:24:37|
|824 forum posts|
The problem with DC brushed motors is that if they are not turning at a reasonable speed then the cooling fan is ineffective and they can overheat. To stop the Asian kit critics trotting out their usual mantra this is a problem with any motor that is dependant on cooling from a shaft mounted fan when it is run slowly and heavily loaded or as in this case looking as if it was overloaded.
|not done it yet||18/02/2020 08:46:46|
|4164 forum posts|
The problem with DC brushed motors
Agreed, likely overloaded, but nevertheless, I am confident my 3 phase motor would stand overload far better than these chinese offerings. Poor design - cheapness? - I reckon, for motors to go pop so easily. That is excluding operator abuse, of course, as I expect I could burn out my motor if I really tried.🙂
If these machines are so sensitive to overload, they should be fitted with a thermal cut out - many cheap welding sets even have one!
|Dave Halford||18/02/2020 09:28:59|
|607 forum posts|
You might need a power meter to keep one eye on as you work. Might help to prevent those overload death moments.
Either that or sell it and go light industrial with a Centec or Tom Senior etc
Edited By Dave Halford on 18/02/2020 09:33:49
|Martin W||18/02/2020 09:56:24|
|824 forum posts|
If these motors are run within their specified limits and duty cycles then there doesn't seem to be a problem with overheating. Again it comes down to price and what people are prepared to pay for a machine. Like most products the features and to some extent quality will be set to meet the minimum standard that customers will accept at a given price.
There are many examples of same problem manifesting itself even on tools supplied by respected manufacturers, a classic example was using mains powered variable speed hand drills at low speed and high loads for extended period of time. Result the same problem damaged motors or hot hands plus magic smoke. I don't whether it is the same now but in the past welding sets used to be issued with duty cycle information to restrict self heating and prevent damage to the machine.
|5344 forum posts|
Umm, not really comparing like-with-like. This is all to do with ratings and cost rather than design.
DC brushed motors are a good choice for machine tools, apart from the brushes. Before 3-phase most big motors were DC, and many still are.
But, as a proud WM18 owner myself, it needs to be emphasised it's a hobby mill, not rated or built for continuous hard work. The owner has to drive it appropriately and drilling a 22mm hole is asking for trouble - pulling lots of power at low RPM runs the motor outside it's comfort zone. Bit like a car, you might drop down a gear or two to accelerate whilst overtaking, but only a fool would drive from London to Edinburgh at 70mph in 2nd gear.
I've never overloaded my WM18, or broken a gear. I increase depth of cut and feed-rate on mine until I hear it distinctly working, but keep it short of labouring. The machine keeps going whilst being pushed hard, but there's no way of telling how distressed the motor, electronics, and gear train is. Better not to risk damage, by backing off a bit. Captain Kirk always gets away with ordering Scotty to red-line the engines. In the real world the Enterprise would end up stopped and smoking on the hard-shoulder and have to be towed to a garage. Captain Kirk would be dismissed the service in Series 1 for wrecking a star-ship against professional advice!
Edited By SillyOldDuffer on 18/02/2020 10:16:52
|Martin W||18/02/2020 11:17:20|
|824 forum posts|
While the use of a power meter might give some indication of the instantaneous power and total power being consumed it is far from ideal and can lead to a very false sense of security. Primarily this type of digital power meter is designed to measure sine waveforms, as one would theoretically expect to be supplied by the energy company, and usually makes a good stab at it plus or minus a few percent.
However when the measured waveform deviates from a a near sine wave then the readings can be grossly inaccurate. This can happen when these meters are used to measure the power being absorbed by a phase switched load as the load current is now a chopped up part of a sine wave. Even what are supposed to be 'True RMS' digital meters have a limited form factor for which they are accurate.
The main problem with these and similarly cooled motors is that when run slowly the cooling becomes very inefficient couple that to being fairly heavily loaded and it spells problems. The current is going to be high, as are the I2R (I squared R) heating effects with limited cooling. I suppose a fairly good analogy would be using a car with the cooling system blocked off and towing a heavy trailer up a long and steep hill. Frequent stops to let it cool down and all would be fine but try it in one go and the engine would soon emit a different type of magic smoke irrespective of build quality.
The use of a Power Meter could be a good idea if they were anywhere near accurate when used under these conditions at least one could monitor the total power being used and set a safe maximum time v power limit.
Edit as post crossed with S.O.D. Dave's post
Edited By Martin W on 18/02/2020 11:19:10
Edited By Martin W on 18/02/2020 11:20:13
|Jim Nic||18/02/2020 11:35:34|
234 forum posts
To answer the OP's question I can advise that 3 years ago I foolishly cooked my lathe motor in a similar way by cutting a large diameter bar of unknown, but tough, steel at too low a speed for too long. The resulting lack of cooling made the motor far too hot to touch even 15 minutes after it gave up the struggle. The cost of a replacement from the machine supplier was close to £150.00.
17296 forum posts
Some of "these" machines do have an overload trip, my mill certainly does as I have tripped it a few times so should not assume that all DC motored mills don't have this feature.
I stalled the lathe a couple of times the first time I went to cut a 9 or 10" iron flywheel, soon learn what it's limits were and adjusted my methods to suit and have not had issues since and that was 10-12yrs ago. I've said it several times on here that they work better run a bit faster and with a shallower or finer cut in the end you get the work done in a similar time. They are quite capable if treated with respect and as hobby machines not treated and used in the same way as heavy geared or belted industrial ones.
For example the typical old advice was to engage back gear and take a deep cut to get under the skin of a flywheel or loco wheel casting. I'd be doing a 9-10" dia flywheel at 3-400 rpm and taking 0.5-0.75 deep cuts with carbide that can handle the speed and not bothered by the skin.
Same for holes I'll work my way up in 3mm increments starting at 6mm and then finish by boring. drills can be wound if at a good feed rate not having to use both hands on the tailstok to force them into the metal as per a recent thread so not a lot of time difference and less strain on the motor and electronics
|Ron Laden||18/02/2020 16:33:45|
1715 forum posts
I am relatively new to machining but one thing I have learnt is the limitation of my machines. I have an elderly Warco 918 lathe and a SX2P mill which are both hobby machines and I try and keep within their capability and quite often well within at the expense of an increase in time/number of cuts etc.
I get good results from both the mill and the lathe and they are quite capable for their size providing what I ask of them is realistic, expecting too much of them especially on a regular basis I think is just heading towards problems and breakages.
Just my two penneth anyway.
Edited By Ron Laden on 18/02/2020 16:35:02
|not done it yet||18/02/2020 22:11:58|
|4164 forum posts|
Well I, just for the fun of it, just drilled a hole about 30mm deep with a 22mm drill into some non-descript steel after piloting with a 6mm drill.
One horse power motor, no problem at all. Lathe only slowed when thick continuous spirals were being turned out - OK with thin continuous spirals. This was in normal speed range, not back gear.
IMO, a 1 1/2HP motor should be up to the job. Methodology, and edge on the drill may have been factors. Otherwise these motors are just not up to the job. I wonder whether the motor rating is input or output. Anyone know? If it is input, what is the motor efficiency?
Seems like it may have been a very expensive hole!
17296 forum posts
Would be nice to know what lathe it was. How does your mill cope with the same size hole as the OP has broken his mill this time, broke the lathe last month.
You need to remember these DC motored vari speed machines are seldom geared so motors don't give their full rating at slower than full speed unlike your (assumed) geared/belted machine. Even then what the motor puts out can differ depending on how the torque settings have been set on the board and by differing boards
Also read yesterday of one of our members stalling his Bridgeport and he does know what he is doing.
This is the only illustration of what I have been saying. A Brushless direct mill first running an HSS slitting saw at the calculated book speed of 100rpm and if can't do it. Up the speed to 210rpm and it has no problem though a slow feed is needed. By contrast the X3 with just a high/low gear box did the same cut at 100rpm in low range and has a lower wattage brushed DC Motor
Edited By JasonB on 19/02/2020 07:04:59
|Ian Parkin||19/02/2020 07:10:37|
727 forum posts
I do have a motor and speed control board that I took off my wm18 that you can have for a good price
i fitted a 3 phase and vfd to mine
|Tony Pratt 1||19/02/2020 07:22:34|
|1024 forum posts|
Don't think the OP mentioned a pilot drill, makes a hell of a difference.
|Paul Lousick||19/02/2020 08:38:09|
|1318 forum posts|
Drilling a 22mm hole on a lathe or mill with a one horse power motor should not be a problem if it is fitted with a gearbox or belt drive speed reduction as the motor is running at full speed and the internal fan is cooling at 100% but if using a variable speed motor, at a slow speed the fan air flow is reduced and can lead to overheating.
Even though the DC motors have good torque at low speed it is less than what you would get a reduction drive system. The WM18 mill has a 1.5kw variable speed motor and is only rated to drill a 16mm hole. My RM-45 mill only has a 1.1kw fixed speed motor and gearbox drive and can drill up to 31.5mm holes. I used to have a Seig SX3 mill with a 1kw motor and to drill bigger holes, up to 36mm, I used a rotabroach instead of a twist drill with no problem.
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