Overloading a Chester Champion V20 Mill

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Overloading a Chester Champion V20 Mill

This topic has 35 replies, 16 voices, and was last updated 8 September 2013 at 21:33 by Peter de Groot.

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15 August 2013 at 18:48 #17142
Peter de Groot
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@peterdegroot14065
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15 August 2013 at 18:48 #127007
Peter de Groot
Participant
@peterdegroot14065
I am about to have my Champion V20 Mill back from repair at Chester tomorrow. I was told by Chester that the control panel blew out, possibly due to 'overload', and that the Champion is 'only a hobby machine'.

Would any Champion (or equivalent) users comment on this in particular do you let your mill cool down at regular intervals or look for signs of overload ? Also is there any other way to avoid this e/g better cooling of the control panel ? Have any of you replaced the Chester controls by third party system or replaced both the motor and the controls for this reason ?

As an aside Chester have been very good about repairing it under warranty, but not having the mill for a month is a nuisance and this is the second time in three months it has gone back for repair (previously the power cable to the motor had frayed inside the Mill (!). Before that I had an intermittent loose wire. I think I may have the Monday morning machine…

Peter
15 August 2013 at 19:13 #127008
Gray62
Participant
@gray62
What do they class as an overload?

What was the exact nature of the fault on the controller board 'It blew out' is a pretty glib statement

They state a max cutter size of 20mm but do they give any indication of max depth of cut, feed rates etc?

Do they give a figure for MTBF?

Do they state a max running time, load limits etc etc?

If you've had to have this repaired 3 times in a short time frame I would be persuing the 'Not fit for purpose' route and request a replacement.
15 August 2013 at 19:19 #127009
JasonB
Moderator
@jasonb
I was looking through a German model eng mag the other day and they had a similar mill where the owned had milled some cooling slots around the bottom of the motor cover and fitted what looked like a computer cooling fan to the top.

What you have to watch with the variable speed machines is running them for a long time on low speed as the fan is fixed to the motor it does not run at full speed all the time unlike a belt or geared head machine so things run hotter.

J
15 August 2013 at 21:36 #127022
Peter de Groot
Participant
@peterdegroot14065
All good questions Coalburner – unfortunately not questions I can answer. Nothing like that is stated in their documentation hence my questions about practical experiences of owners.

Jason yes the cooling fan is the sort of thing I was thinking off, and it's interesting someone else has done that already. My guess is that the control board 'blows out' if the power transistors run too hot, and they are in a closed metal box so just extended running of the machine will heat them up (they are not mounted directly to the control box), almost regardless of load. Thank you also for the advice about not running at low motor speeds. I am milling aluminium and have kept the gearing set to 'High'. I will try it on 'LOW' gearing with the motor running at max refs, and a big mill.
15 August 2013 at 23:00 #127024
Trevor Drabble 1
Participant
@trevordrabble1
Peter,

For your information , in the very good Newton Tesla variable speed package I have on my lathe it states quite clearly that the motor must not be run for long periods below 800 rpm , obviously to avoid over-heating (as per Jasons comment above ) which is why I still use the change belts.

Also, not familiar with your machine , so would ask what types of protection are there on the machine in order to try and prevent the overheating , and since this would appear to be a regular problem , I wonder if someone does a mod whereby a thermal protection device may easily be fitted to the board ? I have in mind as a precident the improved American made circuit boards for the mini lathes.

Trevor
16 August 2013 at 05:19 #127026
Thor 🇳🇴
Participant
@thor
Hi Peter,

This has been discussed previously on this forum, I don't know if you have found it. Johan Crous had a post about how he mounted a fan on top of his Mini-Mill motor. It worked well for him.

Thor
16 August 2013 at 08:03 #127027
Russell Eberhardt
Participant
@russelleberhardt48058
I think there is some confusion here.

Mounting an extra fan on the motor helps with problems related to the motor overheating at low revs.

As I understand it Peter's problem is not with the motor but with the controller board. If this fails due to overheating or extended use it is badly designed and as someone else said, "not fit for purpose". Yes it may be possible to improve it with a heatsink or a fan in the controller box but that shouldn't be necessary.

Russell.
16 August 2013 at 08:55 #127030
Peter de Groot
Participant
@peterdegroot14065
Russell,

Yes they are separate issues, and I was aware that some people have had problems with overheating motors, just not overheating control boards. It is difficult to say if they are fit for purpose or not as the purpose is not specified in detail by the supplier other than it being in a 'hobby machine' category, and I just dont know what that means in practice.

So I'm still interested if people let their mills cool down at regular intervals or watch for some signs of stress like hot quils, control box or motors – anyone ?
16 August 2013 at 11:31 #127036
Russell Eberhardt
Participant
@russelleberhardt48058
Posted by Peter de Groot on 15/08/2013 18:48:11:

I was told by Chester that the control panel blew out, possibly due to 'overload', and that the Champion is 'only a hobby machine'.

They advertise it as a "hobby size machine". Any machine tool should be able to run at maximum load indefinitely. It is very straightforward, when designing a controller, to build in thermal and overload protection.

Having said that I always run my mill in the lowest gear suitable so that the speed controller doesn't have to reduce the speed too much.
16 August 2013 at 11:45 #127038
JasonB
Moderator
@jasonb
Russel can't agree with you there I previously had an Emco Unimat 3 which is definately a hobby machine and it clearly stated something along the lines of 10mins run, 5mins cooling etc.

Peter can you give us some idea of what you are actually doing regarding size and depth of cut, material and how long the motor is running.

I generally find that you spend as long if not longer setting up a piece, changing tooling, etc than the machining opperation so that setup time is sufficient to allow things to rest.

J
16 August 2013 at 13:29 #127046
John Stevenson 1
Participant
@johnstevenson1
Posted by Russell Eberhardt on 16/08/2013 11:31:31: Any machine tool should be able to run at maximum load indefinitely. It is very straightforward, when designing a controller, to build in thermal and overload protection.

I was swapping my gas bottle the other day and was looking at some big 3 phase MiG welders.

Lincoln and Esab amongst them.

The Esab 350 amp welder was rated at 350 amps 40% duty cycle, this means 4 minutes in 10

100% duty cycle was down to 215 amps.

The Lincoln was even worse at 30%.

These are serious bit of kit, well into 4 figures and certainly not hobby machines but still have limitations.

Lets face it these machines are built to a price – full stop.

If they wasn't they wouldn't sell.

So the answer is for the importers to get on to the manufacturers and tell them because you have built to a price you have cut corners and it's not acceptable.

So One Hung Low disapears into the R&D department and comes up with a mini mill equipped with a 1HP 3 phase motors and quality VFD

Unfortunately the price has now more than doubled, the head is that heavy it drops on it's own and the extra weight causes to to tilt and not mill square.

So they go back and redisign the frame so it fully supports the weight.

Problem is now it even dearer and looks like, feels like and costs the same as a Bridgeport but Joe Blogs can't get this in his spare bedroom.

What he really wants is a mini mill for small jobs that he can afford to by with his pocket money and taking a few empties back.

Said if before and will keep on saying it.

There is a BIG difference between FIT FOR PURPOSE and FIT FOR PURSE
16 August 2013 at 14:53 #127051
Clive Hartland
Participant
@clivehartland94829
If you want to mill something big then get a big mill. An industrial milling machine will cut as you wish and I would say that the only limiting factor on such a mill is the tool itself. Plus of cousre a far greater cost of machine and tooling.

Talking of a 20mm cutter, doesnt mean ploughing into a block of steel at 2mm depth full width and hope not to stall the machine with a small DC driven motor. Stalling the machine will either blow a line fuse or as as happened burn out the power diodes on the control board.

having used multi cutter face mills of 250mm diam. trueing up blocks of Alu, no high speed and a slow traverse speed to get a good finish on HE30. The same machine with a 10mm 4 flute Rippa cutter certainly removed metal quickly. This on a Schaublin 13.

The amateur/model making machine has limited capacity to carry out heavy work due to several factors, rigidity, and lack of drive power with attendant vibration from the drive train. My X3 just about gets through with a 1.5mm slitting saw hand fed without stalling. but again with a small dia carbide cutter performs well. Here I have to work within the capacity of the machine power and ability to cope with the work load.

Dont expect too much from these bench machines or you will be disappointed. At the very least work within their capabilities, it will take longer but you will be well satisfied by the quality of finish and accuracy.

Clive
16 August 2013 at 15:41 #127055
Peter de Groot
Participant
@peterdegroot14065
John yes that is one of my questions: what is a practical duty cyle for one of these mills ?

Jason I mill Aluminium only, and I take care not to take deep cuts where the mill appears to strain. Inevitably this means that I have to go over it several times and that means prolonged running times.. The machine did not stall at any time.

Clive with a 1 HP motor and specified max drilling and end milling of 20 mm and table of 700 X 180 this is hardly a toy. I understand the need to work within it's limits, my challange is to understand what those limits are (ie what is the duty cycle) and what the warning signs are for impending overload. I have emailed Chester today to get answers to those questions. Having said that I am keeping my eyes open for a good second hand grown up mill. I did think of trading up with Chester but felt I probably shouldn't dig myself a deeper hole.
16 August 2013 at 16:08 #127058
PekkaNF
Participant
@pekkanf
Posted by John Stevenson on 16/08/2013 13:29:15:

Posted by Russell Eberhardt on 16/08/2013 11:31:31: Any machine tool should be able to run at maximum load indefinitely. It is very straightforward, when designing a controller, to build in thermal and overload protection.

I was swapping my gas bottle the other day and was looking at some big 3 phase MiG welders.

Lincoln and Esab amongst them.

The Esab 350 amp welder was rated at 350 amps 40% duty cycle, this means 4 minutes in 10

100% duty cycle was down to 215 amps.

The Lincoln was even worse at 30%.

These are serious bit of kit, well into 4 figures and certainly not hobby machines but still have limitations.

Yup. There are limitations, but they don't blow up when they heat up. I have had cheap welders and I have a professional welder. The difference is very clear on the duty cycle and ease of use, but even the cheapest piece of crap buzz box will just shut off and after cooling it it will work.

Moreover all these milling machines comes up with a table that will tell what duty cycle they perform.

Electronics that overheats and dies from normal use is just faulty. Plain and simple. Bad design or poor manufacturing. Thermal cutout (on motor and control board) has very little impact on price and practically no impact on weight. A PTC on the motor weight few grams.

I do agree for the rest of the post regarding rating and duty cycle. Any improvement will cost money.

But serously….it is very sily to require a hobbyist to have an ESP qualities of estimating what these machines will do and what not before giving up on ghosts.

Pekka
16 August 2013 at 18:01 #127064
Doddy
Participant
@doddy
Fan mod to my WM14 here http://www.model-engineer.co.uk/forums/postings.asp?th=85711

Edited By Dodweld on 16/08/2013 18:02:05
16 August 2013 at 22:07 #127080
Peter de Groot
Participant
@peterdegroot14065
Thank you all gentlemen, based on your feed-back I am going to first measure the temperatures inside the motor enclosure and control box over time, then see if passive venitlation (vents!) keeps them down sufficiently (I am guessing below 50 C) and add thermal cut outs to both for added protection.

What is a good cut out temperature ? 50 C ?
16 August 2013 at 22:25 #127082
S.D.L.
Participant
@s-d-l
Posted by Peter de Groot on 16/08/2013 22:07:06:

Thank you all gentlemen, based on your feed-back I am going to first measure the temperatures inside the motor enclosure and control box over time, then see if passive venitlation (vents!) keeps them down sufficiently (I am guessing below 50 C) and add thermal cut outs to both for added protection.

What is a good cut out temperature ? 50 C ?

40 C is a good limit for std cheap components. Every 10C rise halves the lives of electronic components. military spec components have higher ratings but don't expect them in budget priced machinery.

Steve
17 August 2013 at 10:43 #127104
Russell Eberhardt
Participant
@russelleberhardt48058
I would say that 55 C should be O.K. in the control box. We often have temperatures over 35 C here and 40 C would be far too low. Most integrated circuits (usually the most sensitive parts) are specified for use in ambient temperatures up to 70 C. The components' case temperatures will be much higher.

As Steve said the MTBF doubles for each 10 C rise in junction temperature but is usually specified for 175 C.

Motor temperature is more difficult. The limiting factor is the temperature of the windings and their insulation. There are several classes of insulation for use at different temperatures up to 175 C. However motors are usually specified at maximum power for maximum ambient (air) temperature of 40 C and should give a life of 20,000 hours at that again halving for every 10 C rise.

So you should try to keep the air in the box below 40 C. If the temperature is more than that you should go a bit easier or let it rest occasionally (with the motor running at full speed with no load if it has a fan driven by the motor).

Russell.
17 August 2013 at 11:50 #127110
Russell Eberhardt
Participant
@russelleberhardt48058
I should add that the case temperature of power devices on heatsinks shouldn't be allowed to exceed 70 C if they are operating near their maximum rating.

Russell.
17 August 2013 at 16:48 #127129
Doddy
Participant
@doddy
Not scientific but I use to let my motor get hand hot then let it cool, since fitting the fan and thermometer it runs to a similar "hand hot" temperature of 50'C so I,ve set myself a limit of 40'C. I work until my thermometer nears 40'C, finish my cut then allow to cool, the fan only takes a few minutes to reduce the temperature back down to 30'C but this is only when taking cuts which are really too big. Just milled the spokes on a brass flywheel, 1/4 inch slot drill, slow feed, and the temperature never rose above 35'C the ambient temperature in the workshop at 21'C

The fan only cools the motor, the only thing I did to the control board was use some heats sink paste to ensure a good thermal connection to the case.

It has been a worth while modification and something I could recommend doing

See my photos on my album

Edited By Dodweld on 17/08/2013 16:52:55
17 August 2013 at 18:33 #127141
dcosta
Participant
@dcosta
Hello, good after noon.

My first milling machine was an Optimum BF20 Vario which after about two years of use was sent to the distributor in Portugal to some light repair. There, someone dropped a heavy object on the table causing deep dents on it.
The dealer replaced it with a new one and some time after its electronic crashed. The distributor's technician came to my workshop and replaced the electronic board with a new one and at the end of the installation I did ask him questions about the load capabilities that the machine was capable of. And he promptly did a test that left me amazed.
He asked me a chunk of cold rolled steel and set an end mill 10mm in diameter in a collet.
Then he started a cutting with about 10mm in depth, manually feeding at high rate which took only a few seconds to both the metal and the cutter to be red hot. He continued to cut a few more seconds until the cutter has cut about 50mm in length and almost all the time the metal and the cutter were some variation of red hot.
At the end he told me something like this: if with this load it did not broke its not likely ever becomes damaged by overload. And, indeed, so far never broke …

After that I concluded some machines are only similar at first sight…

Best regards
Dias Costa

Edited By dcosta on 17/08/2013 18:35:20
17 August 2013 at 22:24 #127157
Peter de Groot
Participant
@peterdegroot14065
Gentlemen thank you for the additional advice on temperatures, I will measure and experiment and report back…

p.s. I really like the dodweld fan mod – nice and simple.
2 September 2013 at 12:39 #128413
Peter de Groot
Participant
@peterdegroot14065
Update:

I emailed Chester to ask for Duty Cycle information for the Chester Champion V20 and this was their surprising response:

"duty cycle is not available for these machines as they are hobby rated and not for use in any kind of setting where the machine needs to run for extended periods of time."

I take this to mean that the only safe use of the Chester Champion V20 is to not use it at all.

I asked them what periods they can be run for but there has been no response to this.

Chester also said that "the capabilities of the machine are listed in the manual". So I checked the manual but there is no duty cycle information in the manual. Nor any information about thermal cut-off so I have to assume there is none.

I thought I would see what other Chester Machine Tools Mills are 'hobby rated'. On their model engineering section (One assumes these are hobby rated) it lists everything from the Micro Mill at £ 268.80 inc vat to the Model T turret Mill at £ 6156.00 inc VAT. Wow, that is a lot of money for something that has no defined duty cycle. And I thought that spending £ 816.00 on my Champion V20 would buy a machine that has a defined performance however limited.

OK so I have learned my (rather expensive) lesson – don't buy Chester Machine Tools (or any other machine tools!) without a documented duty cycle.

I got some temp gauges today and will be doing some measurements on motor and control box with and without load to try and figure out what the duty cycle of this thing is without mods. I am stuck between a rock and a hard place. If I modify the Mill I will void the warranty – If I dont modify it then it will most likely break down again!
3 September 2013 at 17:48 #128515
MICHAEL WILLIAMS
Participant
@michaelwilliams41215
Hi Peter ,

(1) Alter the drive ratio between motor and spindle so that for your normal range of spindle speeds the motor is always running at reasonably high speeds .

Primary cause of your problem is not duty cycle – it is running motor in near to stall high current conditions and having fan running so slowly that it is ineffective .

(2) Fit large electronics type air dissipation heat sinks to metal parts of motor casing . Even a couple of modest size ones can dissipate 70W and that will lower your motor temperature a great deal .

(3) Don’t be over cautious in choosing cutting speeds – in general run spindle as fast as you can get away with for a particular job .

Moderately deep cuts at higher speeds and feeds using smaller cutters will load motor in a more favourable way than taking slow speed / slow feed cuts with big cutters .

(4) In any case take full advantage of modern cutting technology and use cutters which can be run at high speeds .

Regards ,

MikeW
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