Rebirth of a Denford MIRAC CNC Lathe

[awemawson]

Not so sure there Tom, it seems to be one step forward - two back today 

I'd removed the auto oiler / lubrication pump before panel spraying, and also cut a hole to replace the fixed power cord clamp with a 15 amp IEC socket. So today I wanted to refit the oiler and connect up the socket - nice and simple.

First I wanted  to investigate why the oil reservoir was swathed in blue insulation tape - as I'd guessed it was cracked - no big issue, I gave it a good wash out in very hot soapy water (can't use a solvent as I don't know the plastic) to de-oil the crack, then glued it with a speciality plastic glue. Bolted it back on the machine and re-made the five drive wires (this oiler runs when the spindle is turning).

Then I made up a little cableform from the termination block that the the fixed power lead went to, to the IEC input socket. Powered up and it tripped my RCD in my main fuse board. 

Lots of faffing about looking at wiring and scratching my head - it all looked fine - but I dis-connected the oiler anyway, tried again and it was still tripping. Hard to make an error in the Live Neutral and Earth cableform - and no there wasn't !

Lots of experimenting trying to isolate the leakage, but as yet not found it - if I disconnect the earth tag on the mains input it powers up ok and the chassis floats at about 100 volts above earth   

[awemawson]

Now I couldn't for the life of me understand how I could have introduced an earth leakage fault doing what I've done.

So as Sherlock Holmes used to say, when every other possibility has been eliminated what remains must be the truth - look at the old mains lead - sure enough the earth was disconnected - this is NOT a new fault, I've tripped over someone else's unfinished problem   

[b4dyc]

That will give you something to do then. You was looking like you were near finishing otherwise 

[awemawson]

So a bit of diagnostic progress:

Removing the earth from the input IEC connector and putting an AVO8 Mk7 on AC volts between the IEC Earth tag and the removed machine Earth, and the machine powered up I was reading 88v AC - roughly what I'd read  before and enough to give you a tingle on a grazed knuckle - (ask me how I know!).
Now the internal resistance of the AVO is high enough to limit the earth fault current sufficiently to not trip my 30mA RCD in the fuse box, but is low enough to swamp stray capacitive effects that you would get using a modern electronic meter like a Fluke.

So by a process of elimination working though all the mains using devices in the machine I found that the main spindle drive inverter to be the culprit.  Now as inverters switch at high frequencies they do tend to cause quite a bit of earth leakage, but in this case I'm sure it is excessive. I strongly suspect the input filter components in the enlarged view, but getting at them to replace wouldn't be easy.

As I have a 13 amp socket for lighting on my three phase Bridgeport, that is derived from phase 1 and neutral, and the three phase distribution has a 100mA RCD I moved the extension lead from a 30mA protected socket to this 100mA protected socket and sure enough it didn't trip (I'd left the AVO in circuit but rotated the knobs to measure AC 10 amp so effectively a short circuit restoring earth continuity.

Out of interest I turned the knobs back to AC volts and I was measuring very low volts - nothing like before where I had 88 volts AC. All very odd - so I put the machine back onto the 30mA protected circuit with a solid earth by removing the AVO and pushing the faston connection back together, and darn me the bally thing works and doesn't trip the 30mA RCD any more 

The only conclusion that I can draw at the moment is that whatever was causing the leakage has been blasted away by the (presumably) less than 100 mA current that initially flowed, and is now in oblivion 

So although I don't like disappearing faults, at least it's working and no longer dangerous as it was.

To prove all was working I tried to make another M6 brass bolt, but the darn program wouldn't run - couldn't fathom it, until I noticed the little bit of text saying 'Low Lubrication Oil Level' - of course I hadn't filled the reservoir when I glued the crack to give it time to set. Filled her up, off the program went . . . .BUT the crack still leaks 

...ah well . . .

[nrml]

Why don't you fold and solder a sheet metal box that can sit within the cracked plastic oil reservoir? It would be a simple solution for the problem. My personal experience with gluing plastic containers of any sort has always been bad.

Do you think that the tripping might have been caused by a bit of swarf in the electronics which fell off when you were dismantling the boards?

Edit:
The reason I ask is that there appears to be some swarf / dust on the black sheet metal panel and on top of the lowermost mosfet in your last two pictures.

[russ57]

Another possibility ; although I do like the swarf idea.
Moisture in some insulator. Leakage to earth.
Letting it run for a while with higher leakage allows it to dry.
But the smoking gun is still the disconnected earth. Obviously been a long standing problem. Maybe a leaky cap which reformed?



Russ

[awemawson]

Russ and NRML thanks for the suggestions. Swarf is always a possibility but I did give it a comprehensive blow out with an airline several times. I like the tin box idea - I shall store it away - the manufacturers agent says that the reservoirs are still available and I'm awaiting their pricing.

The machine has been in a heated and dry environment for quite a while now so I doubt dampness was the cause, and certainly no sign of it in the culprit inverter.  It was plugged into the 100mA protected circuit for probably less than half a minute - just long enough for me to realise that it hadn't tripped !

As was said, the disconnected earth wire is a smoking gun - someone has been down this path some years ago. If the problem returns I'll have the inverter out on the bench and do a proper diagnosis, my suspicions of the filter components are entirely without evidence - just based on previous experience - so I suppose you'd call it prejudice. (which after all is only making decisions based on prior experience!)

[AdeV]

prejudice. (which after all is only making decisions based on prior experience!)

Hmm... actually prejudice is the exact opposite of making decisions based on (prior) experience...!

My favourite definition which fits here I think: “Intelligence is the ability to learn from your mistakes. Wisdom is the ability to learn from the mistakes of others.” I'm pretty sure that means you have wisdom here 

[awemawson]

Frustrating day today trying to remove the white casing for stripping. All screws removed but it seems horribly likely that there are some only accessible from the rear having removed the large electrical box. This would be a major undertaking - lots of cables between the two. But also rather puzzling, as I'm sure the cover was supposed just to unbolt and lift off to allow servicing of the  spindle motor and stepper motors.

There seems to be a cavity formed in the metal work 'up high' above the lathe itself - and I suspect hat it has a rear mounted access panel under which are the elusive screws.

In desperation I've fired a question off to the Denford Forum, but it's rather in-active so don't have high hopes of help 

Meanwhile the reasonably good news is that a lube oil reservoir IS available at about £30 which isn't too bad.

[awemawson]

So another email from  the Interlube agents, and the 'about £30' has grown to £38 plus VAT plus £20 carriage plus VAT - or actually £69.60 in total. There is a 4-5 week delay 'as they are made to order' !!! The idea of a tin box inside becomes increasingly attractive, or I might even 3D print one.

Meanwhile I'm draining out the old coolant - the constant dripping in the background doesn't half make me want to keep going for a p... 

[nrml]

A 3D printed reservoir is a great idea, but what would you use to seal it to make it water tight? Will epoxy play nicely with lubricants?

[awemawson]

Acetone vapour is supposed to work for ABS. I've not tried it as a vapour but I have dipped parts in acetone. I'd imagine another approach would be to dissolve abs in acetone and make a 'wash' to seal it.

Perhaps one of the 3D printing experts can pipe up - ping Joules !

[awemawson]

So back to the white paint problem 

It looks pretty certain that the only way to lift the cover off is to split the electrical enclosure off the back of the lathe, and gain entry from the rear. However this is by no means guaranteed. It looks that all the wiring for the enclosure enters and exits at the top right hand corner viewed looking into the  enclosure. The two seem to be held together by four large cap head bolts, and the one that is visible from the lathe side is welded to the rear panel of the lathe enclosure with the nut on the electrical enclosure side. Hopefully they are all the same.

Now it certainly looks as though were the four nuts removed and the enclosures separated a bit, the electrical one could be swung through 90 degrees or so to give rear access to the lathe enclosure, which may or my not allow me to unbolt the rest of the cover that I want to lift off  It all depends on there being enough cable slack, and until I try I won't know .

BUT there is a GOTCHA  All the components in the electrical enclosure are mounted on a separate inner panel (which is a common practise) and there are large holes cut in this panel to give access to the nuts, BUT the panel has slipped down and the holes no longer align - a socket or box key will not engage the nuts 

Now it should be fairly easy to realign the inner panel - the machine must have been dropped a bit at one time and it's settled the panel downwards - but if I shift it my PC mounting and PC bezel will no longer fit as they are aligned with the shifted panel.

SO - to attempt separating the enclosures I'll have to very carefully mark where the inner panel now sits, shift it upwards, undo the nuts, hopefully separate the enclosures and then hopefully get the cover off and paint it, and the re-miss-align the inner panel ! What a kerfuffle 

. . . or I could do a bodge job on the paintwork - just hand rub it down, brush or roller paint it and call it done . But I don't like rollered or brushed paint work on machines, and the rusty bits really do need the attentions of a grit blaster . . . . . . decisions decisions . . . . .

[Pete.]

Denford seem to love to make their stuff difficult to dismantle. I bet their designer used to work for Leyland or something. I had a denford lathe that I needed to get the QC gearbox off the front only to find that 3 of the four bolts are easily accessible but the fourth is down inside the headstock sump in the bed and the only way to get at it is to completely remove the headstock, for which you have to remove the motor covers, the splashback, the interlock wiring the belts the motor speed change gear and the chuck guard interlock and even the lo-volt light. All to get at one damn bolt.

[jb3cx]

Andrew I scrapped a couple of bridgeport interacts a few years ago kept just about everything apart from the carcass,I may have a lube oil reservoir lying about somewhere,if that would do the job .
Regards Peter

[tom osselton]

I was just wondering if you have the old one could you make a clay mold or something and use a plastic casting resin?

[awemawson]

Sounds familiar Pete !

I decided this evening after supper to drain the leaking Interlube 'E' lube pump tank and clean it up ready for cloning by 3D printing. But when it was nice and clean the thought struck me that I'd missed a rather obvious other step to cure the leak - apply more glue !

This Bison plastic glue seems to be good stuff - the actual original crack is very firmly bonded and the glue rock hard, so I've over painted the area with some more and in the morning I'll fill it with water and see how effective it is !

[awemawson]

Andrew I scrapped a couple of bridgeport interacts a few years ago kept just about everything apart from the carcass,I may have a lube oil reservoir lying about somewhere,if that would do the job .
Regards Peter

Peter, the Interact ones are much larger - this is a diddy little thing, but thank you so much for the offer

[awemawson]

So morning has arrived and time for a test of the gluing !

Filled up with tap water, stood on a stand-off as part of the crack is underneath, placed on light blue towel that turns dark blue if damp, and left for a couple of hours as I take the dogs for a walk.

Come aback and NO drips  Now I assume water is more able to find cracks than oil as the viscosity is less but . . . .  I'll leave it for the rest of the day anyway before re-installing just in case.

Looks like £2.99 Bison plastic glue won the budget challenge over the £69.60 replacement.

Oddly eBay this morning has been flooded by Chinese lube pumps, many at under £70 including postage, but the smallest is a 1 litre which is twice the size of this one.

[awemawson]

Reservoir  still leak free 

OK so I've finally decided - the cover stays on and I'll prepare and paint it in situ. There are just too many complications removing the cover - it turns out that the cableforms for the tool changer and spindle motor and encoder all go through holes in the cover, and although some have plugs they are too large for the holes.

So I've done a trial strip using a dichloromethane and methanol containing paint stripper and it's worked quite well . There is no question now regarding the colour having removed the tailstock end rubber window trim - it's a very white white !

[awemawson]

OK the trial stripping was a success,  so no more procrastination, get on with it!

The order of operations here of course is all to cock, as the white should have been painted before the black - but I'd expected to be able to remove the cover and as we know . . . . .that wasn't happening.

I have no doubt that I will lose a bit of black paint and have to re-touch in places, as masking tape isn't the best for separating paint and paint stripper - particularly this excellent stuff that passes through neoprene gloves to set you tingling !

One major application of stripper followed by a second 'get the missed bits' followed by soapy water and a stainless steel pan scrubber and it's almost there. I'd really like to do the internals, and I suspect that the panel round the spindle will come off but if I paint the tray it will have to be brushed. The inside of the front panel though is pretty impossible to get at, as is the 'roof'

A load of rubbing down and finessing needed  now but that's for another day.

[awemawson]

I thought that there should just be time before supper to remove the 'spindle panel' that sits behind the chuck. What a palaver 

First remove the internal light as it blocks some screws (covered in swarf glued with congealed oil)
Then unbolt and disconnect the wiring to the Tool Turret
Then unbolt the screws holding the plate onto the headstock when you find actually it's nuts and bolts from the other side !
Then unbolt the wiper arrangement and you think you are there - but no!
Then unbolt the lower wiper (which took a bit of heat to get undone) . . are we there yet  . . . NO!
Then cut off the seized coolant pipe . . .

. . . hooray we have a panel that can be stripped for painting tomorrow as that's enough for today!

[awemawson]

Hopefully this morning has seen the end of removing bits and paint stripping 

I started by removing the control button panel components first of all taking a good picture of the wiring for when it goes back together. I then peeled off the torn Decal sticker and carefully measured it up, making an embryo one for test purposes on the CNC Laser cutter. (I'll do a 'back engraving' job on the final version)

Then I paint stripped the button panel and the swarf tray and the spindle panel (that I removed last night)

It's all been given a pretty thorough clean up, but will need a rub down and more preparation before I actually spray everything. It's going to be great fun masking this lot up 

[awemawson]

Not going to be able to get much done today as I have social commitments,  but I did manage to draw up and cut this masking paper dispenser before breakfast before anyone found me 

I'd got fed up chasing the roll round the table and then trying to cut to length single handed. The tear off cutter is a bit of 'DIN Rail' that was lying about.


I've probably never told you . . . .I love my CNC Plasma table . . . . . . Oh have I, well I never 

[kayzed1]

Dam you can go off people you no
Lyn.