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A strange fluid

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Howard Jones08/10/2010 16:07:17
70 forum posts
112 photos
god no!
the model engineer postbag will be filled with letters of woe.
 
I'd build the spark eroder if only there wasnt a typo.....
wail, gnash, weep. if only there wasnt a tyop.....
 
hey guys. see the big picture not the bloody punctuation in life.
 
in attonement you all owe the editor a decent interesting article on how you use the spark eroder.
 
btw one of our local expert spark eroder users swears by the orange citronella fluid for his dielectric. keeps the mozzies away too he says.
Billy Mills08/10/2010 18:04:46
377 forum posts
I would agree with Howard that the aggro over one misspelt word is a lot of effort over very little. EDM is however an important topic in that:-
You can build a useful machine at home with little outlay.
You can machine fully hardened metals as easily as soft metals
You can cut  splines or rectangles or any other complex shape.
The  EDM process is potentially very precise.
There are still lots of facets of EDM to be explored.
 
There are several published designs that are straightforward and work  well. But there are some issues with the Walter design. Firstly anyone trying to duplicate the design  would find that:-
  1) paper capacitors are obsolete ( for about 40 years)
2) The SAA1027 is a 1970's part also obsolete
3) 48 step 12V motors are virtually obsolete, 200 step lower voltage parts are the norm.
4) there are no mains fuses at all.
5)The ammeter shunt is a hopeless case.
6)The vibrator is ill conceived to say the least
7) The complete lack of EMC filtering is a disaster for those living near.
8) The limit comparitors and bistable are confused and overdone, you only need half the parts to get the same results.
 
It is conventional to use standard symbols for circuit diagrams and to include component values on the diagram so that the diagram can be read- just   "R1" stops us understanding the mind of the designer.
It is completly understandable that stuff happens when you have 3 mags to edit each month. Equally "mechatronics" - the fusion of electronics and mechanics- is increasingly important and interesting. So we want more interesting articles of all kinds- some of which will have some electronics content.  So I would sugggest to David that it would be good to have specialist project parts reviewed by a reader or two who could assist in shaping an article for publication.  I offer to do that.
Regards
Alan.
 
Axel08/10/2010 19:07:28
126 forum posts
1 photos
Posted by Alan Gray 1 on 08/10/2010 18:04:46:
...Equally "mechatronics" - the fusion of electronics and mechanics- is increasingly important and interesting. So we want more interesting articles of all kinds- some of which will have some electronics content.  So I would sugggest to David that it would be good to have specialist project parts reviewed by a reader or two who could assist in shaping an article for publication.  I offer to do that.
Regards
Alan.
 

 I agree totally, "more mechatronics"! ME/MEW feels a bit stale to me at times, still I like both though! I belive more young people would like a more modern flavour (like Model Mechanics was) instead of half a mag full of old fellas riding steam locos. And I add that I like steam (and old people), just so no one feels offended.

David Clark 108/10/2010 21:35:32
avatar
3357 forum posts
112 photos
10 articles
Hi There
Someone is redesigning the circuit using more up to date components and this will be published after the current series is complete.
regards David
Howard Jones10/10/2010 03:02:16
70 forum posts
112 photos
alan has hit the very core of the problem I've faced.
I have had a go at a few the spark eroder circuits and every time I encounter a chip or chips in the circuit that are utterly unobtainable.
what is equally frustrating is that the manufacturers seem to lock the technical info regarding their circuits away so that it becomes near on impossible to locate a suitable workaround to a circuit. now I have electronically savvy friends who say that the problem is trivial and easily worked around but I notice that not one of them has built an eroder despite being well versed in what they are capable of.
so I suspect that the circuit design isnt actually that trivial
my friend the rocket scientist model engineer built amesbury's circuit and used it successfully for 3 years but I notice in his notes that after that period he gradually had to replace every component on the boards. I suspect that amesbury's circuit overloaded the components or drove them at their limits to achieve the result he obtained.
we in model engineering really do need buildable spark eroder circuits.
what can be achieved with a spark eroder and some talent is truely remarkable.
 
btw my friend the rocket scientist solved his problem by buying a $25,000 commercial spark eroder and the work he has done on it is absolutely stunning.
 
my pockets are somewhat shallower and I am really hanging out for a spark eroder circuit I can build.
 
alan you could really do model engineering a service by designing a buildable circuit that didnt over drive the components.
Howard Jones10/10/2010 03:12:46
70 forum posts
112 photos
alans comment "edm can be very precise"
 
a friend who just recently passed away showed me a job he had done for a customer.
it was a paper punch just on a meter in length. it had a platten with a little keyhole shaped aperture about every 5mm. mating with this was the punch which had raised tapered keyholes to punch through the paper
to get the punch to function accurately at all the dimensional tolerance was a tenth of a thou (sandth of an inch) over the metre distance.
the job was done with a wire eroder.
 
utterly utterly stunning work.
Jeff Dayman10/10/2010 12:57:26
2356 forum posts
47 photos
Posted by Howard Jones on 10/10/2010 03:02:16:
 
 
"my pockets are somewhat shallower and I am really hanging out for a spark eroder circuit I can build.
 
alan you could really do model engineering a service by designing a buildable circuit that didnt over drive the components. "

 
 Howard, you can build a working EDM simply. If I can, you can, and I did. The Ben Fleming circuit does work and you can get all the components from commercial electronics houses like RS. The EDM How-To-Book is available from Camden Miniature Steam Service in the UK for roughly 20 UK pounds. The circuit is designed for 120VAC but you would  only need to substitute 240 VAC to 48 VAC transformers and it should work fine.
I did have one problem with one IC that overloaded repeatedly, but I solved this by bypassing the IC with a substituted circuit with heavy duty components. There is a Yahoo dot com forum for the Fleming machine, and when I reported this trouble several people said they had the same issue but many said they didn't. I would say there may be a tolerance problem with the IC itself, and it is operating too close to its limits. Some people may have a problem and others won't. The substitute circuit has heavy duty components but does the same job as the original IC. I put this circuit up on the Yahoo dot com forum for the Fleming EDM. It was very inexpensive to build. I'd be glad to share a copy of the substitute circuit with you. I can't share the Fleming EDM circuit diagram however, as it is copyrighted in Ben's book.
 
The Fleming machine is a simple workable EDM.
 
Howard Jones10/10/2010 15:03:18
70 forum posts
112 photos
I have seen the title of the book in their cattledog but wasnt aware that it had a buildable design in it.
I thought it was book on techniques.
I will hunt out a copy. thanks.
Versaboss10/10/2010 23:01:28
512 forum posts
77 photos

To all those mentioning 'the Fleming machine':

Do you mean the contraption described in the booklet 'Ramah Machines Metal Disintegrator'?

A combination of a vibrating engraver and a welder 

Greetings, Hansrudolf

Billy Mills11/10/2010 01:48:45
377 forum posts
When you publish a circuit it should:-
a) work as stated without tinkering.
b)be reproducable with readily available components
c)be  readable immediatly
For a non-specialist readership, simplicity is also very important.
 
Having built a couple of sinker EDM's for producing punch tooling, building a worthwhile machine is not difficult.  The electronics are very simple, for a sinker the aim is to keep the tool-workpiece gap constant as errosion continues. So you use the gap voltage as a too close/too far indication and drive the motor accordingly.  Capacitors are not a problem but the circuit produces HUGE amounts of electrical noise. If you don't know -or are not  told- how to control  the noise then you might have all sorts of problems. The layout and wiring is very important. Flushing the active region is also very important for longer cuts.
 
A key mechanical element is to  minimise backlash. The working gap is around 0.1mm for some jobs so you need to position within -say- 0.01mm to get good gap stability and cutting rate. If there is too much backlash then you end up with "Hunting" as the gap opens and closes excesivly with only the odd spark instead of a steady stream.
 
It is absolutly silly to have 200Hz vibration. When working correctly you should have hundreds of thousands of sparks per second each cutting away at the workpiece in a controlled way. Opening up the gap at 200Hz rate totally messes up steady cutting.  ULTRASONIC drive is used - at around 200,000Hz by some to cause dielectric pumping- to get rid of the conductive particles out of the gap. There is loads of info for the interested on the web.
 
Regards,
Alan.
 
 
 

Jeff Dayman11/10/2010 14:10:13
2356 forum posts
47 photos
Versaboss/Hansrudolf,
 
No - I mean the Ben Fleming EDM How To Book. Link to it at Camden's is below.
 
Howard Jones11/10/2010 14:55:59
70 forum posts
112 photos
can I just add to allans comments.
the design should be modular so that changing aspects of the design as availability of components changes doesnt mean going entirely through the bowl of spagetti to get it working again.
domestic use of the spark eroder is often quite different from industrial use. industrial savvy is a starting point for technique but isnt the whole banana.
 
some info from my rocket scientist friend.
because the spark craters the job, each time the electrode closes on the job the sparks occur in a different place on the workface. they occur on the nearest surface.
each spark displaces a piece of crud from the workface. as this builds up between the surfaces the eroding becomes less effective. if you dont clear this crud regularly you end up with tide marks along the side of the cut. every few pecks of the electrode it needs to be backed right out and the eroded surface flushed to remove all crud.
when the electrode contact is being made the working fluid needs to be still or it affects the evenness of the erosion.
an eroder really needs to be able to be manually traversed down to the job or up and away from it.
it needs to drive the stepper automatically during the pecking phase.
it needs to have a backout action at some settable interval.
it needs to be able to start and stop a coolant pump while backed out so that the workface can be flushed out.
it needs to be able to stop the fluid circulation while the eroding sequence is running.
ringing in the electrical circuit is the cause of electrode wear and probably the overloading of the chips. that'll do for now.

modeng200011/10/2010 16:52:05
340 forum posts
1 photos
I'm not sure if this link to a spark eroder that appeared in ME July 1976 has been mentioned before so here it is:-
http://www.metalwebnews.com/manuals/spark-erosion.pdf


John
Robert Miller 111/10/2010 18:08:41
19 forum posts
Further to Alan Gray's post at 08/10/2010 18:04:46:

Alan has raised an interesting point.  Increasingly the marriage between the mechanical and the electronic is becoming unavoidable.  Stepping motors and microprocessors are the gears of this century.
 
The electronics side of this marriage presents a barrier to construction by the amateur, and if that isn't enough of a problem there is usually the issue of software as well.  If electronics is to be incorporated into an essentially mechanical project, there needs to be some requirements imposed on the presentation of the electronics in the article. 
 
 As electronics evolve away from parts with a 0.1"  lead pitch toward ever smaller packages with fine pitch 0.5 mm lead spacing or worse, no accessible leads at all such as ball grid array parts, it becomes difficult (but by no means impossible) and somewhat costly for the amateur to implement.  Sparkfun in the US have a number of tutorials on surface mount soldering on their website. ( I have no affiliation with Sparkfun.)
 

At a minimum, the electronics in any project should be accompanied by computer readable copies of the following on the publisher's website and released under some form of copyright copyleft.
1)  A clear and complete schematic diagram.
2)  A parts list consisting of currently available parts identifying the manufacturer and one (or preferably more) vendor(s).
3) A circuit board layout in file formats for the user and for the circuit board manufacturers.
4) A complete commented listing of any software required identifying the language, compiler used, and vendor thereof.
5) A binary file of the object code and instruction for loading it into the target microprocessor.
 
For the hardware, CADSoft's Eagle provides schematic capture and circuit board layout and is available in a free version that is probably suitable for most hobby  projects. (I have no affiliation with CADSoft.) 

For software, things get a bit too complicated to suggest a vendor.  There are many.
 

 
 
 

 
Billy Mills11/10/2010 19:31:53
377 forum posts
Howard
Think you have been slightly lead astray. The gap is small so that the fluid breaks down and allows current to flow into the workpiece. That detatches a small sphere of the job which is in the gap. If you don't flush out the "swarf" it accumulates. You can't have the flow on then off! the flow is continuous. When the spark passes through the dielectric it vaporises the fluid then the vapour channel collapses when the current stops. If you get it working nicely there are hundreds of  thousands of sparks per second.  Each spark is around a micro-second. It makes a nice fizzing sound.  There  is a fair bit of dielectric flow with some jobs however flushing removes the conductive material from the gap, it is more important with deeper jobs.
 
It is common to rough out with a high current then finish cut more slowly at a lower current. If the machine ( and the Operator) is up to it the finish can be  very good. Electrode wear is down to the material that the electrode is made of (- Copper , Copper -tungsten or graphite are common) and the type of pulsing used, Graphite can have much lower wear rates than metalic electrodes and machines beautifully. Don't think ringing has anything to do with it. The physics happen when the channel ionises, not after. EDM is very inneficient in energy terms, the dielectric can get very hot however it does stuff that might otherwise be impossible.
Regards
Alan.

Edited By Alan Gray 1 on 11/10/2010 19:33:35

Jeff Dayman15/10/2010 01:15:25
2356 forum posts
47 photos
To Versaboss / Hansrudolf
 
Just checking to see if you received my private message sent a few days ago.
 
JD
Jeff Dayman20/10/2010 01:47:32
2356 forum posts
47 photos
To Versaboss / Hansrudolf
 
Just checking to see if you received my private message sent a few days ago.
 
JD
Versaboss20/10/2010 23:45:28
512 forum posts
77 photos

Jeff, thanks, the message is here, but I just saw it 2 days ago. I will need some time to digest it, and I don't know when I will continue with my EDM. Anyway, the linear slides are what I also was thinking about..

Seems your system is almost an industrial one; well done that!

Greetings, Hansrudolf

alan frost26/10/2010 20:56:04
137 forum posts
3 photos
I hope I can settle the name of the mysterious fluid-opinions differ -a very few say 'tis "dielectic" , most say 'tis "dielectric" but oi say 'tis "dylectrick" (with apologies to Blackadder). Orwl agree-- it don't matter a lot.
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