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Thread: Reasons to convert a mill to CNC

  1. #81
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    Quote Originally Posted by loose nut View Post
    You could make all your parts on a CNC machine, well the machine is making all the parts not you but they will look like machined parts and not like the original train parts in miniature . You need to use casting if you want it to look right. If you go to Cabin Fever or NAMES (or other shows) you can always tell the models made from castings and the ones that are made from bar stock.....
    JMO but I'd wager half of the "castings" you see at NAMES and Cabin Fever arent after having a conversation with one of the "casting" suppliers whose parts were mostly rough machined stock. From needle scaling to shot blasting, there's literally a million ways to replicate a "cast" finish. A regular part of my day job is creating trade show displays and half the time my CRS has me wondering which parts came out of our foundry and which we machined out of stock.
    "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

  2. #82
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    Quote Originally Posted by loose nut View Post
    Some one asked "where in manual machining is the skill". The skill is manually machining 16 train wheels and having them all turn out correct and the same.
    Not really, if you can crank the handles for one then 16 just takes longer. The number of rejects produced depends on concentration not skill. The skill is in the casting.

    Phil

  3. #83
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    Quote Originally Posted by philbur View Post
    The skill is in the casting.
    I have seen plenty of good castings ruined by bad machining and piss poor ones that have been saved by good machinists. That is where the skill is.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  4. #84
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    Quote Originally Posted by loose nut View Post
    I have seen plenty of good castings ruined by bad machining and piss poor ones that have been saved by good machinists. That is where the skill is.
    Exactly the same applies to CNC machinists or in fact people who dig holes in the ground, so by your measure they are all equalled skilled then. There isn't an activity on this planet that somebody can't screw up. It doesn't necessarily mean a great deal of skill is needed to perform the process correctly.

    Phil
    Last edited by philbur; 01-10-2017 at 06:33 PM.

  5. #85
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    Just one example of how even modern accuracy can go wrong:
    On a construction site I worked on, a fibre-optic communications cable was laid and duly marked up on the construction drawings by the surveyor. Some time later a fence was to be erected and another surveyor marked the fence line. The pole digger cut the cable 17 times before noticing something "funny" in the grit thrown up by his auger.

    As has been pointed out, modern machining methods are no protection against human error, and both manual and CNC machining depend on the human input.

    Greetings from sunny South Africa!

  6. #86
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    Quote Originally Posted by philbur View Post
    Exactly the same applies to CNC machinists or in fact people who dig holes in the ground, so by your measure they are all equalled skilled then. There isn't an activity on this planet that somebody can't screw up. It doesn't necessarily mean a great deal of skill is needed to perform the process correctly.

    Phil
    No I don't think they are equally skilled, I have repeated that over and over, particularly between CNC and manual machines but if you think that there is an equal skill level between machining and digging a hole then there isn't any point in continuing this thread.

    Adios.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  7. #87
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    Note do not under any circumstances engrave RIP or In Memorial plaques for Mother in Law whilst still alive, for some reason this doesn't go down a bundle.

    John Stevenson
    do you mean when you say this does not go down a bundle 1 the engraving or 2 your mother in law, when I say goes down of course I am referring to in the six foot hole. LOL Incidentally how's the love life these days I hope you find happiness old spud you deserve it we all do. Your pal Big Al
    Please excuse my typing as I have a form of parkinsons disease

  8. #88
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    No I don't think they are equally skilled, I have repeated that over and over, particularly between CNC and manual machines but if you think that there is an equal skill level between machining and digging a hole then there isn't any point in continuing this thread
    That could be considered a matter of opinion wouldn't you say L N ?
    still good old de-carte those clever co -ordinates. I personally find C N C is rewarding and of course interesting too. And it is with regards those damned computer packages almost certain to get easier with money nothings stands still. I look and laugh every time someone comes up with another yet must have tool sharpening or similar gadget. Why not just learn to sharpen your tools properly .Ranting so off I goes. HE HE no offense meant dear old loose nut. Al
    Please excuse my typing as I have a form of parkinsons disease

  9. #89
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    Questioning where the skill is in manual machining? How about not trashing cutters, producing parts to the required dimensions in multiples, using setups, and doing it all quickly

  10. #90
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    I have done a lot ,and I mean a lot of casting . All of it lost wax method. I find again, and again, people make the same old repetitive mistakes whichever method you use. The spruing up was the one I noticed mostly usually from being badly ,or incorrectly taught otherwise unless you are careless, or a beginner ,please make sure you always keep the temperature correct and imitate the procedure you did before then all should be ok. Most ! if not all the metalwork I did was either with Gold ,platinum, or chrome cobalt.
    I know of course the techniques in lost wax differ but whatever just try to remember lost wax method we used always included or mostly always included a centrifugal wound up casting machine.
    In centrifugal casting when the spin starts people like to spin the arm for ages, but as an old Surgeon told me when I was still wet behind the ears when the casting arm spins the cast is complete on a quarter turn, just like the Chinese tea lady I suppose not the hundredth spin each time a full 360 degrees.
    As far as spruing is concerned you can't really have too many sprues false in fact but rather more than too few believe me. Although it may be ugly, and also sometimes quite time consuming to cut them off and trim everything up, especially when the trimming with a dental drill means loss of dusty revenue .
    However personally I always used a standard old ships anchor drawn on paper to explain where the sprues should be placed. When deciding this always no ALWAYS remember metal is cooling all the time, but more importantly , PLEASE ALWAYS REMEMBER THIS PLEASE I REPEAT Metal does not like to travel uphill .Stop please and reflect on that when spruing up .
    Oh yes the ships anchor look down and see very clearly when if poured or cast from the top of the anchor when you get to the tips which point up (and please no reminding me that there are many types of anchor LOL ). Repeat I am talking about the anchors that look like two back to back letter J's is that better way of describing what I mean? I cannot do that on my keyboard LOL.
    You will see obviously that the metal if cast from the top down has to climb all the way back up again to reach both awaiting points . Remember I am using this description purely by way of an analogy Obviously if you add two more sprues to the pointy ends up at the highest two points of the anchor oops sorry letters J backwards you will achieve admiral results with those extra two sprues. or sprue it laying flat but as said this is just to make a very important point re uphill casting problems of which I see all the time . Another tip is for short castings where metal starts to cool down before it gets all the way to it's final destination. This tip is to apply reservoirs that is a little back from the end of the sprue in question or sprues in question make a form in wax of a little ball, abut two and a half times the thickness of the sprues min .Question this always allows a little more feed to help finish the casting. In reality the metal reaches the end of the line is met with a colder area and retreats- withdraws or returns a little backwards towards the hotter spot. With these reservoirs you can be sure there is enough metal hot around these areas to fulfil the casting .
    I am sure you have always seen short castings where the ends instead of being nice and sharp, and rounded or blunted sometimes only a very little at the end of the protuberances , as in the case of the anchor, or sadly sometimes more causing a lost cast which can sometimes still be repaired . Another problem you will get is P Severe or Minor pitting or porosity caused by a poor casting.
    This is caused sometimes with dirt crud in the chamber-cavity sometimes this can be broken off particles of casting material of course.
    Another problem for porous castings is when you have the metal overheated. This has to be watched especially with gold , This is quite obviously a no no in dentistry as the holes soon fill up with initially saliva then food particles which become stale and can lead to health problems and apart from the hygiene problems .On top of this obviously it looks very bad ,after all no body wants a tooth riddled with black spots through out it,
    hope this helps if I can continue with more thoughts I will but I am a bit burned out tired in other words Love you guys. Alistair
    Please excuse my typing as I have a form of parkinsons disease

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