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Post by SpaceCadet on Aug 21, 2004 12:17:16 GMT
Hi,
I am a beginner so please forgive what might be a stupid question.
I have in my little workshop, a 12" rule, a set of middle priced digital calipers (£25 from Arc Euro Trade), and an old Myford Super 7 lathe.
With these I have managed to make a Stuart V10, a Stirling Engine, and a vertical boiler to run the Stuart.
The other day, I was reading through a catalogue and saw some micrometers which allowed measuring to, I think, 10ths of a thou (0.0001"). Under what conditions would I need to measure to this precision ?
If we take some examples of work which we are likely to produce, what level of precision, and thus what measuring tools, are we likely (required) to need.
1) Steam Engines 2) Stirling Engines 3) IC Engines 4) Machine Equipment
I have listed these in what I think are those that require least precision to those which require most precision.
And the equipment would be:
1) Rule 2) Calipers (Digital or otherwise) 3) Micrometer 4) Other ?
Again I list these in what I consider to be least precise to most precise.
Regards Ian
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Post by Deleted on Aug 21, 2004 13:05:33 GMT
Hi, In my opinion there are two ways of working and following that two different approaches to measuring. As you already build a Stuart engine, with success, you will know that we ME work with fitting parts onto each other. So precise size is not all that important as long as two parts go together in the needed manner be it interference, sliding or another fit. So as you found out the rule, calliper, and patience suffice. But I must admit that I love to work all over as close as possible to size. I am convinced that if you work all the time to an as close as possible dimension it becomes a habit, I know it is over to make an unimportant frame stretcher to within say 0.05-0.1mm of size but when it comes to it you will have less problems working to fine limits It becomes a whole different game when you have to make parts to fit existing commercial parts or make parts which have to be interchangeable or mate parts made in other parts of the globe as in industry. Then you will have to work within limits given on the drawings. These can be quite close and then the finer measuring equipment might be needed. Aside from that, and most of the time overlooked, there is also the matter of temperature at which parts are measured. I believe the standard is set at 20°C. You would be surprised at the amount of expansion in a piece of 50mm steel when heated to 37°C, body temperature, when measured in 1/1000 mm. Aside from that the finer the measuring instrument the more expensive it gets so overkill can cost a lot of money. O, by the way, when I see the jumble sales at ME shows I get the creeps when I see the second - fifth hand measuring equipment on sale. My advice DON’T. Regards Wilfried Vermeiren users.skynet.be/modelbouw.wilfried
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IP
Involved Member
Posts: 72
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Post by IP on Aug 25, 2004 22:29:00 GMT
Greetings,
I agree with Wilfred re the need for accuracy and the machining of one part to fit another, personally I like to work to 0.0005" ie] half a thou.
Where the real expertise comes in though is knowing what parts will need more clearence than others, for instance I initially machine axel boxes to my usual half a thou [or try to!] and then give it a bit extra with a file when hand fitting to the hornblocks this to allow for variation in the quality of the rail / track laying.
On the other hand I try to make piston rings for instance as close a fit as possible.
For measuring equipment buy some good NEW equipment unless of course you know the pedigree of any second hand stuff that might come your way.
Regards, IP
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