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Milling a curved end

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David Haynes20/01/2012 08:37:55
168 forum posts
26 photos
It is an ongoing discussion that has even permeated the ME competition arena; how do you compare fine ME models that have been built by differing methods? How do you compare a model built from a kit with one built by CNC and one built entirely by hand. The last 'entirely by hand' is a misnomer, because we all depend to some degree on external inputs which may have been anything but 'by hand'. I think a basic acceptance is developing that some folk use different routes to get to a model. The majority may have a manually operated lathe as their main machine tool but some may have the latest full spec CNC system. I am sure that subconsciously we all recognise that different skills are in use in all these variations, some more hands on and 'artisan' than others. We cannot get away from the fact though, that these basic first principal skills remain important, even if only as a step towards more digitally based ones. Otherwise we will simply move straight to computer simulators with an authentic smoke aroma generator at the back!
 
By the way, filing buttons are great, but so is the gadget for machining the curve.
 
Dave
Jon20/01/2012 09:47:24
1001 forum posts
49 photos
Good point there Terry and David regarding learning basic skills before writing progs for CNC.
Maybe there should be three classes, pretty much hand made, by manual machine labour and sat behind a desk.
 
Some of the stuff i used to do it took the best programmers years to get right and could only get it so far. In all parts supplied that needed filing up and fitting by trial and error was best they could achieve.
To cap that the end job takes less time but the overall costs were the same.
Or in other words cnc cant do everything its limited to the programmer and may need specific highly skilled labour to put right.
 
I have made all these individual parts entirely by hand when had to so did my predecessors for 300 years even the screws.
 
What i dislike about cnc made stuff is when the writer knows nothing on how to make traditionally, 'the book says'. Reading books only tells you so much, best way is on the job learning in at the deep end.
 
I have several repeat customers that are brilliant program/operators. They all say what i produce would take them a solid day and a half to proggy a 5 axis machine but parts would come off in 15 mins plus 1/2hr finishing. Fine if doing several hundred each one the same as the next but that aint me everyone different and unique fitting into a niche market worldwide. Paul on here has seen one item.
Different complexities some take 1 1/4hrs, some can take 4 1/2hrs to make complete as a one off.
Now heres the scenario, what i can do as a one off in 1hr 23 mins, cnc made ones are sold 143% dearer a lot more basic and complete with machine markings! And i am making a killing.
 
I am not against cnc i have a lathe some where rotting away bought for doing the repeat laborious jobs.
Cnc is fine its all dependant upon the complexity and time given to writing.
 
I can do two of the three ways very very well, whilst others may be more specific or generalised across the board by other methods.
Which ever method, its still engineering and best of luck.

Ian S C20/01/2012 09:53:29
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7468 forum posts
230 photos
Terry, I'm staying the I am for now, this computerised machining is no good if it can't go out and get a good bargin, load the machine, then call me when the jobs finished, and ready to go. I quite like doing all that my self, even to using the armstrong milling machine (file), instead of setting up the mill to do a simple little job like rounding the end of a con rod, using filing buttons. I make mine from MS and case harden them. Ian S C
Stub Mandrel22/01/2012 20:24:08
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4318 forum posts
291 photos
1 articles
Can I vote for the 'reverse filing' method described above?
 
Making the counterweighted cranks for the H-C nearly 2" long by 5/8" wide, I needed one end curved and rounded at the corners, the other following round the crank.
 
I held them in the 3-jaw between two jaws and pushed up against the third to do the gently curved end, all the other curves donme by hand, using an M6 cap screw as a guide for the crankpin hole.
 
I was amazed at how easy it was to get smooth, blended curves with the handle-down tip-up technique.
 
Neil
Stub Mandrel24/01/2012 18:11:39
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4318 forum posts
291 photos
1 articles
David asked for a picture of the crank. Don't mention the slightly off-centre slot.
 
Now running with black mild steel con-rods (very black as I had to heat them up red hot and bash with a hammer to make them about 1/64" longer - but teh mangled sections will be machined all over.
 
Neil
 

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