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Backdating
23:40 11/05/2006 |
| Well, that's it for now. I'll be doing some more backdating of my mill progress very soon. There's one final installment to
bring us up to the present, and then everything can be written as it happens. There's an entry after this at the moment which
I'll leave.. more here soon |
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On mill envy...
19:55 08/04/2006 |
So I finally got around to installing that ballscrew on the Y-axis of my mill - it's a lot better now with no backlash anywhere
near what the leadscrews used to give. The problem though is that unlike the leadnut (a simple nut with a handle) the ballnut
really is rather massive and the original slot in the mill doesn't extend far enough. You can see in the 2nd picture above how the
mill saddle doesn't even reach the end of the base anymore! Ooerr! Fortunately there is no reason why you can't just extend the slot
yourself - there's no reinforcement or anything else underneath it except for a 1/4" of iron.
I started on this by scribing some lines and drilling a series of holes - the base was far too big for my drill press, so I went in with
my 2800RPM hand-drill! (I'd once made an entire lathe's motor mounting bracket with nothing but a drill, a cold-chisel, hacksaw and a file...)
But 2 broken drill bits, sweating like a creature, and several decibels less hearing later this quickly lost
it's appeal! So (feeling rather emasculated) I just hauled the base of my mill into a local college that does a model engineering
night and dropped it on their mill. Now I really felt neutured - my mill base wasn't even half the length of the Bridgeport's table!
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| Fortunately, the rest went by rather quickly and my undersized mill went unnoticed. ( "It's not the size but how you use it"
really doesn't count when your whole milling machine fits 3 times across the length of a Series 2 Bridgeport's table! - that's
just embarassing... ) However, I wondered to myself why I'd even bothered making all that effort with the drill in the
first place. The nice thing about cast-iron is that (despite what might seem intuitive of it being hard and heavy) it actually
cuts really well. This is because the high carbon content makes cutting self-lubricating - you can dry machine it like aluminium at
really high RPM's. The college milling machine's speed dial is all broken though, so I don't know just how fast it was going, but
I'd guesstimate about 4000RPM with a 1/4" cutter. Unlike steel (or the worst) structural steel you don't get long lines of hard,
sharp, magnetic, swarf, but instead a dense powdery black dust.
The end result was really rather pleasing - the newly machined slot was dead-on, and looked much nicer than the original slot's casting.
A couple of passes with a file to remove all of the nasty burrs (yeow!) and it looked really good! |
An area of concern is that the ballscrew is now exposed to the swarf, oil, and other contaminants when the mill is in operation.
This wasn't a problem before as the saddle could never move back far enough to expose the slot. This is something I'll have to address as
I'm reassembling the mill. I've seen bellows and "accordian" type covers, and can probably employ these to that end.
You can see in the 1st picture below now that the mill has a lot more movement in the Y than it used to! Perhaps even a little too
much, as at it's extreme only about half of the saddle is actually engaging the slide anymore. So it won't be perfectly accurate when
at this extension, but then again, it's going to work totally fine for rapiding around a workpiece, and that's what I really
wanted. There's nothing worse than finding your mill is just big enough to do a CNC job, but the very edge of the toolpath touches
the extents. So the mill has a much bigger work area now.
But one day I am going to buy a series 2 bridgeport, and put it in my lounge! :)
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