On 2009-07-10, Michael Koblic wrote:
DoN. Nichols wrote:
[ ... ]
Chacun a son gout...
After all -- I don't have to worry about the usual virus
infections with the Sun Workstation. They are all targeted at the
easiest target -- Windows. :-)
Yes. Mine has caught the swine flu I think.
What kind of spam does that send out? (Well ... spam is a pork
product, after all. :-)
[ ... ]
O.K. If you are considering purchasing a larger lathe (as
suggested by the questions about lubrication), yes it is more than you
need to do.
It is all about understanding the options and then making the right choice.
The one big unknown is the future performance of the RedNeck beast. I made a
toolpost for it (well, a boring bar holder really) and it will be ready to
go tomorrow. If it does half a decent job the pressure is off.
O.K. Good Luck there.
[...]
Well, it is a close run thing between using the telescopic gauge and
a micrometer and actually making something with the required
accuracy. The last two attempts at making something to a given
dimension I overshot by
0.010" and 0.004" respectively. I suppose I am getting better...
Hmm ... first trick is to make sure that the tool is quite
sharp.
As well as the operator.
Second is to feed something like 1/3 the distance to reach final
diameter, make your cut, and measure what you really got, comparing it
to what you expected. Divide what is left by two, and adjust by how
far off your previous result was. Feed in that much, and make
another cut and measure again. Adjust again for the final cut.
It is difficult to get a very light cut to produce what you
want, because deflection of the workpiece and the tool may prevent
ever taking a bite, so when you finally feed enough to take another
bite, it is too big. So sneaking up on the final dimension can be
difficult, and making larger cuts works better.
I am still struggling to understand fully what happens if you run the tool
over the workpiece in two or three passes without adjusting the feed at all.
Well ... a mill may smooth out the previous cuts, and perhaps
trim off chips which were pressure welded by the previous cut if you
don't use a shop vac or some other flow of air to remove chips from the
work zone.
With a lathe, it will depend in part on the workpiece material,
and in part on the true sharpness of the tool. Carbides tend to not be
very sharp -- though there can be exceptions. And coated carbides are
particularly dull, but are very good at removing lots of metal fast with
a powerful enough lathe. Ideally, you should use the carbide for the
roughing, and switch to well honed HSS for the finish cuts -- but the
problem is that you don't know just how deep a cut the HSS will take
that first pass after the change.
This applies to both the mill and the lathe. In both cases it was the
finishing cut that took me past the specified dimension.
In part, it is spring in both the machine and the workpiece.
You need the workpiece rigidly attached to the milling bed for milling,
which may mean a good rigid milling vise (the vises which let you tilt
the vise relative to the bed are particularly poor in this respect, and
those with a swivel base introduce more give into the holding of the
workpiece too. The column on your milling machine is not that rigid,
and I don't know about the head of the milling machine.
If the milling cutter is dull, it will just skate over the
surface of the workpiece without removing any material until you give it
too much feed, at which point it will take too much material.
For a lathe, the first thing is the workpiece needs proper
support, and if it is sticking out beyond the chuck anywhere beyond four
times the diameter, it needs a live center to support the end.
Also -- the stack-up of compound, cross slide, and carriage all
introduce a bit of give.
And if the edge of the tool is above the centerline, it will be
applying a lot more pressure before it starts to cut.
As for getting the boring to work right -- bore to a few
thousandths undersized, and then use a reamer to get to final size.
The same problems with sneaking up on the size occur when boring as
when turning -- perhaps more so.
I guess this is OK up to about 1/2". Economy-wise.
Or one reamer just for the size you need, not a full set.
Talking about economy: I went to visit the shop that sells my stuff from
time to time. Contrary to expectations their sales were up 35% on last year
so I'd better get going.
Good Luck,
DoN.
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