Homebrew PCBs

soffee83 wrote:

>--- In Homebrew_PCBs@yahoogroups.com, "Mike Young" <mikewhy@s...> 
>wrote:
>  
>
>>After squaring the axis to the table, you can swing a bent wire in 
>>the spindle to square it to the table. The height of the free end 
>>above the table should be the same through a full circle.
>>    
>>
>
>That sounds good (and easy)! It sounds just like the procedure in my 
>radial saw manual, where you rotate the arm with the arbor lightly 
>scraping the table.
>  
>
  It sounds good only if you want to see if your drill is perpendicular 
to the table.  I don't generally care if it's exactly perp. to the table 
or not, I want it true to the motion so it doesn't snap bits.

  Set your axis to 85 degrees instead of 90.  Set your tool back 5 
degrees to the 90.  You're back to perpendicular to the table. Get this 
to zero, then go up and down and see that it's still zero, even though 
you move over quite a bit for any change in depth.  This measurement 
doesn't begin to take out any error in axis motion alignment, it left 
that back at the initial setup for the axis.

  Errors either add, or worse than that, multiply.  All measurements 
have error.  You don't align the axis, let that have error, then only 
align the tool to flat to the table, let that have error, and then let 
the two errors add up.  You measure what you want correct directly, only 
having one source of measurement error, and minimize that error.  The 
off angle motion that that bent wire test can't even detect is way more 
important than whether the tool and axis are exactly 90 degrees to the 
table or not.

  Yes, almost all machinists use dial indicators a lot.  But there are 
still many classes of machinist, most notably the average ones, and 
those that can do truly exceptional things.  I seriously doubt any of 
that higher class would settle for the double error of the indirect 
measures mentioned, I know I don't, and I have barely scratched the 
surface of machining.  What I outlined gives a direct measure of the 
true path of the bit, trying to add up any other couple of measurements 
to get that is going to be a second class measurement.  Lots of people 
like to measure lots of things with lots of numbers and say they're 
highly accurate, but it isn't the case at all if they aren't using the 
best methods and looking through the data to select only the most useful 
and get the best answers.  The alarming thing is just how many of those 
machinists out there with 10x the tools I have can barely beat what I 
can get done with very little, when they should be able to do at least 
10x more easily.  And I find those who insist that all their tools be 
super accurate are often the least accurate themselves, not the most.  
They generally need that super accuracy of everything else to make up 
for the slop in what they do with the tools, it's why they insist on it 
so much.

  I generally don't care if the drill is at 90, or 88, or 75, or 103 
degrees to the table.  The only thing that matters to breaking the bits 
is whether the shaft follows the hole cut by the tip exactly down the 
hole or not.  The best way to measure that is directly.  After you get 
that right, then it's easy to get the whole axis very near 90 degrees, 
and you don't even have to care much if there is error in that 
measurement or not, it has no bearing on snapping bits.  Doesn't matter 
if you do that part first, but checking the tool path directly better be 
done somewhere along the line if you expect to have any sort of high 
accuracy.

  Most machinists would laugh at my setup.  But chuck up a #80 bit, and 
start drilling lots of little holes without breaking bits, and I'm sure 
I can get most of them quiet without much problem.  Especially after I 
stop drilling, wiggle the chuck back and forth probably .010" or .020" 
total with my fingers, then start drilling again and still not breaking 
bits.  Parallel motion is key, basically nothing else matters much.  But 
I'll put some videos up once things are going soon so you can see what 
it'll do for yourselves..

>I've saved Alan's posts for later. They're a bit over my head for now, 
>but I understand most of it. I figure if the pivoting presses are good 
>enough for most work, this thing should be able to get straight 
>enough. I'm considering incorporating some type of screws or shims in 
>the tool holder to make it easier to tweak the alignment if need be.
>
>  
>
    Well the pivot type press works because come out a bit and it's only 
a tiny fraction off from a line, and it's easy to take nearly all the 
play out of hinges.  If what you're doing will have much off axis travel 
or notable play it can easily end up not being as good as the simple 
hinge..  Everything is different, but simple is very good because there 
is less to go wrong.

  With $5 or $10 per 50 or 100 bits, it really won't matter that much if 
things break a bit more than they should.  Even a little sub-optimal is 
still fine for general use if you're not using the very smallest bits..  
.025 or .030 etc bits won't like the flexing and will break more 
quickly, but they don't just snap when you breathe wrong like .016 and 
smaller tend to do.  I've snapped the 80s a few times in my hands or 
while holding what they were in, and you can barely even feel them break..


>PS - If Alan reads this- The camera technique is out of my league, but 
>I got a "forbidden" error when going to look at those pictures. Not 
>sure if others can see them. I'm on Opera 8.51 for Windows.
>
>                        -Much Thanks as Usual!
>George
>  
>

  Suspect Opera for that.  Hotlinking is disabled on my web space, and 
some browsers mask the referring URL.  If your referring URL given by 
the browser is anything besides direct URL entry or link from my site, 
you won't get the file..  Could of course be several other problems 
since I haven't tested it from away lately, but that is the most likely, 
I think it's in the privacy settings of some browsers, seem to have read 
it somewhere a while back.

Alan



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