"Bill Schwab" wrote in message
nk.net...
Harold,
snip-

Let me try to paraphrase. You are saying that I can count off the
desired size plus tool radius plus some wiggle room, take a cut,
measure, and then back up based on relative dial readings. Fair?

Yep! But your first cut on that side should come with the backlash in the
opposite direction... What you're doing is establishing the relationship
between the cutter and the part, but now in reverse, and any movement of the
dial will translate into table or saddle movement, not taking out slop.
By establishing the datum points on all four sides by this method, you can
work directly from your dial, although you will be reading in reverse on two
sides. Mental exercises, nothing more.


If, by chance,
you know exaclty how much backlash the machine has at a given point, you
could calculate that into your reading, but it's not done routinely, if
at
all.

I wouldn't expect that to work - that by no means implies that it would
not work.

The idea assumes that backlash is constant, but I say it isn't. Screws
wear, just as the nuts do. There will almost always be more backlash where
the screw has been used more, say, at the center of the travel. Therefore,
if you use a constant that represents backlash, you'd be introducing error
(+ or -)
everywhere except for specific places on the screw. A machine with
worn screws and nuts is still capable of doing decent work, so long as you
don't rely on them to locate over large areas.
Again, this is a great place for a DRO---which doesn't care what the dial
says.

So far, I have found that I can see +/- 0.1 inch, and the dials do the
rest. It is true that I sometimes have to switch from a 0.5 inch
endmill to a 3/32 drill bit in order to be confident of the center of
the cutter, but that's really not that hard to do (have I said anything
good about ER collets today?g) and beats adding to my scrap bin.

One of the best habits you can acquire is to rely on a scale for movement.
It won't tell you if you miss by a thou, but it can save you from mental
errors, where you might transpose numbers (quite common for some of us) or
if you miss by a turn of the dial. If you're drilling holes over an area,
you might think you can see the difference, but a missed turn on a .200"
dial isn't readily noticeable----especially if you believe you're on the
right track. Keep a 6" scale at your disposal (larger, if necessary) and
use it routinely. Tough habit to acquire, but the best one going. DO NOT
trust your eye alone where dimensions are concerned.


For those not convinced by the "I can get by w/o it" argument, you might
better relate to my desire to get other tools, an RT, boring head and
bars, etc., not to mention more woodworking tools.

You'll not get an argument from me in that regard. Frankly, I pity those
that can't work without a DRO. The necessary skills required to be a
machinist don't come about when you rely on such "cheats". I recognize
how valuable they are, or can be, but I also have total respect for the
knowledge, talent and skill that one acquires that can work without one.
As I've stated previously, I wear my ability to work without a DRO as a
badge of honor. Learning to machine that way doesn't come easily, not if
you do good work.


Another thing that bothers me about a DRO: they can skip. It sounds
like something that will start happening just about the time I grow to
depend on it. Living in FL, lightning is a concern. A direct strike
could knock out my motor, but a DRO would be much more likely to get
fried.

I'll have to take your word for that. As I've stated, I've never used a DRO.
I did experience a lightning strike, though, and I had to replace the board
for the table feed on my Bridgeport. Freak deal, when I lived in Utah.


There is also the problem of moving raw materials (mostly wood).
Renting trucks is a pain, not to mention that I do not like to drive
vehicles that do not belong to me. A pickup is probably in order. I
like my car too much to work on it myself, but a bomb of a pickup will
give me freedom to dabble in simple repairs (all together now - but NOT
THE BRAKES!!!!g).

Brakes are no big deal, not if you're remotely familiar with how they work.
I've done brake jobs all my life and had no formal training aside from one
year of auto mechanics in my sophomore year of high school.

Speaking of pickups, recommendations for make/model/year are welcome.
Gas mileage is not really a concern, because I will not drive it much.
Handling plywood will be a common task. Total cost to keep it reliable
and safe is a factor, and being friendly to an inexperienced shade tree
mechanic (with support from experienced friends) is a big plus. As
shocking as the concept might be in FL, AC is negotiable, and would
likely not be repaired. The one in my car gets what it need$ =:0

While they're not cheap, investing in an early Dodge with a full sized bed
(hauling sheets of plywood) that is Cummins powered is a good combination.
The later models don't appear to deliver the same economy, for reasons that
I don't understand. I drive a '94 with about 98,500 miles on it-----and I
get right at 22 MPG. I'm totally impressed with the engine, and the body
appears to be built well. Only problem I can see is the cost of diesel is
out of line with past history. I also have a '99, 1 ton, that delivers only
about 15 MPG.


If you're cutting a window, and you need to know where the cutter stops
on
four sides, what I do is measure and ignore backlash. Make a little
sketch
of a window, and write the dial locations on each side---and don't worry
about backlash on the third and fourth sides. By measuring, you know
where
you are, and can turn directly to your finished size. That's not a
big
deal for one piece, but if you have multiple pieces to machine, once
you've
marked the dials, you can cut windows in short order. With a final
pass,
maybe a couple thou, climb milling, you can go into corners and out
without
leaving a trace of undercut.

I _think_ I understand. On the sides backlash-safe sides, how do you
account for the endmill radius?

Depends. If I'm working only on a window and don't care how the spindle
relates to the part otherwise, I've been known to reset my dial so the cut
lands on 0 (taking into account the end mill radius) in two directions, then
rely on measuring to establish the third and fourth setting. What I
normally do is start with my spindle set at 0-0, on the part's edges, then
deduct the radius and establish the two edges that are direct reading, often
staying away by an even amount (maybe .010"/.020"), so I can then rely on
the measurement from the established face, minus the amount of material left
for a final pass, and measure back to establish the opposite boundary. I
record my dial setting, measure, then change the numbers I recorded to
reflect the desired setting. Once I get my numbers established, I like to
take a cut all around, staying away by a prescribed amount, maybe the same
..010" I mentioned, or even less, maybe only .005", then measure once again.
That allows for minor corrections if you've missed something due to tool
deflection or a mental error. Once I know where I am and I'm happy, I
usually take my second to last pass by staying away from my mark by a thou,
then climb mill each side to size, taking the last thou. Coming into
corners is an art that you slowly develop. I generally back away by the
amount of the backlash, so as the cutter comes into the corner, instead of
undercutting, it pushes the cutter away ever so slightly, so you don't get
that tiny undercut that is so common. It takes a little experience to do
it successfully----but it's not hard to do. No, you don't get a step----the
cut is seamless.


snip-

Maybe the answer is to get a small horiz/vert table and then see if I
find need for anything bigger. There is certainly no hurry. For now, I
can do what I have in mind with an extra setup or two and a rounding
endmill.

On occasion, you might find yourself having to work on edge-----maybe making
a gear, what ever. The larger diameter table gets in the way in a
hurry----so while I have a hard nosed attitude about table size, that
applies to horizontal work only. The smaller the better when you're working
vertically----so take your own advise and see how it goes. If you're
serious about machining and stay with it, there's certainly nothing wrong
with adding a second setup in the future, finances permitting.


I am grateful for your thoughtful reply independent of whether or not I
agree with every part of it. As it happens, I find that I end up
agreeing with most of what you say.

If I were to look for an area to disagree with you, it would probably be
over the validity of mill-drill machines. You are correct to caution
people about the limitations, but the machine is serving me well. If,
as some here have predicted, I end up with a monster knee mill, the $900
for the mill drill itself will have been well spent.

It will have been especially well spent in that you can make your mistakes
(and they're sure to come) on a less expensive machine, so if you do damage,
you're losses are minimized.

Don't misunderstand my attitude about mill drills. I realize they're
capable of good work, it's just that they're totally annoying to run once
you've experienced a knee mill. It's like small lathes. I hate 'em. If
I can't take a 1/4" deep cut in chrome moly with a negative rake tool, fast
feed, I'm simply not interested in the machine. I had to make time when I
ran machines, for it was my way of making a living, and I had to compete, or
I was out of business. There's certainly nothing wrong with a fractional
hp machine taking lots of light cuts for a guy that isn't in a hurry and
doesn't mind the limitations of smaller or lesser machines. Look at it this
way. If you have the necessary skills to turn the work out to
specifications, can you show me even one individual that can look at the
work and tell you on what machine it was produced?

It's far more important for an individual to gain the skills necessary to
machine properly than to have the perfect machine. I've proven that all
my machining career by getting by with my Graziano when I've had a life long
love affair with an EE lathe. :-)

Harold

Thanks!!!

Bill


Welcome!

Harold