Harold,

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.

It took a few minutes, but after several readings, I think we describing
the same thing.

Speaking of slop, is it true that what you describe has the screw and
nut surfaces in contact to hold the tool against the 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.

Agreed.


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.

My machine should be nowhere close to having such problems. However, it
does perhaps suggest that I might want to be a little more agressive
with the way oil in a few places. I can see the longitudinal screw, but
the transverse is not so readily accessible - maybe from the bottom of
the machine. Anybody with a 31 recall what it looks like from below?
But to be of any real use, I would need a way to reach it through the
stand. OTOH, that screw is shorter, so the oil port is likely to be
more likely to be helpful.


Again, this is a great place for a DRO---which doesn't care what the dial
says.

Good point.

Another suggestion I found interesting is to use a plunge indicator,
though that has obvious range limits.


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.

I'm already doing pretty much that, and it has already saved me time and
materials. The hard part has been getting the scale. I have been
(ab)using my dial caliper for the same job, and look forward to placing
my next order (which will include the scale) so it can get a break.


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.

I am inclined to agree, though I don't yet know enough to cite examples.



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.

A friend of mine had pretty much the same experience. Ok, maybe I'll
loosen up eventually, but not right off.



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.

[snip]

Thanks. In reality, I'm going to keep an eye out for good deals and
ultimately take any candidates to a mechanic I trust. If he talks me
into buying a lemon, he'll never hear the end of it

Fuel economy should not be a factor on this vehicle. It is going to
make weekend trips to building supply places and fall victim to my
mechanical quackery; that's about it.


The later models don't appear to deliver the same economy, for reasons that
I don't understand.

With the heavy trend toward SUVs and other large vehicles, the public
didn't appear too worried about fuel consumption, and I suspect the auto
makers got lazy as a result. Is there a difference in performance?



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.

So you are leaving some metal and later correcting. Do you then simply
assume that a 0.5 in endmill has a radius of 0.25 in and leave the final
cut(s) to clean up the 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.

Nice! I probably couldn't do it right now to save my life, but I see
what you are doing.



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----

I suspected as much - thanks for confirming it. In fact, my initial
thoughts about an RT were for the vertical direction. This time at
least, I'm fairly certain I can fake it other ways.


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.

If I can't afford two rotary tables in my life, I don't want to know
about it =:0


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.

I thought of that one too, but didn't want to temp fate. The biggest
benefit would be all of the questions I will know to ask about any
machine I would buy. The growing pile of R8 tooling would not hurt either.



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. :-)

Don't say lathe right now - my evil twin (the one who buys all of the
machines) might be reading over my shoulder

Thanks!

Bill