re:Re: New guy needs advice!

Jon,

Good advice! Addt'l points below.

>The disadvantage with many of these smaller machines is the
>mechanism for compensating for tool-holder length variations is
>raising and lowering the head on a round column. When you do this,
>you lose the X-Y alignment of the spindle position, as the head can
>swivel on the column.

I have seen (and used) mill/drills with a "key" added to the column
which allowed the head to move up/down with reasonable accuracy. NOT
a knee, but it works!

Also, the 5 inch travel Z axis M/D's can be "compromisedly" set by
careful positioning of the "head" and will work for many parts. (stub
drills, small chucks, extended end mill holders help) Rigidity is
lost, of course, but at least ya can do it!

>So I started calling a lot of CNC companies to find out what's
>available in my price range. I explained that I needed a machine
>that could mill to .001" consistently for prototyping small engine
>designs from RC models to motorcycle size.

>>This is already a tall order. There is machine table accuracy,
>>spindle accuracy and tool deflection to consider. I have a
>>machine that is pretty accurate (for an oldie) but I can't maintain
>>this sort of accuracy without taking a lot into consideration.

So nice to see someone beating this drum! It has always amazed me how
many people think that if the resolution is .001(or better), then my
parts WILL be, too !?! REAL machinists know that accuracy is gained
and lost in small increments, from a NUMBER of places. And much more
easily LOST than gained, IME!

>A standard (Series I) Bridgeport weighs about 2000 Lbs, and many old-
>time machinists (from the days when the horizontal mill was king)
>will tell you that a Bridgeport is really a toy, for light work
>only, and can't handle the 'heavy' cuts due to insufficient
>rigidity! Their idea of a heavy cut is different from ours, of
>course.

Yes. And I miss some of their voices...

>You should really look at used, full size machines.<snip>
>If you are near Michgan or Long Island, there are dealers selling
>machines every week.

But, PLEASE, take someone with you who KNOWS machines! It IS good
advice to look for "old iron", but remember there are TWO major
reasons machine tools are "put out to pasture".

1)They're worn out. Not good for you, since as a new machinist, you
won't know how to compensate for this inherant inaccuracy. A good
machinist CAN make excellent parts on a poor machine(Not that he
wants to :-)...) A beginner will be in the unfortunate position of
not knowing where( or who) the problem really is...

2)They're obsolete. This one is better, but tricky. They can be
obsolete for the "right" reasons (for our purposes). Things like
outdated or "blown" controls, Lack of Ballscrews, etc. Or...
For the "wrong" reasons, like the Gorton mill spindle/collet
mentioned awhile back. ("Standard" parts aren't, collets not
available, Bad year/ model of machine, etc.)

So to you (the New Guy) I say Welcome!, Good Luck!, and we're here to
help.

Ballendo