Homebuilt machine accuracy

[Mcgyver]

Originally Posted by Geof Considering you do not put an upper or lower limit to how many millionths I would say you are spreading your respect pretty widely.

I don't care how big the part is but if the resolution of measurement is in millionths that does it for me

Originally Posted by NC Cams , the RELATIVE size at operating temp is more critical than ABSOLUTE size. .

yup, witness the model engineers who have made marvelous working IC engines without the benefit of even a mic - equiped with treadle lathes and calipers

[mkaake]

I stand corrected

I was under the impression that you had been talking about a home built machine...

In any event, I work for an auto manufacturer, and have been looking at the tolerances that we keep in production - 10 mics is about what we normally hold (that's pretty easy on precision equipment, I know). But what really got me was watching a tool setup a few weeks ago where the x axis moved 3 mics +/- if you accidentally touched the machine during the setup procedure...

Anyhew, didn't mean to stir up any pots, just thought you were talking about home machines. And yeah, it's very hard to run statistics with a sample size of 1 or 2 parts

[NC Cams]

The auto industry is a HUGE driver for precision stuff at dirt cheap prices.

I interviewed at an noted aerospace hydraulic component supplier. He looked down on me since I worked in auto industry previously - his stuff was so hotsy totsy - at least in his mind.

When I mentioned the precision fits of a hyd lifter (at the time in millionths), he said you couldn't make a part like that for under some ungodly sum of money ($25 or $30 or some other absurd price). He liked to you know what when he learned that we SOLD the parts wholesale for $1.25 each at the time and made money doing it.

He also couldn't fathom how we could run valve springs at the stresses and travels we did - his stuff was marginal at a fraction of what they were doing at the time.

At that point I learned that aircraft inspects quality into their parts - the auto people (even with the so-called lame quality they are alleged to have today) build quality in.

ONce you get the setup and have equipment that will hold the setup and tolerances, it is pretty easy to make jewelry. You'd be amazed at the construction and assembly of ball bearings. True poetry and a symphony of motion and Q/C, day in and day out at hundreds of pieces per hour.

YOu can get home machines to be deadly accurate if you spend the time and money. Heck we got a 10 uear old Bridgeport to darn near match the accuracy of a $1.25 million CNC grinder while master milling with TLC and some bucks spent wisely.

[mkaake]

Oh, you should watch a crank being ground on a three spindle machine - one for the crank, and two following with massive wheels to grind the pins... awesome.