[arie kabaalstra]

hy arie such small clearances work when there is no deflection, thus rigid setups

if your setup isn't rigid.. don't bother hitting the green button i always say...

if your machine isn't rigid and repeatable, get a forklift, and throw the thing in a Dumpster..

I've been working on Fairground and Amusmentpark rides.. and these are BIG (now you can imagine what we needed a 6 x 6 x 3.5 meters Mill for..)

2 mm was stil my standard clearance before "entering"the work.. when transferring from 1 end to the other, i moved to 20 mm to take any deformation into account (since most parts were welded sub assemblies that needed milling/drilling afterwards.. first weld, then mill..

I ran series of these parts.. making a "Jig" on the machine by means of clamps, and blocks of steel.. so i could just "Slot" my work in.. Program the lot, Hit start, get of the Operator Console, down the ladder, get part number 2 close to where part 1 is being machined in the mean time, so i could get part 1 out when done, get part 2 in, hit start, and move part 1 out of the way, making room for part 3.. Juggling with parts that would weigh up to 7 metric tonnes.. all in a days work..

[deadlykitten]

indeed arie, anyone wishes for rigidity, but sometimes there may be a weak fixture, or overhang on tool , or whatever

lately some o350 x 550 parts needed external turning with 0.02mm tolerance, after deposition of a hard layer, that simply distroys carbide inserts after 30-50mm, while better diamond tipped inserts would last a few complete passes, but with wear corections among the way

for example, final radial docs are like 0.3 0.2 0.1 0.07 0.05 0.02, while offset corections are aplied, and, to achieve the last 0.02, the tool offset is raised with 0.2mm, or something, thus, in orider to go deeper, the tool is raised there is no linearity between offset and real doc, as the normal aproach was initialy grinding, which is much more stable and finess

as passes are relativley long duration, is easy to loose track of corections, so a log is being kept

this is just a particular example, as, in general, every setup has an elastic and plastic behaviour; and rigidity occurs when elastic behaviour does not affect the tolerance but of course it drives me crazy, i wanna throw the thing in the dumpster, like you said .... but i just have to get it done, what choice do i have ?

.I used 2 mm on the Bridgeport VMC 800, 1000, 600, 610, Interact, Oerlikon Vector, Schies & Froriep, Kiheung, Basically every Heidenhain Operated Machine i ever worked on, but i also used the same 2 mm on Elora controled machines, and on Cincinnatti and Fadal Controls..

the background of the clearances that i discused here, is in conjucton with okuma's codes; is a result of long term homework about cycles times shortening technique, trigering seconds, tens of a second, or even less, each time scale having different aproaches