REV B LANDS · THE TWO PRINTS SIDE BY SIDE · WHAT SURVIVES FROM PART ONE
Rev B landed.
Here is what happens.
STOP · READ · DECIDE · THEN CUT
WHAT HAPPENS TO A JOB WHEN THE DRAWING CHANGES WHILE THE PART IS ON THE MACHINE?
The operation stops where it is and the two prints are read side by side before another chip is cut. What has already been machined, what the new print moves, and whether the datums still hold decide whether the part in the vise carries on, is reworked, or starts again, and you hear which, and whether the number changes, before it does.
By Cyclone Machining Co.Updated
◆01·WHAT STOPS
The old print is void the moment the new one lands.
Nothing is cut to the old revision after the new one arrives. The operation stops at the feature it is on, the part stays in its setup, and the two prints are laid side by side and read feature by feature: what moved, what grew, what disappeared, and which datums the new print measures from. A revision that only changes a note is read the same way, because a note can move a datum.
The reading happens before the answer, not after it. A shop that keeps cutting to the old print while it thinks about the new one is making a part that nobody ordered, and a shop that quotes the change before it has read the part in the vise is quoting a part that no longer exists. Both cost you a part.
◆Two prints, side by side
The old print · void the moment the new one lands
The new print · one feature moved, read against the part
The old print · void the moment the new one lands
The new print · one feature moved, read against the part
THE OLD PRINT IS VOID
Nothing is cut to the old revision after the new one arrives; the operation stops at the feature it is on and the part stays in its setup.
READ SIDE BY SIDE
The two prints are laid together and read feature by feature: what moved, what grew, what disappeared, and which datums the new print measures from.
THE CLOUD MARKS THE CHANGE
A revision block records the letter, the date and what moved; the drawing you send is cut to the letter on it, and the old letter is marked void here.
◆02·WHERE THE CHANGE LANDS
Five places a revision can arrive, and what each one costs.
Before stock is cut: the change is a programming change. The model is updated, the toolpaths re-run, the setup sheet re-checked, and the job proceeds as if the new print had always been the print. This is the cheapest place a revision can land and the one worth aiming for, which is why the shop asks early whether the drawing is settled.
After roughing: the material left on the part decides it. A feature that grew can usually be finished from the stock that was left for it; a feature that moved into material already removed cannot, and the part is read to see whether what is left still reaches the new print from the same datums.
After finishing: the finished features are measured against the new print. Those that still meet it are kept; those the revision moved are either re-cut where stock allows or the part is started again, and you are told which features fall on which side of that line.
After the finish or the blast: a surface that has been honed, blasted or peened has been taken to its final state, and a change that cuts into it starts that operation over. The part is read for whether the finished surface survives the change before the change is made.
After it has left: the part is yours, and a revision that arrives after shipment is a new part cut to the new print, quoted as one. The old part comes back with the new print if you can send it, because what it taught is worth more than the drawing.
◆03·WHAT SURVIVES FROM PART ONE
The setup was planned for the part that comes after it.
Part one leaves four things behind: the setup sheet, the program, the fixture, and what the part itself taught while it was on the bench. A revision spends some of that and keeps the rest. A dimension that moves inside the same setup keeps the fixture and the datums and costs a program change; a feature that needs a face the fixture covers costs a second setup or a new fixture, and that is the line between a small change and a large one.
The fixture is the thing most worth protecting, because it is what makes the next part come out like the last one. It is built for the family the part belongs to rather than for one revision of it, which is how a later revision can still be held by the fixture that held the first. When a change makes the fixture unusable, you are told that it did, because that is where the number moves.
◆04·WHAT TO SEND WITH A NEW PRINT
The new print, and one line on what changed.
Send the new print or model, one line on what changed and why, the old print marked void so the two are never confused, and your decision on any parts already cut to the old revision. If the change came from a part that failed, send that part back with the new print; a print can say what to cut, and only the part can say what happened.
Say which features the change is really about. A revision block lists everything that moved, but usually one feature is the reason and the rest are consequences of it, and knowing which is which decides how the part in the vise is read.
◆05·WHEN THE NUMBER CHANGES
A programming change holds the number. A new fixture does not.
A change that stays inside the setup is a programming change and the number holds. A change that needs a face the fixture covers, a second setup, or new stock is quoted again, and the quote names why. The line is drawn from the part on the machine, not from the size of the change on paper, which is why a large change to one feature can be cheaper than a small change to another.
Either way you hear it first. The choice of carrying on, reworking, or starting again is put to you with what each one keeps and what each one costs, in words, before a chip is cut to the new print. No figure is printed here because the setup decides it, part by part.
◆06·REVISIONS, PLAINLY
What Rev B means, and where it lives.
A revision is a change to a released drawing, recorded in the revision block of the title block: the letter, the date, a short description of what moved, and who approved it. The letters run in order and, by long convention, skip the ones that read like numbers, so the block is not misread on a shop floor. The drawing you send is cut to the letter on it, and the old one is marked void here the moment the new one is read.
Whether a first release is A, dash, or zero is a matter of your own drawing standard, and the shop follows yours. What matters on this floor is only that one letter is current, that the part in the vise is measured against that letter, and that the old letter is marked void, so nothing is ever cut to it by mistake.
THE QUESTIONS PEOPLE ACTUALLY TYPE
Asked by people holding two prints.
6 answers. The questions that arrive with a revision, in the order they get asked on the phone.
Do I have to re-quote?
Not for a change that stays inside the setup: that is a programming change and the number holds. A change that needs a face the fixture covers, a second setup, or new stock is quoted again, and you are told which kind it is before any of it is done.
What happens to the parts already cut to the old rev?
They are yours, and you decide: scrap, rework to the new print where the material allows it, or use as they are. Nothing is cut to the old print after the new one lands, and the parts already cut are measured against the new print so your decision is made on numbers rather than on a guess.
Does the fixture survive the change?
Usually. The fixture is built for the family the part belongs to, so a dimension that moves inside the same setup is held by the fixture that held the first part. A feature that needs a face the fixture covers is the change that does not survive it, and that is said plainly when it happens.
What do you need from me with the new print?
The new print or model, one line on what changed and why, the old print marked void, your decision on parts already cut, and the failed part if a failure caused the change. The line on why is the most useful thing on the list.
Will you sign our NDA first?
Yes, and it is normal here rather than a negotiation. Send it as a PDF with the print and it comes back signed. The print and the model are used to quote and to cut the part, and they go nowhere else.
What does Rev B actually mean?
That the released drawing has been changed once since its first release, and that the change is described in the revision block of the title block, with a date and an approval. The part in the vise is cut to the letter on the print it was given, and the previous letter is marked void here the moment the new one is read.
Sources
They support the general facts. The shop practice is its own.
- What an engineering change order isThe paper behind a revision: what changed, why, and who approved it.
- What an engineering drawing carriesThe title block and the revision block, where a change is recorded.
Send the new print, and say what changed.
The part stops where it is, the two prints are read side by side, and you hear whether it carries on, is reworked or starts again, and whether the number moves, before another chip is cut. The old part is welcome back with the new print.