Quiz - point of origin

[John Stevenson]

OK,
lets say you want to machine a rectangular plate that is 4" wide by 3" deep, thickness doesn't matter for this exercise.

There is a series of holes at differening centres that you have to drill by manual operation, using a DRO or CNC.
You start off with a drawing and lay the holes out then machine the part.
You have 5 possible points you could reference from, each corner and the centre.
State which one you would use looking in plan view, also assume the vise is positioned moveable jaw closest to you.

Not a trick question as there is no definitive right and wrong.
I'd just like to hear peoples views and the why.

.

[Evan]

Bottom left=zero. Resulting coordinates are positive in both axes.

[TGTool]

Unless there were other constraints, I start from the top left, facing the vise. That's because I indicate the left end, fixed jaw of the vise and zero the dials (usually) so I can always just set a part at the left end, aligned with the end of the jaw and can plug a hole without layout, or indicator using regular rotation of the dials and without having to remove backlash. Provided I don't miss a count on the handle, that is.

jm

[hitnmiss]

Upper right is zero zero. Not sure why but I wind up doing most that way.

My cnc mill's control panel is on the right, so maybe it's convienent to edge find on the right side? Use the upper as zero because the fixed jaw on the vice...

[Virgil Johnson]

Upper left or upper right corner. preferably upper left. With the dimensions coming from the solid jaw and upper left or right corner I can put a stop at either location and run multiple parts. When I design machining fixtures I dimension as many details as I can this way so the toolmakers can square all the stock and get as much work done as possible from a single setup.

[pntrbl]

I haven't looked at any other replies and have never drilled anything with a DRO or a CNC either, lol, so this is strictly a common sense for a newb guess. I'd start at the lower/closer lefthand corner and go x,y from there.

Now I'll look at the other replies.......

SP

Well I guess that's what ya get when ya guess! I'll remember this one when I get that B-port home ....

SP

[Uncle O]

Usually for me....Fixed jaw = Y0. Left edge of stock = X0.
Fixed jaw remains Y0 along it's entire length.
Most likely have a dead stop fixed to it for X0, its always there unless part is considerably longer than jaw length.
Kerry

(Assuming stock has already been squared)

[topct]

I would find which two corners of the piece were the squarest. And use those for referance.

With a felt tip pen and a chinese caliper I would scribe where the holes should be and then using a center punch, and an electric drill, make the holes.

Whoops, almost forgot the vise.....ya.... use a vise.

[joeby]

I usually set a stop on the left side of the fixed jaw if using a vise. That way, all your handwheel movements are going to the right. I was taught to remove backlash to the right when I started in this trade, and have done it this way ever since. Don't even think about it anymore, last movement to the right.

This doesn't apply at my job, In most cases, I work off of the center of the part.
We need to leave about .005 per side for grinding after heat treat, so working off the center ensures you have even grind stock on all sides.

Kevin

[lane]

Most all prints are bottom left . but I use top right. because back jaw on vise is solid and table moves from left to right . Besides I perfer to machine from the right side of the vise to the left .

[wierdscience]

Fixed jaw left hand side is where I start,like others said it's where any hard stop will be located and the jaw is fixed.

Add to that when using that location both axis dials clock up when moving from right to left or from back to front.

[SGW]

My usual practice is to use upper left corner as 0,0. Not sure why, that's just the convention I've gotten into using.

[rantbot]

Use the same zero as the drawing, particularly if all the dimensions and tolerances are from zero.

[Marc M]

I have manual mill with a DRO. Assuming the part is square, I use the conventional lower left for the datum point. As Evan pointed out, this keeps all the coordinates positive.

[Your Old Dog]

When I get a complicated setup like that I send it out

(if I was gonna do it at home I'd use lower left for the reasons previously stated. I don't have a DRO on the x-y and things get complicated easily for me working in reverse.)