Build volume vs extruder travel limit

May seem a dumb question, but what is considered an "honest" build volume?

I mean if I want a 300x300 XY build volume, is that considered the limit of how far the nozzle will reach at extremities, or should it travel an extra 10-15mm in all directions to allow for rafts, brims, etc?

What is the standard or considered the done thing?

The standard is and the thing do is to say whatever it takes to sell the printer.

If you ask the marketing department build area will be the bed plate size even though very few printers can really print from edge to edge. Actual build area is hard to predict because it is a function of flatness, leveling, temperature, and size as well as the limits of motion of the extruder/bed. If the bed is heated the temperature will drop near the edges and corners and plastic may not stick reliably. If the bed is 300 x300 but the heater stuck to the bottom is 200 x 200, you won't be able to print much larger than 200 x 200 (for materials that require a heated bed).

The marketing people will tell you the printer's resolution is the mathematical result of the microstepping/by the pulley circumference, even if the frame wobbles and shakes while the printer runs and the thing produces terrible Z aritfacts.

They'll say the machine is "ABS compatible" if the hot end can get hot enough to melt ABS even if the bed can't get hot enough for it to stick and the machine has an open frame.

They'll say the Z axis resolution is 20 um even if the bed isn't flat enough to allow such fine layers over more than the central few cm^2.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
The standard is and the thing do is to say whatever it takes to sell the printer.

If you ask the marketing department build area will be the bed plate size even though very few printers can really print from edge to edge. Actual build area is hard to predict because it is a function of flatness, leveling, temperature, and size as well as the limits of motion of the extruder/bed. If the bed is heated the temperature will drop near the edges and corners and plastic may not stick reliably. If the bed is 300 x300 but the heater stuck to the bottom is 200 x 200, you won't be able to print much larger than 200 x 200 (for materials that require a heated bed).

The marketing people will tell you the printer's resolution is the mathematical result of the microstepping/by the pulley circumference, even if the frame wobbles and shakes while the printer runs and the thing produces terrible Z aritfacts.

They'll say the machine is "ABS compatible" if the hot end can get hot enough to melt ABS even if the bed can't get hot enough for it to stick and the machine has an open frame.

They'll say the Z axis resolution is 20 um even if the bed isn't flat enough to allow such fine layers over more than the central few cm^2.

Ok, so let's go with an unproven assumption that I'm not a marketing department and reasonably honest.

What would be considered a fair and reasonable way to measure the build volume?

Size of the build plate...definitely not for me, as it won't print right up to the edge.

Travel extent of the extruder...probably fair enough if you allow that brims, rafts, etc are included as part of the build.

Common sense dictates the size of the heater pad, I'll use the same size as my build volume.

What would you call the real thing?

How about printing a big cube and seeing how big the printer can actually print? That would be a powerful sales tool (assuming the cube was actually big). I think I saw something like that in a recent Prusa video.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
How about printing a big cube and seeing how big the printer can actually print? That would be a powerful sales tool (assuming the cube was actually big). I think I saw something like that in a recent Prusa video.

Again, not really looking for a "sales tool", but yes if I was going to claim a build volume for a printer I'd built I'd say that a big cube that size would be fair play.

I'd say the honest "build volume" is whatever your nozzle can reach.

Ref your OP, my thoughts are that if you want the build volume to be 300 x 300 then yes, it's possible that you might want to use a brim or a raft on top of that. Personally, I always print a couple of perimeters around the object's footprint before I start printing proper, just to get the filament flowing nicely. That takes up about 3mm or so all around. So, the head travel would need to be at least 306 x 306 maybe a bit more if you want a skirt. Of course, you wouldn't want to be printing right on the edge of the build surface so that ought to be bigger by 10mm or so. Maybe a bit more if you plan on having countersunk screws to hold the build surface. So say 10mm all round for raft/perimeters plus 10mm clearance means the build surface ought to be a minimum of 340 x 340 to be able to get a print 300 x 300. Or conversely if the build surface was 300 x 300, then realistically, the maximum print size would be around 260 x 260. Possibly more if you had say a glass print surface that would cover up any counter sunk screws.

Any raft or brim is part of the build. Notwithstanding DD's very valid comments about the quality/usability of the build volume, I think it's fair to describe the build volume as the smaller of the bed area and nozzle travel (it's possible to have a larger travel than the bed), times the Z travel. Anything else just lends itself to ambiguity.