Borderless printing custom sizes canon pro 100

[Heterochromatic]

Hello all! I would like to print borderless on a non custom size. Sometimes I can do this by choosing a matching standard size on one of the dimensions, for example: for a 5"X7" card, I can print 7" X10" (which is custom and folds to 5X7) borderless by selecting 8X10 (standard) and it sort of works (I have to trim about 1/4 millimeter off one edge). But I cannot find  work-around for my 5.25" X 5.25" cards, as there is no standard that matches. Anyone? And WTF canon, if I can print borderless on standard, why not custom? Is it just a software thing? Is there a patch?  I cannot conceive of a logical explanation for why this restriction on borderless for custom sizes. Anyone know? Thanks.

[jrhoffman75]

When you print borderless the printer oversparyas somewhat to be sure the entire print is covered.

In order to capture the excess ink the printer has sponges. The sponges are placed at dimenstions based on standard paper sizes. No sponges for unknown custom size dimensions.

[Heterochromatic]

Ah, thank you. That makes sense - a hardware rather than a software issue. I wonder what kind of damage I might be doing with my 7X10 workaround. Is it possible to see if there is any overspray on the drum? I don't want to start dismantling my printer! But I do need to keep printing borderless for 7X10.I am now thinking about finding card stock that is, say, 10X10 or 11.5 X11.5 and printing duplicate square images and then just cutting down the center. 

[jrhoffman75]

The primary problem would be ink transfer to prints rather than damage to the printer. 

There red is an adjustment in the driver for print extension. Move that adjustment to the minimum.