Masking shelf ends to prefinish dadoes - an idea

Background:
Bookcases, 3/4" ply. Shelves fit into 3/4" x 1/4" dadoes in the uprights. There are 20 "shelves". (some are tops and bottoms). 12 of those will be finished on both sides. That's 52 pieces of tape, by my count. Swingman has suggested a pizza cutter to make accurate edges. I could almost imagine doing that, but I now plan to do all of the "inside" finishing pre-assembly, and my available time is limited to (fractions of) weekends. Thus the tape could be on for weeks, which is apparently problematic.
I've been mulling this over, and this is what I've come up with so far (the usual caveats about my skill level apply):
http://www.flickr.com/photos/gdguarino/8378418997/in/photostream/lightbox / (use the right arrow to see two detail photos of the "jig")
I quickly screwed together two potential "guard" pieces to cover the last 1/4" of each shelf. I set the overhang by resting the jig in one of the actual dadoes. I figure I could clamp one side down "permanently" and either clamp and unclamp the other side for each piece, or possibly just hold it down manually. I might already have tested it but ran out of time last night.
I see some possible flaws in this plan. Upon looking at it, I wonder if stain and finish would build up on the edges of the thin plywood of the jig, or even seep underneath, "contaminating" the next piece to be inserted. This could conceivably be countered by covering the business end of the jig with shiny packing tape, or something else. I suppose I could use tape and wipe the jig ends off after each shelf face is done.
Then there is the question of the second side of the shelves. I could of course add a bottom "face" to the jigs to hold the shelf above the work surface, holding it of course by only the last 1/4".
So? The makings of a good idea? Or fatally flawed?
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On 1/14/2013 6:16 AM, Greg Guarino wrote:

Pretty novel idea but FWIW I dont worry about stain on the surface that enters the dado. For the most part there is glue on the end of the shelf that was not stained and typically there is a face frame that will also help prevent the shelf from pulling out of the dado.
When in doubt, I will lightly scuff the end of the finished shelf but never mask to prevent stain from getting on a surface.. I will mask to prevent glue from getting on a surface.
While glue does not stick as well to a finished surface as bare wood, it will to some degree stick.
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On Mon, 14 Jan 2013 04:16:16 -0800 (PST), Greg Guarino

What if you combined your idea with the tape?
First, mask off the area of the shelf that would be inside the dado and some of the area not inside the dado. The alignment of the tape need not be critical at this point.
Then place the masked shelf in your "guard" and cut the excess tape with a knife. Then the alignment would be as perfect as your guard and you wouldn't have to be concerned with possible build up for each successive shelf.
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On 1/14/2013 2:29 PM, Gordon Shumway wrote:

I think I may just take your suggestion, or some variation of it. Real life crept up on me over the weekend when I wasn't looking and prevented me from making much progress on the project. That gave me more time to think about the method, and I realized that there is a flaw I hadn't considered. I have made a lot of stain samples, and the one that I chose involves leaving the stain on for a long time (20 minutes) before wiping it off. I can't very well leave each piece in the jig for 20 minutes when I have 32 "faces" to stain.
Now I think I'll have to buy the pizza cutter.
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On 1/15/2013 11:55 AM, Greg Guarino wrote:

Stay away from the Festool model and you'll be ahead of the game.
You do have to be careful, depending upon the stain used, as trying to touch up/blend unstained areas on a previously stained piece can add to the amount of time involved in the project.
I've found this to be particularly true of lighter colored gel stains.
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On 1/15/2013 1:08 PM, Swingman wrote:

No smiley face?

It's a pretty dark stain, and not a gel. (Minwax Wood Finish: Gunstock). But I will be careful nonetheless. You mentioned that the "blue" tape can be a problem if left on too long. Is there some other tape you prefer? I've seen various kinds of artist's tape (the kind you used to see a lot on mixing consoles to label the channels), but the adhesive on those might actually be too weak.
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On 1/15/2013 2:14 PM, Greg Guarino wrote:

Bought any Festool? Your wallet simply won't let you smile until after you've used it.

IME, the darker the easier to blend/fix.

I use the blue tape because I use a lot of it, and it is cheap and ubiquitous. There are other tapes that are advertised to work much better.
This is not a big deal, just my experience that the longer you leave it on, the bigger PITA it is to remove ... minute little blue strips of tape in small cracks and crevices, left behind by well meaning painters and subs, has made my life miserable, particularly when prepping a new home for the market.
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On 1/15/2013 1:23 PM, Swingman wrote:

there's a green tape i've found at car painting places that sticks well and comes off cleanly.
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The green Frog brand tape seals pretty darn good with most every thing except the very thin dyes
I masked off solid white oak already attached to white oak plywood and stained the solid wood with a gel stain and had absolutely no bleed. Then I used a dye stain and had poor results with wicking.
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Greg Guarino wrote:

Flawed, IMO. I can't imagine stuff not wicking under the ply "guard". OTOH, no big deal if it does.
Any reason why you can't mask what you want to finish when you are finishing? That is, not mask everything at one time.
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