Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

Rob's inverted platen build

Built a scanner? Started to build a scanner? Record your progress here. Doesn't need to be a whole scanner - triggers and other parts are fine. Commercial scanners are fine too.
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Rob's inverted platen build

Post by rob » 29 Mar 2011, 18:09

So I was scanning a paperback the other day after doing some hardcovers, and I noticed a few things:
  1. The spine on paperback books is not very solid. It twists a lot.
  2. The spine is nevertheless tight.
  3. The margins on the textblock sometimes go deep into the spine.
When putting the usual platen down onto the book, I found that I had to press down on the platen sometimes to get enough page to show up, to spread the pages out, and then the spine would twist a bit. Also, when lifting up the platen, the book had a tendency to flip a few pages in an effort to close up. I ended up having to lift the platen a little bit and sneak my hand in to hold the pages down.

Then I remembered that some other folks here had built scanners with inverted platens, like this one built by ahmad, and I realized that this would be ideal for paperbacks that don't have a lot of value. I can press the spine onto the platen as hard as I need to. I can hold the spine down evenly so that it doesn't twist. And paperbacks are light, so lifting the book, flipping a page, and putting it down again would take less effort than to lift the platen.

And so, I am now setting out to build an inverted platen scanner, with two cameras.

The first thing I did was to (horror!) remove the platen from my existing scanner, flip it over, and pop a book on it.
IMG_0108.jpg
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This platen was originally made from two picture frames. I'm thinking of going out and finding some 1/8" panes of glass, because the picture frames are made of two 1/16" panes each. I think 1/16" is too flimsy for pressing down on, and I've noticed that dust tends to get in between the two panes of the platen where it's impossible to clean unless I take the platen apart.

So... more as I continue.

--Rob
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Re: Rob's inverted platen build

Post by steve1066d » 29 Mar 2011, 18:23

hmmm... Maybe the thing to try is to make it so my scanner can lock in the "up" position, then press the paperback up against the platen (maybe raising my cameras a bit too).

I'm sure it is easier to press down instead of up, but it would avoid having to make a separate scanner.. something to try I guess.
Steve Devore
BookScanWizard, a flexible book post-processor.

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Re: Rob's inverted platen build

Post by rob » 29 Mar 2011, 18:38

That would be a neat idea: a convertible scanner. But not for me, yet! Also, you do not want to push the book upwards. I've done that sort of thing, and your back will kill you after 20 pages.
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Re: Rob's inverted platen build

Post by rob » 03 Apr 2011, 19:14

Today was a good day at NextFab. I'd count it as Rob 2, Robot Tools 1.

OK, so I need some kind of a platform to put my inverted platen into. Cutting a square hole into some plywood is a good start. I took some 1/2" plywood, and cut it to about 30" wide by 24", and then cut a smaller hole centered in the middle, just big enough for my platen: about 16.8" across by 15". The idea is to fit the platen into the plywood so that it doesn't move, yet can be removed for cleaning. If your hole is slightly too large, you can always add shims, but if your hole is too small, frowns all around.

Cutting a square hole in plywood can be done in several ways, according to Lewis at NextFab. The lowest-tech way is to drill holes at all four corners, then insert a jigsaw and cut your way around. The next step up is to cut out a template from MDF or plywood, and then use a router to route your way around the hole. This is also hellishly noisy. I really hate routers. The highest-tech way is to use a laser cutter, which I did at NextFab. This also gave the the opportunity to add some personal touches.
IMG_20110403_152346.jpg
And I don't mean the hat.
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Next, since the hole is designed to fit the platen, we need a little platform so that the platen doesn't fall through. Since the hole is 16.8" by 15", I told the laser to cut two additional strips, 2" x 16.8". Thank you, Robot!
IMG_20110403_154223.jpg
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Glue up and clamp hard on the underside. Here's the back view. I determined that my particular platen could use a 3/4" ledge to sit on, so that's how far the strips stick out.
IMG_20110403_155220.jpg
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And the front view, so you can see now how the platen will sit on the ledges thusly formed!
IMG_20110403_155247.jpg
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Success! Thank you, Robot!
IMG_20110403_152747.jpg
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Oh, and the one where the Robot Tools won? I was drilling holes in plastic in the CNC (40 holes, to be exact), and it worked fine in the morning. But I did another run in the afternoon and the drill bit heated up, melted the plastic, and then got stuck in a hole. The whole run was ruined. Up yours, Robot! I think that there has to be some kind of cooling that has to be turned on.

--Rob
Never trust robots...
Never trust robots...
You might think that they're your friend...
They'll only kill you in the end.
-- Andrew Thompson, "We're In Business", 2006
The Singularity is Near. ~ http://halfbakedmaker.org ~ Follow me as I build the world's first all-mechanical steam-powered computer.

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Re: Rob's inverted platen build

Post by rob » 10 Apr 2011, 21:25

The next step in the build is to mount the tabletop onto some legs. I wanted to make the height of the scanner comfortable for me while sitting. I should be able to hold my arms out straight ahead or slightly down and touch the top of the platen. For me, that makes the top of the platen about 29 inches from the floor, making the top of the table 21 inches from the floor.

I spoke with Lewis at NextFab for some advice, since I have no experience in building stable tables. The best I did was ten years ago when I took a 4' x 8' piece of plywood and stuck some 2" x 4" legs on. I added some bracing after I realized that it was unstable, and it sort of worked. But I wanted something a little more stable from the beginning.

He suggested building an "apron" around the bottom of the tabletop, made of 3/4" plywood, 3" wide. I decided to leave a 1" lip around the perimeter. My tabletop measures 30" x 23 1/2" -- I cut the plywood to slightly under 24" because I didn't want to assume one edge was perfectly parallel with the axis of the laser. So I subtract 2" from each dimension to get 28" and 21 1/2". That latter dimension is very close to my desired leg height, so I decided to use 21 1/2" for the legs as well.

I cut two strips 3" wide and 28" long, then ten strips 3" wide and 21 1/2" long. Two of each go into the apron. Now, if you're not like me, you've discovered a little problem already. If I were to place the strips like this: |_| then I'd get 21 1/2" plus twice 3/4", which is 23". That gives a 1/4" lip, not the 1" I wanted! What I should have done was make the 28" strips smaller by twice 3/4", or 26 1/2".

So instead I just placed the strips alternately. I ended up with a lip of 5/8", which is fine. Just don't forget the thickness of the plywood strips!

To attach the strips, first mark a pencil line 5/8" from the edge (or however big the lip is) on the bottom of the tabletop. Run a thin bead of wood glue inside the line, and put the strip on top. Clamp in three places:
IMG_20110410_142932.jpg
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Now mark a pencil line 5/8" plus half of 3/4" along the top from the edge. More generally, lip plus half the apron plywood thickness. This is where your screws must go:
IMG_20110410_143119.jpg
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Drill pilot holes through the top -- it helps to use a very small square to make sure you're drilling perpendicular to the top -- then countersink for the screw heads, and screw together.
IMG_20110410_143544.jpg
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IMG_20110410_143711.jpg
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IMG_20110410_143722.jpg
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Once all four sides are on, use a looooooooong clamp to squeeze the sides together. Drill pilot holes, countersink, and screw:
IMG_20110410_145222.jpg
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Use only one screw at the top, because we will later be drilling holes through the apron near the corners.
IMG_20110410_145414.jpg
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We now have a very sturdy tabletop.
IMG_20110410_145647.jpg
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Re: Rob's inverted platen build

Post by rob » 10 Apr 2011, 21:35

For the legs, take a pair of the 21 1/2" strips.
IMG_20110410_152713.jpg
IMG_20110410_152713.jpg (60.86 KiB) Viewed 8656 times
Run a bead of wood glue along one edge, and place the other strip on it. Clamp, pilot holes, countersink, screws. Repeat four times.
IMG_20110410_161251.jpg
IMG_20110410_161251.jpg (77.95 KiB) Viewed 8656 times
Clamp each leg hard into an inside corner of the apron. I'm not going to glue the legs on, since I want to be able to remove the legs. Thus, after clamping, drill four holes through for bolts. I'm using 1/4" holes for 1/4" bolts. Make sure the bolts you get are 1/2" longer than twice the plywood thickness, 2" in my case. Make sure that when you drill the holes for the bolts, they will not interfere with each other. Note that in the below pattern, the bolts will not hit each other.
IMG_20110410_170003.jpg
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Before you take the leg off, mark each leg and each corner with a letter so that you can put each leg into the same corner every time, otherwise the bolt holes won't line up.
IMG_20110410_170957.jpg
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The final result is pretty stable and somewhat Masonic even without bracing. (Bolts not shown)
IMG_20110410_161516.jpg
IMG_20110410_161516.jpg (78.73 KiB) Viewed 8656 times
The next step will be to add some bracing which will also serve the purpose of providing mounting points for cameras and lights.
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Re: Rob's inverted platen build

Post by E^3 » 10 Apr 2011, 23:22

Hi Sir Rob,

That is awesome, so excited to see it.

E^3

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Re: Rob's inverted platen build

Post by rob » 11 Apr 2011, 18:14

Thanks! I'll post more pix next week, and hopefully by then I'll have gotten some bicycle brake cables to add remote triggering without having to use CHDK (but that is the subject of another post).
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Re: Rob's inverted platen build

Post by spamsickle » 11 Apr 2011, 19:46

rob wrote:I'm thinking of going out and finding some 1/8" panes of glass, because the picture frames are made of two 1/16" panes each. I think 1/16" is too flimsy for pressing down on, and I've noticed that dust tends to get in between the two panes of the platen where it's impossible to clean unless I take the platen apart.
Perhaps you've considered and rejected my suggestion to use a single piece of plexiglass with a heat bend in the middle, but I'd like to suggest it again anyway. It would solve the "dust in the crack" problem -- no crack! I used 1/8" or 3/16", and still haven't gotten around to doing it again sideways "for real", but it's just a matter of clearing a block of space and time. I have the plastic, the heat gun, the suction cups, etc.

Anyway, here's the link to the mock-up: http://diybookscanner.org/forum/viewtop ... 8150#p8150. The right slab of plastic on that nifty frame you've got there looks like it would be "plug and play".

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Re: Rob's inverted platen build

Post by rob » 12 Apr 2011, 09:19

Spam -- thanks for reminding me of your work! I'll have to get some acrylic and practice bending it under heat. Your results definitely speak for themselves, and if I can get the acrylic to behave, I'll certainly upgrade my platen!
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