Digitizing board recommendations

      Digitizing drawings that are larger than the tablet. July 24, 2002

Is anyone doing work on a regular basis with a larger digitizing tablet? How much bother it is to digitize a drawing larger than the size of the tablet, i.e., digitize left half, shift the sheet with the drawing and then digitize the right half?

I have a rough idea of how to do this but would like to hear from others who have actually done so. I'm thinking about buying a 36" x 48" or larger tablet. I'm running AutoCad LT97.

Forum Responses
From contributor P:
A large digitizer will be a large investment. I have done what you are suggesting many times, and if you are careful, you can digitize one part of a drawing, then remove and recalibrate the tablet, then digitize the next part of the drawing. Just be sure that you accurately measure and lay out reference lines in order to "lie" to the computer when you recalibrate.

From the original questioner:
We currently digitize large drawings (up to 10' wide) on our CNC router using a laser pointer and recording the points and then inputting them into AutoCad. This process takes about 10 minutes to record the points (average 6' wide drawing), and about 5 minutes to enter the points into AutoCad. So the process start to finish on a 6' tracing is 15 to perhaps 20 minutes, typically.

Will I see an improvement in speed with the tablet and a shifting of the tracing? Our process on the CNC router with the laser pointer is dead-on accurate.

From contributor P:
I don't think the digitizer will be any improvement in your input process at all, unless it takes a lot of time to mount the laser pointer on your machine. The obvious downside is the fact that you are losing production time on the router while you are inputting info from these drawings. Who is doing this large of a drawing manually? Can they not start out digitally?

By the way, we just got a big 4' x 6' GTCO whiteboard for our distance learning classroom that I have used as a digitizer. It is basically the same thing (a big electromagnetic field) that cost about $1200.

From the original questioner:
We make curved mouldings for architectural applications. Customers take large sheets of various types of paper and tack them over the window. Then they will make an impression of the inside edge of the window jamb right through the paper. Finally they'll go over that impression a second time with the side of a crayon or pencil. That is the line we digitize.

As to the laser, we always leave it attached to the router anyway. It's just a cheap Radio Shack laser pointer that we've clipped onto the router housing. As to router time, the router only runs about 1 to 2 hours per day anyway. So, given all this it sounds like the digitizing board really wouldn't be that much of a step up. Please tell me more about the GTCO whiteboard.

From contributor P:
The whiteboard is a peripheral that attaches to a computer port. Its stylus allows me to write with different colored (virtual) pens, erase them, move these scribbles, etc, just like a big piece of notepaper or chalkboard. I can then save these images and print them out. The really cool thing is that it also allows me to use a LCD projector to shoot my computer image onto the board, and even control the computer via the stylus right at the whiteboard. I teach AutoCAD, AlphaCAM, CabinetVision, and other subjects using this thing, and it's a great teaching tool to be able to alternate between using the program and scribbling right on top of it to emphasize a point. We use our interactive videoconferencing system to send this image out to others that are connected to our Center.

From contributor J:
If you measure the same two points in both setups, you should be able to import the two halves into one CAD file (use different layers). Line them up (translate and rotate) using these two points as tooling points.

Using your example of a part that is too wide: digitize the left side of the part and also digitize two points, one at the top and one at the bottom - the farther apart the better, on the far right of your digitizer. This will be in the middle of your part. Shift the part on the digitizer to the left and digitize the same two tooling points and the rest of the right side of the part. Then move the right side geometry so the two sets of tooling points line up with each other.

By the way, the tooling points can be completely arbitrary. Add them yourself if there aren't any convenient features in the middle of the part.

From the original questioner:
Except for the great idea of using the two layers, the above explanation is pretty much what I had in mind.

However, this whole issue may be a mute point, as I've got a used 36" wide bed scanner coming. I found it in Texas and it's on the way up here now. If that works as I think it should, I'll be sitting pretty. I already have raster to vector software I'm familiar with, so as long as the scanner works, I should be all set.

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