Precise hand cutting of ribs

[NenadM]

In conditions when the ship ribs are not laser cuted, and there is only an old draft made ​​with old technology (hand drawing and photocopying - the so-called blue-print) may occur mistakes with consequences for further work

 

As a consequence of old copy technique, the thickness of drawn lines in the draft is about 0.7-0.8 mm. When the drawing is transferred to the plywood at the beginning of cutting, we will determine the cutting saws 0.1-0.3 mm thick

 

In other words, it is possible to cut above, or to cut below, or just in the middle of drawing line, which is almost twice as thick as saws. If you add in the inevitable loss of material during the sanding after cutting, it can be almost inevitable errors of about 1 mm when the rib put into its place on keel, since there is an same error in the hole - the hole in the keel to set the ribs, and in holes - holes in the ribs.

 

This one milllimeter ( even up to 1,5-3,0 mm if you are not precise enough) can significantly affect the precise location of the deck - especially if wants to preserve the longitudinal and transverse curvature, and also causes vertical motion which causes vertical moves of horizontal lines for good planking

 

Usually there is a lot more than just a one rib, and the error is necessary to multiply.

 

How to avoid? What is the real position of the line cutting?

 

Edited July 5, 2013 by Nenad M

[druxey]

You are absolutely correct: the thickness of pencil lines matters! If you draw your own plans, these should be as thin as possible. In the case of plans such as you show, it can be a problem.

 

One test might be to know the thickness of the bulkhead material and see which side of the lines of the slots match this. If that is not possible, then I'd cut to the outside of the lines. It's easier to sand a bit more off than glue it on again!

[NenadM]

In my opinion, some kind of testing must be done. Also cut outside and then correct with sanding. Very important to begginers