(For beginner)Film Faced Plywood knowledge& Manufacturing Experience Part 6 : Stitching veneer Finger Joint core veneer & Scarf joint core veneer ?

There are many many factories asked me if they could use finger joint core veneer to make film faced plywood ,because finger joint core veneer can make a flat panel under the top poplar face veneer ,I told them there should be some risk if use finger joint core veneer to make film faced plywood,because the finger joint is just for making the plywood flat purpose ,not making the plywood strong .

There are many different types of veneer joint structure ,such as finger joint ,stitching joint ,scarf joint ,butt joint …

FYI,by the way,here the finger joint core veneer is different from the recycled finger joint plywood platform .

Finger joint core veneer normally used for furniture grade plywood,no need strong strenght to support heavy materials ,means no bearing loading capacity requriements .If used for film faced plywood,the plywood are easy to break .

Scarf joint core veneer can be used for film faced plywood need good strength and need good surface ,flat .

Finger joint and scarf joint core veneer are normally used under the top and bottom poplar veveneer to make sure the surface is good flat and smooth .

The stitching core veneer is normally used as the top and bottom core veneer under the film or the wood face veneer to have a good surface .
Butt joint core veneer ,normally this is traditional core veneer joint method ,using hand lay-up and glue tap and randomly lay-up ,this will cause so many overlaid veneer and joints ..,more and more factories already gave up this traditional way to make plywood core structure .

 

Scarfing core veneer  – scarfing jig

A scarf joint (also known as a scarph joint) is a method of joining two veneer end to end in plywood core veneer construction. The scarf joint is used when the material being joined is not available in the length required. It is an alternative to other joints such as the butt joint and the splice joint and is often favored over these in joinery because it yields a barely visible glue line.

 

the veneer will have to be joined into longer pieces. The issue is how to connect it together so that the joint between the veneers will have the same or very close properties as the rest of the veneer. This means that the bond should not fail easily when the veneer is bent/flexed, the ‘seam’ should look visually clean, the joint has to assume curvature to the same degree when bent or twisted as the surrounding material and last but not least, the joinery must be easy to make in an average shop with common tools.
thinner veneer will limit the number of practical joint configurations. The examples below shows a few common types:
  Scarf joint

Advantages:
» large bonding / gluing surface
» skins as well as the core bond to each other across the boundary = continuity and strength
» degree of bending “curve of curvature, “fairness” or “second derivative of curve” very close to the    surrounding plywood
» allows small degree of misalignment between joined sheets without forming gaps
» same thickness as surrounding plywood
» relatively easy to do
Disadvantages:
» difficult to make accurately especially without specific tools and a jig



  Butt joint with a block

Advantages:
» clean and tight joint line
» very easy to do without any jigs
» OK for no-twist, low-bend or flat panels in structurally non critical areas
Disadvantages:
» the degree of bending “curve of curvature” in tight curves or in twist may be very different than the    surrounding plywood resulting in an “unfair” surface with a sharp ‘kink’ or ‘flat’ section at the joint.
» strength of joint depends on the cohesion of surface skin within the plywood
» interruption in surface thickness – bad for fiberglassing the affected side
» heavier than other joint types

 

 

 

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