Re: The Kohnen Scarfing Jig


Gerard Mittelstaedt
 

Some years ago I made a "scarfing jig" by welding a few pieces of angle iron, making a frame, and bolting a router on to a heavy plywood carrier to move back & forth across the 4 ft  width of a piece of plywood.  It sort-of worked,but the 1/4 in plywood (yes the plain stuff not the high dollar stuff0 did not want to lie flat enough that there in lied the difficulty.  - - since I have sandwich secured  plywood sheets between layers of 2x stock and scarfed with a belt sander using a rather coarse sanding belt. 
  Then at glue-up doing the thin epoxy first for soak-in and epoxy thickened with corn starch or very fine wood flour for adhesive glue-up seems to work great.  use a couple of very small finishing nails to keep the scarf from squeezing apart as I clamp the whole scarfed area with 2x on each side - wax paper between the 2x and the plywood and some added thickness in the middle (remember I am scarfing whole 8ft x 4ft plywood sheets) to keep the clamping tension sufficient in the middle..  Yes, this is odd business, but what can one do when one wants plywood more than 8 ft long and has decent bending qualities.  It worked for me - may work for you.   - AND the work surface was indeed large to accommodate the length of the 2 pieces being scarfed.  - - Best of luck on your projects -
Gerard Mittelstaedt in McAllen, (deep south) Texas


On Fri, Apr 3, 2020 at 2:20 PM John Kohnen <jkohnen@...> wrote:
Thanks for looking that up, Jove. I'll have to print that out and post
it in the shop so I can remember. <g>

So, Randy's Kohnen Scarfing Jig is clearly a "jig". Something that, say,
positions stock on a drill press table to bore evenly spaced holes is
clearly, a fixture. But what about the device Randy used to cut scarfs
on the table saw? It doesn't guide the tool, but it actively guides the
stock into the tool. The same conundrum applies to countless table saw
sleds and guides. Hmmm... How many angels can dance on the head of a
pin? When in doubt, I'll just call them "gizmos". <g>

On 4/1/2020 10:40 PM, Jove wrote:
> Ok..... I had to google it!
> “The most basic difference, is that a *jig* is a type of tool used to
> hold and support the workpiece but in addition to this, A *Jig
> also* controls the location or motion of tool. On the other hand, a
> *fixture* is a support or work holding device used to hold work in
> place. It never guide the tool.”
--
John <jkohnen@...>
I am patient with stupidity but not with those who are proud of it.
(Edith Sitwell)


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--
Gerard Mittelstaedt  -- mittel48@...
McAllen, Texas
USA

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