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Bridge City Kerfmaker Geometry

#42890 by tdubnik » Sun Jul 19, 2009 7:05 am

I have been studying the Bridge City Kerfmaker pictures and videos and was intrigued by this little device. It's pretty ingenious and pretty simple when you think about it. I played around with it in Sketchup until I had a working mock-up shich I'll post and describe below.

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This would be the basic set up with all parts collapsed. There are basically 3 pieces plus the locking devices. With all parts collapsed the offset between the top 2 parts and the bottom part determines the maximum blade width.

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You would set the Kerfmaker to your blade or cutter width by sliding the middle part out until the offset between it and the bottom part matched your blade and then lock it down. I used a 1/8" saw blade for this example.

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You would set the device to your material thickness by sliding the top two parts (which are now locked together) until the gap between them and the bottom part matches your material and then lock them down. My example shows a 3/8" material thickness.

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This shows how the device is butted against the stop for the first cut. Notice that the stop has to be narrow enough that the stop will slide into the notch created by the offset of the device. In my example I show a cut at the very end of the Kerfmaker for illustration purposes. You can set it up to make a cut anywhere along your board.

continues on next post...

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Bridge City Kerfmaker Geometry - continued

#42891 by tdubnik » Sun Jul 19, 2009 7:08 am

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The kerfmaker is now flipped over and butted against the stop again, but this time the notch does not slide over the stop. This makes the second cut to the precise distance as your material thickness. You will notice that the measurement from the inside of the blade on the first cut and the outside of the blade on the second cut is 3/8"; which matches the thickness of your material.

I am thinking of making a prototype and looking for a knurled thumbscrew nut about 1/8" thick that looks like the Bridge City one. If anybody knows where I can find one let me know.

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#42892 by dusty » Sun Jul 19, 2009 8:02 am

Very impressive.

http://www.youtube.com/watch?v=PQ6_S6lZKLI

http://www.bridgecitytoolworks.info/Categories/What%27s+New

---

"Making Sawdust Safely"
Dusty
Sent from my Microsoft Surface Pro using Firefox.

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#43927 by keakap » Thu Aug 06, 2009 9:29 pm

tdubnik wrote:I am thinking of making a prototype and looking for a knurled thumbscrew nut about 1/8" thick that looks like the Bridge City one. If anybody knows where I can find one let me know.


Very nice drawings and explanation. Thanks. (Although it will take the edge off my anticipation somewhat, while I await delivery.)

About the knurled nuts or knobs, have you looked at Bridge City itself? I know at least at one time they sold knobs of various sizes without the usual RW inlays, so you could turn your own. I believe the parts like that were 'blanks' of the various sizes used in their special tools, like the Squevel, CenterScribe , etc., so they might offer Kerfmaker type pieces as well.

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#43956 by tdubnik » Fri Aug 07, 2009 5:14 am

I found knurled thumbscrewsthat work at Stewart-MacDonald.

I've already completed my prototypeand it works great.

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