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PostPosted: Fri Feb 07, 2014 2:19 pm 
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Cocobolo
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Joined: Wed May 26, 2010 4:15 pm
Posts: 183
First name: Joe
Last Name: Ulman
City: Bellevue
State: Washington
Country: US
Focus: Build
Rosette/Circle Cutter – How it’s made by Joe Ulman

Attachment:
image001.jpg


This simple rosette/circle cutter is made by laminating 5 pieces of wood. Start with a block of 1” thick hardwood by roughly 6” long. Slice off 6 pieces with the following thicknesses (inches): 3/8, 3/8, 1/2, 13/64, 1/8, 1/8. The fourth piece 13/64 is the width of the cutter blade, so adjust to meet your cutter.

Attachment:
image004.jpg


I ordered a custom blade from Ron Hock similar to what he makes for LMII’s cutter but a longer version. The extra length helps facilitate setting the depth and makes for easier handling when honing. The 13/64 slice is used to form the wedge slot and also make the wedge (there should be enough extra to make a couple wedges from the cut off).

The 13/64 piece (with the wedge section cut out) is sandwiched between two 1/8” thick pieces. This laminated 3 layer assembly is then cut off to a total length of about 2.1” with the wedge slot roughly centered as shown.

Attachment:
image006.jpg


Attachment:
image008.jpg


Attachment:
image009.jpg


The laminated 3 layer assembly is roughly 1/2” thick to match the 1/2” center sliding piece. After the laminated wedge slot assembly is cut to about 2.1” long (sorry no picture of this), it gets sandwiched between two full length 3/8” thick pieces.

The main assembly is drilled for a 1/4” bolt and wing nut (two holes spaced about 1” apart seem to give an adequate range of operating radii). The 1/2” center sliding piece is cut to a length of about 3-1/8” and drilled for 1/4” pin (or diameter of pivot pin you will use). Slot for a 1/4” fixing bolt with sufficient slot length for an adequate sliding range; around 2 inches +/-. The disassembled circle cutter:

Attachment:
image011.jpg


Of course you will need to adjust all dimensions according to your own cutter blade, pivot pin, and any other requirements you might have. Assembled cutter:

Attachment:
image013.jpg


It should be noted that a proper workboard is key to the performance of this cutter as the precision and ease of cut is really obtained by the secure fit of the pivot pin in the underlying workboard rather than relying on the soft soundboard wood surface. This also constrains the tool on the vertical axis with no rocking longitudinally or laterally whatsoever and so the cutter blade always travels along a very precise radius. The full depth of cut is set in the tool initially and the cut is easily made in a few successive light passes with the tool providing excellent feedback during the cut.
For a workboard I use 1" MDF that is leveled and a (perfectly vertical) hole drilled that has a very snug fit on the pivot pin. The tool can then be lifted, smoothly sliding up the pin without dislodging it from the workboard, for changing directions of the cut or to check your work and test cuts.

Attachment:
image015.jpg


I also find the small Veritas router plane (shown in picture) works nicely to flatten the excavated rosette channels.


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Last edited by JoeUlman on Sat Feb 08, 2014 3:26 pm, edited 1 time in total.


These users thanked the author JoeUlman for the post (total 3): Beth Mayer (Tue May 20, 2014 6:57 pm) • mkellyvrod (Sun Feb 16, 2014 6:34 pm) • Colin North (Tue Feb 11, 2014 5:48 am)
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PostPosted: Fri Feb 07, 2014 5:38 pm 
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Joined: Fri Dec 17, 2010 6:22 pm
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First name: Miguel
Last Name: Bernardo
Country: portugal
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thanks for this. clever!

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PostPosted: Tue Feb 11, 2014 5:54 am 
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Thanks for that, still trying to work out how to do a micro-adjust (which I would like) for something like this.

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PostPosted: Tue Feb 11, 2014 7:03 pm 
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Joined: Sat Apr 19, 2008 10:08 pm
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Location: Missouri
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Last Name: Hanna
State: Missouri
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Hey, Joe,
Very nice of you to post this, and it's beautifully made, too. I made one similar in function, but not nearly as pretty, many years ago. I do believe that a tool worth building is worth building WELL. The only problem I have with this sort of cutter is the difficulty of knowing exactly where the knife is going to plunge down. I've peered under mine with a strong flashlight!
You have inspired me to build myself a new one.

Patrick


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PostPosted: Tue Feb 11, 2014 9:44 pm 
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Cocobolo
Cocobolo

Joined: Wed May 26, 2010 4:15 pm
Posts: 183
First name: Joe
Last Name: Ulman
City: Bellevue
State: Washington
Country: US
Focus: Build
Thanks guys for the compliments.

Colin, I also thought about adding a micro adjust. I think it could be done by using a pair of plates, one attached to the back of the slider and one to rear of the tool, connected with a finger screw but I decided not to bother with it after using the tool as is a few times.

Patrick, yes I agree. I've found it helpful to set the cutting radius using the rosette assembly form(s) adjusting so the blade is pressed against the wall of the form, or alternatively using the cutter blade in hand to make a deep(ish) indentation at the desired radius on the soundboard in the area where it will be covered by the fingerboard. Of course with a well honed blade back in the tool it does require a light touch to find the indentation and not just make a new one wherever the tip comes down.

Joe


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PostPosted: Sat Feb 15, 2014 5:40 am 
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First name: colin
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JoeUlman wrote:
Thanks guys for the compliments.

Colin, I also thought about adding a micro adjust. I think it could be done by using a pair of plates, one attached to the back of the slider and one to rear of the tool, connected with a finger screw but I decided not to bother with it after using the tool as is a few times


Yes, I did something like that with araldite, small wooden blocks and nylock nuts on a a dremel circle router (supplied with a boxed set) before I got my current circle cutting jig.
I'm sure it can be done, just I've got my head full of jigs to build at the moment! :?

Perhaps a see through circle cutter from acrylic ....... [uncle]

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PostPosted: Tue May 20, 2014 3:37 pm 
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Joined: Thu Oct 04, 2012 3:50 pm
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Location: Austria
First name: Michiyuki
Last Name: Kubo
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Country: Österreich
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Joe,

Thank you very much for sharing how to make one of these I really very much appreciate it. I was debating on designing a circle cutter or buying one. I am glad you have posted the design already for us to use. Much obliged.

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