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Rosettes for Newbies

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Re: Rosettes for Newbies

Postby Bryan Bear » Tue May 02, 2017 3:01 pm

Alan Carruth wrote:That is, on the outside limit cut you go from the upper and lower edges of the rosette toward the left and right sides, while the inside limit cuts go from the sides toward the top and bottom. That way, when the blade decides to follow the grain it's wandering into the part you're going to be cutting away anyway.


If I ever learned that, I have forgotten it. Thank you for pointing that out!
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Re: Rosettes for Newbies

Postby Randy Roberts » Tue May 02, 2017 10:40 pm

I'd recommend a laminate trimmer with a 1/8 reducing collet over a dremel if you don't do it the hand cut way.

And definitely use a spiral downcutting bit, no tear out and a very clean cut.

Also recommend getting dyed wood rather than fiber strips for the thin lines. The fiber just doesn't give the deep black that dyed wood does.
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Re: Rosettes for Newbies

Postby Todd Stock » Wed May 03, 2017 6:35 am

The best of the jigs I've found is the Wells/Karol type, which has a range limited only by the length of the guide rods used...I've used mine on furniture projects as well as instruments. Accuracy in setting is excellent, as the adjustment thread is a 1/4-20 (0.050" for turn). Sylvan Wells has the plans on his website (paid access), but the video from Chris Paulick linked below covers all of the essential measurements, bill of materials, and process to build one. Much more accurate than any of the Dremel-based jigs, and on par with the $$$ solutions from MicroFence.

Chris Paulick shows installation of a PC 7301, but the less expensive $99 Ridgid 2401 has much better depth setting repeatability, variable speed, soft start, and a lifetime warranty - we use these in most of our jigs that require a smaller router. Besides all the standard modern router features, the Ridgid has decent LED lighting, comes with a functional edge guide that can be kit-bashed into a number of useful jigs, and has outlasted my Bosch Colts and PC's in use. We use the brass StewMac 1/8" shaft adaptor for 1/8" shank bits.

Here's the first of Chris Paulick's three-part series on building and using the base:

https://www.youtube.com/watch?v=9oRqUK-CMIo

A few observations:

- Plunge bases are not needed...the cut is so shallow (0.050"-0.060") that even a cut starting in the field will not show plunge irregularities with sharp bottoming end mills or downcut router bits. Start and stop any cut under the area to be covered by the soundboard extension, or on the upper centerline where the purfling ends will meet for Weissenborn or J-35 style rosettes where the upper ring butt join is not covered. A scarf can minimize the visual noise here as well, but I find an accurately cut butt joint exactly on the centerline looks purposeful.

- Three ring rosettes need graduated spacing between inner and outer rings...the spacing on the outer ring needs to be about 15% greater than the inner, so a 0.100" inner gap generates a 0.115" outer gap. In practice, this is easier to do the uniform ring size, as the inner ring channel is routed, then center, then outer, and a minor error - up to 0.005" either way is not noticeable (or likely, given below).

- Make up a dummy rosette from 1/2" - 3/4" MDF or scrap ply and 1/4" rod stock. Do all jig setting and trial cuts on the dummy, then mill the top. Most of my rosettes are one-off efforts, but saving the dummy with pin pulled and measurements noted in Sharpie can save some time on identical guitars.

- A 1/8" downcut spiral is great for milling out wider channels, while decimal and fractional inch bottoming end mills (about $6 or so each from various suppliers) work for 0.022", 1/32", 1/16", and 3/32" channels

- Ditto other recommendations on always bordering a trim element with a defined border, such as 0.010"-0.020" black fiber or purfling line...shell or wood set in the top looks unfinished - your eye needs help with seeing the transition, and those scant few thou of edge tells the eye where the rosette is intended to end...intent is important!

- Multi-piece wood rosettes are best milled separately after assembly on a backer of 1/64" aircraft plywood...fiberglass double-sided carpet tape holds everything on a sacrificial MDF milling board and releases with naphtha once the job is done

- For wood rosettes, mill the channel a few thousandths oversize, glue into play, then after that dries, rout the purfling channels and glue them in place...much cleaner than trying to complete the rosette off the guitar.

- Wide shell is at best an acquired taste - most shell rings look wider than they really are due to the surrounding black purfs. I don't go any wider than 1/16" theses days, as wider reminds me of other bad fashion decisions, like super-wide disco shirt collars and wide-wale corduroys.

- Sharp bits are cheap...most downcut fractional bits will mill cleanly for a couple of tops...after that, reserve them for wasting large areas of inlays or toss...a fuzzy edge on a narrow rosette channel cannot be easily fixed

- The 1/4" holes in the jig benefit from a 0.2505" chucked straight shank/flute reamer - the same one you'll want to finish up 1/4" shaft tuner holes...about $20 for a good one from MSC or Amazon Prime
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Re: Rosettes for Newbies

Postby Eric Knapp » Wed May 03, 2017 1:52 pm

Todd Stock wrote:The best of the jigs I've found is the Wells/Karol type, which has a range limited only by the length of the guide rods used...I've used mine on furniture projects as well as instruments. Accuracy in setting is excellent, as the adjustment thread is a 1/4-20 (0.050" for turn). Sylvan Wells has the plans on his website (paid access), but the video from Chris Paulick linked below covers all of the essential measurements, bill of materials, and process to build one. Much more accurate than any of the Dremel-based jigs, and on par with the $$$ solutions from MicroFence.
https://www.youtube.com/watch?v=9oRqUK-CMIo
...

That's a great jig. I read the comments on it and Chris mentions that he wouldn't use UHMW again. He recommends a few other things including Delrin. I just happen to have some Delrin left over from a long-ago project. It is 5/8" thick but Delrin is stronger and machines better so I think it will be fine. I have enough that I'm going to make one for my PC laminate trimmer and one for a blade. I'll see what I like better. I think the precision needed for this task might make me use a power tool, since I already have the trimmer.

Thanks,

-Eric
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Re: Rosettes for Newbies

Postby Todd Stock » Wed May 03, 2017 11:31 pm

Delrin works well...after a lot of use, still tight and accurate. Scrap is not tough to find if you have a plastics place nearby.
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Re: Rosettes for Newbies

Postby Steven Smith » Thu May 04, 2017 11:47 am

Mines made from some scrap Delrin I had, works great.
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Re: Rosettes for Newbies

Postby Eric Knapp » Thu May 04, 2017 11:56 am

Todd Stock wrote:Delrin works well...after a lot of use, still tight and accurate. Scrap is not tough to find if you have a plastics place nearby.


Steven Smith wrote:Mines made from some scrap Delrin I had, works great.

Thanks for the confirmation on Delrin, guys. I need to get the right sized bits too. I don't have an F or a 7. I tried tapping a 3/16 and while it did work it was a lot of work. A 13/64" bit is closer to a 7 and a 17/64" is pretty close to an F. Maybe I'll try those instead. I still need some set screws and 1/4" rod stock.

-Eric
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Re: Rosettes for Newbies

Postby Todd Stock » Thu May 04, 2017 3:48 pm

One thing to add was a mod I did on my jig back in 2006 or so - undersized pivot pins or wear can cause some slop, so adding a small delrin or nylon set screw to bear against the pivot pin becomes a set-and-forget adjustment when the same pivot pin stock is used in the shop.
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Re: Rosettes for Newbies

Postby Eric Knapp » Sat May 06, 2017 6:50 pm

I stole a bit of shop time and made this circle cutting jig based on the videos from Chris Paulick. I already had a Porter Cable laminate trimmer that I used to use to, um, well, trim laminate. :D I might have laid an acre of formica back in the day.

rosette-cutter - 1.jpg
Circle Jig 1

I used what I had on hand which was 5/8" Delrin. I decided to use two set screws and two thumb screws. It feels a little firmer to me that way. The other variation from Chris' jig is I use a gold plated volume knob that I happened to have.

rosette-cutter - 2.jpg
Circle Jig 2

I used a 1/4" pivot point as that was from the 1/4" rod I got. It is press-fit into the Delrin and feels very solid.

I don't have a spiral downcut but yet so I haven't tried it.

I've been hanging on to that Delrin for a long time. I was tempted to chuck it many times since I had no idea what I'd ever do with it. Ha!

Thanks for all the advise, folks. I couldn't have figured this one out on my own. I hope to make a similar jig that uses a knife someday. I like the idea of hand tools but this jig might win. With the right bit this thing will probably make very precise channels.

-Eric
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Re: Rosettes for Newbies

Postby Barry Daniels » Sat May 06, 2017 8:55 pm

Looks good, Eric.

One small but useful thing I discovered is using a couple of small off-cuts from a guitar top (or back plate) which are useful to hold the router above the working surface while you set it up and adjust the radius. The off-cuts keep the protruding router bit from marring the work surface. When you are ready to make the cut, turn the router on, pull the off-cuts from under the router, and let it settle onto the surface as you start to pivot the router base. A tight fitting pivot point lets the router lower slowly keeping the unit from engaging too quickly which could cause a kick back.
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Re: Rosettes for Newbies

Postby Beate Ritzert » Sun May 07, 2017 4:51 am

Barry Daniels wrote:I have two recommendations. 1) Use wood or fiber instead of plastic. 2) Always have black ebony or black fiber purling bordering the edges ...


As You mention fiber, which may not easy to obtain any more: what Do You think of using black cardboard as a replacement?
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Re: Rosettes for Newbies

Postby Todd Stock » Sun May 07, 2017 10:58 am

Do the adjustments on a dummy top - 1/2" mdf or the scrap 12mm marine ply I have left from a recent boatbuilding project are both perfect. Make the adjustment and check on the dummy top, then make the cut on the top. Sounds tedious, but takes just a little extra time and allows momentary instances of cranial/rectal colocation to be identified and remedied prior to project impacts.
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Re: Rosettes for Newbies

Postby Barry Daniels » Sun May 07, 2017 12:03 pm

Beate Ritzert wrote:
Barry Daniels wrote:I have two recommendations. 1) Use wood or fiber instead of plastic. 2) Always have black ebony or black fiber purling bordering the edges ...


As You mention fiber, which may not easy to obtain any more: what Do You think of using black cardboard as a replacement?


Luthiers Mercantile has fiber purling. Cardboard is not the same thing and would not work, though I have never tried it. But cardboard swells and comes apart when it gets wet.

I actually like wood purling better than fiber. But plastic is a distant third.
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Re: Rosettes for Newbies

Postby Todd Stock » Mon May 08, 2017 7:16 am

Vulcanized fiber (aka, fish paper) is used in a number of industries (electronics, power generation and transmission, automotive), so perhaps a search for 'vulcanized fiber' versus the end product for guitar makers might provide EU-based sources for black fiber in suitable thicknesses.
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Re: Rosettes for Newbies

Postby Beate Ritzert » Mon May 08, 2017 10:32 am

Thanks.
Despite of that it is actually pretty hard to find offers here which ship in small amounts, that i actually used card board to cover two headstocks (in low budget projects).
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Re: Rosettes for Newbies

Postby Clay Schaeffer » Mon May 08, 2017 3:43 pm

Phenolic is just paper impregnated with resin. It's pretty tough stuff. I have thought about experimenting with colored card stock to make "lines" for rosettes and soaking them in CA to harden them up.
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Re: Rosettes for Newbies

Postby Bryan Bear » Mon May 08, 2017 4:15 pm

One thing to consider with paper products is how light-fast the dye is. You want to make sure the color will not fade over time. I have a ton of construction paper artwork on my 'fridge that is no longer the same color it was when made. Obviously, this is the bottom of the list of paper products one would try for this application, just food for thought.
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