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Question about cutting and gluing rosettes with purfling
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50915		 Page 1 of 1
Author:  broken1812 [ Tue Aug 21, 2018 1:42 pm ]
Post subject:  Question about cutting and gluing rosettes with purfling
I’m in the process of building my first acoustic and I’m currently working on the rosette.

I will be using a circle cutter to cut a rosette from a stock piece of Black Limba, and then placing purflings on the inside & outside of the rosette.

Since the rosette stock is thicker than the purfling, my concern is if I cut one big channel on the soundboard and try to fit it all in there at the same time, I won’t have enough clamping pressure on the purfling portion since my caul will be only touching the rosette (since the purfling is shorter).

What’s the standard operating procedure for this?

Do I glue the purfling into the Rosette first and then cut it out as one piece to put on the soundboard?

Also - is it safe to assume wood glue is fine for the rosette and purfling?

Thanks
Author:  doncaparker [ Tue Aug 21, 2018 1:55 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
I think a lot of folks do it like this:

1. Lay out the pencil lines so that you know where the inside radius purfling lines will go, where the wood rosette will go, and where the outside radius purfling lines will go.

2. Cut a channel only big enough to hold the rosette, but don't make it a super tight fit.

3. Glue in the rosette, let it dry, and then go ahead and level the rosette down to the top.

4. Set up the router again and rout both the inside and outside radius channels for the purfling. Make sure the bit cuts a little bit of the rosette along with each channel.

5. Glue in the purfling lines, let those dry, then level the purfling lines down to the top and the rosette.

6. Make sure you don't cut out the soundhole plug until all of this is done, because it gets super hard to do it right after the soundhole plug is gone.

Yes, regular wood glue is fine. In fact, be careful using anything else, like super glue. Super glue can stain top woods. The thing to watch with regular wood glue is that it has a lot of water in it, so it will make things swell. Don't make the channels too tight when everything is dry, because everything will swell up when wet with glue, and it can be hard to shove everything in place.

Good luck!
Author:  mountain whimsy [ Tue Aug 21, 2018 2:19 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
Good instructions above. Though if your purflings are narrower than your bit, or even the same as your bit, it is hard to get the correct width on the purfling channel. I prefer to cut my rosette channel so it is an easy fit. I then very slowly expand the outer and inner cuts and do a test fit with the rosette and purfling (inner and outer). I can creep up to the correct dimensions pretty easily to ensure a nice tight fit. I then glue everything up at the same time. The purfling is always a bit taller, but it can be leveled easily with a scraper and/or drum sander. Wood glue is great with wood rosettes (noting the swelling issues above), but if you use shell, I use Devcon Duco Cement (green tube). Dries clear and bonds to the shell really well, and no wood discoloring.

A couple other things to keep in mind.
1) I like to seal the top with a couple of coats of shellac before cutting the channel. Helps with chip out at the channel edges.
2) Run the router at high speed. Again for cleaner cuts.
3) go slowly
4) practice on scrap wood!

-T
Author:  J De Rocher [ Tue Aug 21, 2018 2:28 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
I do the same as Don described above.

His point about leaving a slight bit of room for swelling of the purfling and top wood after the glue is applied is important to remember.

I agree with Tony's advice about creeping up on the final dimension of the channel. That's the way to do it.

Also, always measure the width of the actual pieces of purfling that you are going to use with calipers. I've found that the dimension is not always exactly the width specified by the seller and it can vary slightly from one piece to another and even within a single piece. Doing this helps ensure good clean fits of your purfling. A couple thousandths of an inch can make a visible difference in the fit.
Author:  broken1812 [ Tue Aug 21, 2018 3:09 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
Perfect, thanks for the help everyone!
Author:  Mark Mc [ Wed Aug 22, 2018 12:24 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
I also find that the method Don described works well. An additional tip is to bevel the purfling strip a bit by scraping some material off the inside bottom edge of your purfling strip (the side that is going to end up at the bottom of the channel). I do this by scraping it with a razor blade or cabinet scraper along one edge, for maybe half the height of the purfling material. This means that it slips into the slot more easily, but when you push it down to full depth there will be a slight wedge effect that will give a tight fit and eliminate gaps.
Author:  ernie [ Wed Aug 22, 2018 7:33 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
HAD many difficulties using homemade router based circle cutters and matching the purflings and rosettes to fit exactly . I switched to a cheap metal circle cutters from HF and had individual cutters made and sized to meet the needs of my purfling sizes 1/16in 1/8in etc they are exact within .002 to .004 so that they look very accurate , fast and easy using super glues.I got the idea from watching peter howletts uke videos and his use of individual reworked metal circle cutters
Author:  Woodie G [ Wed Aug 22, 2018 7:53 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
We glue up most rosettes with CA, which requires very little slop in the channel. Provided the top is well sealed with platina or other super-blonde shellack, thin CA has enough penetration and avoids the wait for water-based glues to dry (the BSI brand thin is widely available in hobby shops and is the right viscosity for the job).

If your channels are coming out with too much variation, you might move from a drill press circle cutter to a trim router-based jig like the Wells-Karol (see the linked YouTube video or buy ready-made from Sylvan Wells)...the trim router will also come in very handy for bindings, truss rod channels, etc. The new DeWalt or the Ridgid trim routers have the best depth adjustment and rigidity we've seen on this base - typically +/- 0.001 with two or four flute end mills, and have bits which mill down to 0.022" for replicating 18 style rosette inner and outer rings.

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

If committed to the drill press, some scrap tool steel may be softened, ground, filled, and hardened to make custom-width cutters, but having used them, the Wells-Karol jig is so much more precise and easy to use.
Author:  Bri [ Wed Aug 22, 2018 9:34 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
I am with Woody on this, 2 coats of shellac to the excavated area and glued in with CA.
No clamping required. Have not yet seen any top staining and I typically use very white englemann.
The only caveat is to be sure the rosette is into the bottom of the channel or you can sand through.
Ask me how I know.????

B
Author:  meddlingfool [ Wed Aug 22, 2018 10:36 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
Same as above in regards to CA. Hit the channel with shellac and you’re good to go almost right away as far as leveling. With wood glue you need to wait 24 hrs before leveling, otherwise as the glue dries your rosette can actually sink below the surface.

Another advantage of CA is that you can get all your bits in place and then add glue, whereas with wood glue, you have the added fun of needing to inlay everything whilst the wood glue is getting tacky...
Author:  Freeman [ Wed Aug 22, 2018 11:49 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
What Ed, Brian and Woodie have said. I put on a wash coat of shellac, route the channel and fit all the little pieces (if I'm doing some pearl I'll put in the teflon), push the purfling all the way down, then wick in some thin CA around all the edges. Plane, scrape and sand everything back at one time.
Author:  doncaparker [ Wed Aug 22, 2018 12:13 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
The above responses regarding the use of super glue are obviously helpful for those who want to use super glue. For those of us who like to avoid super glue when we can, and in further answer to the OP's question about using regular wood glue, there is nothing wrong with the use of regular wood glue for this operation. You just have to plan around the properties of that type of glue, which is always a good thing to do, whatever adhesive is used.

I actually like using hot hide glue (with urea added) for rosette installation, but I purposefully limit myself to using just hot hide glue for everything that goes on a guitar, so my views are slanted in that direction.
Author:  DannyV [ Wed Aug 22, 2018 12:27 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
After all your layout and the rosette blank is double sided taped to backer ply.

1 - Cut outside purling channel in the SB. Use appropriate size bit to fit the purling into it. 1.3 mm usually works for me.
2 - Change the depth setting to deep enough to cut the outer rosette radius and do that.
3- Cut the inner purling cannel in the SB.
4 - Repeat 2 in the inner radius.
5- Hog out the remaining wood in the rosette pocket. Done

I cut a small section out of the rosette to make life easier to fit it in. The whole process can be done in about an hour and I'm pretty sure there is no more easy and simple way. If it fits a little sloppy use Titebond and that will swell things up a bit. Otherwise CA is good.

I think this came from a never again spoken of person with the initials B. P. :lol:

And BTW. There is a reason for cutting the outside first. Guess why! DAMHIK :?
Author:  Woodie G [ Thu Aug 23, 2018 7:17 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
More about fit than a specific glue, given earlier comments in the thread, Mr. Vincent - we love our hide glue as well!

One of the little demonstrations done here is a study of just how much common rosette materials expand when soaked with water, and the properties of various glues in terms of expansion/contraction during cure or drying. I found it useful to work through measuring dry and soaked vulcanized fiber/wood purflings, veneer strips, and stuff like solid wood rings to get an idea of the channel width allowance to provision...if nothing else, it makes clear why trying for an exact-fit channel on a solid wood rosette ring can be so entertaining at glue-up with water-based glues!

One other consideration for Titebond and hide in particular - with their limited open time and shrinkage during cure/drying - was evident in a retop we got in for evaluation. The repairman had not seated the Titebond-glued purfling fully into the rosette channels during glue-up, resulting in severe settling of finish over the inner and outer rings. Besides illustrating the need to allow water or acetone-based adhesives to fully dry before further work is done to show surfaces, the sunken rosette ring illustrated the power of adhesive shrinkage to shift trim elements over time where the joint will take some time to fully cure/dry.
Author:  DannyV [ Thu Aug 23, 2018 11:40 am ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
Woodie G wrote:
we love our hide glue as well!


I love my Hold Heet! By the layer of dust on top I can tell precisely when I need to do a thorough cleaning. One day........
Author:  nathanpeirson [ Sat Aug 25, 2018 12:42 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
Has anyone tried building the Rosette with bindings added in a piece of UMHW with the appropriate channel size and depth? Seems like you could accomplish a lot in terms of fit and some leveling before top insertion. Or, is this too much of an extra step?


Sent from my iPhone using Tapatalk
Author:  ernie [ Sat Aug 25, 2018 1:10 pm ]
Post subject:  Re: Question about cutting and gluing rosettes with purfling
If you look at classical guitar construction by john bogdanovich, he preroutes his rosette and purflings on a scrap piece of mdf to make sure it all fits perfectly , as always if its/ your first one practice on scrap .It is very easy to make errors on rosettes
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