Double Bass Purfling, how far from edge can I go?

[bengreen]

Hi all,

I'm making a Grandfather Lott copy per Peter Chandler's plans.

It has square corners and a flat back. The back is shaped and bent. My edge overhang is 5mm and combined rib and lining thickness is 6mm. The plans call for 3mm overhang and purfling inset 10mm from the edge (though pics I have of the bass look like the overhang is larger).

I started out trying to teach myself purfling by hand but the yuck results convinced me I could either spend the next year trying to develop some technique or cheat and get a dremel attachment. No contest. I got the StMcD attachment and it works great. I draw the purfling channel with dividers, continue them into the corners with french curves, cut the corners by hand and continue them where they meet the scribed line with the dremel.

I've made several reproductions of the c-bout profile and about 8" above and below on first pressboard and then maple flat stock. I've been practicing purfling on these pieces and feel ready to take the plunge and purfle the actual back. My miters are decent, not perfect, but I'm tired of stressing and need to move forward. Time is an issue too. Taking this to Oberlin and would like get the back and ribs mated in a week so I can lose the mould, get top linings in and top outline finalized before I leave in two and a half weeks.

So, the quandry (finally): a purfling channel 15mm in from the edge lets me use the dremel almost to the point in the corner, but I know it's too much. A 10mm inset leaves me about 2 inches of hand work and the sharp point looks kind of lost in all that fat corner area. A 12mm inset gives me about 1.25 inches of hand work to do and looks more pleasing to my eye, filling the corner better with a slightly blunter point.

I know I can do whatever looks pleasing on the flat back but how about on the top? At what point am I infringing into the re-curve area? How far in can I risk going before my 2.5mm high (with hopefully 2mm into the top) purfling is either gouged away carving the re-curve or is structurally untenable? On my Pollmann the purfling seems like it's sitting over the lining but there's a lot of chip carving inboard of that confusing the picture. Any ideas? Thanks.

 

[1st Bass]

Hi, Ben! Awfully good to see you!

On violins, violas, five-string fiddles and cellos, I make the purfling the same distance in from the edge as the (average) thickness of the plate edge. Perhaps that is what I did on my one and only bass, too, but I can't recall. That would put your purfling pretty much on top of the linings, too, if that is OK.

Perhaps, in the long run, it will depend upon how closely you want to follow the model you started with.

Have a good time in Oberlin!

 

[bengreen]

Hi, Ben! Awfully good to see you!

On violins, violas, five-string fiddles and cellos, I make the purfling the same distance in from the edge as the (average) thickness of the plate edge. Perhaps that is what I did on my one and only bass, too, but I can't recall. That would put your purfling pretty much on top of the linings, too, if that is OK.

Perhaps, in the long run, it will depend upon how closely you want to follow the model you started with.

Have a good time in Oberlin!

Hi Chet,

Thanks, I'm looking forward to it and thanks for the rule of thumb.

I think this one might break the rules though because of the flat corners.

I'm new here and never have tried uploading photos but let's see what happens.

First the ribs (with my sorry attempts at inserting the linings into the corner blocks):

And some of the purfling trials

For my taste 10mm from the edge leaves too much empty space in those big corners . I like the 12mm better but I'm just worried about how it would work on the arched belly. I was initially toying with square corners to mimic the ribs but ended up thinking it looked a little corny (though the furniture makers in my shop voted for that one)!

If I make it through this with my pride and sanity semi-intact, I want to have a second go at this model except I think the corners will be a bit less monumental next time.

 

[1st Bass]

Looks Great! Hope I get to hear it play someday! I surely enjoyed listening to you playing at Fort Collins.
I'm not sure I understand your notations, but I think the upper one looks better...FWIW.

 

[Ortsom]

Hi Ben,

this sounds like a very interesting project, and I will follow your thread with interest and admiration!

I'm ashamed to admit that I have never done proper purfling myself, hence my council on it is inherently unreliable.
Yet I believe the purfling should be at the outside of the recurve, which would be approximately above the linings, typically (as Chet says) 1 edge plate thickness inward from the edge of the finished plates. I would suggest the outside edge of the purfling roughly 7-9mm inward from the edge of the finished plates (which is actually a bit more than Chandlers plate edge thickness). To me all your examples seem to be a bit far inwards.

If it helps in your process of purfling, you could consider the make the plates initially a bit wider, and remove a few mm after the purflng is in. Or maybe glue a temporary strip of ply around the blades for the purfling. Not sure if that helps in the corners of the side blocks. Maybe your choice of wide sideblocks necessitates the purfling to follow a similar line there, with a short extra piece, perpendicular to & in-between the conventional ones.

 

[james condino]

Lookin' good!

Be careful with the Dremel. Everyone who owns one for detail work like this buys them thinking they will solve all of their problems and then shortly finds out that they have major issues with runout in the bearings that challenge everyone. Also be very leary of the Stew Mac inlay bits. I had a set of brand new ones last month that I used to cut a guitar rosette with a student and I also had a brand new set from Whiteside. The Stew mac left unacceptable chatter and gaps and the Whiteside done with the exact setup were incredibly accurate and crisp, like it was a cnc machine. As for the purfling, I find it much better for my own work to glue the top on the ribs and then make the adjustments for overhang and inlays after it is set and a lot of days, it is just easier and faster to use a sharp exacto knife and a steady hand.

With a big project like this it is important to remember that the fussy details are nice, but really it is all about the sound and playability. I just strung up in the white a new smaller instrument this week that I spend hundreds of hours on the details but for the last six hours that I have played it, I have not once even looked at the details because I am so enchanted by the voice and the setup is dead on. I have to figure out how to delicately tell one of the best shops in the country that I am going to keep this one for my self and we'll work out another for them later...

Congratulations, building your own bass is a fantastic life journey and lesson!

j.
www.condino.com
www.kaybassrepair.com

 

[bengreen]

Thanks Ortsom and Chet,

You've got to the nub of the problem: the large corners.

The back is already shaped and bent with the back break brace glued in. The shape was set by running a pencil with a 5mm spacer around the ribs. I made a beginners mistake carving the corner blocks beefier than they should have been. And it reflects in the shape of the back plate.

Peter Chandler was a super nice guy. I had called him with a question about the bass early on and he mailed me 8x10 color photos of the original at his own expense. But he was in his 80s when he drew these plans and they have issues. The bass went in the closet for years while I concentrated on bow making and playing. When it finally came out (so to speak) Peter was gone, so I couldn't get corrections from him. If I had properly looked at those pics before cutting, this wouldn't have been such an issue, but at this point I've got to deal with what I've got.

I can adjust the spacing of the purfling from the edge quite easily. I'm using a dremel with a 2.2mm routing bit and an adjustable router guide (same as in the Stew Mac catalog) for everything but the corners and under the button. It's a little nerve wracking but works great. The only limitation is that it has to be done while the plate is still separate from ribs.

Chandler gave a 10mm edge to purfling distance (with 3mm plate/rib overhang) and it does seems to be accurate when I use calipers to measure on the photo and then scale it up. But you've given me and idea. My overhang is a bit larger than Chandlers. I had made one of those test boards with a 3mm overhang and then used that 2mm extra at the corners to give them more of a shark fin look (it's the white one in the pic at the bottom of the stack with the squared corners facing towards the back of the bench). So it's possible to massage that corner shape a little and maybe the point from the closer edge spacing won't look so dwarfed there.

Gotta go hit the trash bins and see if my furniture making cohorts have left some suitable pickins' there to make one more test piece with slightly tapered corners. It would mean varying overhang at the corners but I can live with that.

BTW Ortsim, Roger Hargraves made a pdf book of his adventures making an Amati copy bass. It's on his web site and includes his method of gluing purfling which I'm finding to be a life saver. He glues the purfling strips ahead of time and lets them dry. He also cuts them so that there's a vertical scarf joint in the middle of the "C", i.e. there's two pieces of purfling in the one bout. Then it's simply a matter of inserting the purfling into the channels. If the length isn't exactly right, no problem, the scarf joint takes care of it. Lastly activate the glue by brushing with hot water. It's brilliant. No ticking time bomb of hide glue gelling while you're struggling to get the pieces lined up.

 

[bengreen]

Lookin' good!

Be careful with the Dremel. Everyone who owns one for detail work like this buys them thinking they will solve all of their problems and then shortly finds out that they have major issues with runout in the bearings that challenge everyone. Also be very leary of the Stew Mac inlay bits. I had a set of brand new ones last month that I used to cut a guitar rosette with a student and I also had a brand new set from Whiteside. The Stew mac left unacceotable chatter and gaps and the Whiteside done with the exact setup were incredibly accurate and crisp, like it was a cnc machine. As for the purfling, I find it much better for my own work to glue the top on the ribs and then make the adjustments for overhang and inlays after it is set and a lot of days, it is just easier and faster to use a sharp exacto knife and a steady hand.

With a big project like this it is important to remember that the fussy details are nice, but really it is all about the sound and playability. I just strung up in the white a new smaller instrument this week that I spend hundreds of hours on the details but for the last six hours that I have played it, I have not once even looked at the details because I am so enchanted by the voice and the setup is dead on. I have to figure out how to delicately tell one of the best shops in the country that I am going to keep this one for my self and we'll work out another for them later...

Congratulations, building your own bass is a fantastic life journey and lesson!

j.
www.condino.com
www.kaybassrepair.com

Thanks J.

I'm a player and agree entirely and can't hear that too often.

My bits are from International Violin. I don't know where they source them but so far so good. They leave a bit of frayed strands at the rim of the channel that are easy to scrape but the channel itself looks pretty crisp. I'm going to try sizing with a bit of dilute hide glue and/or shellac next test to see if I can lose the strands. I'm using a friends older dremel which so far hasn't shown any obvious runout but I don't want to wreck his tool either with too much testing.

I'm using a 5mm overhang rather than the plan's 3mm because I want a little wiggle room for the glue up. In reality, I'll probably leave it at that, but I may try to come in a bit at the corners after the corpus is closed to get something more articulated looking.

In an ideal world I would love to do this all by hand but my skills just aren't there (yet) and time is an issue. I need to get the back glued on so I can finalize the outline of the top and get as much of the preliminaries (flattening, plane the ledge around the edge) before I take it up to Oberlin in two weeks where there will be plenty of guidance available for the arching and graduating, the two jobs I don't want to try to learn on my own.

Just for finality, do you think the purfling on the top needs to be over the ribs/lining or is 2 or 3mm inside a problem?

Thanks,

Ben

 

[robobass]

I would also look at other rotary cutters besides the Dremel. I haven't used tools like this for such precision work as cutting purfling channels, but did use them extensively in a former life as a packaging model maker. Jewelers prefer the brand Foredom ($$), and cringe at the mention of Dremel, and there are air powered "pen grinders" which might also be worth consideration. The air tools typically run at much higher speeds, which might reduce the effects of runout, but at the cost of torque. They can be quite cheap and very useful. Then there are dental grinders which run on air, but have high torque. Probably expensive, but for your application might be worth every penny. Maybe your dentist has an old one? My last dentist (now retired) used to give me a Ziplock full of old scrapers every time I came in

 

[bengreen]

I Jewelers prefer the brand Foredom ($$), and cringe at the mention of Dremel

Thanks. I played with a Foredom with the expensive guide at ISB Ft Collins and had to retreat in ignominy after unintentionally tilting it and massively screwing up the purfling channel on one of the two tops there. It took all of about a millisecond. One of the other, more capable, guys there had to patch it and clean up my mess (think it might have been Matthew Tucker). The Stew Mac guide is actually fairly massive and resists tipping. If you use it with a foot switch (I do) and go slow and careful, it works great. Or at least it has so far. All my mess ups have been with my hand work.

 

[Don Kasper]

Hi, Ben! Awfully good to see you!

On violins, violas, five-string fiddles and cellos, I make the purfling the same distance in from the edge as the (average) thickness of the plate edge. Perhaps that is what I did on my one and only bass, too, but I can't recall. That would put your purfling pretty much on top of the linings, too, if that is OK.

Perhaps, in the long run, it will depend upon how closely you want to follow the model you started with.

Have a good time in Oberlin!

Forgive my ignorance (I don't build or repair...), is there any sonic or structural purpose associated with purfling? Or, is it purely decorative?
(I would probably just use a Sharpie!)
Thanks to ALL/anyone with the patience, guts, skills, tools, and temperament, required to make "something" out of "something else".

 

[bengreen]

Forgive my ignorance (I don't build or repair...), is there any sonic or structural purpose associated with purfling? Or, is it purely decorative?
(I would probably just use a Sharpie!)
Thanks to ALL/anyone with the patience, guts, skills, tools, and temperament, required to make "something" out of "something else".

I've only encountered three purposes.

1. Yes, decorative.

2. Because it's a glued in ply crossing the grain of most of top and back it can have the effect of resisting a crack that starts on on the perimeter from progressing inward, sort of like a stop-drill hole prevents a crack in acrylic or sheet metal from enlarging.

3. To put new makers like me properly in our place when we find we're so bad at it.

Okay, maybe just two but....

 

[Don Kasper]

I've only encountered three purposes.

1. Yes, decorative.

2. Because it's a glued in ply crossing the grain of most of top and back it can have the effect of resisting a crack that starts on on the perimeter from progressing inward, sort of like a stop-drill hole prevents a crack in acrylic or sheet metal from enlarging.

3. To put new makers like me properly in our place when we find we're so bad at it.

Okay, maybe just two but....

Re: #1 - Understood.
Re: #3 - That's COLD! Gee, it's almost like the Performance World!
Re: #2 - has anyone ever considered the installation of (a) cross-grain strip(s), inlaid into and across the width/grain of a NEW top plate, from "inside" the top, as a way to perhaps minimize those top cracks that are often seen on many instruments? These would not be seen from the outside of the instrument, but would be purely structural reinforcements. Is there an aversion to such Frankenstein-ian thoughts in the Luthier World?
Thanks for your time and expertise.

 

[james condino]

Yeah...ditch the Dremel and Stew Mac base and your already $200 investment. Get a $300 Foredom; everybody loves 'em. Then get the $200 fancy router base for it, then after get a $400 micrometer fence, then really go big and have Bishop Cochran custom make you one of his kick @$$ alloy cnc'd $400 basses and then...........realize tool mania caused you to have spent almost $1500 for little spinning noisy handheld machines that took 87 hours of working your crappy day job so you could do a task that one of my mentors taught me how to do with a 50 cent exacto blade and a popsicle stick in about 3 hours that was everything you could ever make a metaphysical Mr Miyagi's karate kid zen task into. Like old Eugene used to say to me, "Why would I ever need to go to yoga class or take up fly fishing when every day I get to French polish my guitars...."

j.
www.condino.com
www.kaybassrepair.com

 

[Ortsom]

Recognising the dangers of tool mania, yet coming back to the purpose of purfling:

• Chipping. When going through the rigours of life, basses & other violins often get chipped at the edge. With purfling in place, that chip normally stops at the purfling. Those chips are often seen in older instruments, and it is effective in areas where the purfling crosses the grain, as well as where it is parallel to the grain of the plate. This for me is the prime purpose, and for that reason the purfling should best not be inward of the rib/lining.
• Cracks (Ben's #2). Purfling may aid in preventing the propagation of cracks in those areas where it crosses the grain of the plate. Not sure how well it does that, and cracks still happen. Of course not all cracks start at the edge of the plate.
  
• Flexibility. Purfling is thought to enhance flexibility in that area, which will allow the plate to vibrate more freely. While I recognise it will somewhat enhance flexibility in areas where the purfling crosses the grain of the plate, I personally feel this is a minor effect. Yet there are whole schools of thought that believe purfling is essential for precisely this reason.
• Decorative/ornamental, as mentioned. There are many examples of extra purfling on or just below the button, which are mostly decorative. (But if it extends below the block, there it will also enhance flexibility a bit.)
• It gives us something to talk & worry about. (Ben's #3.)

The document Roger Hargraves published on the making of the bass he built together with René Zaal is a fountain of wisdom and guidance; it is an impressive work and I thank him for publishing it.

 

[Jeff Bonny]

This is definitely a thread I'm doing more listening than talking. I do have many, many hours doing fine work grinder work though and will say do not waste time or money on anything other than a Fordom.

 

[keiranohara]

I'll jump on to the foredom band wagon and add more to the shopping list with the Invalid Link Removed purfling attachment. We've modified ours to the maximum extent to optimize for basses and it will cut a channel about 10mm edge to center.

The foredom is certainly more skookum tool, the difficulty with more power and speed is mistakes can happen faster. I try and treat those as learning experiences. Good luck and see you in Ohio.

 

[Jeff Bonny]

The foredom is certainly more skookum tool, the difficulty with more power and speed is mistakes can happen faster. I try and treat those as learning experiences.

Quite true...you will say "ah ****!" more than once while you're getting comfortable with it. But with a selection of much lighter hand-pieces and a foot pedal for the speed once you are comfortable you have much more control. Plus the thing will last a lifetime and then some. Mine's over thirty years old.

 

[Ortsom]

Yes Keiran, that does look like a slick tool, but at a price. Thanks for the pointer.

 

[bengreen]

I'll jump on to the foredom band wagon and add more to the shopping list with the Invalid Link Removed purfling attachment. We've modified ours to the maximum extent to optimize for basses and it will cut a channel about 10mm edge to center.

The foredom is certainly more skookum tool, the difficulty with more power and speed is mistakes can happen faster. I try and treat those as learning experiences. Good luck and see you in Ohio.

Hi Keiran,

Good to hear from you.

I love weird words and you totally got my attention here: skookum!

I'm finding everything from powerful, ultimate, brave, reliable to monstrous and prison.

So, one of the above? All of the above?

Seriously, this (and I mean the wandering thread) is fun but I've really just been trying to get an answer to a specific question without taking advantage and bothering everyone on the Oberlin mailing list.

It's the purfling for this square cornered bass: should I make sure it doesn't stray inboard of the lining? The plan's arching profiles barely , if at all, show any recurve. But the plans have proven problematic and the photo shows strong recurve.

So if you were where I am right now, ready to purfle, edge overhang 5mm (which I could reduce to 3mm later if needed), edge thickness about 7-8mm (have to double check when I get to the shop), combined rib and lining width 6mm, big blunt corners, how far in from the edge would you set the outside of the purfling (or center if you're more used to using that)?

And same for flat back as arched front?

This is the thing I really need to settle ASAP.

Thanks, and looking forward to seeing you,

Ben