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I have a client who wants to have Purflex http://purflex.net/Purflex/Purflex_Strips.html installed on a classical commission. I am currently set up with a Williams-style jig, laminate trimmer and LMII binding cutters. Those cutters only allow a channel up to 0.230", so what are my options?

I suppose switching to Josh's stationary jig (http://www.canadianluthiersupply.com/products/binding-jig) is one option. My reservation is that it might be tricky to use with a neck on the body. While I hate having to control that spinning bearing, the Williams jig gives me lots of control near the neck and when approaching intersecting purfling lines. And I'm used to it!

Are there other 1/4"-shank rabbet cutters with bearings that folks use for these wide channels? Maybe http://www.leevalley.com/en/wood/page.aspx?p=30112&cat=1,46168,46176 -- would be great if the LMII bearings fit!

Other ways to skin the cat?

Tim



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I've used a wide rabbet trimming bit similar to the Lee Valley one that you show. It worked quite well. I needed to install purfling on a Lacote style guitar and my specialty Stew Mac bit did not go wide enough.

Scared me to use it! You do need to ensure that your linings are plenty wide.

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Expectation is the source of all misery; comparison the thief of joy.
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I use a Williams style binding jig with a slight modification to the router carriage that allows you to use a spiral bit to cut a channel of any width. Check out the photos on Dave White's website. I stole the idea from him.

http://www.defaoiteguitars.com/page32.htm

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sweat the small stuff.

You can always use a schneider gramil and a chisel.

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Will you have side purfling? If so, and the total height of the side purfling plus binding is 11/32" or more, maybe you could cut the binding/side purfling channel first and then run the bearing along the wall of the binding channel to cut the top purfling channel. That would increase the possible width of the purfling cut by the thickness of your binding. I don't know if that would be wide enough for your needs. I have the LMI cutter and bearings too. I checked mine and the vertical distance from the bottom edge of the cutter blade to the bottom of the bearing is 9/32". So if your binding plus side purfling is 2/32" or more taller than that, it could allow you to make a purfling cut that's wide enough and deep enough for the Purflex (which according to the web site is 0.070" thick).

If your binding jig gives good control over the router, maybe it wouldn't be as precarious as it might sound. Just an idea.....

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The LMII cutter is 1.000" diameter with a 0.187" inner bearing diameter. Rabbeting bits are available in in a number of sizes including 1.250" and 1.500" diameter with 1/4" shafts at big box home centers and woodworking specialty stores - these bits may take LMII bearings without issue and even Stewart MacDonald bearings with a .250" x .187" sleeve adapter. The common 1/2" diameter bearing on flush trimming bits for laminate (one comes with every Ridgid trim router we use) will fit on your LMII bit as well.

Our bearing size versus channel size spread sheet shows the following channel width combinations using common sized and LMII binding bearings with LMII 1.000", standard 1-1/4" diameter rabbeting bit, and standard 1-1/2" diameter rabbeting bits, respectively:

Bearing Size/LMII Bit Channel Width/Freud 1.25" Bit Channel Width/Freud 1.50" Bit Channel Width:

0.500"/0.250"/0.375"/0.500" (standard 1/2" diameter guide bearing)
0.540"/0.230"/0.355"/0.480" (LMII bearing)
0.580"/0.210"/0.335"/0.460" (LMII bearing)
0.620"/0.190"/0.315"/0.440" (LMII bearing)
0.625"/0.188"/0.313"/0.438" (standard 5/8" diameter guide bearing - may require sleeve adapter)
0.660"/0.170"/0.295"/0.420" (LMII bearing)
0.700"/0.150"/0.255"/0.400" (LMII bearing)
0.740"/0.130"/0.235"/0.380" (LMII bearing)
0.750"/0.125"/0.230"/0.375" (standard 3/4" diameter guide bearing - may require sleeve adaptor)

You might wish to double-check my numbers - I am pulling them from a printed table in the building guide that I have not yet proofed! I also expect that some off-brand bits may not measure exactly 1/14" or 1-1/2" in diameter. Our larger rabbeting bits are Freud and Whiteside branded, and are accurately sized.

We mill these wider channels with several passes when working top woods, and use the smallest bit possible to minimize the shaft deflection of those slim 1/4" shafts under load. In reading the description of the purfling material, it sounds as though the depth of channel will be 0.700" or less, so even on a thin top, that should leave some top wood under the channel.

Good luck with the installation of the purfling, and I would love to see some photos of your completed instrument! I have added a Purflex project to my 'Big List of Things to Do'!

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A constellation only takes shape when one maps the whole.
- Beth Brower

Interesting, Heath, thanks for that!


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This is very encouraging. If I understand correctly, you've found a way to fit the LMII bearings with their smaller 0.187" ID on to the 0.25" spindle on the Freud bits. What does this 0.25 x 0.187" sleeve adaptor look like, and where can one get it? This would seem to be key.


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I apologize if my post was confusing - we are talking about the LMII bit's guide bearing on the bottom of the bit (opposite the shaft) - this bearing is 3/16" inside diameter (ID). I believe you will find that most 1/4" shaft rabbeting bits designed to mill up to 1/2" width rabbets (these would include 1-1/4", 1-3/8", and 1-1/2" diameter bits) will use the same 3/16"/0.187" ID bearings as the the LMII bits.

There should not be a need to use an adapter sleeve for bits such as the Freud 32-100 or similar. We had 1/4" to 3/16" sleeves made up by a local machine shop so that our Stewart MacDonald bearings could be used on the LMII router bits, giving us additional sizes outside of the SM or LMII bearing/bit sets, but IIRC, these may be had from good bearing suppliers, and cut to length. Whiteside makes similar rabbeting bits that should work as well, and the 1/2" diameter bearing on all of our 1/4" flush trimming bits are also 3/16" ID, so a direct fit. We routinely tap these sleeves into and out of the StewMac bearings to get those in-between sizes.

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A constellation only takes shape when one maps the whole.
- Beth Brower

Sounded like an idea, but your cutter must be older or newer than mine. I have more like 3/8" between the bottom of the cutter to bottom of the bearing. Even your measurements might require a much deeper strip than I would normally want on a small classical.


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A little off topic but with purfling that wide how deep do you go so that there is still some top left attached to the lining?

One of the bigger parts of my voicing technique is thinning the edges of the top on the lower bout after the box is closed but before binding. This limits me to thin purfling, usually not over 0.060.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I suppose switching to Josh's stationary jig (http://www.canadianluthiersupply.com/products/binding-jig) is one option. My reservation is that it might be tricky to use with a neck on the body. While I hate having to control that spinning bearing, the Williams jig gives me lots of control near the neck and when approaching intersecting purfling lines. And I'm used to it!

My jig is only designed to cut channels up to .235", which may not be wide enough. And you are right that it would be tricky to use with the neck on.

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Josh House

Canadian Luthier Supply
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House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

We do much the same as Dr. Kennedy, thinning the outer edge of the lower bout to get relatively uniform displacement of the top, and often ending up in the 0.095"-0.105" range on top thickness at the rim. In reading the description of the purfling material, it appears as though the backing is about 0.030" and the design material is 0.040" in thickness, for a total of 0.070". A channel depth of 0.055" would appear to leave about 0.025" of the design and about 0.040"-0.050" of top wood under the channel, depending on the final thickness of the top at the rim.

So the question is how much top wood needs to be left under the channel to deal with loads and abuse? I can see the case for extending the linings beyond the channel, but would like to understand if it is really necessary. For wider purflings like herringbone or radial purflings, we usually mill the channel depth to retain at least 1/16" top thickness, but that does not appear to be an option here, given the fixed 0.030" backing material. How thin can the design material be sanded and still look good? My math might be off, but the difference in stiffness between 0.040" and 0.063" is close to a factor of 4, so that 0.023" difference appears to be something worthy of concern.

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A constellation only takes shape when one maps the whole.
- Beth Brower

Ok, that clarifies things. I already have a complete set of LMII bearings, so it sounds like I simply need a larger diameter Freud or Whiteside cutter -- easy.
Thanks, Woodie!



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