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binding and bearing problem
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=35276		 Page 1 of 1
Author:  stan thomison [ Sun Feb 05, 2012 6:44 pm ]
Post subject:  binding and bearing problem
I have to redo the binding on a guitar and decided after I routed out the old, to redo the herringbone purf also. No problem right? I have routed many, many channels. So I take the .740 bearing, for a .130 channel out, test run it just to make sure (just a habit) and go around the body. However, it only routed about 1/2 the purf and left only a small channel. I test it again, and the test piece of purf is right in depth and width. Go over it again, but not taking out the remaining purf. Check the to make sure the bearing is riding on the side right. Not a problem there, so try again, same result.

So I take the next bearing in line .720 for .140 channel. Test it, OK and go to the body and run it around. Same result of not taking the purf out. So make sure body is square in the cradle and trimmer is square on the binding rig. Not a problem. So then flip it over and do the back, but same deal.

I also have checked and re-checked the bearings diameters to make sure they are good, and the LMI site to make sure I am not having a senior moment and using the wrong size bearings. But I may be having a senior moment there and not reading things right.

I have no idea of what the problem is or what to do. In 10 years of routing out channels with this rig this has never happened.

Any thoughts on what the....I am doing wrong or what the problem may be to fix. I thought to try an even smaller bearing and wider channel, but reluctant to do that and then have a way to wide channel, to far into the body.
Author:  bluescreek [ Sun Feb 05, 2012 6:58 pm ]
Post subject:  Re: binding and bearing problem
Herringbone is around.130 and the binding is .060 so you need .190?
Author:  Colin North [ Sun Feb 05, 2012 6:58 pm ]
Post subject:  Re: binding and bearing problem
Before touching the body of a real guitar, I always test my bearing/router combination on a square piece of wood and check the cuts for depth and width with a digital caliper, could be worth a try.
Just a thought, but cut depends not just on bearing diameter, but on router bit diameter also.....?
Author:  Fred Tellier [ Sun Feb 05, 2012 7:02 pm ]
Post subject:  Re: binding and bearing problem
I think you are not allowing for the depth of the binding. If the HB is .130 and the binding is say .070 you need to cut .200 not .130, or have I misread what you are doing.
Author:  stan thomison [ Sun Feb 05, 2012 7:12 pm ]
Post subject:  Re: binding and bearing problem
dang, I wish there was a way to delete post. About 2 seconds after I posted, it came to me I forgot the binding width.

Put this in that thing that goes in here about dumb butt of the month contest. Along with posting such a stupid thing as easy to figure out. But I use .080 binding. So .210 total for purf channel and think about .530 bearing.

Yea Colin, I do test cuts and check them each time. I have been down the road of not checking before. Not a pretty thing.


I am doing a batch of 6 now, and this was the only one I had a problem with. For some reason the binding just did not set well in the channel. My wife and the guy getting the guitar didn't see it and he didn't care. He is one of my disabled vets I build for. But I could see it and I thought about leaving it, but I lost sleep over it and decided to redo the binding and purf to just make sure. It may be a freebie for the guy, but I do the same effort as the commissions for money.
Author:  Trevor Gore [ Sun Feb 05, 2012 7:20 pm ]
Post subject:  Re: binding and bearing problem
So that makes it two senior moments, right, Stan?

I use a look-up table for this stuff to avoid what you just did. My table says use a 0.54" or a 0.52" bearing (for the LMII cutter) depending on the binding thickness I'm using. Saves me having to think on the days my brain doesn't feel like it! ;)

To get a better "sit" in the channel, try relieving the inside corner of the binding/purfling (i.e. sand/scrape off the inside corner so it's not pushing the binding/purfling out)
Author:  stan thomison [ Sun Feb 05, 2012 7:49 pm ]
Post subject:  Re: binding and bearing problem
Trevor, yea those things are getting more common.

I was telling my wife today while looking up the channel stuff I needed to print out the LMI chart so I don't have to go to the computer every time I do these things. As you know in batches there can be different schemes, though most of mine are pretty standard. It had been awhile since a HB purf job. So after this nitwit thing, I printed and put it in plastic so readily available.

In the batch coming up, there are 3 different binding and purf schemes to go on. So now I will be ahead of the game. Hopefully.

Do you just round off the inside bottom corner of the binding. I have been putting an angle on the bottom inside on plastic stuff, but did that on this batch with some wood binding. I don't know why this one didn't sit right. Like I said, it was me knowing more than anyone else seeing it. But it bothered me, so changing it. Hate doing that with really good and curly koa. Such a waste.
Author:  Trevor Gore [ Mon Feb 06, 2012 7:50 am ]
Post subject:  Re: binding and bearing problem
stan thomison wrote:
Do you just round off the inside bottom corner of the binding.

Yes, or a small bevel if I use a scraper.

Depending of the curvature of the top or back (backs with high curvature tend to be more problematic) because of all the complex slopes, even if you have a router jig that keeps the axis vertical you can get channels cut where the included angle in the corner of the rebate is greater than 90 degrees, even though the vertical axis ensures an even cut depth. It tends to be worst around cutaways. Some of these you have to square up by hand to get a real tight fit.
Author:  Dave Stewart [ Mon Feb 06, 2012 9:22 am ]
Post subject:  Re: binding and bearing problem
I keep a sample stick handy that has a 2" long section of the step made by each successive bearing. Good for testing the actual binding combos before anything is set up.
Author:  Link Van Cleave [ Mon Feb 06, 2012 1:32 pm ]
Post subject:  Re: binding and bearing problem
Quote:
Depending of the curvature of the top or back (backs with high curvature tend to be more problematic) because of all the complex slopes, even if you have a router jig that keeps the axis vertical you can get channels cut where the included angle in the corner of the rebate is greater than 90 degrees, even though the vertical axis ensures an even cut depth. It tends to be worst around cutaways. Some of these you have to square up by hand to get a real tight fit.


The included angle in the rebate is determined by the cutter. The cutter doesn't care what the back or sides are doing. If the cutter is ground at 90° then that is what it will cut. No matter how you tip the router the bit will cut a 90° rebate. It may be tipped relative to the sides or top but the included angle will be 90° And if your jig keeps the shaft of the bit parallel to the sides then the included angle between the side of the guitar and the bottom of the rebate will be 90°. The angle between the side of the rebate and the top or back will of course vary depending on curvature.
L.
Author:  Trevor Gore [ Mon Feb 06, 2012 6:57 pm ]
Post subject:  Re: binding and bearing problem
Link Van Cleave wrote:
The included angle in the rebate is determined by the cutter. The cutter doesn't care what the back or sides are doing. If the cutter is ground at 90° then that is what it will cut. No matter how you tip the router the bit will cut a 90° rebate. It may be tipped relative to the sides or top but the included angle will be 90° And if your jig keeps the shaft of the bit parallel to the sides then the included angle between the side of the guitar and the bottom of the rebate will be 90°. The angle between the side of the rebate and the top or back will of course vary depending on curvature.

Sorry, Link, but the geometry dictates otherwise.

The problem is worst when working the binding route on a cutaway on the back of the guitar that has a lot of back panel doming and body taper.

The router set-up in that situation looks like this when the router is mounted in vertical axial bearings (drawer slides or similar) which keeps the axis of the router parallel to the plane of the sides.
Attachment:
Router.jpg

I can most easily explain the geometry problem by making some analogies. Suppose you cut the binding channel (at the cutaway, approaching the neck) with a router bit of the same diameter as the binding is thick and the cut was approached at that tilt angle. In that situation, a section through the bottom edge of the rebate would look like this:
Attachment:
Cut_1.jpg

Now increase the diameter of the router bit and what you get is what I see:
Attachment:
Cut_2.jpg

In most cases, the out-of-square is not enough to be troublesome, but in some cases it is.
Author:  stan thomison [ Mon Feb 06, 2012 7:19 pm ]
Post subject:  Re: binding and bearing problem
Thanks Trevor. Makes sense.
Author:  Link Van Cleave [ Tue Feb 07, 2012 2:16 am ]
Post subject:  Re: binding and bearing problem
Quote:
Sorry, Link, but the geometry dictates otherwise.


No need for sorrow.

I gave a poor example and was trying to say if you tilted the router off of vertical, perpendicular to the direction of travel the angle would still be 90° Saying it this way was confusing for sure. When you said vertical I assumed you meant plumb not just in plane with the sides.
I realize how you can get the cut you illustrated but wouldn't you have to tilt the router. Tilt the router and run it horizontally. It would cut a cove for sure. Very much like how one can cut a cove on a table saw. I don't see how you can get the cut you illustrated if the router shaft stays plumb. That being said if you tilt the router and follow curve of the back that would seem to minimize the cove affect if the shaft of the router was at a radiant to the curve of the back.
No ?
Author:  Trevor Gore [ Tue Feb 07, 2012 4:50 am ]
Post subject:  Re: binding and bearing problem
Link Van Cleave wrote:
I realize how you can get the cut you illustrated but wouldn't you have to tilt the router.

Well, the router and the work piece have to be tilted relative to each other. The router stays upright (in its sliding bearings) but the work piece (the guitar back, usually) changes tilt as different parts of it pass beneath the router. Mostly, this is not a big issue and goes unnoticed, except when you have large tapers and large domes on the back, when it creates the effect I drew.
Link Van Cleave wrote:
if you tilt the router and follow curve of the back that would seem to minimize the cove affect if the shaft of the router was at a radiant to the curve of the back.

Yes, using a hand held router like that minimises the coving effect, but then you run into the tilted rebate effect (rebate side not parallel to the guitar side). Again, in most cases, especially with fairly wide bindings this is no real problem and having a wedge router base helps. But if you are using narrow bindings and high domes the scraped down binding can have a thickness differential that is hard to disguise.

At one stage or another I've tried most of the rebating techniques and they all have a downside, some more apparent than others. The router in vertical sliding bearings works well enough most of the time and is my current method. When I have to fix some "coving" its usually not over any great length and takes just a few seconds with a sharp chisel.
Author:  pvg [ Tue Feb 07, 2012 12:04 pm ]
Post subject:  Re: binding and bearing problem
It appears to me (maybe I'm mistaken?) that Trevor and Link are "using" 2 different router bit profiles; Link's description seems to assume a square bottom to the bit while Trevor seems to be describing a radiused bottom.
Apples and oranges? What am I missing?
Being in the process of building my first guitar, these discussions are important to me as I hope to discover what problems are "lurking" and how others have dealt with them. beehive
Binding channels are obviously one of the problematic areas judging from the amount of discussion there is on this subject in this and other forums.
Any elucidation here would be appreciated.
pvg
Author:  Trevor Gore [ Tue Feb 07, 2012 5:08 pm ]
Post subject:  Re: binding and bearing problem
pvg wrote:
It appears to me (maybe I'm mistaken?) that Trevor and Link are "using" 2 different router bit profiles; Link's description seems to assume a square bottom to the bit while Trevor seems to be describing a radiused bottom.
Apples and oranges? What am I missing?

We're both using "square bottom" router bits, but you only get a flat bottomed channel if the relative motion of the work piece and the router axis remain perpendicular to each other. If one tilts (in the case I described it is the curvature of the work-piece causing an effective "tilt" relative to the cutter) you cut a channel with a curved bottom, just like you can cut coves with a Safe-T-Planer by tilting the drill table (or with a table saw by passing the work-piece obliquely over blade, as Link pointed out).

Have a look at the pics again and you'll see what I mean, or take a flat bottomed router bit, tilt it, then imagine the shape of the cut you'd get if you dragged it along at that tilt angle.
Author:  pvg [ Wed Feb 08, 2012 1:25 am ]
Post subject:  Re: binding and bearing problem
Okay, thanks Trevor; now I understand. I think Link also explained it, but I'm a little slow... I was assuming the router shaft and the sides were staying vertical, but there's obviously no law that requires this :oops:
Again, I appreciate these discussions, because they help me to visualize and understand the processes that are going to present themselves eventually.
regards to all
pvg
Author:  Ken Franklin [ Wed Feb 08, 2012 1:58 am ]
Post subject:  Re: binding and bearing problem
When the sides are parallel to the router bit axis the back slants most between the upper bout and the waist. To address this problem I first route the channel with the sides that way, parallel to the router bit axis. Then I clamp the body so the area between the upper bout and the waist is parallel to the table top and route that area only. This makes for a flatter bottom in the channel with the added benefit of more consistent binding height when using an LMI bit and guides.
Author:  theguitarwhisperer [ Wed Feb 08, 2012 10:43 am ]
Post subject:  Re: binding and bearing problem
I see what Trevor's talking about. Took me a second, but it makes sense. What you would need to eliminate that effect completely would be a system that keeps the bottom of the bit vertical to the sides as well as parallel to the top, something like this: http://www.luthiertool.com/binding%20cutter.html or this: http://www.kennethmichaelguitars.com/portattach.html.
I have the Kenneth Michael version, works perfectly.

I also have the Stew-Mac Tru-Channel gimmick, which apparently has this particular quirk described in this thread, but I've never used it.
Author:  Link Van Cleave [ Wed Feb 08, 2012 12:09 pm ]
Post subject:  Re: binding and bearing problem
Trevor is right. I was not considering one plane in my visualization. (there are a lot of potential ways the router can move and tilt.) It has been a good discussion for me because it made me really get my head around it. I never really bothered to get the complete picture. Use the jig, mostly understand the situation but don't get the complete picture. It was like when you are going somewhere and someone else is driving and you don't have to fully pay attention. You can get there but do you really have complete picture of where you are.
Ken Franklin and I where talking about it and he pointed out something I was missing as well. It is always a good thing the learn more.
L.
Author:  Trevor Gore [ Wed Feb 08, 2012 7:11 pm ]
Post subject:  Re: binding and bearing problem
theguitarwhisperer wrote:
I see what Trevor's talking about. Took me a second, but it makes sense. What you would need to eliminate that effect completely would be a system that keeps the bottom of the bit vertical to the sides as well as parallel to the top, something like this: http://www.luthiertool.com/binding%20cutter.html or this: http://www.kennethmichaelguitars.com/portattach.html.

I've used that type of thing and also the good ol' rolling pin router and they work pretty well, except around tight cutaways on highly domed backs. If you can get the thing in there, you tend to be able to follow just one surface, not both. Most of my backs are on a 3 metre radius and nearly all my steel strings have cutaways. The vertical slide router arrangement works well enough most of the time and is quick. The few seconds it takes to square up the bottom of the channel over the short length that requires it is a very small hassle given the other benefits.
Author:  theguitarwhisperer [ Wed Feb 08, 2012 7:38 pm ]
Post subject:  Re: binding and bearing problem
Trevor Gore wrote:
theguitarwhisperer wrote:
I see what Trevor's talking about. Took me a second, but it makes sense. What you would need to eliminate that effect completely would be a system that keeps the bottom of the bit vertical to the sides as well as parallel to the top, something like this: http://www.luthiertool.com/binding%20cutter.html or this: http://www.kennethmichaelguitars.com/portattach.html.

I've used that type of thing and also the good ol' rolling pin router and they work pretty well, except around tight cutaways on highly domed backs. If you can get the thing in there, you tend to be able to follow just one surface, not both. Most of my backs are on a 3 metre radius and nearly all my steel strings have cutaways. The vertical slide router arrangement works well enough most of the time and is quick. The few seconds it takes to square up the bottom of the channel over the short length that requires it is a very small hassle given the other benefits.


I haven't messed with cutaways on my own stuff. Thanx for the heads up.
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