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Backstrip inlay
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10122&t=46510		 Page 1 of 1
Author:  BradHall [ Thu Oct 15, 2015 9:03 am ]
Post subject:  Backstrip inlay
The search function didn't answer this for me. Maybe someone here can. I picked up a herringbone backstrip from LMI yesterday. The plates are already glued up and thickness sanded. (KMG rosewood kit). I need to route a channel. My concerns are ;
1. How deep do I make the channel? 1/2 the plate thickness?
2. Route it now while the plates are flat? Will this be an issue when the radius back braces go in?
3. The strip is easily twice as tall as the plates. Is this typical?
4. I am assuming I just plane it close to finished height after glue up, and finish up with a scraper?
Here to learn. Thanks.
Author:  dpetrzelka [ Thu Oct 15, 2015 9:28 am ]
Post subject:  Re: Backstrip inlay
Brad,

This is the same process I followed with my first build - glued plates, routed back strip channel, glued in, hand planed nearly flush with the surface, and then finished with a sharp card scraper. I'm far from experienced, so take all of this as intended - just one way to do it.

1. I routed to at least half the thickness. Be sure to keep in mind where you are in the process - how much additional back thickness will you remove in fish sanding/scraping, final target thickness for the back.

2. Yes, rout it with the back flat. I used a Bosch Colt with a 1/4" carbide down spiral bit, and ran it along a straight edge clamped flat along the back. If you run some test pieces first you can calculate an exact offset from the straightedge and get your channel perfectly aligned. Be aware of the direction of rotation of your router bit as running the router one direction will pull it nicely up against your straight edge. Run it the other direction and it can tend to pull away from your straight edge guide, and give you a less than straight channel.

3. Typical or not, it's not a problem - it will all depend on the dimensions of your plate vs back strip material. You'll plane it down flush.

4. Yes, plane it close - but work lightly, and don't plane down too far, its easy to get into the back wood.



Image

Image
Author:  Hesh [ Thu Oct 15, 2015 11:13 am ]
Post subject:  Re: Backstrip inlay
What Daniel said! Well done Daniel!

The only thing to add is a sharp scraper is your friend.....

Also... some folks just butt joint the decorative back strip in the process of joining the plates. I never had much confidence in this method so I always inlaid the strip as Daniel is showing. More gluing surface, more strength.
Author:  kencierp [ Thu Oct 15, 2015 3:25 pm ]
Post subject:  Re: Backstrip inlay
Adding the Zig Zag and other stripes is one of our options -- anyway I'd suggest a couple of things. Once you decide the center line of the channel use a straight edge on both sides of the router. In years gone by we made plenty of book cases, cabinets etc. the dual edge is just a bit of insurance, you hope to never need.

And as Hesh pointed out some of that back strip inlay can be pretty fragile. We do assemble it in sandwich fashion -- posted below is an early version of our joining fixture which is designed to accommodate stripes of different thicknesses. The trick if you will is to flood the inlay strip with thin CA after the joint is dry. I scrape any glue residue off before applying CA.

http://kennethmichaelguitars.com/Jointi ... alves.html
Author:  BradHall [ Fri Oct 16, 2015 9:37 am ]
Post subject:  Re: Backstrip inlay
Thanks for the quick response. I've done my share of using a router in various applications over the years and know about the hazards involved. I did buy a new trim router for this, my first build. It is my only square base router and setting up a two sided guide will be easy. I've never used down or up spiral bits before. I assume they reduce tear out. Any good online sources you can recommend? The build is coming along nicely. My biggest obstacle is patience. I'm trying to limit myself to about 2 hours or so a day. My natural inclination is to dig in and have to be dragged away. Supposed to be a winter project. If we ever get a winter here in NorCal. Again, I appreciate the help and education.
Author:  Hesh [ Fri Oct 16, 2015 9:55 am ]
Post subject:  Re: Backstrip inlay
We like precisebits.com for bits, service, price, etc.
Author:  kencierp [ Fri Oct 16, 2015 11:10 am ]
Post subject:  Re: Backstrip inlay
We get our 1/4" and 1/2" shaft bits from BAM Carbide -- the smaller ones from Midwest Circuit Tech both sources carry the down spiral (less chip out) versions we prefer. All are used in our 3.5 HP CNC machines, no failures (except when we do something stupid). Very reasonable pricing.
Author:  BradHall [ Thu Nov 05, 2015 11:29 am ]
Post subject:  Re: Backstrip inlay
I routed the channel using 2 guides. I'm here to learn and share what I learn. I pressed the backstrip into the channel to test the fit. Nice & tight. I applied the Duco cement, spread it thin on all 3 sides, and pressed the strip in. Now I had a high spot about 1 1/2" long. Decided to tap it in....Wrong! Managed to separate the plate bond. I cleaned all the glue residue off, re glued the backplate halves. I widened the channel by about 1/2 a sharp pencil line and slightly beveled the sides of the strip. Went is nicely. I used a very sharp block plane to remove the bulk of the excess strip and started with a scraper. I found the process to be both enjoyable and satisfying. It looks beautiful and the rosewood is amazingly smooth and flat. I applied the bevel step to the rosette and scraped it flush also. Once again, nice results. Thanks for the pointers.

By the way, I did order the 1/4" spiral down cut router bit from BAM Carbide. The shipping for a single bit was more than 1/2 the cost of the bit. I did ask for and got a sizable reduction using USPS. I doubt I'll get it again, but nice customer service nonetheless.
Author:  Tom West [ Tue Feb 02, 2016 7:03 pm ]
Post subject:  Re: Backstrip inlay
kencierp wrote:


And as Hesh pointed out some of that back strip inlay can be pretty fragile. We do assemble it in sandwich fashion -- posted below is an early version of our joining fixture which is designed to accommodate stripes of different thicknesses. The trick if you will is to flood the inlay strip with thin CA after the joint is dry. I scrape any glue residue off before applying CA.


I also sandwich and been building since 70's and have never had a back seam failure. I would think that most guitar manufacturing companies also sandwich and I think their failure rate is very low. I may be out to lunch on this assumption. Routing to me just adds another step that could go bad. For me sandwiching works and is easier.
Tom
Author:  BradHall [ Sat Feb 06, 2016 3:45 am ]
Post subject:  Re: Backstrip inlay
I am certainly learning as I go. You are right, the extra step of routing the channel is just more work with failure possibilities. In my case I just wasn't aware that I could have ordered a backstrip completed set with my KMG kit. My next build will be from scratch and lessons learned here will be used.
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