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Decorative backstrip process
http://www.luthiersforum.com/forum/viewtopic.php?f=10122&t=53073		 Page 1 of 1
Author:  flemsmith [ Sat Apr 04, 2020 8:34 pm ]
Post subject:  Decorative backstrip process
First kit guitar. Getting ready to do a center strip on the outside of the back. What I have is a rosewood strip, about 0.160"wide and .038" deep, bounded on both sides by a similar strip of cherry, although a little taller, about 0.060" high, then BWB on both outsides edges, 0.040" wide by 0.080 or so tall, I forget that number, but it's irrelevant to my current question(s). On a practice hunk of mahog, I routed a channel that's about 0.479" wide and 0.034" deep. Dry fitting shows it's a pretty tight fit, all except a couple of inches at the lower bout that have a bit of a gap I'd estimate to be a little more than 0.010". So I'm thinking some ebony sanding dust, but I'm not clear on the best process for one of not so considerable talent.

What I'm thinking is I'll do is a little shellac in the channel after routing, dry fit all the parts, taped down crosswise so they're stable, but with gaps between the tape that let me use CA and Accelerator to stabilize the components in the channel leaving space(s?) where I see a gap. In the area where I have a gap ( I think it's only one), should I:
1. Use titebond hoping the wood strips will swell a little, then press in the ebony sanding powder? Or
2. Fill the gaps with the ebony powder first and then some light CA
3. Develop some fixture that lets me CA the wood strips together first? That freaks me out a bit.
4. Use some process y'all have had success with that I dunno...

I do know it's gonna be a tight fit that will probably need a little judicious tapping in most of the channel.
Thanks in advance for any advice. Roy
Author:  Alain Lambert [ Sat Apr 04, 2020 9:25 pm ]
Post subject:  Re: Decorative backstrip process
If understand correctly, the gap is in your practice piece of mahog. You have not routed your back yet.
Then the gap is caused by an uneven width of one (or some) of the strips or by some wandering of the router.
What I would do is rout the back a little narrower and sand one( or the two cherry) so the strip acomodate the channel.
Author:  CarlD [ Sun Apr 05, 2020 12:16 pm ]
Post subject:  Re: Decorative backstrip process
Roy, is the back glued together yet? I usually glue the strip between the halves joining them all at once.
Author:  Freeman [ Sun Apr 05, 2020 12:53 pm ]
Post subject:  Re: Decorative backstrip process
I do the same as Carl - sandwich the back stripe between the two pieces of the back. Sometimes it is a little thinner - I just push it down against the backing board and then cover the inside with the cross grain reinforcement. If the insert is thicker than the back it can be sanded down.

I know people do join the back and then route a channel for the backstrap, I think that is doable but I've never done it.
Author:  flemsmith [ Sun Apr 05, 2020 6:59 pm ]
Post subject:  Re: Decorative backstrip process
I did it the way Alain suggested, picking one of the many cherry strips I cut that made the assy a tad too large thru the middle and locked my calipers to the minimum thickness of the strip, then sanded the edges down til it just fit thru my calipers. That gave me a really tight fit I could use CA to mount. My description was on a test piece, but then I routed the real back when I figured I was close enough to make something work. I had quite a few cherry strips similar to those two and had test fitted about 5 of them in conbinations.

Image

I had enough trouble getting a light tight fit between the two plates, I can't imagine how I could use strips of wood mounted totally between the plates and get it light tight. Mebbe if I had a light box, and was using materials that were cut by a process much better than my bandsaw...For now I at least have a process I feel like I can duplicate. Thanks for the response, they were actually helpful.
Roy
Author:  banjopicks [ Mon Aug 17, 2020 9:35 am ]
Post subject:  Re: Decorative backstrip process
I just went through this myself. I will probably never try to put one in after the fact again.
Author:  Tim Mullin [ Mon Aug 17, 2020 12:52 pm ]
Post subject:  Decorative backstrip process
I always inlay backstrips and I’ve done them between 3 and 16 mm in width. I clamp down a heavy steel straightedge on the back as a fence and choose a cutter that is a bit smaller than the strip. After making the first cut, I can then add strips of purfling, binding and tape along the fence to shift the router as much as needed to get the required width. Some tight spots can be eased 1 or 2 thou by running through some sandpaper. Once all the parts press into place, I hit it with CA. With few exceptions, back and strip materials behave well with CA, so no need to use shellac or other sealant.


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