Official Luthiers Forum!
http://www.luthiersforum.com/forum/

3M stickit sandpaper ok for finished top?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=25494		 Page 1 of 1
Author:  ayavner [ Thu Jan 14, 2010 9:12 pm ]
Post subject:  3M stickit sandpaper ok for finished top?
I wanted to find out if anyone knows - is that self-adhesive sandpaper that comes on a roll (gold stickit i think) too sticky to be stuck to a finished top?

Reason i ask, is i am ready to install the bridge, and I wanted to place some sandpaper right there so I could sand the bridge down to the right radius at that spot, but I am afraid this stuff might be too sticky.

Anyone have any ideas for this? I know i have read about it, but how it was done and with what escapes me at the moment.

Thanks guys!
Author:  Hesh [ Thu Jan 14, 2010 9:59 pm ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Here's how I floss a bridge and I wouldn't use the self-stick 3M for a several reasons. What you see in the pic, self explanatory, works fine for me. Also, use some tape pieces to mark on the sides of the sand paper the exact place on the top that the bridge will go. Then do you flossing as close to the final location as possible. Not every spot on your dome is going to be exactly the same and flossing in the bridge's final location gets a nice, tight fit.

Attachment:
2006-11-26_205938_DSCN2085.jpg
Author:  Steve Brown [ Thu Jan 14, 2010 10:13 pm ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I did that ONCE! Do I need to say more? Use Hesh's method.

Steve Brown
Author:  Pete Brown [ Thu Jan 14, 2010 10:31 pm ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Pink sandpaper AND a banjo? wow7-eyes

Cheers
Pete
Author:  Terence Kennedy [ Fri Jan 15, 2010 12:59 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I usually cover the area with 3M low tack drafting tape and stick the sandpaper to that.
Author:  Mattia Valente [ Fri Jan 15, 2010 6:24 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I have a small 'dome' for rough-sanding the shape (scrap of MDF, 5 minutes with your radius dish will get you there) and finish up with some sandpaper stuck to the top with low-tack masking tape.
Author:  Hesh [ Fri Jan 15, 2010 7:47 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
A couple more points if I may please.

I have a block with a dome in it too but stopped using it several years ago because even though I build my tops in a dish that may say what radius it is once braced and voiced my domes are not exactly what the dish is/was. Instead the dome is what it is, what ever that is, and that's fine with me. So I now have to fit my bridges to a dome that is unknown in it's radius. Also gluing bridge plates etc. change the dome in specific areas so again with lightly built and braced tops the dome may not be what we build it to in a dish.

Flossing on the top ensures that what ever the top is the bridge will fit well. I do my flossing prior to finishing the guitar and since my shop is always in the 45 - 48% after bracing (I take the RH lower to brace more in the 42% range) after the guitar is finished I let it acclimate to my shop again for a week or so before gluing the bridge. This way the bridge is glued on in the same RH as it was flossed to fit the top. You can check this out for yourself by flossing to fit at one RH and then checking the fit after you finish the guitar but before it is back in controlled RH - the bridge won't fit well....

Lastly I prior to gluing the bridge lightly scrape the bridge underside and the top where the bridge will be glued. A freshly prepared joint (15 min is what I shoot for) glues better with HHG and some others.

Pete bro I'll get you for that on the ANZLF... :D
Author:  ayavner [ Fri Jan 15, 2010 8:34 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Some great advice here, and glad I asked!!

Thanks guys, its starting to look like a guitar now!!
Author:  Terence Kennedy [ Fri Jan 15, 2010 9:41 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Your right hand position looks pretty weird Hesh. Are you a real banjo player or do you just use it as a chick magnet.
Author:  Hesh [ Fri Jan 15, 2010 9:55 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Terry chick magnet..... :D [xx(] :shock: :roll: :) Just like guitars are.... [xx(] :D
Author:  ayavner [ Fri Jan 15, 2010 10:06 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
A couple questions on finer points:

1. I presume you want to do this with as little pressure as possible, as not to flex the top while sanding? I would think that could cause inconsistency?

2. Do we shoot for basically a consistent pattern of scratches along the bottom of the bridge so we know that all points have been touched?

3. Since my top is finished, do I remove the finish from that spot first, then tape down the paper? I would think probably get the bridge sanded to fit first, THEN scribe the lacquer for fit, but thought I would ask, for my own notes.

thanks!
Author:  Dennis Leahy [ Fri Jan 15, 2010 10:07 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Note that Mattia said he starts by using the dome-shaped sanding block, then finishes up by using the top. To me, best of both worlds: the sanding block takes off the bulk of the material, so you're not rubbing the bridge on the top for 200 strokes, and the final fitting is done on the actual soundboard for a custom fit to that one soundboard's actual dome.

To ayavner's question: I would definitely not stick PSA sandpaper to a top, finished or otherwise. A little trick when you have to break the rules and stick something to something else, and want less tack than the adhesive has: stick the tape or PSA adhesive side to the palm of your hand a few times. That transfers some oil to the stickum, so it won't have as much tack. If you want a lot less tack, stick it to your T-shirt or blue jeans first.

Dennis
Author:  Terence Kennedy [ Fri Jan 15, 2010 10:20 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I sand on the finished top before scribing and finish removal. I also start with a domed sanding block and fine tune on the top.
Terry
Author:  Hesh [ Fri Jan 15, 2010 10:24 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I missed that Dennis and yes using a block for the heavy lifting is a great idea. My bridges unless I make a one-off are pre-radiused to 25' so I have very little flossing to do.

Adam bro:

1) Correctomundo! :D

2) Use a white pencil or any pencil and make lines across the bottom of your bridge. When the lines are gone your bridge will fit. Be sure to make lines all over on the bottom including the corners of the wings since that is generally the last place to contact the paper.

3) No - tape the paper with low tack tape on the finish and do not remove the finish first where the bridge will go or you will have a ridge under the paper not unlike when the folks who put down your carpet were too lazy to pick up the trash on the floor first.... You will feel it.... [headinwall] This happened to me and I made the builder come back, lift the carpet and remove the workman's 1/4 pounder wrapper that they left under my carpet.... :x :D Sorry I digressed...
Author:  WaddyThomson [ Fri Jan 15, 2010 1:52 pm ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I'm making classical bridges, but I do something similar. I have an insert that I put under the belt of my 4x36 sander, that is the approximate radius of my tops. Then, before mounting the bridge, I do the "flossing" right on the top, which only takes a little work to get a perfect fit.
Author:  Hank Mauel [ Fri Jan 15, 2010 2:19 pm ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Another $.02 tip..
you might want to get a couple old bridge pins, plastic or whatever, insert them in #1 & #6 holes and cut off the ends so they are flush to the bridge bottom. They will give you a couple of points to grab onto (handles) while sanding as most bridges are pretty smooth and curvy, making it hard to hold them.
I put my right hand thumb outside #6 and my middle finger outside #1 and pinch together. I then put downward pressure with my left hand as I sand the bottom to fit.
It also saves on sanded knuckles. ;)
Author:  Eric Reid [ Sat Jan 16, 2010 1:08 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
Todd Stock wrote:
Another school of thought: the bridge is the biggest, beefiest brace on the guitar - I figure if it's there already, I might as well use it to maintain my design top radius. In any event, once the strings are on, any bridge radius done without string loads will yield as large an error as one done to design radius, so why not try to retain the design geometry?


To take Todd's idea one step further: I've seen a lot of successful classical guitars that were built with the top dead flat, and had a dome pulled into them by clamping on an over-curved (17' radius) bridge. It sounds crazy, and it makes figuring neck angle (with a Spanish integral neck joint) a little more complicated, but the end result is a neatly recurved top with no increased tendency to shift or crack as the years go by. Richard Brune believes that this is how Hauser built Segovia's guitar. I think Mr. Brune also suggests that Torres may have experimented with the idea.
For my own bridge contouring, I use the face of the instrument as a step in fitting arch-top bridges, but stick to templates for glued bridges. In both cases, I do a final scraping of the center contact area to insure that there will be good contact at the edges ( and to leave a clean--not sanded--gluing surface).
Author:  Ken Franklin [ Sat Jan 16, 2010 1:25 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I do the same thing as Hank but I use a wood saddle to get a grip. I also use a reverse radiused board with slightly greater radius to presand. That makes it easier to insure a tight fit in the corners.
Author:  Hesh [ Sat Jan 16, 2010 7:48 am ]
Post subject:  Re: 3M stickit sandpaper ok for finished top?
I just added a bridge fitting toot in the toots section and I would invite you guys, all of you, who have added value to this thread with your ideas/methods to add to the toot so that all may benefit from the collective knowledge here and of course have it be in a location that they can easily find.

http://luthiersforum.com/forum/viewtopic.php?f=10117&t=25513

Many thanks
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/