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Driving the mini-bus (…or why I love the OLF)
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=55912		 Page 1 of 3
Author:  bcombs510 [ Tue Sep 19, 2023 9:25 am ]
Post subject:  Driving the mini-bus (…or why I love the OLF)
Sharing here a tip I found in the archives. I was looking for information on ways folks sand the X brace into the dish. I usually sand each leg individually using a disassembled combination square to keep things vertical. This works well enough:

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However, I came across this gem from 2012 where Link Van Cleve shared an approach that I had to try. Here is the original post: viewtopic.php?t=34929

This worked so well. It takes about 10 minutes to set it up but went so much faster than anything I’ve tried to date. I used blue tape and CA instead of double stick tape which made it even easier to release. I used 150 grit stickit in the dish. Any questions let me know.

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Brad


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Author:  banjopicks [ Tue Sep 19, 2023 9:41 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
So many ways of doing everything. Awesome!
Author:  Chris Pile [ Tue Sep 19, 2023 10:15 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Working smarter instead of harder.
Author:  DennisK [ Tue Sep 19, 2023 10:16 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
What happens to the sandpaper in the dish? That stuff's expensive!
Author:  meddlingfool [ Tue Sep 19, 2023 11:05 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Brad,

Do you not have a radius dish completely covered in sandpaper? How do you put in the final profile of your top and back?
Author:  bcombs510 [ Tue Sep 19, 2023 11:06 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
DennisK wrote:
What happens to the sandpaper in the dish? That stuff's expensive!

I reuse it, it can be stuck and removed a number of times. I put shellac on the dish so it doesn’t pull up any of the MDF.

Yes, it’s like 35 cents a foot so wouldn’t want to pull and toss with each brace. :)


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Author:  bcombs510 [ Tue Sep 19, 2023 11:07 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
meddlingfool wrote:
Brad,

Do you not have a radius dish completely covered in sandpaper? How do you put in the final profile of your top and back?

I do, but it’s like 60 grit or something. I use that for the rims, but for braces I’ve always used the 120-150 stickit.


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Author:  Barry Daniels [ Tue Sep 19, 2023 11:10 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Sorry to criticize but that is a lot of unnecessary effort. I have one side of the dish entirely covered with sandpaper and plop the X-braces fitted together firmly (but without glue) and sand away. The braces are plenty stiff enough to sand without a backer.

Also, you don't need to sand the brace on the exact position in the dish. The arch is the same everywhere.
Author:  Bryan Bear [ Tue Sep 19, 2023 11:25 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
I just sand my braces on the relatively rough paper of my radius dish. I scrape the surface immediately before gluing so I'm not worried about a bad surface from rough sandpaper. Someone will come along and say that scraping compromises the precise shape obtained by the radius dish. But. . . remember that if you sand your brace in the dish, then offset that brace from the dish by the thickness of the top you are gluing to, the radius is not the same anymore. Don't get too hung up on machinist precision here. Get a close shape with a good surface and clamp it all down.
Author:  bcombs510 [ Tue Sep 19, 2023 11:30 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Barry Daniels wrote:
Also, you don't need to sand the brace on the exact position in the dish. The arch is the same everywhere.


This has not been my experience. It’s possible it’s because I’m using the radius workboards in the gobar deck and not a true “dish”.

Conceptually I get the idea that the dish is a true radius and you should be able to put it anywhere, it’s just not what I see in practice.


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Author:  Barry Daniels [ Tue Sep 19, 2023 11:53 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
My home made dishes are accurate enough to give the same arch all over. Makes it a bit easier.
Author:  SteveSmith [ Tue Sep 19, 2023 12:01 pm ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
I just mark the radius on the brace then plane them to the line. Run a pencil mark down the brace then a quick clean up in the dish and they’re done. To keep things square while sanding I just use a block of wood with a good square edge.


Steve
Author:  Bryan Bear [ Tue Sep 19, 2023 12:13 pm ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
SteveSmith wrote:
I just mark the radius on the brace then plane them to the line. Run a pencil mark down the brace then a quick clean up in the dish and they’re done. To keep things square while sanding I just use a block of wood with a good square edge.


Steve


I actually do that too on the longer braces . Planing close to the curve saves a ton of annoying sanding. Especially after you learn not to plane the edges of your thumb off because you are an idiot and didn't pay attention to how you were holding the brace as you planed :)

I actually used to just plane to the curve and glue them in. Once I made a motorized radius dish for the rims (which meant I have a dish with sandpaper in it) I started sanding the final radius. I don't even bother planing the finger braces and bridge plate, I just sand those in the dish now.
Author:  banjopicks [ Tue Sep 19, 2023 12:21 pm ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Mmm... motorized dish. Insert Homer Simpson and donuts. Same reaction here. Someday I hope.
Author:  Ken Nagy [ Tue Sep 19, 2023 12:56 pm ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
I saw a video on getting the arch on a back. He cut the braces long enough to get some bend in them, and placed them in the linings. Then he put glue on the top of the braces, and glued the back on, starting at the middle toward each end. When the glue was dry, he lifted the back off: because the braces were not glued in; with a perfect arch. He added the strip down the middle, and rough cut the outline. Then he glued the back on.

It will only work on backs. It could work if you just use ladder bracing.
Author:  SteveSmith [ Tue Sep 19, 2023 1:28 pm ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Bryan Bear wrote:
... I don't even bother planing the finger braces and bridge plate, I just sand those in the dish now.


I don't plane those either.
Author:  doncaparker [ Wed Sep 20, 2023 7:17 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
I never sand braces in the dish. I always profile the bottoms of the braces to the appropriate arch (28’ radius for top braces, 15’ radius for back braces) using templates, then glue them in using the go bar deck, with the dishes in the bottom of the deck. The lower deck of my go bar deck is essentially a torsion box, so I don’t get any deflection from the proper arch due to the pressure from the rods. The upper deck does bend a noticeable amount. The braces fit great. If I sanded them in the dish, I would likely roll an edge, so I don’t run that risk.
Author:  bcombs510 [ Wed Sep 20, 2023 8:26 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Probably going to open a can of worms with this, but… in the spirit of learning… :)

I want to better understand how braces that are cut to a template on a table saw or routed, and / or braces that are sanded “anywhere in the dish” are still well fit when glued down.

I can visualize how a brace that is cut or sanded to a specific radius over its whole length should fit well anywhere in the dish, but this only makes sense to me if the brace is 1pt wide. Of course braces have width which means that if sanded in a dish in a specific location it is also taking the radius across the width of the brace. That is essentially why I’ve always sanded in the location of the dish where the brace will be later glued.

For those that don’t sand the brace in location… Is this just being overcome with clamping pressure? Is it so slight it doesn’t matter? Am I just not understanding the geometry at play?

Brad


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Author:  banjopicks [ Wed Sep 20, 2023 8:39 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
That same radius exists there as well so there's still a perfect fit.
Author:  jfmckenna [ Wed Sep 20, 2023 8:51 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
bcombs510 wrote:
Probably going to open a can of worms with this, but… in the spirit of learning… :)

I want to better understand how braces that are cut to a template on a table saw or routed, and / or braces that are sanded “anywhere in the dish” are still well fit when glued down.

I can visualize how a brace that is cut or sanded to a specific radius over its whole length should fit well anywhere in the dish, but this only makes sense to me if the brace is 1pt wide. Of course braces have width which means that if sanded in a dish in a specific location it is also taking the radius across the width of the brace. That is essentially why I’ve always sanded in the location of the dish where the brace will be later glued.

For those that don’t sand the brace in location… Is this just being overcome with clamping pressure? Is it so slight it doesn’t matter? Am I just not understanding the geometry at play?

Brad


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I never thought about the radius across the thickness of the brace but when you think about it, it's tiny and insignificant. I use a hand plane to plane the arch in the braces to a marked line from a template. Then I test fit to the solera (I don't use a radius dish so it is different for different brace locations) and adjust as necessary. If there is a tiny gap at the end of the brace I don't worry about it and let clamping pressure take care of it. Gaps in the middle though are not acceptable.
Author:  bcombs510 [ Wed Sep 20, 2023 8:52 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
banjopicks wrote:
That same radius exists there as well so there's still a perfect fit.

Would you mind to elaborate a bit on that?

Here is another example, the side profile. If you look at a side template which accounts for the radius and the taper of a side, the shape is not uniform to a specific radius. It’s got a high spot near the waist area. That’s because the waist area is near the center of the dish and therefore less material would be removed when “driving the bus”. The edges of the bouts are at the outside of the dish and therefore more material is removed.

There must be a YouTube video out there that can show me the light! :D


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Author:  bcombs510 [ Wed Sep 20, 2023 9:00 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
jfmckenna wrote:
…but when you think about it, it's tiny and insignificant.


Thanks, John. Yeah, I’m coming around to this as well, that it just doesn’t matter, especially at a 30’ radius.


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Author:  banjopicks [ Wed Sep 20, 2023 9:07 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Sorry, you'll have to wait for someone else to go into depth on this. It just makes sense to me that it works. That's all I've got :-)
Author:  doncaparker [ Wed Sep 20, 2023 9:33 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Brad—

In my view, the width of the brace (1/2” max for the UTB; less for the rest) is not enough distance for a difference between flat and a 15’ radius to matter. I hope that makes sense. In practice, I know it works. There is no daylight under my braces.
Author:  banjopicks [ Wed Sep 20, 2023 9:38 am ]
Post subject:  Re: Driving the mini-bus (…or why I love the OLF)
Every place the brace is touching has the same radius, Flat would be a microscopic problem.
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