Burly strong magnet managers

[David Farmer]

Here is my take on an aid to work with sketchy strength magnets. This is a split off from the Uke crack thread.

They can be positioned as though they are weak magnets then the crushing force applied in a controlled way.

I have incrementally worked my way up to pairs of 3/4"diam. x3/4" tall n48 magnets.

Wood is Hickory ( had it in the pile and it has heroic split resistance).

Nuts and bolt are non magnetic stainless.

White cap is UHMW plastic (packing tape works too)

Steel cups protect magnet corners and knock the mag field down in directions that are not helpful.

Continuing to screw the bolt down forces the magnet out of the steel cup.

[Mike Kolb]

Very clever!  

[Mark Fogleman]

Thanks David! This looks good for preventing the pinch.

[Russell Kingery]

Smart! Very smart, I'm making a pair!

[Hesh Breakstone]

Very cool David!!!  I want some!!!

[Rico]

These are beautiful and ingenious.

[Lee Gendvilas]

Hi David. This is a great idea and I would like to try to apply it to broken guitarron bridge I'm working on. Would you be interested in helping me understand if it's possible to apply the magents to my current project?

[David Farmer]

This not my invention. Just my version of it. I think Frank Ford made the first version I saw years ago.

If there is a benefit to the ones I have made it's that they are quickly and easily made with simple woodshop tools and off the shelf hardware.

For a long time I used smaller weaker magnets for some tasks but working with truly strong ones is difficult  "free hand"

 Over the years I have developed a whole set of reverse motor skills for working through a mirror, but I find I'm still learning to "think in magnet".

It takes a while to internalize what they want to do in various multiples and mixes of polarity. Their desires are often not clear until it's too late, and very strong!

Lee,

I'm sure it's possible to use magnets for a bridge re-glue but that would be more complicated for me than typical soundhole clamps.

Is there a reason "normal bridge clamping is restricted?

I usually reserve magnet's for difficult to reach areas. I would think on a Guitarron you could drive a pickup truck inside and set up shop.

Pictures always help cut to the chase.

[Hesh Breakstone]

Thanks again Dave!!!

[Lee Gendvilas]

Hi David. Thank-you very much for replying! Sorry about the previous post, I should have been clearer in my question and sent pictures. I have a post (July 1st-this summer) about the guitarron and what I believe I need to do is get the top laminations back together then get the bridge on. Frank replied "cyanoacrylate flood makes sense - it can tie the layers back together, fill gaps, and hold the bridge on". Since cyanoacrylate sets up quickly and this will be a larger area than I normally glue, I am looking for the quickest way to clamp the laminations together. So I just thought I'd ask if you thought using a magnet setup might be quicker. I went to the CMS magnetics website and saw that they come in many pull force strengths. So if it's possible to use magnets, is it possible to calculate the pull force thru wood, or would it be trial and error?

Looking forward to your reply.

[David Farmer]

Lee,  you touched on the biggest problem using magnets for bridge clamping. The force of magnets drops extremely quickly as the distance between them is increased.

They work great for crack alignment because they are only the thickness of the top apart.

I think you will get universal agreement here that regular clamps are the way to go on your project.

Large quantities of CA glue don't set nearly as fast as small thin layers but I have never re-glued a bridge with it.

Here are  pictures of a bridge clamping set up for speed. In this case, hide glue.

The clamps are just swung into place and a few turns on each can be done in seconds.

[Rico]

Nice setup, David. Can I ask you what are those black clamps? I like the look of them. I've been looking at f-hole clamps as you suggested on the other thread. They seem cool, but not particularly versatile. I'd prefer to load up on clamps that have wider applications and these black ones look strong yet small. Can you point me in the right direction?

[David Farmer]

Rico, those are clamps from Stewart Mcdonald. They are good for guitars but I don't think they will fit on a Ukulele bridge. they are most likely too long.