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268312 | "Ed O'" <edo@e...> | 2019‑04‑21 | I need some engineering type help with switched magnets for jigging |
Kind of on the periphery of the charter so please do a direct reply if you have info and think it is too far afield. I am attempting to create a work holding device or jig to hold some stuff while I work on it with hand tools. I think the basic question is: do any properties of what a magnet attaches to affect the strength of the bond? Short question that gives a feel for what I want to do: Magnetic bases for dial indicators are switched so you can engage or disengage the magnetism. Is the hold strength of the magnet affected by the mass or thickness of the iron that it will attach to? In other words if I use a piece that is 2 x 3 x 1/8 will it result in less grip than say using a piece that is 2 x 3 x3/8? Longer question with more specifics: When using a hand screw the reach is limited by the length of the jaw from the threaded rods. I am attempting to create something that would not have this throat limitation. I am using a Magswitch (https://www.amazon.com/Magswitch-8110005-MagJig -150/dp/B001B8HMKG/ref=sr_1_2_sspa?keywords=magswitch&qid=1555873085&s=gateway&s r=8-2-spons&psc=1">https://www.amazon.com/Magswitch-8110005-MagJig-150/dp/B001B8 HMKG/ref=sr_1_2_sspa?keywords=magswitch&qid=1555873085&s=gateway&sr=8-2-spons&ps c=1) in one jaw and a piece of mild steel in the other jaw. I am currently using 1/8 thick steel. If I try and hold two pieces of veneer between the 2 jaws it holds well, 2 pieces of 1/8 thick stock and it holds, but not well. Does altering the thickness of the mild steel side effect anything? Here is a picture of the prototype holding some 1/4 inch stock (it actually will be 2 x 1/8+ pieces that I want to work, that I need to maintain the orientation of and cannot use glue or carpet tape to hold together) https://www.edoii.com/auction/magswitch/img_1981.jpg https://www.edoii.com/auction/magswitch/img_1982.jpg https://www.edoii.com/auction/magswitch/img_1983.jpg https://www.edoii.com/auction/magswitch/img_1984.jpg I bought a piece of 3/8 flat bar stock from HD and the hold appears to be slightly better than with the 1/8 bar stock I already used. I don't want to cut it up and make another prototype just to find out the hold is going to be just nominally better. Any engineering types out there that can point me in a direction? Thanks, Ed O' |
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268313 | curt seeliger <seeligerc@g...> | 2019‑04‑21 | Re: I need some engineering type help with switched magnets for jigging |
> > Ed has a cool project in mind, but I don't quite know where my undergrad texts are right now... > I am attempting to create a work holding device or jig to hold some stuff > while I work on it with hand tools. > One thing you seem to be running into is magetisms inverse-squared relationship between force and distance. So the force between the jaws holding something 1/8 the of an inch thick is 4x weaker than holding something 1/16th of an inch thick. You might think of it from the other direction-- how much force do you want for holding your work, and how thick will it be? That'll tell you how strong your magnets need to be. A typical clamp generates about 400 lbs or more of force, and if your piece is 1" thick and your vise faces are 3x5 inches, you'll need a metric boatload of Gauss to make the vise work. Might give these folks site a try: https://www.kjmagnetics.com/blog.asp?p=how-much-will-a-magnet-hold They have a calculator that shows a 3x5x1 inch magnet of their strongest material seems to get you to the ballpark https://www.kjmagnetics.com/calculator.asp?calcType=block Thanks for sharing this, bucko. Seems like a fun adventure to be on |
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268314 | Erik Levin | 2019‑04‑21 | Re: I need some engineering type help with switched magnets for jigging |
Ed asked a series of questions regarding switched magnets (no electrons used, and with a history to the beginning of the 20th Cty)starting with: > I think the basic question is: do any properties of what a magnet attaches to> affect the strength of the bond? Yes. Many properties. > Magnetic bases for dial indicators are switched so you can engage or disengage > the magnetism. Is the hold strength of the magnet affected by the mass or > thickness of the iron that it will attach to? In other words if I use a piece > that is 2 x 3 x 1/8 will it result in less grip than say using a piece that is 2 > x 3 x3/8? Yes. Thinner material will have less hold, but beyond a certain thickness, the difference is minimal. What thickness depends on the particular magnet. I have some that will hold at near maximum force on 1/8" material, and others that have only a small percentage (maybe 25%) on on 1/8", but hold near maximum on 1/4" to 3/8". The strength of the permanent magnet determines the actual force, but the distance between the poles and their size are the primary factors in how it reduces with the surface you put the magnet on and what gap (magnetic) there is between the magnet poles and the steel. > If I try and hold two pieces of veneer between the 2 > jaws it holds well, 2 pieces of 1/8 thick stock and it holds, but not well. > Does altering the thickness of the mild steel side effect anything The force drops off rapidly as the distance between the magnet and the steel increases. Thicker steel wont help much beyond a certain point, and you are probably already there. You may do better with a switchable that used a different pole configuration, or another magnet on the other part rather than steel, if you can find a switchable (or modify one such that it has) with the opposite pole configuration. A switchable with a different pole setup might do better as well. *** This message was sent from a convenience email service, and the reply address(es) may not match the originating address |
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268315 | Christopher Dunn <christopherdunn123@g...> | 2019‑04‑22 | Re: I need some engineering type help with switched magnets for jigging |
Ed I agree with Curt and Erik. The force exerted by a magnet will increase with the thickness of the metal it's attracted to, up to a point. Beyond that more metal doesn't help. Making the metal bar longer might help to reduce the distance that the returning magnetic field lines need to travel, or it might not do anything depending on how the magnets are configured. We have some magnets at work (McMaster part number 5848K93 i believe). By accident, two of them came together and it took two of us pulling as hard as we could to get them apart. We made this mistake only once and now store them separate wooden boxes. If you put one in your fist, small pieces of metal will leap off a table a few inches away, but it takes little force to remove the metal from the back of your hand. The point being, it doesn't take much of an air gap to reduce the force a magnet exerts. An electromagnet allows for very high levels of force with the ability to turn them on or off, but they aint cheap. Thanks, Chris |
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268318 | Kirk Eppler | 2019‑04‑22 | Re: I need some engineering type help with switched magnets for jigging |
Lee Valley has a little bit on the use of cups around their magnets to increase their strength. Click on the "tech" highlight in the ordering section. http://www.leevalley.com/US/wood/page.aspx?p=58750&cat=1,42363,42348 These may help, if you embed these in the far jaw of your vise, away from the magswitch. Also, what about 2 Magswitches, or are they opposed and push each other away? Could you reconfigure them to be a pair? Or two on the same side to pull your plate? Here is a page on magnetic field strength that may give more clues. https://www.kjmagnetics.com/blog.asp?p=surface-fields-101 We did a thing back in HS on field shape, with metal shavings on top of a thin piece of ?plastic? and could see the shape of the field change wiht the magnets. We didn't have supermagnets back then, so I don't know if it would be as dramatic as now, or more so. I had an industrial magnet that the teacher wouldn't let near his setup. Finally, when trying to separate two magnets, go sideways, not away. Rather than lifting them like LPs on a spindle, slide them and scratch the LP. Much easier. KE On Sun, Apr 21, 2019 at 12:56 PM Ed O' |
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268322 | Don Schwartz <dks@t...> | 2019‑04‑23 | Re: I need some engineering type help with switched magnets for jigging |
On 2019-04-22 5:41 p.m., Kirk Eppler via OldTools wrote: > Finally, when trying to separate two magnets, go sideways, not away. > Rather than lifting them like LPs on a spindle, slide them and scratch the > LP. Much easier. LV suggests a little jig for this. Drill a hole the thickness and diameter of one of the magnets, drop a stuck pair in it, and slide the top one away. Works every time - and no blood blisters! Don -- “It is better to be killed by a woman with a knife than by a man with a gun.” Che Guevara A thermometer is not liberal or conservative. - Katharine Hayhoe Of all the tyrannies that affect mankind, tyranny in religion is the worst. Thomas Paine Being offended doesn't make you right. |
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268324 | Ed Minch <ruby1638@a...> | 2019‑04‑23 | Re: I need some engineering type help with switched magnets for jigging |
Luthiers (I play one on television) use magnets a lot for clamping small pieces. Sliding the two apart is the trick they use. The ones I have are about 7/16” diameter and 1/8” thick and the sliding is very easy for this size. Ed Minch |
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