Simple Jig Uses Electromagnet For Clean Angle Grinder Cuts

We like it when hacks are literal hack jobs, put together with what’s on hand to do a specific job. This quick and dirty angle grinder circle cutter certainly fills the bill, and makes decent cuts in sheet metal to boot.

The build starts with an unlikely source for parts – an old automotive AC compressor. The one that [Made in Poland] chose to sacrifice was particularly nasty and greasy, but after popping off the pulley, the treasure within was revealed: the large, ring-shaped clutch electromagnet. Liberated from the compressor, the electromagnet was attached to a small frame holding a pillow block. That acts as an axis for an adjustable-length arm, the other end of which holds a modified angle grinder. In use, the electromagnet is powered up by a small 12-volt power supply, fixing the jig in place on the stock. The angle grinder is traced around and makes a surprisingly clean cut. Check out the build and the tool in use in the video below.

At the time [Made in Poland] recorded the video, he noted that he did not have a plasma cutter. That appears to have changed lately, so perhaps he’ll swap out the angle grinder for plasma. And maybe he’ll motorize it for even smoother cuts.

22 thoughts on “Simple Jig Uses Electromagnet For Clean Angle Grinder Cuts

  1. This AC lamp switch is not designed for DC use, especially with inductive loads. It will fail quickly.

    Don’t hold an angle grinder with a single hand. What if angle grinder kicks back? It’s very likely that magnet will not hold it. Neither will your hands as your grip seems weak and relaxed.

    Do you really trust your welds? Especially when they hold the grinder in a single point.

    Never stand right in the way of a cutting disk. They can and do fail. When they do, they turn into deadly shrapnel.

    I’ve worked for a few years in the ER and saw enough nasty accidents caused by “smart” homemade “jigs” failing. Just because you can doesn’t mean you should. Not with cutting wheel rotating at 12.000 RPM.

        1. Yeah… I guess like HVAC systems… plus needs a starter capacitor on the 120V output circuit… whichever one of the two types used for HVAC systems. Maybe someone can clarify… seems logical from my cruder understanding of electronics.

    1. Could? It will shatter; they do that even if you’re (trying to) cut straight. I use an angle grinder every day and i treat it with the utmost respect. they are dangerous!

  2. I know we always get “safetyOMGlulWTF” comments here on Hackaday, in this case I think they’re very justified.

    The disc on an angle grinder is only supposed to cut in straight lines. Forcing it to cut on a curve is asking the the disc to shatter and painfully pepper any nearby meat containers.

    An electromagnet for holding the spinning wheel of death is also asking from trouble. If that magnet fails the angle gringer becomes a high speed traction wheel, dismembering anything in its path.

    Finally, failure of the electromagnet is highly likely. The power cables ARE IN THE PATH OF THE CUTTING DISC.

    1. When you start cutting the circle with low cutting pressure, the whell probably does not shatter but just grind a wider cutting path than its width. Do not apply to much pressure.
      The operator still has to hold and guide the angle grinder. It’s no self driving car. :-) If the magnet loses power, the result will be no perfect circle any more, but its very un likely that the grinder gets out of control.

      1. I agree, but on my side I would make sure that it’s on a surface that stick or even better clamp the metal sheet… if the whole sheet start to turn it could get ugly. working with metal sheet is dangerous if you do not take care

    2. Cutting curves with an angle grinder in 1mm 2mm steel is fine. You’re not embedding the angle grinder in the sheet you’re touching the top of it.

      Besides which you must have arms of unobtanium if you can free hand cut a perfect straight line with an angle grinder.
      The thin disks bend and flex and are great for small variations and small curves in thicker stuff.
      No one is talking about tight radius curves in 8mm plate.

      And for stuff that’s mega thick and other matrials, oh look, specific blades for the job:

      It’s not going to fly off and kill the cat. The very first picture, he’s holding it with two hands – likely because without a hand on the grinder the loose fitting mount will allow it to move.
      This is a guide for the grinder to hold it steady, not a rigid tool mount for remote operation.

      But being all health and safety, you neglected that he’s only wearing a T shirt which isn’t enough padding against exploding blades and only has eye protection, not a facial impact protection shield. Gloves are for debate by many, personally I do with blades but dont with wire brushes.

      I’m peronally aganist spelling out the obvious. If you’re dumb enough to pick up any tool without first understanding how it’s used (either through instructions or sense or asking) then no amount of warnings will be heeded so dont bother.
      Which part of high speed cutting blade designed to go through steel wouldn’t have most people treating it with a touch of respect? The rest will remove themselves from the gene pool at some point anyway.

      1. I deliberately didn’t mention the PPE (gloves, t-shirt etc) because that’s obvious.

        Trust me, being a Land Rover collector means having lots of experience using angle grinders, welders, hammers etc. I’ve done lots of stupid stuff that I wouldn’t recommend with an angle grinder and have so far managed to keep a full compliment of sensors and actuators (my age has now given me the wisdom to know I’ve been lucky). I’ve had many near misses however and know better than to advocate activities that could lead to something serious if you don’t treat angle grinders with the respect they demand.

        But, like you say, they could but considered Gene Pool Purifiers.

  3. One of these days I’m going to put one of those electromagnetic clutches in the alternator (with a backup pin/bolt to jam in of course if fails) of my truck once I get to that project with the additional batteries installed. Still looking into a Viper or Lincoln fan for a dirt cheap price.

  4. Dude I was working with got creative with using a grinder. The wheel shattered, split his cheek all the way up to his ear. My takeaway, don’t get creative with using a grinder.

  5. Don’t listen to any of the naysayers. I’ve done this to make five 14 inch nave plates in 3/8 steel, there were no accidents or deaths (other than an angle grinder) and my jig was way crappier. The 4inch center hole was chain drilled and ground with a grinding discas opposed to the cutting disc.
    Obviously when you hack something to that which it was not intended you take extra precautions, unless you’re making a YouTube video, in which case you take unnecessary and stupid risks.

  6. Necessity is the mother of invention. John Britten, Burt Murno and Bill Hamilton all became world leaders at making stuff which would have been unfeasible, unimaginable and horrendously unsafe to most. Burt was racing motorbikes at 200mph at 65 years old, Bill and his wife were similar aged and still took their handbuilt jet boats franging around the rivers. Check out John doing some backyard engine casting if you want some unsafe hacking.

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