How NOT to throw your lathe chuck key through your Porsche windshield!

Like many of you Home Shop Machinists, shop space is at a premium. My shop is located in my garage where I also store a few motorcycles and my  vintage sports car.

A big fear I have is one day turning on the lathe accidentally with the chuck key still in the chuck, and flinging it across the shop into the windshield of the Porsche!

I needed to create some type of interlock so I could not start the lathe unless the chuck key was removed and stored somewhere.

A simple solution was a piece of aluminum tubing with a lever switch tied into the lathe’s electronics.

A piece of tubing was turned to the proper dimensions and a slot was cut to attach a small “lever switch”

$3.50 from Radio Shack

CAUTION!!! Use a properly rated switch to interrupt  your circuit. This 5A switch is not rated high enough to interrupt the AC  line voltage to most lathe motors. I’m using a DC controller on this lathe and interrupting a low voltage area of the circuit. Be sure you are using approve wiring and electrical shock shielding standards. If you do not understand these things, please hire a qualified electrician. Improper installation could kill you!

 Using JB Weld, the switch was attached to the aluminum tubing

A couple holes were drilled and countersunk to attach to the lathe

Two holes were drilled and tapped in the lathe

A wire to interrupt the circuit (see warning above) and a bit of heat shrink tubing finishes the deal.

Now, no chance of a broken windshield!


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12 comments on “How NOT to throw your lathe chuck key through your Porsche windshield!”

  1. davidh Reply

    great idea, I’m going to do it this afternoon, a simple solution to an ever present problem. thanks for sharing .

  2. Phil Reply

    Thought this was going to be a silly idea, and was going to suggest the old spring welded to the chuck key trick………..but I like this idea, I like it a lot (provided you are breaking low voltage with the microswitch!)This would go down well in schools and training shops!

    • Roy Bertalotto

      All my chuck keys came with the spring you are refering to. I removed them as they proved to be an annoyance. Thanks for the kind comment!

  3. Brooks Ravenscroft Reply

    Would a magnetic contact work instead of a mechanical,switch? I am not an electrical guy but it would eliminate the poi ileitis of mechanical malfunction.

  4. O'PossumTX Reply

    One place I worked, we had a rig similar to that on a drill press in the shop. That one consisted of a handy box with a lever switch inside that interrupted the control circuit to the drill motor contactor. It worked great until one of the Einsteins in the shop discovered he could just put a drill bit in the box and go on as before. He got about four lashes across the snozola with the dog chain that secured the chuck key to the drill press when he started the press with the chuck key inserted in the chuck. He was lucky!

  5. spdalcher Reply

    Great idea! I have been a home shop machinist for 20 years and always took great care to never leave the Chuck key in the Chuck. Until last fall. I was in a hurry doing 3 things at once and threw the key across the basement. No damage or injury, but scared me pretty good!. Thanks for sharing a great idea.

  6. Jerry Reply

    Any pictures of the finished product. The description alone does not show me what you have done with this. I would like to try it.

  7. tester Reply

    One dangerous lathe accident that I witnessed was in a staggered line of production lathes. One operator put a piece of 1/8″ round stock in the lathe collet. There was about 5 feet of the stock hanging out the back. When the operator turned on the lathe it was in high speed. The 1/8 dia rod whipped around like a big propeller and struck the next operator down the line. The injured operator was only superficially injured but quite shaken as was the operator of the first lathe. Like at the range, you have to stay alert and keep your eyes open around you.
    Nice group of articles, thanks for posting all.

  8. Bob Reply

    Seen a chuck cover, the type used as a splash guard to keep oil/lube from being slung all over but it had a switch like this tied in so when it was flipped up so a chuck key could be inserted, it cut out the lathe motor. I am thinking about adding one done like that but after seeing the way you did it, I could possibly go this route also.

    I just never leave my chuck key in the chuck though, it is kinda like driving without a seat belt, I just can’t do it. I am 59 and have not drove a car without a seat belt since I was 17. Seeing a chuck key setting in a lathe chuck gives me the willies. I simply can’t take my hands off the key and leave it in the chuck and walk away. Conditioned myself like that.

    Just got a huge 16″ lathe that could fling a chuck key hard enough to kill me so I think I’m going to have to put in a interlock like this, just so I can feel better being around that 100 lb plus 12″ chuck, what a MONSTER. Was thinking about maybe a chuck key on a swing down pivot that is spring loaded and would swing up vertical when not being used. If it swings even a bit down towards the chuck the interlock switch would cut out the lathe motor. The spring would be fairly beefy so there would be no possibility of it swinging towards the chuck without a good grasp and hard pull towards the chuck.

    Swing it down, align the key, tighten or loosen the chuck and release it and it swings right back up out of the way and self stores in vertical position. Gonna permanently install a cheap torque wrench on it also so I can rotate the chuck, hit all the key points and torque each to the same tightness plus have the ratchet action of the torque wrench.

    The pivot action would cause the torque wrench to swing down and self store and when used it would automatically allow me to pivot it to the perfect position for tightening the chuck. Chuck keys are a PITA. This system when done would turn using the chuck key into an easy thing, not a pain. Getting arthritis in my wrist, I’m gettin old so that sweet spot of position and the extra leverage of the longer torque wrench would make getting the huge 12″ chuck tight but not to tight easily.

    Best thing about it would be when my hands are not on it, spring tension would swing it up and away from the chuck with zero possibility of mindlessly turning away, leaving the chuck key in the chuck and hitting the go switch. I’m definitely building this. The interlock switch will make it even better as a “just in case” safety feature.


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