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Doofus-Proof Drawbar Whacker

July 15th, 2014

You Need It

Here is an update on my machining.

I have the parts for my CNC lathe conversion mostly done, and I’m going nuts trying to pick motors, controllers, and so on. I have nothing coherent to say about that. But I do have something helpful for people who–and I know nobody who reads this blog would do this–are absent-minded enough to leave a box wrench on the nut of a milling machine drawbar. The big problem with this is that if you turn the mill on, the wrench spins with the nut, and depending on which way it goes, it will either loosen the drawbar or snap the shear pins inside it. Or, if you have a crappy drawbar with no shear pins, it will spin the drawbar in your taper and mess it up.

I know someone who has a Grizzly mill with a solid drawbar, and he now has grooves inside the taper. Some imbecile left a wrench on my mill’s drawbar (no need to reveal his identity), and when he snapped the pins, all he had to do was order an $18 replacement off Ebay. And he was able to cram a new pin in the old one to make it work until the new one arrived.

For God’s sake, go check your drawbar right now. If it doesn’t have shear pins, get a new one. They’re cheap. If it has pins, you will see their ends through the finish close to the point where the thin part goes into the fat part.

Anyway, a drawbar wrench should be able to perform two purposes: it should tighten and loosen the drawbar nut, and it should also be heavy enough to whack it to make collets and stuff drop out of the taper. I came up with a tool that will do those things AND which can’t be left connected to the drawbar.

I made a cylinder of aluminum with a hex protrusion on one side, to fit snugly in a 3/4″ box wrench. I tapped the hex part for a 1/4″ screw. Then I stuffed the hex into a wrench, added a screw and washers, and I was done. Here are two photos of it being made.

07 15 14 drawbar hammer on rotary table

07 15 14 drawbar hammer assembled on bench

If you’re a machinist, you will appreciate this. Last week I wised up and got a 4-jaw chuck for that rotary table, because a 3-jaw is a really stupid choice. I found I had to make special nuts to hold the 4-jaw on the table, and I have not finished that job. I haven’t really needed the 3-jaw and table for a while, so I had no issues with removing the table to use it to make the nuts. That was like 3 days ago. And today, naturally, I needed the 3-jaw for this job. So I had to put it on the table and indicate it. Isn’t this always how it goes? The minute you break something down, you need it.

Most people use brass for drawbar whackers, but it doesn’t matter. Aluminum works fine.

I haven’t Loctited this thing, because I want to add better washers. I considered machining one, but I really don’t feel like struggling to machine thin work today.

Tubalcain, the machining star of Youtube, has a similar project, but mine is way cooler. He didn’t pretty his up. Mine is chamfered, and the exposed sides were turned on the lathe. His left baby toe knows more about machining than I do, so I feel smug about doing one thing better than he did.

I hate to doink this thing up by using it.

The wrench is a Husky from Home Depot. You may think it’s not important to mention that, but it is. It’s surprisingly hard to find a long 3/4″ open wrench that isn’t offset.

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7 Responses to “Doofus-Proof Drawbar Whacker”

  1. og Says:

    Nice work!
    The wrenches on conventional KURT vises are 3/4″ specifically so they can be used to tighten/loosen the drawbar on a mill, and they used to make them with aluminum knobs to that purpose. They don’t make them that way anymore, but you can still find them on ebay.

    Using an open end wrench is smart if you have someone operating the mill who might be likely to leave the wrench on.

    Another way is to take a 3/4″ deepwell socket, machine an aluminum or brass “hammer head” that fits in the square drive end, and drill a hole in the side of the socket to accept a small hammer handle. This does an adequate job of tightening the drawbar and if you- er, someone manages to forget, the wooden handle is just broken. The upside is you always have a soft faced hammer at the mill.

  2. Steve H. Says:

    Thanks, Og. I am not getting a lot of positive feedback on this thing. People seem to think the box end is a necessity, so they can hang the wrench on their mills’ nod nuts. I couldn’t care less about hanging it. I just want to keep it from wrecking the mill.

  3. Steve H. Says:

    I am thinking it would be nice to have something like a 3-handle wrench with a spring-loaded spider connection, so I could leave it up there all the time. If something like that turned with the spindle, it wouldn’t matter.

  4. og Says:

    The problem with that is that they cause some unbalance of the spindle. better to see if you can find an automatic drawbar- they’re pushbutton electric or air things. Work nice.

  5. Sigivald Says:

    And today, naturally, I needed the 3-jaw for this job. So I had to put it on the table and indicate it. Isn’t this always how it goes? The minute you break something down, you need it.

    See, this just means you need two lathes…

  6. Steve H. Says:

    In other news, I finally got my steppers, controller, and driver ordered. I went with Dynomotion. I was considering a Smoothstepper and a Gecko G540, but I didn’t want to get stuck with Mach3, and Dynomotion makes a controller and a driver that snap together. Supposedly less buggy than a Mach3 setup.

    I guess I will find out.

    Apparently I am now a C programmer. I better find out what that means.

  7. Sigivald Says:


    int Main(void) { prinft(“Hello, World”); }

    I hope your keyboard has good {} and ; keys.