darmach's blog

tech junkie

Hobbed bold hobbing

One more thing I need for the extruder is the hobbed bolt. Somewhere on the internetz I’ve found an opinion (I don’t really remember where..) that hobbed bolt which teeth are cut from the threaded part of the M8 screw have even better grip than tapped one. So I got few M8 fully threaded screws, and constructed a tool for hobbing. It uses dremel flexible hose, and those thin cutting disks – 0,6 mm disks allow for a finer teeth to be cut.

Rotating disc that holds the screw have 20 holes – which are a match for a 6mm ball pushed against it by a spring. This way I could measure each step I’m cutting. And here is the final result – isn’t she a beauty?!

The result

The result

I also made a video while hobbing – a little bit shaky, but it’s hard to hold camera with one hand while cutting… …probably will have to get some stand in the future.

3 Responses to Hobbed bold hobbing

  1. curious says:

    nice design, making nice use of polish hardware store parts :)
    cool for bootstraping :)

    i do use something like this :

  2. curious says:


    i’ve remixed plastic bolt hobber to make it hob bolts more close to the end of the nut (which is important for extruders like collaborative wade where you use full length of the bolt and can’t afford to insert any washers to adjust hobs position)

    also i’ve tested 0.25mm jewellery disks – they are quite durable, do not tend to break or anything like that, but they are not perfectly flat (so they do not reach true 0.25mm precission)
    Still they allowed me to hob the bolt in a way which left the hardened surface of the bolt intact while allowing very deep cuts at same time.
    Also even though they are not really rated for hardened 12.9 steel , they do not wear too much (one disk can probably cut at least ~5 bolts)


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