I need feedback on this fixture :)

Hey guys, David here. I’m pleased with how supportive this community has been so far and I am very confident I will be buying a 30x30 MK1/MK2 Longmill in the very near future. In preparation for my purchase, I wanted to get some feedback on a future fixture that I intend to use with my 30x30 Longmill.

I created this document to help me best illustrate what we intend to do:

Four Questions:

  • What works about this setup?
  • What doesn’t work about this setup?
  • What seems unclear?
    *What ideas might you have?

Hi David,

That looks like a great start - 3D printing your fixturing can get you some good dimensional accuracy, and allows for rapid prototyping. A few things I would consider:

  • Perhaps make the fixture longer so that none of the part you are machining is unsupported / wobbly. As shown, it looks like the fixture only supports the area where the fasteners are. The additional area need not be fastened down, just supported from below to avoid the part bouncing / bending.

  • You will want your fixtures to be square to the machine bed. This should be pretty easy to accomplish by using the machine itself to cut a reference edge / pocket / feature in the bed within which to situate and fasten your fixtures.

  • I like how you plan to have a feature to locate the touch plate in your fixture. This will make setup super easy - situate the fixture squarely (as mentioned in the point above), set up the touch plate, and zero things. Personally I have only used the manual touch plate (not the auto zero) so someone else may have to comment more on that.

I’m really looking forward to seeing your progress - I’m sure there are others as well. We all love seeing pictures of what people are doing with their machines!

Ed

Thanks Ed! I definitely planned on making the part longer to eliminate wobble, so I’m glad your intuition seems to match my future design plans :slight_smile:

Are there best practices for making reference edges/pockets/features in the bed that I should keep in mind?

I can really only speak from my trial and error experiences there, but I would say there are a few options:

  • Establish a “vertical” (parallel to the Y axis) reference - whether cut into the bed, cut into a waste board fastened to the bed, or a piece of MDF that you fasten to the bed and then use the machine to cut parallel to the Y. (I could see this one being most useful. If you do remove this reference, you will either have to realign it manually, or cut a new one). This is more or less giving yourself a fence against which to align things.

  • Alternatively, fasten a piece of MDF to the bed and cut a reference pocket into it, sized to fit your fixturing exactly / nearly exactly. Downside here is if you remove the piece of MDF, you will have to realign the pocket. You could kind of think of this as a fixture for your fixture - it would locate your fixture positively every time you needed to install it.

  • On your 3D printed part, ensure you have a 90 degree intersection in a pocket that you can positively position the touch plate within.

Whichever route you go, keep your order of operations in mind - the last operation you want to do is cut the actual reference surface(s) - so before doing so, locate and bore your hold down holes in the bed and thread in some inserts so that you can positively locate your fence / pocket board. Fasten the board down, then mill it to its final size / alignment - this way you are certain the pocket / fence is suitably parallel and perpendicular. If you unfasten the alignment feature, you will have to re-align it (or re-cut it).

I know there are far more robust and incredibly accurate means of fixturing for cutting metal, but for your use I think that MDF and some threaded inserts will get you inexpensive repeatability that you can work with and improve upon easily.

I have been meaning to get creative with some 3D printed fixturing, but haven’t tried anything yet. I’m looking forward to seeing how you do things!