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  1. #21
    Gold Member
    Join Date
    Sep 2006

    Re: Mill column design questions

    Quote Originally Posted by gbrose85 View Post
    I don't understand the flat plate on the bottom.
    What you want is another closed box about the same size and shape as the Z column.

    I went through several iterations looking for something simple and (I hope) sufficient. One of the first was close to your design, though retaining the large plate for the added mass. Then a constructed box and then just the welded on extension. Moved to the bolted 2 plate configuration thinking that the benefits of adjustability outweighed the added complexity. In any case, FEM seems to indicate that the simple welded on extension won't measurably deflect -- well under a mil with an applied 150lb static load.

    Is there any reason that stiffeners or a box support could not be added later?

    Is there a build thread for your Frankentag? What level of precision are you getting (deflections at the spindle nose when milling different materials)? What size linear rails are on the vertical axis? Did you look at the SC-15P epoxy by Precision Epoxy Products?

    Thanks for the comments. If there was one change to be made, what would make the most difference in terms of ultimate precision?

    Hmmmm......tricky question.........but my two pennoth worth would have to be..... abandon the XY table set up as it's dove tails and they are not the ideal CNC moving medium.....keep the column as is and weld a base plate to the bottom for bolting.......make a bottom rectangular tube extension to form an L shaped base that the column bolts onto, welding a 20mm thick pad to the end face to bolt the column down on...........cut the old base plate to the same length as the new base tube extension and have it 50mm wider than the L shaped base tube to form the mill base with 4 holes for bolting down to a bench etc

    That would give you a basic mill structure.....add two steel strips 20mm thick X 50mm wide to the top of the base tube to mount the Y axis rails on etc etc.

    David Decaussin's UMC-10 mill is something like this configuration..

    Basically it's two pieces.....a column and a base .......it's as simple as you can get.

    The base steel tube needs to be wide enough to directly mount the linear rails on with steel strip pads.

    As you're going from scratch, I'd make the column and base from the same steel tube with the thickest wall you can get.

    It's difficult to give dimensions for the column and base etc, as it has to be proportionally derived from whatever mill work envelope you decide on,........ I'll attach a sketch of a typical fabricated all welded steel design I think is almost self explanatory........it's main components are 10mm steel plate, but steel tubing is also in the same category........in this design the column is bolted internally from the bottom without the normal exterior side flanges.

    BTW, in the sketch the column can be a just a simple square steel tube with two 10mm thick angled side plates welded on for added resistance to flexing......this will give you added mass where it counts most.

    The cost of materials compared to iron castings is minimal if you can do the welding yourself or a with a friend.

  2. #22
    Join Date
    Jul 2018

    Re: Mill column design questions

    Hi Gb - Did this machine get finished and any comments on its performance? Build photos? Peter

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