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CNC Challenges

1271 Views 8 Replies 9 Participants Last post by  OutoftheWoodwork
I am making a new Mechanical Marvel (stay tuned for another Amazing Adventure in the Land of Prof. Henry), and used the CNC to make a part out of a 3/32” thick brass sheet. I was happy with the result and thought it was going to be a splendid part of the mechanism … until I weighed it.

The part weighed 3.125 ounces, and since it will attach to another much heavier piece that needs to be counter-balanced, I needed to shave some weight. So I set up a new file that would remove weight by cutting out the interior of the part. All I had to do was put it back on the CNC and cut out the section to be removed.

But how? CNCs are easy to set up for making your cuts, but it’s challenging to realign things once you’ve removed the piece from the machine when you didn’t plan ahead. Now I had an awkwardly shaped, roughly 4.5" x 4" piece that I needed to get square on the table, and somehow identify the center where the original cut was zeroed.

[Cue quiz game music while The Professor ponders.]

My solution was to go back to the CAD program and create a new file using the existing part’s vectors and center them on a larger piece of MDF. By cutting a shallow pocket the shape of the part, I could place the piece of brass in the pocket and know that everything was square and centered for making the new cut.

Once the pocket was cut on the CNC, I placed the brass part in the pocket and held it in place with double-sided tape. The result was a new cutout on the existing part with no problems and no missteps, and I was able to lighten the part by a third. Now I need to get busy on the rest of the parts.


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Excellent job and thought process, Prof! Something to keep in mind for when that crops up, for sure. Good job!

I've had to do something similar but I had not removed the waste piece from the spoilboard so I placed my cut piece back into the cavity best I could. It worked pretty good, actually.

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So how long are you going to keep us hanging for "the rest of the story"? Inquiring minds want to know what this Mechanical Marvel is going to be or not to be. I'm on a roll and without meds.......maybe that's the problem. Just kidding, all is fine, really. Godspeed Professor.
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Nice to be able to make parts like that, Oliver. Good idea for realigning the part for the mod.

I'm looking forward to the Further Adventures of... :)
Come on Oliver, you could have put some decorative cutouts in that brass piece, instead of that big hole, to help us guess what it is for!

Looks like it will be used as a hinge for a box that will hold some well designed anti doomsday machine or perhaps a part for adjusting the elevation for a trebuchet for throwing electrified gazing balls into the night sky, or for ???????

See you make it really hard to figure it out!

By the way, that's a good solution for locating parts for extra machining.
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That is a great idea! Me being a newbie was thinking about this the other day when i was working on a practice piece.
(stay tuned for another Amazing Adventure in the Land of Prof. Henry),
When it comes to waiting for a new Prof. Henry project, I'm like an out of work Doctor... no patience
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As usual, Oliv-uhhh I mean Professor! And as usual, you are way above my comprehension :lol:
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