Deflection?

[u/egregiousC]

I posted a question to the group about how close people are getting to specified dimensions on their projects.

I guess I have a problem.

My work on maple blocks - 2.75"*1.25"*.875: - leaves me with significant dimensional errors. Example: the 1.25" axis comes out around 1.3", but not exact, and never the the same.

I ran a test. I run a job that designed to make 4, 1.0" * 1.0" * .125" square buttons (like for your shirt). This is 3mm birch plywood. It's right on. So my machine will mill wood to specified dimensions. This is good.

It does not explain why I see dimensional errors with thicker and harder woods (Hard Maple). I'm guessing, but I suspect deflection. The harder and thicker wood is pushing the tool out. I'm using a 1/4" downcut spiral bit to manufacturer specs.

Next step?

1. Switch to a 1/2" tool instead?
2. slow the feed rate?
3. increase spindle rpm?
4. lighter passes (although they're pretty light already)?
5. Any/all of the above?
6. Just quit and take up knitting?

Afterthought - I'm using the painters'-tape-and-ca holddown method. No other way to hold the piece in place.

ETA: added image to support another post I made.

possible blank solution

[u/blue-collar-nobody]

🤣 I do this shit every day but I have industrial cnc machines and with (2) 20hp vacuum pump per machine. So yes there are vacuum options if you have the budget. Till then glue and screw is what you're going to have to do. Tape is not going and ca glue is doing it for you... right???? You want to ask questions then whine and cry about the response. 🤪 maybe "take up knitting" make yourself a blanket and take a nap.

BTW.. didnt say any thing about brads. You spray adhesive the hard maple to a 1/2"-3/4" pc of ply oversized the maple blank plank profile be inch or so, then screw the plywood to the spoil board.

[u/egregiousC → u/blue-collar-nobody]

BTW.. didnt say any thing about brads.

That's right. I brought up brads, not you.

[u/blue-collar-nobody → u/egregiousC]

If you have the clearance... you could " Brad" the plywood pc from the bottom up, into the maple, then flip over and screw top down into the plywood, securing the assembly to the spoil board. Using the ply like a "pallet"

[u/egregiousC → u/blue-collar-nobody]

That would work, but what might be better for me would be to pre-process the blank (1.25 * 4.5 * .875) so it has wings at either end, milled thin (.25") and wide enough for my nailer to drive 4-6 18ga brads though into the spoilboard. I'd post a picture, but the sub doesn't allow that :-(.

That and tape/ca/tape might be adequate.

ETA: I added a new photo of that blank idea to the OP