What am I doing wrong?!?

970 Views 5 Replies 4 Participants Last post by maddog, 8 mo ago

CNCNewb

Discussion Starter · 8 mo ago

I've been having significant problems w/feeds and speeds. I had this other thread here where it seems to be that (1) I was likely using the wrong bit and (2) I was likely going way too slow on x/y/z but too fast on RPMs. I've adjusted a bunch of stuff, got a new bit, etc., and yet...

First I'll show what's happening and then break down every single setting/thing I'm doing, because I really have no idea what's wrong.

Here's the damage:
Youtube video of destruction in action

This is a brand new, 1/4" 2-flute compression bit (here -- cheap, but I really don't think that's the problem). I'm making a single 3" straight, 0.1" deep cut as a test. The wood is oak, iirc. I've set the router to "1" which is 10K RPM, matching the settings of the program below.

Following settings:

Rectangle Font Parallel Slope Screenshot

For some reason the Bob's program is recommending an even slower spindle speed, but I feel like based on the video this was actually too slow.

I'm using the mm post-processor as my machine itself is also set to mm:

Rectangle Font Parallel Electronic device Screenshot

Rectangle Operating system Font Personal computer Screenshot

I begin by setting project center and zeroing x/y, then using my z-probe to get height above material.

After that, I hit send and watch the whole thing go to hell.

Any advice?

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difalkner

· #2 · 8 mo ago

First observation is that you need to go deeper than the upcut portion of the bit. For the 1/4" compression bit I use that's 0.25" or deeper so I usually cut 0.3" or greater on the first pass. Second is that your work piece is not sufficiently secured, it's too loose. Third is that your machine is either not rigid enough or has some serious play in the carriage/mount for the router because it's moving all over the place.

Are you seeing the same things? Video is good, btw, and well represents the situation. And thank you for shooting video in widescreen and not portrait!

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CNCNewb

Discussion Starter · #3 · 8 mo ago

I clamped the piece relatively well, but not fully, simply because I knew this was likely to happen and I wanted to allow the piece to jump free, if so, instead of possibly damaging the machine.

I just did a few tests using various feeds and speeds. I found that 22K RPM and 58.5"/min feed will cut well enough, both on a 1/4" and 1/16" bit. I feel like the RPM is too high but anything with a higher CL seems to have issues. I'm not sure if it'll help to reduce the RPM or to keep it as-is. What's crazy is that is a CL of only about 0.0013 or so. That's really, really low when I look at calculators online. I don't get it... although this is a birch plywood-based hobbyist machine as opposed to some professional rigid steel beast.

I'll try to post a video when I get some time. I still don't like the way it sounds when moving at full CL... I just can't tell if I'm going too fast (RPM) or if something else is going on.

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difalkner

· #4 · 8 mo ago (Edited)

CNCNewb said:
I just can't tell if I'm going too fast (RPM)

I run mine at 18k rpm for 99% of my jobs, fwiw.

Letting the work piece move is counterintuitive to preventing damage to the machine, I believe. By allowing the piece to move as it did you're now introducing a new factor into the machining by having a moving work piece and opening the opportunity to break a bit. I would lock the work piece down as much as possible, lower the rpm slightly, and give it another shot with that 1/4" bit.

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MarkJonesRanger

· #5 · 8 mo ago

Davids right. That compression bit has a upcut on the bottom of it to pull the chips out faster. If you don't get it down on the first cut below that upcut part it will pull your wood up and give you what your getting. The down cut that gives you a clean edge on top starts on the bit when your first cut is past the first part of that compression bit. Just cut deeper on your first cut.

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maddog

· #6 · 8 mo ago

How deep are you trying to go? If you're only going say a 1/4" I'd use a Down Cut bit running at 18K. Always make sure your work is totally secured.

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