Endmill failure or wrong feeds and speeds?

[CNCOlly]

Thanks for all the info Lee. I've read it a few times trying to absorb it.

You haven't said if you also adjusted the spindle speed, I'm going to assume you never and that's what allot of people do, they assume slower feed rate equals "safer" but its not always true, especially if they don't understand the feed rate/spindle RPM relationship to chip size/load.

Good assumption for the 6mm endmill I used 4000mm/min feed rate 18000RPM and a 3mm DOC, stepover 40%

Lets do an example on the assumption of Oli not having changed the spindle speed and what those numbers then tell us about the chip size he was producing that may have caused the cutter fail.

To do this we will need to do the maths the other way:

Chip Load = Feed Rate (millimetres per minute) / (RPM x number of flutes)

Feed Rate: 4,000 mm/min
Spindle: 18,000 RPM
Tool Edges: 2

That tells us our chip load is: 0.111 = 4000 / 36000

So we could assume that when the cutter failed for Oli it was because rather than producing proper chips sized at 0.483 it was instead "rubbing" the material away and producing dust relatively speaking, this rubbing then caused the tool to get hot and combined with it just not being up to the job, to then fail.

Oli when you recovered the project using the 6mm solid carbide cutter, what feeds and speeds did you use, the chips in that second video look better, though it dose sound like its screaming a little bit still. The cheap bits are not a total waste of time, you just have to be a little more conservative with them, don't be nervous mate what's the worst that can happen, just "send it" and be confident in your work, we learn from the ways that don't work :-)

With the bit screaming as you suggest which setting would you have adjusted? I'm guessing you would have adjusted the RPM down? I would have probably been tempted to reduce the feed rate. I probably need to practice different settings on a scrap piece of wood to get a better feel for it.

Hopefully I've given you enough info to answer your later questions on how to approach F&S etc, if not just ask away that's what the forum is for, for now keep the stepover small just while you find your feet so to speak, once you feel better about it all and get to know your machine and tooling more, then you can start looking to push their limits, I don't think there is an issue with your spindle, I think you would see problems in the bottom of the pocket (finish) if it was out of true etc, Andrew is correct on the using your ears and I'll add eyes (chip size) to help establish if things are running correctly, also another good easy to do tip is to check the cutter after a job to see how hot it is, warm to the touch is ok :)

Lot's of info thanks, The cutter was warm after this project not too hot to touch which is a good sign.

Key tray looks great, brilliant feeling when you take something off the machine for the first time isn't it :)

Never get tired of it, it's great seeing a design go from the PC screen as you intended it to.

Did you get a Jazzy (Dean) machine in the end or something else ?

Yes mate I did, It's a great machine that Dean and Jared made for me. Really pleased with it.

[Lee Roberts]

With the bit screaming as you suggest which setting would you have adjusted? I'm guessing you would have adjusted the RPM down? I would have probably been tempted to reduce the feed rate. I probably need to practice different settings on a scrap piece of wood to get a better feel for it.

Yes mate I did, It's a great machine that Dean and Jared made for me. Really pleased with it.

I'm not sure but the main point is you shouldn't need to guess at any of it, as long as you maintain the known good chip size as you change the feeds and speeds, then everything should to go plan for you, what CAD/CAM software are you using ?