Total newbie, hobbyist question: Screeching with countersink in aluminium

[pixartist]

Hey, I finished building my DYI cnc and started with drilling holes and countersinking. Drilling works fine, but I have issues with countersinking. I'm using a super cheap 6 flute 12mm countersink (82°) with a very slow feed rate of 15mm/min and RPM of ~2400. I can't go lower with the rpm because my 1.5kw china spindle will get stuck below that. (btw. can I make it keep a steady rpm under load somehow ? I'm using the standard Huanyang 1.5kw inverter). Well at these settings the countersinking is reasonable, but still sounds a bit painfull, especially when going a bit deeper into the material (doing 10mm radius countersinks on 5mm holes). As soon as I go higher with the RPM I will get a deafening screeching sound. Any tips ? Is it the crappy tool or am I doing something totally wrong ? I heard I should go way lower with the rpm, but my spindle just can't handle that.

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[awerby]

What are you trying to countersink these holes in? Wood, aluminum, steel? Are you using any coolant? 12mm is a pretty large diameter ; normally it would want to be run slower than that, but it should be okay if it's just wood. If your spindle is slowing down under the load, you might be pushing it too hard. Also, as you're already finding out, crappy tools don't work as well as good ones - sometimes they don't work at all.

[pixartist]

It's aluminium (see title) (a pretty hard alloy I think). I wonder why my 1.5kw spindle can't handle this at lower speeds. Maybe it's because it's 6 flutes?

[Jim Dawson]

I normally turn countersinks at 500 RPM or less except in wood. My favorites are M.A. Ford single flute, or 0 flute, pretty chatter resistant. WD-40 would be helpful. You might try countersinking with a hand drill at low speed, I do that a lot. Also a countersink pretty much lives in my drill press for quick deburring and countersinking.

I'm surprised your spindle will work at all as low as 2400 RPM, usually the floor on those is about 6000 RPM. They produce almost no torque at low RPM.

[pixartist]

Well, I was drilling at 4000 rpm through 8mm aluminium alloy and it worked like a charm. but below 2500-3000 rpm it gets weak.

[gjersey121]

The reason behind the screeching is the quality of the tool.

[pixartist]

The reason behind the screeching is the quality of the tool.

Could you recommend a decent tool for countersinking and one for chamfering too maybe ? Thanks