I am trying to cut 14mm x 14mm (.55 in x .55 in) holes in an Aluminum sheet that is 1/16" thick so that they can fit cherry mx style key switches.
I used 1/16" bits from Spetools to do test profile cuts and have broken 8 bits in the process of trying to find the right settings.
So far I have had success with rpm (bit manufacturer recommended number), 25 in/min feed rate, 15 in/min plunge rate and .15mm (. in) cut depth on each pass. Any deeper cut depth (0.20mm or 0.25mm) or faster feed rates (35 in/min) or higher rpm () breaks the bit.
However I have to eventually cut around 300 holes in a 1ft x 3ft sheet and with the current settings it would end up taking nearly 10 hrs (if the bits hold up).
I’m looking for a way to bring down the time to less than 3 hrs. I’ve these options things in mind
1. Get a better 1/16" bit from another manufacturer (Amana?) which will hopefully support higher speeds and/or deeper cuts and hold up better.
2. Get a 1/8" bit to do the profile cuts with dogholes to avoid rounded corners (Thanks Danny Miller for this suggestion) - but I’m not sure if the key switches will still fit snugly.
3. Get a 1/8" bit to do the profile cuts and do a cleanup pass with a 1/16" to get perfectly square corners
Am I missing anything else? Any suggestions on which option I should go with? Also, if you can share which bit sizes/manufacturers/settings worked for you for aluminum, that’d be welcome too - I don’t want to spend too much time/money on buying/trying/breaking bits.
Does it even make sense to try to cut a sheet this big with this many holes on a CNC or should I just find a laser cutting service? Anyone knows how much laser cutting costs?
It’s not about heat dissipation… you have to drastically low your spindle speed. Going from 1/16" to 1/4", you’re going to have 4 times the speed at the tip of the cutter. So much closer to 1/4th the spindle speed, while keeping the same feed rate. And if you lower you feed rate, you have to lower the spindle speed as well.
I frequently used 1/8" endmills to cut that exact thickness of aluminum, and I’ve bought some 1/4" endmills to try them out.
Cutting aluminum is about cutting super slowly. A high tip speed will cause galling, which will quickly kill your bits(as you found out). Watch the chips you produce, ideally they’ll almost be like a thin fingernail shaving, though I never really was able to get those. If it looks like little squares of glitter, that’s at least acceptable. Powder means you’re going way too fast. I’m sure someone will chime in with better advice, but maybe this can be a start point. Feed/speed calculators are important with metal, the “good” window for feed & speed is super narrow. Too fast, and the metal will gall because it skips over the top of the metal, rub and generate a bunch of heat, melt the metal onto the bit, and then break it. Too slow, and you’ll try to cut out too much at once, and break the bit that way. You have to be within roughly 20% of “right” to get it to cut consistently.
Drilling your entrance holes cuts down the amount of work the endmill has to do. I use the cheap 1/8" endmills from amazon, and found pre-drilling my holes so I didn’t have to plunge or ramp make it work much better, my bits lasted much longer.
I was drilling holes in solid aluminum with a friend of mine. He was fighting left and right to get them to drill, fighting and shoving super hard to get it to cut, while I was just breezing through them. I let him dull a (cheap) drill bit before showing him how to use the exact same (cheap) bit at a very slow speed… almost the slowest my cordless drill would go, and knocked them out super fast because I was cutting “right”. (I’d gone through the same thing a few weeks earlier…). The bit needs to get a proper bite on the metal, not just rub on it.
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