2 part ? reducing drill deflection and engraver chatter

[nateflanigan]

Hello, two unrelated questions:

1) I tried using a drill end mill for the first time last night (1/4 dia on anodized aluminum) and noticed a fair amount of deflection when the tip first made contact with the material. My peck depth was only 0.03", plunge rate 10 ipm. How can I reduce deflection? Slow down plunge rate? reduce peck depth further?

2) I use a 60 deg 0.005 single flute bit for engraving, suggested chip load is 0.0012. I run it at 18,000 rpm 20 ipm which V carve tells me is 0.0011 chip load. I do two passes, one at 0.003 depth of cut and second at 0.004. My results aren't bad at all, but if I look with a magnifying glass there's a fair amount of pearling or chatter at the bottom of the cuts, any advice? I can slow down my dewalt 611 to 16000 and reduce my feed rate accordingly, any other ideas? Maybe even lighter passes?

Thanks friends

[Tailmaker]

The anodizing layer is aluminum oxide (aka sapphire) and very hard. A drill bit with a tip tends to wander around until there is enough pressure to break the thin layer (you may notice the powdery substance). Not sure if that can be totally avoided, especially if the bit is long or the machine not very rigid like the SD100.

I have had better success drilling holes in anodized aluminum with a spiral ramp inside profile toolpath using a smaller endmill, e.g. 1/8" for 1/4" hole. That is also cheaper because the anodizing layer will dull the bit quickly and may be faster without the annoying peck movements. Some compressed air can help for deeper holes as well as a bit of lubricant (e.g. 1/3 alcohol and 2/3 water with a drop of Dawn). I would try 20 ipm feed and plunge with such a bit and conventional spiral toolpath at 0.02" pass depth. You can run that twice for best diameter accuracy. But that may need some experimentation, depending on the bit and aluminum alloy type.

No idea about the engraving problem.

[nateflanigan]

Thanks, that's how I typically make holes. It had been recommended to me to try a drill end mill as milling holes is one of the more time consuming aspects of my panel making process so I thought I'd give it a try. Any experience with center cut flat end mills for hole making?

[Tailmaker]

You could try something like that: https://www.ebay.com/itm/5-1-8-CARBIDE- ... 3886863211

But I have used whatever cheap eBay 1/8" carbide upcut bit I had available. IIRC the fishtail ends worked better than the bottom cutting ones but did not last as long. I have not cut aluminum for a while.