Unibits getting clogged - any ideas?

[Taylor]

My unibit clones seem to not be working very well lately. They get clogged with aluminum, which I guess is heating up from drilling and then hardens in the cutting groove of the bit. It seems like almost every hole, I have to scrape out the groove with a little nail, which greatly decreases the convenience factor of these bits. I'm pretty sure it wasn't like this a while ago, but maybe it's just that I'm drilling more boxes and noticing more.

I'm wondering if it's just time to get some new bits, or if maybe the disgusting heat of summer in New Orleans is to blame? Or should I be using some kind of lubricant? The bits are cheap so if it's just a matter of dulling I can buy more.

Anyone had this problem?

[funkbass187]

using some cutting fluid/oil should solve that.

[amptramp]

You can get "cutting fluid" that will tend to separate the cutting swarf from the tool.  It is in common use in machine shops and there are a number of places that cater to machines (such as lathes and milling machines and their attachments) that carry the stuff.  You may find some specialization in that some cutting fluids are used for machine tools such as drills and lathes and others are used for manual tapping where not so much heat is generated.

[MmmPedals]

Not sure if oil is your problem. sounds more like a dull bit. I would use the oil anyway. It keeps everything noticeably cooler. Smallbear sells small bottle which last a long time.

[petemoore]

  Seems like the flat edge of the scallop [groove] could be touched up, perhaps it's slightly burred. Grinder like dremel might fit and could be used lightly with fine grind to flatly [try not to put new angle on it] clean up and sharpen the shear-edge.

[composition4]

+1 on cutting fluid.  I have a jar of molybdenum grease (bought it in an auto store) I use and it works well.

Also, are you drilling too fast?  Could be causing the bit to heat up too much.  Check this link out for recommended drill speeds, I'd go by the twist-bit recommendations for a step-bit.

http://www.ibiblio.org/twa/info/drillSpeedChart.pdf

Jonathan

[R.G.]

Tool wear. Sharpen or replace. And use an aluminum cutting fluid with the new/sharpened bits. They'll last longer.

[Mark Hammer]

In all the years I worked in my dad's machine shop, the cutting fluid was always running and dripping onto the milling and drilling bits.

[R.G.]

In all the years I worked in my dad's machine shop, the cutting fluid was always running and dripping onto the milling and drilling bits.

Yep. What actually goes on at the sharp end is that the edge of the bit so concentrates the driving force on a small area that it exceeds the local shear or flow strength of the material being cut. The work expended in that micro-region is converted to waste heat. Chips come off a well-run lathe at a temperature which turns the chip brown to blue from air oxidation within a few seconds.

Very sharp tools concentrate the force better, so the machine cuts with less driving force, and the area being sheared/heated is smaller. The heat generated is enough to in some instances weld the material being sheared to the cutting edge. This forms a burr which effectively dulls the cutting bit even if it's not itself dulled.

Cutting fluids work two ways: lubrication and cooling. The lubrication part is no help at all for the heat at the cutting edge, since there is no room there for any lubricant between the cutting edge and the material being cut. But it does help the sheared chip ride up and over the tool bit as it slides away from the cutting edge. This reduces the driving force as well. The cooling part keeps the bulk of the material being cut and the tool bit from getting hotter, and cools the cutting edge by conduction from behind. This is one reason modern cutting fluids are mixtures of mostly water with a fraction being soluble oil. The oil helps lubricate and (theoretically only, my machinist friends assure me) keep the machine from rusting, and the water does the cooling better than oil would.