G

gfb

Well Known Member
Hi folks. Used the unibit for the first time enlarging holes in wing ribs and they are coming out terrible. The holes are rough, jagged, and nowhere near round, hexagonal even. Any ideas what I'm doing wrong?

Thanks!
 
Are you using a stepped drill bit with one flute or two?The two fluted ones are **** on aluminum.
 
Wow, sorry to hear that. I had never used a unibit before the build. I find it makes pretty good holes. The only issue I have had is that it will walk sometimes. I'm using a stepped single flute.

I always use a relatively low speed so maybe it's a speed (rpm) thing??
 
Maybe turning the bit too fast? Are you using an airdrill? I use a commercial duty cordless drill and boelube.

However, for cutting larger holes (larger than 3/8) in thicker aluminum (thicker than 063), I like to use a hole saw similar to this one.

http://www.starrett.co.uk/shop/holesaws/tct_stainless_steel_hole_saw/

You may find them at your local electrical wholesaler.

Works beautifully on stainless too like the firewall for engine cables, fuel fitting and wires.

Bevan
 
Yes, single flute, slow speed, and mark the step AFTER the one you want in red sharpie all around. Then you know what the last step is, it won't wear off, and I use the pilot for the next step as a deburr.

Yes, it will move off center easily, so if you want an accurately placed hole, make a guide from .063 and clamp it in position. Then be sure you walk each step to ensure it is centered.

I have a few different ones from HF - cheap but work great on aluminum.

Oh - be sure you make a test hole on scrap and measure it - some of mine were made too large and the snap bushings were not tight. I did not make them - I don't know who did (QB or previous owner). As a result, I check all holes to be sure before creating new scrap.
 
Step drill

BillL said:
Yes, single flute, slow speed, and mark the step AFTER the one you want in red sharpie all around. Then you know what the last step is, it won't wear off, and I use the pilot for the next step as a deburr.

Yes, it will move off center easily, so if you want an accurately placed hole, make a guide from .063 and clamp it in position. Then be sure you walk each step to ensure it is centered.

I have a few different ones from HF - cheap but work great on aluminum.

Oh - be sure you make a test hole on scrap and measure it - some of mine were made too large and the snap bushings were not tight. I did not make them - I don't know who did (QB or previous owner). As a result, I check all holes to be sure before creating new scrap.
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Works for me as well.
I try to use a press with light pressure and let the cutter do it's job.
 
I do not know if the rake angle is the same on all step drills or not but the performance can be different. I had a name brand step drill that came with my tool kit that lasted about 3 holes. I decided not knowing any better that if they wore out that quick I would just get a cheap one next. I bought a set of 3 at Harbor Freight that has lasted about 5 years so far and still working great. I run them slow and use Boelube. Make test holes in scrap until you are comfortable with them. They will walk if the pressure is not straight.
 
If you don't have boelube a shot of wd40 will work. Not sure of your exact problem. I use them in a chordless drill and they work fine, even the cheap ones.
 
Another thing that I have found helps is to back the thin sheet with a chunk of 2x4, and do not use a lot of pressure.
 
Thanks for all the suggestions folks! I'm out of town but will try them as soon as I get back.

I suspect I'm running it too fast. I have it on the drill press running at 2700rpm. I'll try bringing it down to the slowest speed and see what happens.

On that note, how do you guys use boelube? I have some and its a flakey wax consistency. How do you get that to stick to the bit?
 
gfb said:
On that note, how do you guys use boelube? I have some and its a flakey wax consistency. How do you get that to stick to the bit?
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You can get it in liquid form too. But for drill bits, really any oil should do. Doesn't have to be blessed by Boeing.
 
I've had good results from the cheap step drills from Harbor Freight too. Even worked well drilling thru the stainless firewall. Like everyone else said, use some kind of cutting oil.
 
2700 is likely way to fast. Slow it right down and moderate pressure. You can always tell if a drill is happy by the chips it makes and the noise. When cutting well it should be quiet. No horrible screach etc. step drill can get up to a pretty big cutting diameter which will make the speed at the cutting edge quite high so you have to watch your rpm. Experiment with scrap and you will see that rpm has quite a large affect on the quality of cut. The hole should be perfectly round if the bit is cutting properly. So change the belt on the pulleys on your drill press to slow it down, use some lube and the chils will silently slide off the bit like you are cutting butter.
 
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