Terrible unibit holes

[gfb]

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!

[C-FAH Q]

Are you using a stepped drill bit with one flute or two?The two fluted ones are **** on aluminum.

[aeroaddict]

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??

[JDA_BTR]

Mine stunk until I starting doing them at 250rpm on a drill press. Then they were awesome

[Bevan]

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/holes...teel_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

[BillL]

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.

[wirejock]

Originally Posted by BillL

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.

Works for me as well.
I try to use a press with light pressure and let the cutter do it's job.

[SMRacer]

If you want to cut perfect holes in aluminum sheet, try these:

http://www.hougen.com/cutters/sheet-...e-cutters.html

Jim
N444JT

[Charles in SC]

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.

[sblack]

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.