eric_marsh

eric_marsh

Well Known Member
I bought about $70 worth of #40 & #30 drill bits so that I would always have what I need in hand. This included four 6" bits, two 12" bits and a bunch of standard length drill bits labeled as "jobber." I figured I'd buy a bunch of cheap ones so that I could just toss them away as they wear out or break.

When it came to drilling the skin to the anodized spar the standard length bits just didn't do the job. They had a hard time penetrating so I used the 6" bits. But drilling hundreds of holes in the skin I'm finding that they don't cut very cleanly and some work better than others.

At this point I'm thinking that I should buy a smaller quantity of higher quality bits and possibly a drill bit sharpener. This is especially true for the #40 bits. But there are a variety of different quality and styles of bits available and I'm wondering just where the best price point is.

Does anyone have any suggestions as to the best choice of standard length drill bits for drilling 2024 T3 ?
 
You get what you pay for...

Cobalt 135 deg. Split Points
You can get them from the many suppliers that support this community.
 
Eric,

I bought two #30 and two#40 standard length bits and a 12 inch length bit in each size from Cleveland Aircraft Tools when I started my project. I'm flying now (RV8 QB) and I never had to buy new bits, nor did I sharpen them. They still drill perfect holes. I always used a drill motor that turned the bits about 2500 RPMs for the aluminum drilling. I also used Boelube for thicker pieces (real good stuff). I think it pays to buy top quality tools. It's hard to beat Cleveland and Avery; they both sell quality products.
 
For aluminum and other soft materials, use high speed and low pressure.
For steel and other hard materials, use low speed, high pressure, and lubricant.
This will make holes clean and round.
 
As mentioned the Colbalt stay sharper longer. When you use a bit on steel or fiberglass, put a piece of tape around it and don't try and use it on Al again. A couple dozen bits should last through the project.

The split point makes the bit come to an exact point so that center punching is not necessary. If these bits start to wander they either have a chip on the end, or they are dull and need replaced.

It is worth mentioning that when enlarging prepunched holes you should use a #40 or #30 reamer. The drill bit is designed to follow its taper into the material. A reamer is designed to center itself in an existing hole. The result is a rounder hole with virtually no deburring to do. One set of reamers will last through the kit (or until you drop the drill).

I have not found a cheap drill sharpener that works well on the small bits, and certainly never found one that is a payoff over just replacing the bits (for a non-commercial use). We have a $2000 bit sharpener in our machine shop that does a decent job on the #40's. We used to offer the service, but shipping and sharpening was often more than replacement cost. If anyone has a large qty. we can probably work something out.

Also mentioned prior, high speed, low feed is the key to keeping them sharp.
 
A few 6 inch bits are useful, and might be easier to use and stiffer if they are cut down to about 4 inches.

A standard length (jobber) drill bit usually cannot be used next to a cleco in an adjacent hole with the standard RV hole spacing. The drill chuck will interfere with the cleco. A slightly longer drill bit eliminates this problem...:)
 
Keep you eyes open on Craigslist or Ebay for a sharpener.

clevtool said:
I have not found a cheap drill sharpener that works well on the small bits, and certainly never found one that is a payoff over just replacing the bits (for a non-commercial use). We have a $2000 bit sharpener in our machine shop that does a decent job on the #40's. We used to offer the service, but shipping and sharpening was often more than replacement cost. If anyone has a large qty. we can probably work something out.
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Click to expand...
But not the cheap ones, they dont work.
I picked up a Black Diamond industrial sharpener for $250 in great shape with all the collets. It will pay for itself. I have drawers full of old dull bits that can now be recycled.
However, if all you are doing is your RV, it wont. Buy and replace new as required.
 
Use Reamers

I'll second the motion from Cleaveland Tools. For all the prepunched holes, use a reamer! I bought one #30 and one #40 reamer when I started and they've lasted me the whole project so far through my finished fuselage. They are easy to use and leave a superior hole. I liked them so much I later added other sizes to my toolbox collection for the larger holes. This will also greatly reduce the number of drill bits you need to buy. One 12" long #30 and #40 and a small number of 6" bits have lasted me through the project.
 
YEP....I forgot to mention that I used my reamers quite a bit. They do leave a very nice hole. Using the reamers took some of the work off the drill bits and that's why the bits lasted so well. Also, my kit was a quick build. That surely cuts down on the drilling required.
 
Another vote for reamers, of all sizes, and the appropriate numbered bits to bring the holes up to a few thousandths of final size prior to reaming. Christmas a few years ago Santa brought a complete drill index 1-60 set, and I added a few #31 and #41 bits (for reaming to #40 and #30).

I'm most pleased with the reamers on the larger holes for AN bolts and screws...they *definitely* make a superior, round, clean hole, to tight tolerances and thus a good, tight fit with the fastener. I have about a dozen in different sizes now. (And you'll need a couple of oddball sizes to ream gear leg attachment holes, etc....don't cheap out...get 'em for those important tasks, if nothing else).

Steve
 
Drill point grinding

Beware that some (cheap) drill bits may be ground incorrectly. Look at the rake angle of all the cutting surfaces. They should all be angled such that the bit tries to screw itself into the workpiece, including the tiny little grind that leads up to the split point. I've found some have a portion of their angle going the wrong way which makes the bit want to ride up on the surface it should be cutting into.

At one point I performed a test and found that a brand new #40 bit with slight incorrect grinding took about 1/3 longer to drill a hole than a very old and heavily used Cleaveland Tool bit.

As another poster mentioned, you get what you pay for.
 
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