Metal Magic: Using Reamers For Accurate Holes

[@stearman456]

The only thing I'd add to this is you never spin a reamer backwards - like NEVER - because it's the fastest way in the world to damage it and good reamers are expensive (and don't buy cheap reamers. If a hole is important enough to need reaming it's an important hole, so use a quality tool. Also, if I can get the piece in a drill press or milling machine I prefer to ream it that way, nice and square, and slowly with a good lubricant like Boelube or Mousemilk or something similar. Great series, Paul - keep up the good work!

[@CF-yb4wq]

Pro Tip (thanks to Scott McDaniels at Van's): With bare aluminum, or even aluminum with the blue film on it, you can align the reamer perfectly straight with its reflection to achieve good perpendicularity. Same thing holds for rivet sets, which is what Scott addresses in his video on building RV fuel tanks.

[@CF-yb4wq]

My personal experience with drilling large holes in thin sheets is the larger the hole, the more important it is to work your way up step by step through a sequence of drill bits (or reamers) of increasing size, until the hole is big enough for a final size piloted reamer to become effective, then finish off the hole with the reamer. If you just use a drill bit, you can end up with a very ragged hole, especially if a drill bit grabs the edge of the hole and lifts it up.

[@mgwaite10]

Surely overlooking the purpose is to have the finished hole 🕳 with a clean and round inside edge finish to avoid crack propagation. That’s why a ream has straight flutes unlike a drill. It’s also nicer to team by hand with a tap wrench.

[@Factory400]

For the best hole condition......slower RPM works better. Generally, that holds true for drilling as well. I see most people using the fastest possible RPM and the drill is just rubbing its way through allowing it to wobble all over the place. A slower RPM and firm feed pressure ensures the cutting edge is actually shearing the material. This reduces heat and wobble which makes a better hole and the bits last longer. For many of the sheet metal holes for rivets - it probably does not matter, but where you want to be precise. I have machined many millions of (extremely precise) holes over the last 20 years, so I am not making this up. Hope it helps.

[@mgwaite10]

Correct pilot hole drilling avoids all that nonsense, step by step to the finished diameter.

[@dennisjohnson8753]

Very good explanation

[@timwintersoncntr]

Pro Tip: Never reverse rotate a reamer while reaming; clockwise in, clockwise out.

[@Artiscrafty]

I have vise envy

[@mattwiley4530]

Was that drill bit a 15/64?

[@bwalt6779]

I thought a reamer was done in reverse. That is, drill slightly under then slide shank of reamer into hole backwards, then load end into drill. Then pull the reamer BACK through the hold. The cutting part of the reamer is off the shank. End of the reamer is square so dont know how the cutting blades would center well on the smaller starter hole.

[@KitplanesMagazine]

Paul says, "If the reamer won’t start into the hole with the slightly tapered front end, then your hole is too small and needs to be upsized before reaming! Usually just a few thousandths under."

[@AutodidactEngineer]

What about metric? Imperial is confusing and overly complicated!