Reaming #30 Holes Question

I have been match reaming v.s. match drilling my #40 holes in thinner materials (e.g., skin to ribs) with nice results. My #40 reamer has a small point that helps maintain alignment.

On #30 holes through thicker materials (e.g. angle and spars) I am not getting such nice results when match reaming. Typically the bottom hole of the thinner material becomes a bit oblong or less round.

My question is, can I match drill to 1/8in (i.e., 0.125, slightly undersized) and then separate the components and ream each hole to #30 independently? Will they align well when I go to rivet if I do this? I figure this will give me some room for error when drilling.

This is "way overkill" in my opinion, and I consider myself a perfectionist. I'm an A&P / IA.....accepted practice is to simply drill with a #30 drill bit. No reamer involved. I have been known to use a #41 drill bit rather than a #40 to tighten things up a little on #3 holes....but don't have that same option for #4 size holes with numbered drill bits. Don't worry about this.... you will have other, more significant things to worry about during the build process. Just wait until you get to the canopy... . Ellis

no matter what you do a ''match'' on i would think a 4 flute reamer would make a rounder hole than a drill bit. i did reaming quite a bit on my 12. no matter what others ran into my prepunched holes from the factory would not let a drill bit shank pass thru the hole . i matched a lot of holes and never noticed anything but that i liked the reamer better than a drill.

Reamers

As they say, it won't fall out of the sky. Or is it, you're building a truck not a Ferrari.
Whatever. I ream every hole. Typically drill .005" smaller with a drill bit and final dimension with a reamer.

just me

I match drill to 1/8" and then ream for #30; or 3/32 then #40.

By match drilling to 1/8" (0r 3/32"), the clecos are much tighter and the parts stay together tight and matched. I found when I went to final size (#30 or #40) sometimes I had to rotate the clecos to keep everything in perfect alignment.

But it is your airplane, not mine, so consider the advice and build on.
But do build on.
JMHO. YMMV

Wire Jock, do you ream the pieces separate or while clecoed together?

Reaming

RV701775 said:

Wire Jock, do you ream the pieces separate or while clecoed together?

Click to expand...

Always clekoed or clamped. As mention by others, drill 1/8" and insert 100% clekos. Usually it's a gap in parts or some slop in the clekos that allows parts to move enough to cause an offset hole.

Why ream them? When you dimple the holes are going to change size anyway. Just match drill to number 30 or number 40.

I find the drill vs ream an interesting discussion.

Does it increase the strength of the joint? There is no data to support that. The strength data in the FAA structures handbook, MMPDS which the RV structures are designed to, is developed from test data with drilled holes. So the structure will meet intended strength without reaming. Does it increase fatigue life? Practically speaking, not unless one or both of the parts is highly loaded cyclically. Further, once the dimple is formed it changes the hole size and any precision fit from the reaming is lost. In any case, the reason that we use solid rivets is that they expand to fill the hole to make a zero clearance fit and provide for shear loading

Structurally we do precision ream fits for fasteners that don?t expand, like Hi-lok?s and other hi shear fasteners.

So what is the advantage?

dan,
i think i get a ''rounder'' hole with the reamer and i know using the reamer feels smoother and no tendency for the tool to be pulled into the work with the reamer.seems like material is removed more uniformly around the edge of the hole. i chuck the reamer into one of those dinky electric screw guns and it is effortless .

Using reamers has many benefits for close tolerance holes as we all know...

BUT

I use a reamer for match drilling (not 100% of the time) for one reason...

Less DE-BURRING

bobnoffs said:

dan,
i think i get a ''rounder'' hole with the reamer and i know using the reamer feels smoother and no tendency for the tool to be pulled into the work with the reamer.seems like material is removed more uniformly around the edge of the hole. i chuck the reamer into one of those dinky electric screw guns and it is effortless .

Click to expand...

It may be true that the hole is rounder, but the rivet expands to the hole either way. Unless your hole drilling is really off, a hand drilled hole should yield a hole with less than, .003? out of round.

I will caution, that CherryMax rivets, while structural, have much less hole filling capability. While a reamed hole isn?t necessary, they are much less tolerant of oversized or elongated holes. This is especially true in sheets less than .032? thick.

Always reamed

I actually acquired the #30 and #40 reamers. I found that they would create a very round hole while creating minimal burr on the backside as the reamer passes through. Yes it was a bit of over kill but the reaming was just as fast as the drilling so I used this process on my entire project.