Using reamers

[cgroves]

I was watching the talk with RV on Plane Lady's youtube channel and the comment he made about using a reamer for the final hole got me interested. I've never used a reamer in sheet metal work and can't seem to find good guidance on making the most of one (other than never, ever reverse one). Is it like a drill in that you can pilot at #40 and then use a #30 reamer to open it up in one step? Do you need to drill it up to something like a #31 or #32 and then use the reamer? What are the ideal RPMs? What types of reamers are good for aircraft skin use?

[GeoffP]

You do need to have the pilot hole very close in size to the reamer size for them to work. You couldn't use one to go up from #40 to #30 for example, but I use reamers that I got from Cleaveland Tools and for the pre-punched holes (skins, ribs etc) the #40 reamer works well.

One benefit of a reamer is that it won't walk like a drill bit and therefore there's much less chance of it elongating the hole. I prefer to use reamers on anything pre-punched, though a drill is still necessary where there's genuine match-drilling involved (like with longerons or J-stringers). Some guys will use a smaller drill (like a 3/32" or #31) then ream to the final size, and I've found that when drilling for either AN3 or AN4 bolts that running a reamer through after drilling cleans up the hole and makes the bolt fit much easier.

[rv8ch]

Originally Posted by cgroves

... What are the ideal RPMs? What types of reamers are good for aircraft skin use?

They make really nice holes, but are kind of expensive.

https://www.cleavelandtool.com/colle...t-flute-reamer

If you use a regular drill bit with very high speed, you can get a pretty good hole. If you use a reamer, you can get a really smooth and round hole. Just more flutes to keep things in the right position.

[JIM_NORCAL]

As a wise builder once said to me... If you want a hole, use a drill. If you want a round hole use a reamer,

[wirejock]

Originally Posted by JIM_NORCAL

As a wise builder once said to me... If you want a hole, use a drill. If you want a round hole use a reamer,

That's the short answer! I have #40 up thru 9/16.
Typically a hole is drilled up to about .005" less than final and finished with a reamer. Far less deburring and a round hole.

[tims88]

I've used a #12 reamer to enlarge a #19 hole several times. I probably would have gotten closer to the #12 size if I had drill bits in sizes between #19 and #12 but it worked just fine. A #30 reamer would probably work to enlarge a #40 hole but I can't say for sure if I've ever tried that.

I believe I read on this forum somewhere that you want to use slower speeds with a reamer. I use my cordless Dewalt drill on the slower setting for as much final drilling as I can.

I usually buy reamers from Cleaveland and if they don't have the size I need then I get them from Yardstore.

[Taltruda]

Originally Posted by wirejock

That's the short answer! I have #40 up thru 9/16.
Typically a hole is drilled up to about .005" less than final and finished with a reamer. Far less deburring and a round hole.

I have readers and drills.. I tend to use the drills for #30 and #40 sheet metal. I remember also hearing the argument that the imperfect holes that drills make may be beneficial for riveting.. the slightly out of round hole may hold a rivet better when the rivet expands to fill the hole. Also, if you ever drill out a rivet, the rivet won’t spin when drilling through it. Splitting hairs, but it makes me feel better about using the cheaper drill bits!

[fixnflyguy]

For laymen's term explanation ,here it goes. The MAJORITY of fasteners in an RV (or any plane) are loaded in "shear". The strength of the joint is the ability to carry load into the members through the fasteners. In a shear loaded installation, the surface area of the inside of the hole that contacts the fastener is the key factor in how good the load can be carried. A rivet, is a "hole filling" fastener. When installed by driving it, the shank expands to fill the hole nearly 100% if its even remotely a good hole. Therefore, you have good shear load transfer. A bolt however, must have a better hole/bolt shank mate-up, typically only achievable by reaming to a true and round condition at nearly the same diameter as the bolt is. This gives you best load transfer. That is the reason Vans does the spar carry through with a closer tolerance fastener and hole. Ultimate failure of a shear joint occurs when the fastener has movement within the hole and eventually leads to a crack. I could go into much more detail, but the laymen's explanation is really all that's needed. I have drilled millions of holes in my 42 year career, but almost never used a reamer in skin (except if thick skin and a fastener different than a rivet)..its really just a waste of time and money.

[Walt]

My go-to drill for primary structure are double margin drills.
Close to reamer quality without the hassle.

https://www.panamericantool.com/doub...in-drills.html

[FinnFlyer]

Reamers for bolt holes, drills for rivet holes.

Bolts do not expand to fill irregular holes, rivets do.

Finn