How Do You Deburr M5 Holes on Both Sides When Only One Side Is Accessible?

The most reliable way is a back-chamfer or backspot-facing tool run through
the hole from the accessible side, since it cuts the far-side burr without
needing physical access to that face. If the far side truly can't be reached
by any tool, the fallback is designing the burr out with drill point geometry
and feed, because there's no deburring method that reaches a face nothing can
touch.

Why the far side is the problem

Any drilled or tapped hole leaves a burr where the tool exits, because the
last bit of material gets pushed rather than sheared as the point breaks
through. On a hole you can approach from both sides, you flip the part or
run a tool from each face and it's a non-issue. The trouble is a part where
the far side sits against another feature, inside an assembly, or is simply
unreachable in the fixture without a second setup you don't want to add.

Back-deburring tools

A back-spotfacing or back-chamfer tool is built specifically for this. It's
a tool with a pilot that's smaller than the hole and a cutting blade or
carbide flag that folds flat while passing through the bore, then springs or
rotates open once it clears the far face. Retracting the tool with the
spindle running drags the blade across the far-side burr and cuts it off.
These exist in fixed-size and adjustable versions, and for M5 specifically
you're looking at a small pilot diameter, so tool runout and pilot fit matter
more than they would on a larger hole.

This is the right answer when the far-side burr is a functional or cosmetic
problem and the hole is a through-hole with clear axial access from the near
side, even though the far face itself is blocked.

When a back-deburring tool isn't practical

If the hole is blind, or the far side has a feature too close to the exit to
give the folding blade clearance, a mechanical tool won't work. At that
point the options are:

• Reduce the burr at the source. A drill with a proper point geometry and
  a reduced feed rate for the last few thousandths of breakthrough produces a
  smaller burr than a standard drill run at full feed straight through. This
  doesn't eliminate the burr, but it shrinks the problem before you try to
  fix it.
• Vibratory or media finishing, if the whole part can be run through a
  tumbler afterward and geometry allows media to reach the hole exit. This
  works well for M5-scale burrs on aluminum and mild steel, less predictably
  on stainless where burrs tend to be tougher and more rolled-over than
  sheared.
• A hand deburring tool with a long shaft, reaching through the hole from
  the accessible side to scrape the far-side edge. Slower and operator-
  dependent, but viable for low volume where a dedicated back-deburring tool
  isn't worth the investment.

What to do about it

For a real production run, buy or build the back-deburring tool. It's a
known, repeatable process that doesn't depend on an operator's patience, and
it doesn't add a second setup. For a one-off or low-quantity part, evaluate
whether the burr actually matters functionally before spending tooling
budget on it — a burr on a non-critical exit that gets covered by an
assembly might not be worth chasing at all.

The practical takeaway

Don't default to "flip the part." If access genuinely doesn't allow it,
back-deburring tooling solves the problem from the one side you do have, and
reducing burr at the drill or tap in the first place makes whatever
deburring step you use afterward faster and more consistent.