Guides / Design and Fit

How a Shop Holds a Keyboard Case While It Cuts Six Faces

October 15, 2026

A machined keyboard case has six faces: top, bottom and four sides. A machine tool reaches some of them in each setup and none of them while the part is moving in the vise. Everything a shop does about holding the part, which is called fixturing, decides how many times the case is flipped, where the joins between operations sit and how likely a clamp is to leave a mark on a surface you care about.

For a designer or a group buy runner this is worth understanding for one reason. Fixturing is the largest cost the quote does not show you, and it is the reason two shops can price the same model far apart.

What one setup can and cannot reach

In a three axis machine the tool comes straight down from above. In one setup the shop can cut the top face of whatever is held, any pocket opening upward and the vertical walls of those pockets. It cannot reach the face that is clamped, and it cannot undercut.

A keyboard case therefore usually needs at least two setups, and often more:

1. Underside and interior. The billet is held in a vise or on a fixture plate. The shop cuts the bottom face, the internal pockets, the screw bosses and the gasket shelf.
2. Flip. The part is turned over and located on the features cut in the first setup. The shop cuts the top face, the outer profile and the top edge details.
3. Extras. Side port cutouts, a weight recess or an angled feature may each need their own setup if the machine is three axis.

Each flip is a point where the part must be located again, and a part located twice is never located exactly the same way twice. That is why the line where two operations meet is often visible if you look for it.

The common holding methods

The shop chooses a method from what the part needs, not from what is cheapest in the abstract. This is a typical list with the trade-offs.

Method	Typical use	Cosmetic risk	Fixture cost	Notes
Plain vise on the billet	First setup, billet still square	Low, billet is later cut away	Very low	Needs enough stock to grip
Soft jaws cut to the part	Flip setup on a part with a profile	Medium, pressure marks possible	Low to moderate	Jaws are machined for this case and reused on repeats
Fixture plate with dowel pins and clamps	Repeat runs and several parts per plate	Low if clamps touch hidden faces	Moderate to high	Best repeatability between parts
Sacrificial tabs	Five axis or one-hit machining	Low, tabs are removed last	Low	Leaves a small mark where the tab was
Vacuum or adhesive holding	Thin plates, rarely a thick case	Low	Moderate	Not common for a deep case
Custom form fixture	Complex shapes, high value runs	Low	High	Often worth it above a few hundred parts

The vise is the cheapest and the plate is the most repeatable. Between them sits a large range of practical jobs, which is why asking a shop how it intends to hold the part tells you a lot about the quote.

Why the witness line exists

Anywhere a tool path from one setup meets a tool path from another, the two surfaces can differ by a few hundredths of a millimetre. On a flat face the eye rarely catches that. On an edge with a chamfer, or a side wall with a visible step, it can.

A shop reduces the problem in three ways:

• It cuts the finished outer profile in the same setup as the face it borders wherever it can.
• It uses a finishing pass that overlaps the joint slightly rather than stopping exactly at it.
• It puts the join where the part is least visible.

You can help by saying where the join is allowed to sit. A note on the drawing such as “witness line permitted on bottom edge only” is a perfectly good instruction and costs nothing. See how to write drawing callouts for the wording.

Clamp marks and pressure

Clamping force is a cosmetic problem as well as a positioning one. A vise clamp on a finished face leaves a mark, and a mark that exists before blasting and anodising will usually survive both.

The safeguards are simple and the shop should be doing them:

• Clamp on a surface that is going to be cut away, or on a hidden face.
• Use soft jaws, with a plastic or aluminium liner, when a finished surface has to be held.
• Keep clamping pressure just high enough to resist cutting forces, since thin walls on a case can distort if they are squeezed and then spring back when released.

A case with long thin walls, such as the side of a low profile design, is the most sensitive to that last point. The wall measures correctly while clamped and measures differently once free. Ask whether the final pass is cut after the clamp has been released or loosened.

How fixturing shows up in price and schedule

Fixturing is a one-time cost on the first run and mostly a saving on the repeat. A first run might include one or two soft jaw sets or a fixture plate, plus the time to prove them on a first article. On a second run those are already built.

Three consequences follow for a group buy:

• First quote versus second quote. A quote that includes tooling will look high next to a quote for a repeat of someone else’s case. Ask for the tooling as its own line.
• Quantity. Fixture cost spread across fifty cases is a visible part of each one. Spread across two hundred it nearly disappears. The same is true of the finishing batch, which is covered in what a machined case actually costs.
• Schedule. A fixture has to be designed, cut and proved before the first good part. That is a few days that sit in the lead time but never in the cutting time, and it is one reason the lead time is longer than the cutting suggests.

What a designer can do to make fixturing easier

You do not need to design the fixture. You can make it easier to design.

• Keep one flat reference. A large flat underside or a flat bottom shelf gives the shop a stable face to locate against in the flip.
• Avoid tight cosmetic features at the join. A tight chamfer or a fine line that crosses the boundary between setups is the likeliest place to show a step.
• Allow some stock on hidden faces. A small amount of extra material on the underside, or a hidden tab, gives the shop a place to hold the part without touching a visible face.
• Do not model features that need an undercut unless you mean it. An undercut means another setup or a five axis machine, and the second costs more per hour.
• State the cosmetic zones. If the shop knows the underside is a hidden zone, it can clamp there. The cosmetic standard template has a three zone scheme you can copy.

Five axis changes the equation

A five axis machine can tilt the part or the tool, so it reaches several faces in one setup. The part can be held by one small area, often a tab or a stub of billet, and that area is cut away last.

That removes most of the flips and so most of the witness lines. It also costs more per hour. The saving is real when the part would otherwise need four setups and not when it needs two, which is the same conclusion reached in five axis versus three axis for a keyboard case.

Questions worth asking a shop

When you compare quotes, these five questions bring out the differences in fixturing quickly:

1. How many setups do you see in this model, and what happens in each?
2. How will you hold the part in the flip, and what touches the finished faces?
3. Where will the witness line sit, and can I choose?
4. Is fixture cost a separate line, and what does a repeat run cost without it?
5. Is the final pass cut with the part clamped or released?

A shop that answers these plainly has almost certainly done this work before. A shop that finds them strange has not, and that matters more than a difference of a few percent in price.

Before you send the files

• One large flat reference face on the underside
• Join location stated in the notes
• Cosmetic zones marked on the drawing
• No undercuts you do not need
• Tooling requested as a separate quote line

When the model is ready, send it through the RFQ form and we will match it with shops that cut cosmetic aluminium and can tell you how they plan to hold it.

Frequently asked questions

Keep reading

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