Which Feeder Drive Suits 300 SPM: Servo or Cam?

Two Machines That Both Feed 300 Times a Minute

The cam feeder inherits its timing from the press. Every stroke delivers the same feed at the same point in the cycle, with no control loop involved.

The servo feeder generates the motion itself and synchronises to the press through a resolver or an encoder signal.

Mechanically, the cam version is simpler and has fewer failure modes. Electronically, the servo version can change what it does between one stroke and the next.

Both are legitimate answers. The mistake is buying one for a job the other was designed for.

Feed force is where the two diverge mechanically. A cam linkage multiplies press torque, while a servo motor supplies its own.

That difference shows on wide thick strip, where a servo may need a larger motor than the frame size would suggest.

Comparison on the Criteria That Decide It

The first and last rows are where most of these decisions actually land. Feed length change frequency and pilot timing tolerance.

Strip width matters as much as thickness here. Above about 600 mm the roll assembly and its inertia start to dominate acceleration demand.

At 300 SPM the feed has to complete in roughly 90 milliseconds, so any control loop lag eats directly into the window available.

Repeatability is usually quoted as one figure, which hides the question that matters: does it hold across the speed range?

Ask for the figure at 100, 200 and 300 SPM separately. A machine that holds 0.05 mm at 150 SPM may not hold it at 300.

The same test applies to a cam feeder. Linkage wear shows up as length variation that grows with speed rather than as a flat error.

Neither machine should be judged on a single-speed demonstration, and the buyers who have done this before never allow one.

Bring your own strip to any demonstration. A machine that performs on clean 1 mm mild steel says nothing about your 0.7 mm coated coil.

Ask what the feed length tolerance is at the shortest feed in your schedule, which is where acceleration limits show first.

Why 300 SPM Is the Number Where They Cross

Below about 200 SPM the servo feeder's acceleration demands are modest and the cam's mechanical simplicity rarely pays for itself in a mixed-die plant.

Between 200 and 250 SPM both work well, and the decision is usually made on flexibility rather than on capability.

Above 300 SPM the cam feeder starts to win on repeatability at the very top of the range, because there is no control loop to lag.

That advantage is narrow and only matters on a dedicated die running the same feed length for months at a time.

For anything resembling a job shop, 300 SPM is firmly servo territory, and the reason is changeover rather than speed.

Where the Cam Still Wins

A dedicated line running one product for years should not pay for programmability it will never use.

Cam feeders also tolerate a dirtier environment. There is no encoder to lose signal and no drive to fault out on a hot afternoon.

They are simpler to repair in a plant without an electronics technician, and the failure modes are visible rather than coded.

And at the very top of the speed range, mechanical timing has no following error to eliminate. On a single-die contract that can be worth real money.

A badly tuned servo feeder shows following error at the top of the speed range and nowhere else, which is easy to miss during a low-speed trial.

A cam feeder with worn linkage shows feed length variation that changes with press speed, which is easy to misdiagnose as a material problem.

Where Servo Is Bought for the Wrong Reason

Plants sometimes buy servo because it looks modern, then run one die on it for a year. That is an expensive way to feed strip.

Others buy it for speed they never achieve, because the press or the die limits the line long before 300 SPM.

And some buy it expecting the control to fix a mechanical problem, such as a badly aligned pass line or worn guides. Servo compensation hides those faults rather than repairing them.

A servo feeder earns its price on changeover count. Count how many feed length changes happen in a month before deciding.

Pilot release timing is the quiet advantage of the servo. On a die with 0.02 mm pilot clearance, five degrees of timing is the difference between clean and marked.

A cam profile can be changed, but the change is a mechanical rebuild rather than a parameter, and it is priced accordingly.

Choosing in Five Questions

Ask how many different feed lengths the plant ran last year. That single number predicts the answer better than any technical comparison.

Plants running under three a year rarely recover the servo premium. Plants running twenty will not tolerate a cam changeover.

The press feeder range lists feed length range and motor rating per model, which is where this comparison should start.

• How many feed length changes per month? Above four, servo pays for itself in changeover time.
• Does the die need adjustable pilot release timing? If yes, only servo can deliver it per job.
• What is the longest feed length? A cam stroke is fixed, and exceeding it means a different machine.
• Is there an electronics technician on shift? If not, a cam feeder's failure modes are easier to live with.
• Will the line run one product for more than two years? If yes, mechanical timing is the cheaper answer.

Answer all five and the decision is usually obvious. The plants that get this wrong tend to answer the first question with a guess.