Crank Lockout or Constant Pull: Choosing a Tennis Stringer

Why the tension system matters more than the machine

A tennis stringing machine is only as good as the way it applies and holds tension. Two tension systems dominate the market: crank lockout and constant pull electronic. Most buyers spend their research budget comparing clamps, bases, and mounting hardware, but the tension system is the part that decides whether the finished job holds its tension through the session and the following day. The choice between the two also sets the maintenance you will do for the next decade and the cost of the machine itself, so it deserves a look before anything else. The working tension range of a racquet sits between 40 and 90 lbs, and that number is the whole game these machines are built around.

This guide walks through how each system works, where they diverge in practice, and which one fits your weekly volume and budget, using the Tourna 350-CS Premium Crank Stringing Machine as a concrete crank example. The goal is to separate the engineering that changes your stringing results from the marketing that does not, so you can buy the machine that matches how you string rather than the one with the most impressive spec sheet.

How a crank lockout tensioner applies tension

A crank lockout tensioner uses a spring loaded mechanism and a calibrated track. You set a target tension, grip the handle, and turn. As you pull, a ratchet advances in small increments. When the spring force reaches the set value, a lockout pawl releases with a click and the string is clamped at that tension. The whole chain is mechanical: no motor, no sensor, no power draw. Repeatability stays tight, typically within plus or minus 1 lb, as long as the mechanism is clean and the springs have not fatigued.

The trade is effort. You supply the pulling force, so a heavy job on 64 lbs class racquets gets tiring over a long session. But the failure modes are simple, and there is no circuit board to corrode and no firmware to drift. A stringer who knows the machine can diagnose most issues by sound and feel, and the same light maintenance that keeps the ratchet smooth every 20 to 30 pulls is enough to keep it honest for years. That mechanical simplicity is also why a well made crank outlasts the shop it sits in: the parts that move are few, and they are the easy ones to keep in tune.

How constant pull electronic tension works

A constant pull electronic tensioner applies the target tension with a motor and then holds it. Once the string reaches the set value, the motor keeps a small corrective pressure on, so the tension does not decay during the dwell period. Digital readouts land within 0.1 lbs, which removes the guesswork of manually compensating for stretchy strings. For a pro shop running 20 to 100 racquets a week, that digital precision and the faster cycle time are where the value shows up. Most electronic machines also log each pull, which a shop stringing on a customer request form can use to keep a tension record per racquet.

The flip side is complexity. Motors wear, sensors drift, and the electronics need periodic calibration. The same shop that gains speed on constant pull has to budget for that upkeep. And none of the haptic feedback of a crank carries over: you trust the readout, not your hand. When the readout is the only truth, a small calibration error is invisible, and the string comes out a pound light or heavy without the operator ever knowing.

String creep and why the tension drifts

Every string loses tension after it is cut, a behavior stringers call creep. The polymer strands relax, and the string sags by roughly 2 to 5 lbs below the set value in the first hours. Crank stringers compensate by setting the tension slightly high on stretchy poly and at target on stiff synthetic gut, then clamping quickly. Constant pull systems do that correction automatically, which is the clearest argument for electronic tension at high volume.

The amount of creep depends on the string material. Polyester strings relax more than multifilament and far more than natural gut, so a stringer working across several brands is constantly adjusting the target on the fly. That is a cost of knowledge: the more you string, the better you learn to read which material needs the lift. A crank makes that skill visible, because you feel the string fighting back through the handle, while an electronic system hides it inside the numbers.

Frame protection through the mount

A racquet under full string tension takes a hard pull across the frame. The mount is what keeps that force spread evenly instead of concentrating it on one side and warping the hoop. Two point and four point mounts get the job done on entry machines. Six point mounts spread the load more evenly, and a self leveling design conforms to the racquet shape so the stringer does not have to dial in each contact by hand. Mount quality matters more than the tension system for protecting an expensive frame, which is why anyone upgrading from a drop weight should look at the mount before the tensioner.

The rotating base is part of the same story. A full 360 degree turntable with a brake lets the stringer hold the racquet at whatever angle a particular pattern needs, so the stringer is not fighting the frame to reach the last crossing. A heavy base keeps the machine from shifting under a hard pull, and that stability shows up as a cleaner job. Entry machines skip these touches; the better ones build them in.

Clamps that grip without crushing

The clamp holds the string through the pull. A good clamp grips with enough force to stop the string slipping, but not so much that it crushes the filament or leaves a flat spot. Clamps with a sand blasted face hold the string at lower force, which matters for the softer strings that deform easily. A flat spot is not a cosmetic problem: it changes the way that string crosses the bed and loses tension faster than its neighbors, so a well cut clamp protects the playability of the whole job, not just the moment of clamping.

This is where the Tourna 350-CS Premium Crank Stringing Machine earns its premium price: the CNC clamps and self leveling mount are the same hardware that sits on a constant pull machine costing 2000 to 3000 dollars, packaged on a crank body at 1499 to 1795 dollars. Machined from a solid block instead of cast, the clamps hold their tolerances longer and grip more consistently over the life of the jaw.

Matching the machine to your weekly volume

Budget six point machines run 400 to 600 dollars with standard steel clamps. Mid tier crank options near 1200 to 1500 dollars trade brand name for a simpler tensioner. Electronic constant pull machines start close to 2000 to 3000 dollars and climb past 5000 for the top of the line. If you string 1 to 10 racquets a week at home, a well built crank in the 1500 to 1800 dollar range is the sensible buy. If you are a shop stringing 20 to 100 racquets a week, the constant pull speed and digital precision pay back the cost of an electronic tension head upgrade within a season.

The economics come out the same way. A pro strings a racquet for 15 to 30 dollars, and a player restringing a couple of racquets a month spends 360 to 900 dollars a year on outside stringing. A home machine that costs once pays that back within one to three years, after which each restring costs only the price of the string. That is the number to run before the spec sheet, because it tells you whether the better machine is the cheaper one over the years you will own it.

Where the crank still wins

For most stringers who are not running a shop, the crank lockout system is the durable default. It is cheaper to buy and cheaper to keep alive, it holds 64 lbs class racquets steady, and the short mechanical chain means a trip to the workshop is rare. The body itself measures 35.5 x 21.75 x 14 inches and weighs 29.03 kg, or 64 lbs, which is heavy enough to stay planted under a hard pull and still light enough to carry to a club. A 15 to 25 minute cycle per racquet runs slower than a 12 to 20 minute electronic cycle, but at one to ten racquets a week that gap is minutes, not hours. The crank also hands the stringer real feedback through the handle, which is something no motor can replace.

There is a two year warranty on the machine, and the maintenance it needs is the kind a stringer already does: clean the ratchet, check the clamps, tighten the mount. No calibration schedule, no motor service, no parts waiting on a circuit board. It pulls from 40 to 90 lbs of tension, the working range most racquets sit in, and the lockout click lands cleanly across it. Over the life of the racquets you string, that adds up to the cheapest tension system to own, and the hardest one to break.

A buying framework that keeps you honest

Size the decision on volume, not on which marketing term sounds more technical. Fewer than a few racquets a week and drop weight territory is enough. A handful of racquets a week for a serious home stringer points at a crank with a real six point mount and quality clamps. A steady stream of club or shop racquets is where constant pull electronic pays for itself.

Run the numbers on your own volume before you look at the price. Count the racquets a week, multiply by what a pro charges, and compare that annual cost to the machine. Whichever system you choose, verify the mount and clamp hardware before you commit, because protecting the frame is the job that outlives any single tension system. Buy for the racquets you will sit down to string, not the one the showroom makes sound the most impressive.