Dongguan Pinsi Machinery Co., Ltd. is a professional linear motion manufacturer & supplier since 2013, we specialized in Precise Linear Motion Products like Linear Guides, Ball Screws, Cross Roller Guides, Linear Module, Linear Motor and more for various industries. In addition, we provide one stop linear motion solution.Welcome to contac us.

A customer sent me this last month:

"I need an SFU1605 for a 100 kg table. Will it work?"

I didn't answer right away. Not because I didn't know, but because the question as written can't be answered honestly. A 100 kg table on a horizontal axis with proper linear guides is a very different problem from a 100 kg table on a vertical Z-axis. Same screw. Same weight. Completely different result.

And that's the thing about SFU1605. It's one of the most common ball screws in small CNC and automation, and it's also one of the most misunderstood. People see the model number, look up a load rating, and assume that number is the answer. It isn't.

So let me explain how I actually think about it—not from a catalog, but from machines I've built, fixed, and in a couple of cases, watched fail.

A practical guide to preload, lost motion, and when replacing a ball screw actually makes sense
When an operator reports about 0.05 mm of backlash on the X-axis, the first reaction is often: “Should we replace the ball screw?”

That is usually the wrong first move.

Lost motion at the tool or table does not automatically mean the ball nut is worn out. The error may be coming from the coupling, bearing support, nut housing, linear guide system, or even the machine frame. If the real source is somewhere else, installing a higher-grade screw or a new screw assembly may cost a lot of money and change very little.

Preload is important, but it is only one part of the picture.

A ball nut with the right preload can have very small internal clearance and good axial stiffness. But if preload is increased too much, the machine pays for it through higher friction, more heat, greater motor torque demand, and faster wear.

That is why preload should be treated as a design decision, not as a knob t

A customer sent me a video last month. The screw was spinning on a test stand, and you could hear it—a rising whine that got worse as the RPM climbed. By the time the motor hit around 1800 RPM, the whole assembly was shaking hard enough that he didn't want to run it anymore.

He asked me if the screw was defective.

I asked him three questions instead.

What's the unsupported length? What support blocks are on each end? And how fast are you trying to run it?

His answers were: about 1100mm between supports, BK12 on the fixed end and BF12 on the floating end, and he wanted 2500 RPM so he could hit 25 m/min with a 10mm lead.

That right there told me the screw was probably fine. The problem was that the support arrangement and the operating speed didn't match.

This is one of the most common issues I run into when people order ball screws for CNC machines. The diameter is right. The lead is right. But the screw still doesn't run well, and nobody can figure out why.

It's almost never the

A customer once sent me a message:

“I need a 1610 ball screw for my CNC router. 1000mm travel. Quote please.”

I asked what motor he was using. He said a NEMA 23 stepper, around 3 Nm, with a 36V supply. Then I asked how fast he wanted the machine to move.

He said, “As fast as possible.”

That’s when I knew the 10mm lead was probably a mistake for his setup. Not because 10mm is bad, but because his motor wouldn’t have enough torque to actually use the speed he was imagining. He had picked the larger lead because it looked faster on paper.

That conversation happens a lot. People see “10mm lead = double the speed” and stop the calculation there. But lead changes more than speed. It changes thrust, acceleration, motor RPM, and sometimes the whole feel of the machine.

So if you’re trying to choose between 5mm and 10mm, let me walk through how I actually think about it.