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SFU2510-3/4 Ball Screw, 25 x 10 mm, 2,954 kgf Dynamic Load

A router builder in Poland sent us a drawing last spring. His Z axis used a 25 mm screw with a 5 mm lead, driven by a 3,000 rpm servo through a 2:1 reduction. He wanted 12 m/min rapids. The screw could not get there - not because the motor was small, but because a 5 mm lead needs 2,400 rpm at the screw to reach 12 m/min, and his shaft length put the critical speed well under that. He did not need a bigger motor. He needed a 10 mm lead.

That is the case the SFU2510-3/4 is built for. Same 25 mm shaft as the SFU2505, twice the lead, so the screw turns half as fast for the same linear speed.

Dimensions and load ratings

The table below is the SFU2510-3/4 exactly as it appears in our catalogue, alongside the two other 25 mm options so the trade-off is visible.

Two things in that table are worth stopping on.

The nut body grows. Going from a 5 mm to a 10 mm lead takes the nut length from 44/51 mm to 70/85 mm and the flange thickness B from 10 mm to 12 mm. If you are swapping a 2505 for a 2510 inside an existing housing, the nut will not fit the same pocket. Check the 85 mm figure, not the 70 mm - the longer value applies to the 4-circuit variant.

The ball diameter changes too: 4.762 mm against 3.175 mm on the 2505. The larger ball is what lifts Ca from 1,724 kgf to 2,954 kgf. It is not a marketing number; it is the same 25 mm shaft carrying a bigger ball circle.

Why 10 mm lead, and when not to use it

Higher lead buys speed and costs resolution. With a 10 mm lead and a 10,000 count/rev encoder, one count is 1 µm of travel before any reduction. That sounds fine until you remember that the mechanical resolution is not the same as accuracy - see how accuracy grades actually work on a ball screw before you commit to a C7 screw on a machine that needs to hold 0.02 mm over a metre.

The 2510 makes sense when:

• Linear speed matters more than force. Routers, laser cutters, pick-and-place with light payloads.
• You want to drop a gearbox. Direct-driving a 10 mm lead screw at 3,000 rpm gives 30 m/min, which is often enough to remove a planetary reducer from the BOM.
• The axial load is moderate. At 2,954 kgf Ca you have real margin, but a 10 mm lead screw is a poor choice for a press or an injection mould clamp where the load is high and the speed is low - the motor torque per unit thrust is worse than a 4 or 5 mm lead.

The 2510 is the wrong choice when you need static stiffness in a holding application. A 4 mm lead with the same 25 mm shaft gives you Coa 3,795 kgf and a finer mechanical advantage. Read the difference between rolled and ground ball screws if your positioning tolerance is tighter than 0.05 mm/300 mm.

Speed limit: do the check before you order

This is the mistake we see most often on 2510 enquiries, and it is not a small one.

A 25 mm screw with 1,200 mm between mounting surfaces, fixed-supported, will not spin at 3,000 rpm. The critical speed falls with the square of the unsupported length, and the permissible speed is the lower of two figures: the critical speed of the shaft and the DN limit. THK publishes a 0.8 safety factor on the critical-speed calculation, and requires you to compute both the A and B spans on a fixed-fixed arrangement and take the smaller result.

Ask your supplier for the critical speed at your actual span. If they quote a speed without asking for your span, they are quoting the motor's limit, not the screw's.

Buckling is the mirror problem. THK applies a 0.5 safety factor to the buckling load, and on a fixed-fixed shaft you again take the smaller of the two spans. A 25 mm screw in compression over 1,500 mm is a different component from the same screw in tension.

Mounting and support

The SFU2510-3/4 is a standard flange nut with an M6 lubrication port (dimension Q). Pair it with a BK12/FK15 support unit at the fixed end - the 25 mm shaft and the BK12 bore are matched, and using a smaller support to save cost is how you get axial float that no amount of preload will fix.

Preload: THK's guidance is that preload stays effective up to roughly three times the applied preload, so the optimum sits near one third of your maximum axial load, and the preload should not exceed 10% of Ca. On this screw that ceiling is around 295 kgf. We have written separately about how preload interacts with accuracy - the short version is that over-preloading a rolled screw to chase stiffness shortens its life and heats the nut.

What we need from you to quote

Shaft overall length, thread length, the span between bearing supports, end machining drawing (or the support unit model you are using), and whether you need a nut housing. Without the span we cannot confirm the speed, and we will ask for it before releasing the drawing.

For selection help across the range, start with how to choose the right ball screw or send the load case directly.

Catalogue figures in this article are from the OND SFU series table. Accuracy grade definitions follow ISO 3408-3:2006 and the THK technical handbook. Verify the final specification against the drawing supplied with your order.

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