# Ball screw

A ball screw's shaft, or its flanged single ball nut, from TBI MOTION's SFU and SFNU series. The nut's flange follows DIN 69051 Form B: a round flange with two flats and six bolt holes.

- **Screw** (`part = "screw"`): the shaft, `length` long, standing on the XY plane along +Z, with its ball track, a right-hand helical groove of the lead (`detail = "full"`, the default). `detail = "simple"` gives a plain cylinder at the screw's outside diameter d. A shaft up to 150 leads long is grooved all the way. A longer one has 40 leads of track at each end and a plain middle at d. A real screw is grooved throughout, so read the plain middle as an envelope.
- **Nut** (`part = "nut"`): the flange, A across and B thick, with its face on the XY plane and its flats H apart, parallel to Y. Six X holes sit on the bolt circle W. The body, D across, rises from the flange to the nut's length L. The bore is the screw's outside diameter d.

| Model | d x lead | Ball Da | D | A | B | L | W | H | X | Nut weight | Shaft weight |
|---|---|---|---|---|---|---|---|---|---|---|---|
| SFU01204-4 | 12 x 4 | 2.5 | 24 | 40 | 10 | 40 | 32 | 30 | 4.5 | 0.13 kg | 0.87 kg/m |
| SFNU01605-4 | 16 x 5 | 3.175 | 28 | 48 | 10 | 45 | 38 | 40 | 5.5 | 0.183 kg | 1.56 kg/m |
| SFNU01610-3 | 16 x 10 | 3.175 | 28 | 48 | 10 | 57 | 38 | 40 | 5.5 | 0.215 kg | 1.56 kg/m |
| SFNU02005-4 | 20 x 5 | 3.175 | 36 | 58 | 10 | 51 | 47 | 44 | 6.6 | 0.306 kg | 2.45 kg/m |
| SFNU02505-4 | 25 x 5 | 3.175 | 40 | 62 | 10 | 51 | 51 | 48 | 6.6 | 0.336 kg | 3.83 kg/m |

## Source

TBI MOTION's ball screw catalogue, from a copy hosted by the distributor Anaheim Automation (document L011848, PDF of 2025-03-12): <https://anaheimautomation.com/media/anaheim/files/manuals/forms/L011848_-_Catalog.pdf>.

- "SFNU/SFU (DIN 69051 FORM B) Series Specifications", page C76 (rolled ball screws), with the same rows on page C48 (precision ground): d, lead I, ball Da, and the nut's D, A, B, L, W, H and X. The drawing for d ≤ 32 shows six X holes on the bolt circle W, 45° apart either side of the axis between the flats, at 45°, 90°, 135°, 225°, 270° and 315° measured from the flats' normal (the X axis here). It also places the flange at one end of the nut.
- "2-5 Ball Screw Weight List", page C85: the nut and shaft weights above.
- "2-1 Nominal Model Code of Ball Screw", page C35: S is a single nut, F a flange, and NU the NU-type nut.

**The names.** The old catalogue names these sfu1204, sfu1605, sfu1610, sfu2005 and sfu2505. The names carry no maker: in the market they mean a ball screw of that diameter and lead with a DIN 69051 Form B flanged nut. Each is mapped to TBI MOTION's model with that standard, diameter and lead. For 12 x 4 that is TBI's SFU01204-4. For the others it is TBI's SFNU type, a single flanged nut with TBI's NU-type nut inside, in the same DIN 69051 Form B table. TBI's SFU (U-type nut) rows don't have 16 x 5, 16 x 10, 20 x 5 or 25 x 5.

**Proportions, stated plainly.** The catalogue says TBI's groove is a Gothic arch (page C02, Fig 1.1.2) but doesn't dimension it. So the track is drawn as one circular groove of 1.04 times the ball's radius, its centre on the outside diameter d, which makes it that deep. It is drawn in six straight steps a side. The outside of the shaft is drawn at d. The catalogue doesn't dimension the nut's inside, so the nut's bore is plain at d, with no track. The oil hole Q and the wiper aren't drawn.

**Mass.** The material is steel (`steel-generic`). TBI's shaft weights are the plain cylinder at d: 0.888 kg/m for 12 and 1.578 kg/m for 16, against TBI's 0.87 and 1.56. The `simple` shaft matches them within 2 %. The grooved shaft is about a fifth lighter, 1.27 kg/m for 16 x 5, because the track takes that much away and TBI's weight list doesn't count it. The nuts are solid between the bore and the outside, without the ball track and return channels, so they come out heavier than TBI's weights: SFU01204-4 148 g against 130 g, and SFNU01605-4 218 g against 183 g.

## Catalogue models

The old catalogue's ball-screw entries have no models to measure. Each `<name> ball screw L<n> simple` entry maps to that model's shaft preset of that length, which has the track. `detail = "simple"` gives the old catalogue's plain shaft. `<name> ball nut` and `<name> flange ball nut` both map to the model's nut, which has a flange. The `<name> nut housing` entries are left out: a nut housing isn't part of TBI MOTION's ball screw series, and the entries name no maker of one.