Zinc Alloy Pillow Block Bearing (KP / KFL)

Shafts and rails · 19 models · Bore 8–35mm · 2 materials · 28 options in stock

Shafts, rails, ball screws and carbon rod — the straight-line backbone of a machine. Everything else on the axis is sized off these. The parameters are listed in order of importance: the one at the top decides the most, and no amount of care further down makes up for getting it wrong.

This page lists 28 options: Model KFL000 / KFL001 / KFL002 / KFL003 … 19 total, Bore 8–35mm (9 options), Material 304 stainless steel / Zinc alloy, Style / variant Heavy duty / Heavy duty P5 / Lightweight / Weighted loose fit. From ¥1.89.

The parts of this item

Figure 1 — This family is all long stock: quote diameter, length and end treatment together

What each parameter decides

Every parameter below shows the real range available on this page, and what goes wrong if you pick it wrong. Work through them in this order and you will not go far wrong.

How to choose, step by step

1. Diameter first — 8–35mm (9 options)ss, load capacity and — just as importantly — which bearing fits on it.
2. Then hardness and finish — Plain shaft, chrome-plated hardened shaft, stainless shaft. The difference in wear and rust resistance is large and the price difference is small.
3. Then support — Over about 600 mm span, use a supported rail or a supported shaft. An unsupported shaft of that length will sag, visibly.

A relationship worth remembering

Two shafts of the same diameter sag under their own weight as δ ∝ L⁴ / D² — the span enters to the fourth power, the diameter only to the second. Double the span and the sag grows sixteen-fold; double the diameter and a quarter of it is left.

So when a span gets long, the effective fix is a mid-span support, not a thicker shaft. Going up one diameter size buys you a quarter of the deflection; adding one support at the middle cuts it by a factor of sixteen.

How the options on this page are distributed

Figure 2 — how the 28 options on this page are spread across each parameter: the bars on the left show how many options sit in each band, the panel on the right shows the real range of every parameter and how many steps it has.

Variant quick reference

Reading the part numbers

You can order by part number or by selecting the parameters. The part number is fastest, but it does not always encode every parameter — the selector on this page is the authority.

8 common mistakes

1. Span goes with the fourth power. An 8 mm shaft over an 800 mm span sags several millimetres under its own weight — the carriage runs downhill into the middle and back up.
2. Shaft diameter and bearing bore are the same number. A 10 mm shaft in an 8 mm bearing is not a loose fit, it is impossible.
3. Plain shaft is not hardened shaft. An unhardened shaft running in a ball bearing develops grooves within a few hundred hours.
4. Chamfer the cut end. The burr left by a cut-off saw destroys the bearing seal on the first pass.
5. A ball screw is not a shaft. It transmits motion; its radial load capacity is poor and it will bend.
6. Measure the span you actually have, not the stroke you want. Support spacing is what decides sag, not travel.
7. Measure before you order. Take the old part off and measure it, or send us a photo with the caliper reading — that beats guessing from a model number every time.
8. Everything here is in millimetres. Where a size is imperial, convert it: 1" = 25.4 mm, 1/4" = 6.35 mm, 3/32" = 2.38 mm.

When to replace it

You do not replace this until it fails — but "still looks usable" and "still reliable" are two different things. Any one of these and it is time:

• Scratches, rust spots or dents on the running surface — the balls click over them once per pass, forever.
• Straightness gone: lay a straight edge along it and you can see daylight.
• Chrome worn through to the base metal. Once that starts, wear accelerates quickly.

Fitting and use

Check before assembly

• Wipe every mating surface with a lint-free cloth. No chips, no burrs, no old grease. One chip is enough to make a bearing noisy.
• Measure the fits — shaft, bore, centre height — against nominal. More than 0.02 mm out and you should check whether you have the right part.
• Check the orientation: the side with the shoulder, step or oil hole has to face the right way. Fitted backwards, it is usually scrap on removal.

Assembly

• Press if you can; do not hammer. If you must tap, use a brass or nylon drift and put the force on the ring that is being fitted, never through the raceway.
• For an interference fit, heat to 80–100 °C first (oil bath or hot plate — never an open flame on a bearing). Hot fitting is easier and safer than cold pressing.
• Tighten fasteners in a diagonal pattern in 2–3 stages. Taking one down fully first distorts the housing and cocks the shaft.

Running in

• Turn it by hand first. It should be smooth, with no tight spot and no axial play. If there is a tight spot, loosen and reseat — do not run it in.
• Run it slowly and unloaded for 10–20 minutes, then feel the temperature. A clear rise means too much preload or poor alignment.
• Re-torque the fasteners after running in, then apply load.

Three things not to do

• Do not hammer. It brinells the raceway, you cannot see it, and it whines forever afterwards.
• Do not mix brands or precision classes in a matched pair. The load shares unevenly and the poorer one always fails first.
• Do not skip lubrication on parts that need it. A few hundred hours dry and it seizes.

Matching parts

• Linear bearings and blocks of the same diameter
• Shaft support blocks SHF / SK
• Couplings and screw support blocks

Lead time, custom work and shipping

• Stock sizes: dispatched in 1–2 working days, subject to stock
• Custom: non-standard sizes, materials and treatments are possible — send quantity and drawing
• Shipping: from Shenzhen; domestic courier by default, DHL or dedicated line for export
• Volume: quantity pricing available, contact us for a quote

If you cannot find the size you need, or you are not sure which one fits, send us the problem you are solving — what machine it goes on, the dimensions of the part you have, what it has to achieve — and we will match it.