Linear Guide Replacement: Measure, Match, Replace

A replacement block fails for one reason: it does not sit on the old rail. The mounting height, the body width and the block length have to match what the machine was built around — the name cast into the old block does not settle it. This page lists the numbers to measure, the HG-standard sizes we supply, and what to send so the first quotation is the right part.

The eight numbers to measure

Measure on the machine, not from a photograph. A caliper and a dial indicator are enough for the first five; the last three need the rail clean.

• H — block height, from the mounting face to the top of the block. This fixes the carriage plate height.
• W — block width across the body, which fixes the clearance in the carriage.
• L — block length along the rail. A longer block changes the end stops.
• Wr — rail width, measured on the profile body.
• Hr — rail height, from the mounting face to the top of the rail.
• P — hole pitch: centre to centre of two adjacent rail holes.
• E — end distance: from the rail end to the centre of the first hole.
• Bolt size — the thread in the block and in the rail, which decides whether the old bolts can be reused.

If the old block carries a grade or a preload mark, photograph it. Z0 and ZA are different parts with different clearance, and SP or UP accuracy only leaves the plant as a matched block-and-rail set.

HG-standard blocks, 15 to 65 mm

These are the square HG-standard blocks we supply. If the existing machine was designed around the HG standard, H, W and L below are the only numbers that have to agree.

Block dimensions and ratings from the Yuantong product manual, HGH-CA dimension table, p.39 (printed page 33). Rail dimensions, pitch and end distance are on each rail page.

The rail side decides whether you replace one part or two

A block can be changed on its own when the rail is still straight and its tracks are not worn. Check the rail with a straight edge and look at the ball track under a light: a polished, pitted track will wear a new block quickly, and replacing the block alone then buys a few months rather than a fix. When the rail is worn, the block and rail are ordered together, and the hole pitch and end distance are what make the new rail fit the existing bed without re-drilling.

Rail width and height also set the block: an HGH block will not run on an EG rail of the same size number, because the two families mount at different heights. Measure Hr before assuming the family.

Three ways a replacement goes wrong

Measuring the block and not the rail. Two guides with the same block width can sit at different heights. The height is the number that decides whether the carriage plate still lines up with the drive.

Choosing by photograph. Square and low-profile blocks look alike in a picture. The low-profile block is lower on the same rail, which is exactly what an existing frame cannot absorb.

Assuming preload or accuracy. A free-running block and a preloaded one are not interchangeable in use. If the old part ran tight and the new one is ordered loose, the axis will show it before the first cut.

What to send

• The eight numbers above, or a photo of the old block with a caliper on it.
• The old model code if it is still legible, plus any grade or preload mark.
• How many blocks and how much rail, and whether the rail is being replaced too.
• The machine and the axis, if the load or the orientation is unusual.

That is enough for a quotation against the exact configuration. See the replacement lookup for a single part number, or the HIWIN-compatible mounting page for what carries over from an existing HG-standard design.

Related

Replacement lookup by model · HGR rail lengths and hole pitch · Installation and preload · How to check a supplier · Catalogue