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EGH20SA Linear Guide Block, 28 mm Low Profile, 7.23 kN

A packaging machine OEM we work with had a stack-up problem, not a bearing problem. Their gripper carriage sat on HGH20 blocks, and the assembly height put the gripper jaws 30 mm above where the product drawing said they should be. They had three options: redesign the frame, machine a pocket into the carriage, or drop the block height. They took the third.

That is what the EGH series exists for. Same 20 mm rail, same bolt pattern family, but the block sits 2 mm lower and the whole assembly is shorter front to back. Two millimetres does not sound like much until it is the two millimetres you do not have.

Dimensions and load ratings

Read the EGH20SA row against the EGH20CA row directly above it. The rail, the height, the width, the bolt size and the rail weight are identical. The only thing that changes is the block length - and with it the load rating.

The SA gives you 7.23 kN dynamic against the CA's 10.31 kN. That is a 30% reduction, and it is not a rounding difference. It comes from fewer load-bearing balls in contact: the short block carries less of the raceway. If your carriage has an overhung load or a moment, the SA block will be the first thing to complain.

Block-to-block dimension details (C, L1, L, K1, K2 and the lubrication port G) vary by size and are set out on the catalogue drawing for each size; quote those from the drawing rather than from a summary table.

When the short block is the right call

Take the SA when three things hold:

1. The load is centred and mostly vertical. A gantry Z axis, a pick head, a light XYZ table.
2. The stroke is short or the block count is high. Four short blocks on one carriage often beat two long ones, and they distribute the moment better than two SA blocks would.
3. Height or overhang is the binding constraint. This is the whole point of the series.

Take the CA when the carriage overhangs, when there is a cantilevered tool, or when the machine takes shock loads at the end of travel. The static moment ratings tell the story plainly: MR 0.13 kN·m on the SA against 0.22 kN·m on the CA. If your moment calculation lands near 0.13, you are already outside what the SA should be doing.

The mistake that costs people a rebuild

The EGH and HGH series share a rail size and a bolt size, so they get treated as interchangeable. They are not, on two counts.

Height. HGH20CA sits at 30 mm; EGH20SA sits at 28 mm. If you built your frame around one and swap to the other, every downstream dimension moves. We have seen a machine arrive with the gantry 2 mm low and a homing sensor that no longer triggers. There is a separate applied-height dimension H1 (4.6 mm on HGH20 against 6 mm on EGH20) because the rail groove depth differs too.

Preload and clearance are ordered separately. A block is not "ready to run" out of the box by default; you specify the preload class and the resulting clearance. If you have not specified it, you have not fully specified the part - and the same model number from two suppliers can behave very differently on a machine that needs stiffness. We cover the interaction with screw preload in linear guideway preload and ball screw accuracy.

Mounting notes that matter more than the datasheet

Rail joint and datum surfaces. The rail is bolted, not clamped, and it needs a shoulder to register against on at least one side. Two rails parallel to each other without a common datum will bind on a four-block carriage no matter how good the blocks are. We wrote about how to align linear guideways during installation because this is the single most common cause of a "defective" block coming back to us.

Bolt torque. The EGH20SA rail is fixed with M5×16 bolts on a 60 mm pitch. Tighten in a sequence working from the centre outward, and re-check the rail straightness after the first pass - pulling a rail down onto a surface with a burr will bend it, and a bent rail wears blocks out in weeks.

Lubrication. The port is G, on the end cap. A block run dry in a wood-dust environment will seize before it wears. Fit a bellows or a wiper set if the machine cuts MDF.

Pairing with the drive

The EGH20 frame is a natural match for an SFU2005 ball screw - the flange nut SFU1605/SFU2005 range covers it - or a rack and pinion if the stroke is long. If you are still choosing between the two drive types, rack and pinion vs ball screw sets out where each one stops being the sensible answer.

For a longer-stroke machine where the rail has to be joined, read joining gear racks for long travel for the alignment logic - the same datum discipline applies to rails.

Quote checklist

Rail length, rail quantity, number of blocks per rail, preload class, whether you need a rail with dowel holes, and your mounting surface tolerance. Send the assembly drawing if you have one; the height check takes us two minutes and saves a redesign.

Dimensions and load ratings from the OND low-assembly EGH-CA/SA catalogue table, p.30. Confirm the final part number and preload class against your order drawing.

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