Hose skiving: why the rubber is removed before crimping
The ferrule of an interlock fitting must grip the steel reinforcement of the hose, not a layer of rubber. We explain external and internal skiving, when crimping without it is not allowed, the typical mistakes — and the machines that do the job: the powered LT-S50 and the manual LT-SH50.
Rubber is a sealant, not a load-bearing element. All the load in a hose is carried by the steel braids and spirals, and it is these that the crimped joint must grip. While the ferrule is crimped over the cover rubber, an elastic layer sits between the ferrule metal and the reinforcement metal: under pressure and temperature it gradually creeps and the grip loosens. For braided hoses with no-skive fittings this is allowed for in the ferrule design, but heavy spiral hoses are assembled with interlock fittings — and there the seating of the ferrule and nipple directly on the reinforcement metal is mandatory. That is what the hose end is skived for before crimping.
External and internal skiving
- External skiving — the cover rubber layer is removed from the hose end down to the metal of the spiral, exactly over the ferrule length. The ferrule is crimped directly onto the reinforcement.
- Internal skiving — the inner layer is removed for the skirt of the interlock fitting's nipple, so that the nipple also bears on metal. It is done on the same machine; on the LT-S50 and LT-SH50 in the 3/4"–2" range.
The skiving depth and length are not "by eye": they are set by the ferrule of the specific fitting and stated in its manufacturer's catalogue. That is why a skiving machine has an adjustable cutting depth and a length stop.
Skiving mistakes — and how they end
Under-skiving. A rubber layer remains on the reinforcement — after crimping the ferrule grips partly on it. The joint passes installation, but under pressure and heat the grip creeps away; the end is a blown-off fitting, one of the scenarios covered in the article on crimping defects.
Over-skiving. The knife went deeper than the cover layer and cut the wire. Every cut wire is out of work — the reinforcement is weakened exactly in the zone of maximum stress at the ferrule edge. From outside, after crimping, this cannot be seen.
Uneven length or a "step". A skewed skiving edge shifts the ferrule seating; unequal length around the circumference causes misalignment. A correct cut is perpendicular and of one depth all around.
The machines: LT-S50 and LT-SH50
LT-S50 — a machine with an electric drive: the hose is clamped, the tool removes the layer to a preset depth. The speed is low — 145 rpm: the layer is cut off without overheating or smearing the rubber, and the operator stays in full control. External skiving 1/4"–2", internal 3/4"–2"; supply — three phases 200/220/380/440 V or single phase 110–240 V, power 0.4 kW, weight 57 kg.
LT-SH50 — a manual machine with the same ranges: it clamps to a bench or a van side and needs no power at all. The natural choice for mobile service and shops with occasional skiving.
Both come with the standard tool set: external skiving 1/4", 5/16", 3/8", 1/2", 5/8"; external and internal — 3/4", 1", 1 1/4", 1 1/2", 2"; additional sizes on request. In the shop process chain skiving is the third stage, between cutting and marking.