Bernardo Corundum Abrasive Disc Ø 250 mm K 220 – 180 rpm for NTS 250 Pro
The Bernardo corundum abrasive disc is for those working with NTS 250 Pro and NTS 250 P. Unlike generic discs, this one is certified by the manufacturer: the same grit, the same hardness, the same dimensional tolerances repeated batch after batch, ensuring the disc does not become unbalanced during rotation, does not leave irregular streaks, and does not wear the mounting flange more than expected.
The K 220 grit (220 nominal microns) is the Bernardo standard for finishing work on scissors: it removes roughness from grinding, prepares for the final cut, and leaves a clean edge. Recommended for precision work on stainless steel and light alloys. For aggressive material removal, Krollit also distributes K 120 and K 180 upon request.
Critical technical parameters for correct installation
The outer diameter Ø 250 mm is standard for the Bernardo NTS 250 flange. The central hole Ø 12 mm fits the scissor shaft; tight tolerances (H7) ensure precise centering without play. The width of 50 mm is the maximum compatible with the scissor's geometry; thicker discs (70, 100 mm) do not physically fit.
The maximum rotation speed of 180 rpm is the thermal and mechanical limit of the corundum disc. Beyond this regime, the material tends to fracture due to centrifugation. Bernardo specifies this parameter because NTS 250 Pro scissors have an adjustable motor; an inexperienced operator could accelerate beyond the limit. Our technical team recommends setting the motor to 150 rpm for ordinary use, 180 rpm only for aggressive work on soft materials.
Maintenance and durability
A K 220 disc typically lasts 200-400 hours of continuous work, depending on the load and material being processed. When you notice wear (the disc becomes flat, not abrasive), replace it.
Technical specifications
Dimensions and geometry
| Disc outer diameter |
Ø 250 mm |
| Width (thickness) |
50 mm |
| Central hole |
Ø 12 mm (H7 tolerance) |
| Weight (estimated) |
600-700 g |
Performance and operational parameters
| Grit (FEPA standard) |
K 220 (220 nominal microns) |
| Abrasive material |
Corundum (superior corundum/edelkorund) |
| Maximum recommended speed |
180 rpm |
| Recommended operating speed |
150 rpm (to extend lifespan) |
| Disc hardness |
Medium (suitable for finishing, not aggressive removal) |
Compatibility
| Compatible scissor models |
NTS 250 Pro, NTS 250 P |
| NON-compatible models |
NTS 100, NTS 150, NTS 200 (different diameters) |
| Mounting |
Standard Bernardo flange, Ø 12 mm shaft |
Compliance and safety
- CE – Machinery Directive 2006/42/EC
- EN 12413 (abrasive disc specifications)
- Maximum speed labeling visible on the disc
Standard equipment
- Complete abrasive disc, individually packaged
- Technical sheet with operating parameters (German/English; Italian translation by Krollit)
- Safety warnings on disc label
Accessories and available variants
Bernardo produces the same Ø 250 mm disc in different grits. Available to order from Krollit:
-
K 120 — Aggressive removal, for initial deburring (less frequent)
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K 180 — Medium-fine, versatile (alternative to K 220)
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K 220 — Standard finish (THIS PRODUCT)
-
K 320 — Fine finish, for tight tolerances (special order)
We recommend testing K 220 before ordering variants; it is the standard that satisfies 85% of Krollit customers.
Frequently Asked Questions
Can I use a generic Chinese abrasive disc instead of Bernardo?
Formally yes, technically no. A Chinese Ø 250 mm disc can physically mount. However: imprecise grit (K 220 declared but 180-240 real), hole tolerance ±1 mm (poor centering), absent balancing (unbalances during rotation), variable hardness between batches. Over 100 work cycles, you will consume 15-20% more discs, waste time cleaning and realigning, and risk irregular streaks. The Bernardo costs 5-8 € more than the Chinese; in a year of professional use, you amortize the difference in the first month.
What is the typical lifespan of a K 220 disc?
200-400 hours of continuous rotation, depending on the material being processed and the load. On mild steel, it lasts longer. On stainless steel, it wears faster. Determining factor: rotation speed. At 150 rpm, it lasts longer than at 180 rpm. When the disc becomes visibly flat (loses its abrasive shape), it's time to replace it.
How do I install the disc on the NTS 250 Pro scissor sharpener?
Procedure: 1) Turn off the scissor sharpener and disconnect it from the electrical circuit. 2) Remove the old disc by loosening the central screw. 3) Clean the flange of dirt. 4) Insert the new disc, aligning the Ø 12 mm hole with the shaft. 5) Tighten the central screw by hand (do not overtighten, 5-10 Nm is sufficient). 6) Manually rotate the sharpener without power to verify that the disc is centered and does not rub. Total time: < 5 minutes. Krollit provides free phone consultation for the first change.
What grit should I use for my type of work?
Recommended table: K 120 = aggressive removal (initial deburring, heavy load); K 180 = medium-fine (versatile); K 220 = standard finish (smooth edge); K 320+ = fine finish (very tight tolerances). If you are unsure, start with K 220 (this product) and add variants after testing. Contact Krollit for application advice.
Can I use a speed higher than 180 rpm?
No, it is the limit declared by Bernardo. At higher speeds, the corundum tends to fracture due to centrifugal force; the disc can explode during rotation (high risk of injury). Bernardo specifies 180 rpm because laboratory tests show that beyond that limit, the material's resistance significantly decreases. If your application requires a higher speed, contact Krollit to check if a reinforced variant exists (usually with reduced width and smaller diameter).
What is the difference between K 220 and K 320?
K 220 = 220 microns (medium-fine grit). K 320 = 80 microns (fine grit). K 320 leaves a smoother and shinier finish, but wears faster and removes less material per pass. Use K 220 for most of the work; switch to K 320 only for the final passes if you have critical tolerances. K 320 is a special order from Bernardo, with a lead time of 2-3 weeks.
What warranty covers the abrasive disc?
Bernardo Warranty: manufacturing defects for 24 months from the date of purchase. It does not cover wear from work cycles, unbalance from dropping, or damage from excessive speed. If the disc fractured during normal use (not chipped by impact), Bernardo will replace it. Contact Krollit to manage the claim; we coordinate with Bernardo Austria.
Is it worthwhile to order in bulk (10-20 discs) to save money?
Yes, if consumption justifies it. Krollit applies progressive discounts: 5-10 discs = -5%, 11-25 discs = -10%, 25+ discs = -15% + free shipping. A workshop with 3+ NTS 250 Pro scissor sharpeners justifies a quarterly order of 10-15 discs. Additionally, bulk orders reduce the risk of production downtime due to disc shortage. Contact Krollit for a custom quote.
