Drawing dies are polished in stages: start with the coarsest grit the surface condition requires — a grit chosen too fine cannot remove larger surface defects. Once a grit has delivered its maximum achievable finish, move to the next finer grade until the desired roughness is reached. At Leng, the final mirror finish is largely achieved by hand polishing with diamond compounds and suspensions from 45 µm down to 3 µm.
Why polishing governs die life
The surface finish of reduction cone and bearing determines friction, lubricant film and heat generation in the pass. A mirror-polished surface also delays the point at which early wear starts feeding itself: rough spots trap abrasive particles and deepen quickly into drawing rings. That is why polishing is as much part of our tool manufacturing as grinding — and why it pays off in the user's own tool maintenance too.
Choosing the right starting grit
The ground rule from our shop floor: start with the coarsest grit the surface condition requires — and none coarser. A grit chosen too fine cannot remove large defects; a coarser grit removes them considerably faster. Starting needlessly coarse on an already good surface, however, creates scratches you then have to polish out again.
| Surface condition | sensible starting grit |
|---|---|
| visible drawing rings, scoring | 30–45 µm |
| dull, worn surface without deep defects | 9–15 µm |
| refreshing an intact polish | 3–6 µm |
The grit sequence
Once a grit has reached its maximum achievable finish, switch to the next finer grade — for example 45 → 30 → 15 → 9 → 6 → 3 µm, skipping stages depending on the starting condition. Repeat until the desired roughness is reached. Important: clean tool and lap thoroughly between stages so coarse residue does not contaminate the finer step.
Oil or water base?
Our diamond suspension was developed specifically for polishing drawing dies: the stable carrier distributes the diamond grit evenly during cutting and polishing, and the base's temperature resistance prevents drying out during the work. Both bases are available in 3, 6, 9, 15, 30 and 45 µm:
- Oil-based — the classic for hand polishing of dies; temperature-stable, does not dry out. Sizes: 40, 100, 250 ml.
- Water-based — easy to clean off, suited to machine processes and wherever oil interferes. Sizes: 100, 250 ml.
Polishing sticks and felts serve as laps (on request); for reworking the bore itself we stock electroplated diamond grinding pins for bores from about 1.2 mm. Our shop is in German — English inquiries are welcome via the accessories page.
When to stop polishing yourself
If drawing rings run so deep that the bearing loses its size, no polish will help — the die belongs in reconditioning: we regrind the geometry and polish to the next size. The decision aid: Reconditioning or replacement?
Order diamond suspension — all grits 3–45 µm, oil and water base, from stock. English inquiries welcome.
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