Every shop has run into it. The part comes off the CNC, somebody picks up a hand polisher, and ten minutes disappear into an edge the machine was supposed to finish. Do that on forty parts a week and you have paid for the hand blending twice: once in labor, once in the cycle time you thought you were saving.
Here is the part most people get backwards. When an edge comes off the machine needing work, the problem is almost never in the position you are looking at. It was set two or three positions earlier, and by the time you can see it, no amount of extra polishing will take it out.
This is a troubleshooting walkthrough: symptom first, cause second, fix third.
First, the thing that makes this counterintuitive
A profile is cut by a stack of wheels, normally seven positions, 0 through 6. Positions 0 to 3 are metal-bond wheels that cut. Positions 4 to 6 are resin polishing wheels that remove zero material.
Read that last part again, because it is the whole reason edges fail. Your polishing positions cannot remove a scratch. They close and refine a surface, they do not cut one. So a scratch left behind by position 3 is still exactly where it was when the part comes off position 6. The finish you get is decided before polishing ever starts.
Symptom: a fine scratch pattern you can see under raking light
Cause: the step from your last metal position to your first resin position is too big.
Position 3 is the last wheel that actually cuts. If it leaves scratches deeper than position 4 can close, the pattern rides all the way through to the end of the sequence. Two things usually cause it: a worn fine metal wheel that is no longer cutting to its rated finish, or a skipped position in the program because somebody was chasing cycle time.
Fix: check the wear on position 3 before you touch anything else. Then confirm the program is actually running all seven positions. Shops skip position 2 more often than they admit.
Symptom: a hazy or burnished band on hard material
Cause: the bond is too hard for what you are cutting.
A diamond wheel works by wearing out on purpose. Spent diamond breaks away, fresh diamond gets exposed, and the wheel keeps cutting. That release is what the bond controls.
On dense material, quartzite and porcelain especially, a hard bond holds worn diamond too long. The wheel stops cutting and starts rubbing, and rubbing shows up on the edge as a hazy band that polishing will not lift. A softer bond dumps the spent diamond faster and keeps cutting.
This is why bond choice beats diamond quality on hard material. A premium wheel in the wrong bond loses to a mid-range wheel in the right one, every time.
Fix, by material:
- Granite, quartz and engineered stone: standard metal bond through position 3. The general-purpose case, and the one most sets are built for.
- Quartzite: go softer. Dense and abrasive, and the most common place shops discover their bond is wrong.
- Porcelain and ultra-compact (Dekton, Neolith, Laminam): a bond coded for ceramic. Vincent codes these CERAM2 and CERAM7. A general-purpose wheel will not survive the job, let alone finish it.
- Marble and soft stone: the easiest case on the list. Do not overspend here.
Symptom: finish quality that changes part to part
Cause: feed rate, usually on the polishing positions.
Published feed rates are engineering limits, not suggestions. Run a polishing position faster than about 4.9 ft/min (1,500 mm/min) and it skips surface it was supposed to close, which reads as an inconsistent finish rather than an obvious defect. Meanwhile, running a roughing position slow does not buy you a better edge. It just heats the tool and burns cycle time.
Target numbers to check your program against:
| Positions | What they do | Spindle speed |
|---|---|---|
| 0 to 3 | Metal bond, cutting | 4,800 to 5,500 RPM |
| 4 to 6 | Resin, polishing at zero stock removal | 2,700 RPM |
Symptom: it was fine last month, now it is not
Cause: a glazed wheel, or a set that has been run past its useful life at the wrong feed rate.
Glazing is fixable. A dressing stick reopens the wheel by knocking off the smeared bond and exposing fresh diamond, and it takes a minute. If a wheel glazes repeatedly on the same material, though, the dressing stick is treating a symptom. The bond is wrong for what you are cutting.
Worth knowing: running above the published feed rate is the single fastest way to shorten a set's life, and it costs you the finish you bought the set for. You pay twice for the same mistake.
A note on mixing brands across positions
Plenty of shops do it and it can work fine. The risk sits at one specific place: the handoff from position 3 to position 4. Different manufacturers finish the last metal position differently, and a resin wheel is built expecting a particular starting surface.
So if you are actively chasing a finish problem, run one manufacturer through all seven positions first. Not because mixing is wrong, but because it eliminates a variable, and troubleshooting with a mixed stack means guessing.
Where throughput comes from
Once the finish is right, the next question is how fast you can get it. Vincent publishes two grades of slotted profiling wheel, standard and EPIC. At the same position they remove the same amount of material, but EPIC runs roughly double the feed rate at positions 1 and 2, up to 31.2 ft/min (9,500 mm/min) against 16.4 ft/min (5,000 mm/min).
Those are the two positions that eat the most cycle time, and the removal per pass is unchanged, so the finish does not move. For a shop running unattended, that is the cheapest throughput on the machine.
The short version
If an edge needs hand blending, work backwards, not forwards. Check position 3 for wear, confirm no position is being skipped, verify the bond suits the material, then check your feed rates against the published numbers. The polishing positions are almost never the culprit, because they cannot be. They remove nothing.
Chasing a finish problem on a specific profile, radius or machine? Call 916.277.8877. We run these tools in our own shop and will tell you when a cheaper option does the job.
Related reading: Which CNC profile wheel leaves the cleanest edge on stone? covers position-by-position stock removal and how to spec a set from scratch.