| Regrinding of CDX Carbide Drills |  | |
Recommendations
Follow these instructions with the drawing of the CDX point geometry as a reference.
- Regrind so that the coating in the flutes and on the lands is undamaged.
- The variations in web thinning should be <0.025 mm.
- Use a diamond grinding wheel and a liberal supply of cutting compound.
- Use a stable grinding machine.
- If in any doubt we suggest you take an unused CDX drill and use this as a pattern for regrinding worn drills.
Avoid
Do not use the drills for too long before regrinding. Do not grind by hand.
Procedure
In order to restore the drills to a condition for best possible results after regrinding, we recommend the following three-stage process:-
|
| l. Grinding Primary and Secondary Clearances (see drawing below) |
1. Set the machine to a 130º point angle.
2. Set the secondary clearance angle to 17-25º.
3. Grind the secondary clearance angle until it is in a position beyond the centre line on the cutting side.
4. Set the primary clearance angle to 6-10º.
5. Grind until the junction of primary and secondary clearance is over the centre line of the tool to the heel side to result in a chisel angle of 102-110º.
Point angle: 130º ±2º
| Clearance: | 6 - 10º, ground over the centre line shown in fig. 1 |
| Diameter
mm | Dimensions
A and B mm |
| | |
| 3.0 - 8.0 | 0.10 - 0.25 |
| 8.1 - 12.0 | 0.15 - 0.30 |
| 12.1 - 16.0 | 0.20 - 0.35 |
| 16.1 - 20.0 | 0.25 - 0.45 |
|
| ll. Web Thinning |
1. Use a 60º diamond-grinding wheel with a corner radius. We recommend the following:
Diameter
mm | Grinding Wheel
radius | Length of web
thinning |
| | |
| 3.0 | 0.25 | 0.50 - 0.80 |
| 4.0 | 0.25 | 0.60 - 0.90 |
| 5.0 | 0.25 | 0.70 - 1.00 |
| 6.0 | 0.25 | 0.95 - 1.25 |
| 7.0 | 0.35 | 1.10 - 1.50 |
| 8.0 | 0.35 | 1.20 - 1.60 |
| 9.0 | 0.55 | 1.30 - 1.70 |
| 10.0 | 0.55 | 1.40 - 1.80 |
| 11.0 | 0.55 | 1.40 - 2.00 |
| 12.0 - 13.0 | 0.55 | 1.50 - 2.10 |
| 14.0 - 15.0 | 0.70 | 1.70 - 2.30 |
| 16.0 | 0.70 | 1.95 - 2.55 |
| 17.0 - 18.0 | 0.90 | 2.10 - 2.90 |
| 19.0 - 20.0 | 0.90 | 2.35 - 3.15 |
2. Set the machine so that the axial rake at the secondary cutting edge by thinning is between -1º and -4º.
3. For best results, grind until the amount specified in the regrinding figure (dimensions A and B) is achieved.
4. The web thinning must never go beyond the centre line, (FIG.3).
|
| lll. Negative Rake |
A negative rake edge with an angle of 20-35º along the full cutting lips, with a width acc. to the table above in the direction of grinding, all the way into the secondary cutting lips is recommended. This should be produced by grinding or with a diamond finishing stick, to produce a smooth surface finish.
| Negative rake on cutting lip, dim. F | 20-35º negative |
| Diameter mm | Width of rake mm
(Axial) |
| | |
| 3.0 - 6.0 | 0.03 - 0.07 |
| 6.1 - 10.0 | 0.03 - 0.10 |
| 10.1 - 14.0 | 0.03 - 0.12 |
| 14.1 - 20.0 | 0.03 - 0.15 |
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| Grinding instructions for CDX Drills |
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