Central drills serve for do central hole in the weight for turn between centres. They help to also start boring holes. Dank their gross rigidemo, these utilities no devias easily.
Many use central drill of #2 until #5 for everything possible. That happens commonly during manlaboro on lathes and freziloj. Genua grinder operates more well in low turnrapidoj.
How to Use Central Drills
Election of the apt pace and paŝlongo are inherent. For instance, for materials with 100 Brinell-dureco, pace of 80 surfacpiedoj for minute. This value one depresses in 10 surfacpiedojn for every additional 50 Brinell-spots.
Formula for surfacpiedoj for minute: 0.2618 occasionally borila diameter occasionally RPM. With karbidaj utilities one reaches 60 SFM from the biggest wanted diameter. #1 central drill with 0.047-cola peak requires 30 SFM and 2438.3 RPM.
#43 drill of 0.089 inches at 30 SFM turns in 1287.6 RPM. Widely during central boring, the cone twists that much quickly as maybe according to the material. Conical paces reach around 1000 RPM for centrado, but varies according to type.
Nekoroda steel requires 1000 RPM, soft steel 5000 RPM, aluminium 10 000 RPM.
Paŝlongaj values are likewise inevitable. For feraj materials the thumb-rule says: 0.001 inches for revolution each every 1/16-inch of diameter, plus-minuso 0.001 inches entirely. Occasionally paŝlongon confine to 4 milumoj for revolution.
For #1 central drill one bid 0.002 inches each tooth, or indication of 1.5 until 2. Inches for minute one counts by means of paŝlongo each revolution occasionally RPM. With 0.031-cola drill in 303 nekoroda steel, 0.0005-cola paŝlongo and 3000 RPM operates well.
The corner of the utility plays role. Punkta drill requires corner likewise big or more than that of the tordborilo. Like this the tordborilo touch first by means of peak, no edges, for better centrado.
With HSS-drill choose punktan drill with corner less than either equal to it, for instance 90-grada spot for 118-grada drill. For karbidaj drills take punktan with corner bigger than either equal to the drill. Stiff 90- or 120-gradaj punktboriloj give precise centre.
Start by means of central drill and later go to 60-grada utility can cause early fiĝon of the drill.
