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Nick
Experienced Roboteer
Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW
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I think you got a dud! I have had many cs bits from cheap to expensive and they all cut at low speed just fine - the cheapo ones just went blunt faster and cut less evenly.
There are several countersink designs. there is the fluted bit:
Which can have from 3 to 6 flutes and then there is the "zero flute" design:
If you have some extra cash, I really recommend countersinks with combined drills like this:
This bit gives a fantastic result in ali sheet - always centered, no chattering and a better appearance.
For aluminium, a 3 flute design and LOTS of feed preassure is recommended by most textbooks and it definitely works for me. Under 1000 rpm definitely. If you use higher RPM or less feed preassure, you will likely get chattering, resulting in an uneven countersink. If you are cutting harder material. more flutes will give faster stock removal. The zero flute design is good for deburring and for plastics where normal bits grab and dig in. They don't work well in ali!
Here is my 'trick' for getting neat, repeatable countersinks with a bench drill:
Take a smallish piece of scrap sheet the same thickness as you commonly use and drill it for all the common screw sizes you use. Next, carefully countersink each hole for it's screw size. Take it slow and get the screw heads exactly flush with the sheet. You now have a template to set your drill to.
When you need to make a countersink, put in your bit, put your template on the drill table
with a sheet of paper under it,
lower the bit into the correct template hole size and then set the depth stop so the cs bit cannot go any deeper. Take out the template and paper and drill your job with neat, right-sized countersinks
The paper spacer is to compensates for the extra pressure you put on the drill when you are cutting the cs for real; 2 thicknesses of bond paper, an envelope or a piece of wet N dry sandpaper makes a good starting point.
BTW: for Lexan, use less feed pressure, the slowest possible speed and no lubricant. Frequent pauses to let the plastic cool off helps too. _________________ Australian 2015 Featherweight champion
UK 2016 Gladiator champion
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Sat Apr 02, 2005 11:13 pm |
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