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kustomdon

Posts: 20
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I bought a package of 25 mixed drill bits at a swap meet this guy was showing how they can drill thru leaf springs and they do it very well the problem is I like them so much I want more and don't know were to find them? There different looking than any drill bits I've seen.There twice a normal drill bits length some start with a small bit then go to a bigger one.At the end were you put it in the chuck it is larger and it has 4 little dimples I'm assuming they were a quick disconnect?? does anyone have any ideas were to get them? Thanks KustomDon

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unklian

Posts: 517
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One might expect to find them on Ebay,
but be prepared to wade through a LOT of other stuff.

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kustomdon

Posts: 20
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Do you know what kind/brand they would be what would I be looking for? KustomDon............

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rog02

Posts: 84
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Hi Don:
What you have are called "Collet" drill bits. U.S. Tool carries them as do several other aircraft supply places.
I got lucky on a trip to Boeing Surplus in Witchita a few years ago and found a collet chuck in one of the bit bins. To chuck a bit you just pull the collar on the chuck out and drop in the collet bit, small balls in the chuck lock into the "Dimples" on the bit. Quick and easy bit changes. Bits come in all lengths and sizes, step drills for oversizing rivet holes and several other speciality bits that Boeing needed for aircraft fab.
Most of the bits I have are number bits since they are for drilling rivet holes, but if you dive in the bin and hold your breath you can find a lot of different sizes and lengths up to 12".
Since the bits are mostly for drilling sheet metal the longer lengths normally only have flutes about 1 1/2".
Roger

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kustomdon

Posts: 20
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What makes these drill bits so good that they can drill through a leaf spring.I can't do it with my cobalt bits? KustomDon...............

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rog02

Posts: 84
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Hi Don:
The simple answer is "Money". Those bits are purchased to do a government contract and when that contract is completed they dump the bits on the surplus market.

Without seeing the bits you got, I can only guess at this. All ther bits I have from those sources and the lot my supplier has (somewhere around 10,000lbs.) are sharpened to 135 degree split point. This point is used mainly to avoid tip wandering and promotes agressive removal of material. While it cuts well, drilling hard material dulls that tip pretty quick and breakage becomes a major concern. To promote drill life most cobalt bits are ground to a flatter 140 degree tip.

http://www.desktopcnc.com[...]omy.htm This will show you the difference in tips that are common to metal cutting drill bits. There have been Volumes written on the science of drill bits and how to sharpen them. There is no single bit that is optimum for all applications. Other considerations are lubrication/cooling, cutting speed, and feed rates.

Roger

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kustomdon

Posts: 20
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thanks for the reply, yes the bits that I have are almost flat on the end and they do break very easy I just assumed it was the length. will a drill doctor work because I suck at sharpening. Are you telling me that if I sharpened my cobalt bits the same way they will cut just as good?? Thanks KustomDon

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rog02

Posts: 84
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Hi Don:

Probably the reason the bits are breaking is because they are not designed to drill through leaf springs. The split point is too aggressive so it tends to dig in and stop then the drill motor twists the bit off.

Split points are difficult to sharpen in the shop and require a fixture and a carefully dressed grinding stone. I haven't used a "Drill Doctor" but have heard people both Yeah and Nay on them. I have a sharpening fixture and a dedicated grinder set up.

Before you start grinding on your cobalt bits you might want to do some research in Machinery Handbook or similar reference materials. As I said in an earlier post, there are volumes written about drilling holes and the tools to accomplish that task. The ideal bit for one material may be totaly inappropriate for the next job.

Roger

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hottrodzz

Posts: 60
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SMALL BIT TIP
TO LARGER DIA.
AND A ALMOST FLAT CUT ANGLE SOUNDS LIKE
( BULLIT POINTS / TIPS )
DEWALT & BLACK N DECKER BOTH SELL EM.

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kustomdon

Posts: 20
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Thanks for the info I'm sure that is the reason they are breaking. I have broke them mostly using a hand drill using 1/8 & 3/16 plate.hottrodzz thought they are bullet point bits they are not I have a set of them they work good.They don't tend to jerk the drill when you get to the end of your hole.They are another drill bit that I don't know how to sharpen. Thanks KustomDon.............................

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fattuna

Posts: 1
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hey all. new to the site but its a great wealth of info. I bought some bits that worked well/great but since have not been able to locate anymore.
Are the bits you guys are talking about....any help would be great.

cheers

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