Centering Drill Bits

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dankc908

dankc908

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In another forum I presented a problem I was having with drilling acrylics. I got a lot of GREAT advice. One common thread was to use a center drill bit before actually drilling. My question, now, is what size(s) do I need - I, primarily use 7 mm, 8 mm and 27/64 drill bits. I will be doing more different pen kits in the future as well. Secondly- where is a good place to obtain the bit or set of bits??

Dan
 
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A 1/4inch is probably all you need. Once you have established the starting hole the other bits will "follow" it just fine.
I know penturnersproducts has them.
 
Dan, most places have a "set" of center bits, usually 3 to 5 bits in the set. I would suggest going that route rather than figuring out which one you need. Over the past few years I've used every one of mine at one time or another.

Places like Little Machine Shop usually have sets on sale for under $10.
 
Texatdurango said:
Dan, most places have a "set" of center bits, usually 3 to 5 bits in the set. I would suggest going that route rather than figuring out which one you need. Over the past few years I've used every one of mine at one time or another.

Places like Little Machine Shop usually have sets on sale for under $10.
Click to expand...

agreed. LMS had the 5 piece set for about $7 when I ordered mine.
 
If you want to "cheap out", you can buy that HF 5 piece set for around $4. This is one exception where I'll use cheap tools instead of good tools. The center bits only need to go into the material about 1/4 inch or so, AND SHOULDN'T put much stress on the center bit.

Has I known LMS had a $10 set, I'd have bought them. But $25 for a set of Irwin's at Lowes was just too much for me to pay.
 
A follow on after using centre drills DeWalt make DT5050 Extreme 2 Drills the 7mm one is labled HSS-G 7mm DIN338 they have a range of these. Made in America I use them for a variety of purposes with incredible success.

Kind regards Peter.
 
pwhay said:
A follow on after using centre drills DeWalt make DT5050 Extreme 2 Drills the 7mm one is labled HSS-G 7mm DIN338 they have a range of these. Made in America I use them for a variety of purposes with incredible success.

Kind regards Peter.
Click to expand...

I did a search on Dewalt for DT5050 and HSS-G 7mm. I could find anything.
 
Dan; A common problem with drill bits is they tend to "skate". The bit wobbles a bit as the center point of the bit touches the material so the hole is off-center to the drill bit. This is why sometimes you can see the drill bit wobbling as it goes into the blank. You can see this very well if you drill on the lathe where the blank spins and the drill bit is stationary.

The center bit is very stiff and short which minimizes the skating effect. The center drill doesn't have to be an exact size, just a bit smaller than the finished hole. Drill in until the hole just begins to be cut by the angled flutes of the center bit. You want the cutting edges of the drill bit to touch the material first, not the center point.

Hope this helps.
 
Dan, I have the centering bits, but with most blanks, the mark left by my old Starret automatic center punch starts a shsrp drill bit. I use very good quality drill bits and keep them sharp.

If the automatic center punch does not leave a good dimple, time for the center drill and a fresh drill bit. Or if in doubt, go for the center bit.
 
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