Center Drill Bits

**Lee Roberts** · 22-06-2008

Hi, i have recently recived some center drill bits as recomended by another member, i know what they are and how to use them.

I was just wondering if anyone had any advice or Tip when using them, i have been using them to make nema 23 motor mounts for my cnc machine:

**Lee Roberts** · 22-06-2008

Sorry kip i hit the wrong button, kips posts are below:

Be careful when using small ones on hardened steel...they break!

And use a scriber rather than a marker pen as it's better for accuracy and never rely on a piece of metal being "square" when marking out.... :D

**Lee Roberts** · 22-06-2008

Yes it did take me a few go's to get the holes right, i managed to get the holes close enuff that i could then file out a small amount so my screws would line up with the motors.

Now i have a template i just use that to make/mark out new plates and so on:

**Robin Hewitt** · 23-06-2008

Originally Posted by CheekieMonkies

i managed to get the holes close enuff that i could then file out a small amount so my screws would line up with the motors.

You really need CNC it makes it so easy and everything lines up just perfect. No more swapping centre drill then bit then countersink/bore on every hole :D

I draw everything with AutoCad, convert the milling to G code and overlay the .dxf file on the cut file. Then I can use the "Move to hole" feature which puts me on the hole nearest the mouse.

**Hogout** · 14-05-2009

Originally Posted by Robin Hewitt

I draw everything with AutoCad, convert the milling to G code and overlay the .dxf file on the cut file. Then I can use the "Move to hole" feature which puts me on the hole nearest the mouse.

Hi Robin,

Can you share some more info on this process?

Cheers.

**Robin Hewitt** · 14-05-2009

Originally Posted by Hogout

Can you share some more info on this process?

It's home brewed software that pumps Gcode out to the parallel port as steps.

It is a bit simple minded when it comes to arcs and you have to boot DOS so it has full control of the timer interrupt, but you are welcome to a copy if insane enough

Robin

**John S** · 14-05-2009

Forget centre drills, they are a throwback to earlier days and were designed for putting in the support holes for centres on lathes, hence the name.

No commercial CNC shop would dream of using centre drills today, instead using what are called NC spotting drills.

These are very stiff short fluted drills that will start a hole off without wander and not break like the flimsy centre drills.

Nearly the same results can be obtained using a good quality stub drill.

John S.

**Robin Hewitt** · 23-06-2008

There are some really naff centre drills around, regular PITA when they snap off. I got some cheap, centred 2 holes then lobbed the lot straight in the bin.

Caveat emptor, I've gone back to Plan A, don't use anything but Dormer :D

**Lee Roberts** · 23-06-2008

Originally Posted by Robin Hewitt

There are some really naff centre drills around, regular PITA when they snap off. I got some cheap, centred 2 holes then lobbed the lot straight in the bin.

Caveat emptor, I've gone back to Plan A, don't use anything but Dormer :D

I got mine from ebay, dont think they cost much more then £10. I take my time with them and they seem to be ok, now i think just a small drill bit would have more then likly done the trick anyway :)

CM

**alan2525** · 07-04-2010

Originally Posted by Robin Hewitt

Caveat emptor, I've gone back to Plan A, don't use anything but Dormer :D

Dormer aren't what they used to be...I picked up a set of drills, made in Mexico of all places. Drilled a hole in a piece of 1/4" mild steel and managed to snap a brand new 10mm drill bit straight in half with just the torque from a cordless drill and in a hand tightened QR chuck too!

That's the first time I've ever managed to break a drill over about 4mm in diameter!

Complete carp!