The drill before the real drill

[mmayo]

What is the exact name for the starting drill to assist or getting your drill bit to start and stay centered.

Does it work with most pen bits?

What about brad point bits?

Thanks, Malek

 

[Jack Parker]

Are you referring to center drill bits?

 

[jsolie]

I think center bits are what you're after. They work best with normal drill bits, and not so well with brad points. They start a nice hole and put a 60 degree bevel on the inside. For a regular drill bit, they lead it right into the material. I picked mine up at Harbor Freight and they were not terribly expensive.

 

[randyrls]

Yes; Harbor Freight has them, Enco, and anywhere you can get metalworking tools.
Center Drill Countersink Set 5 Pc

PS; You have to make sure the body of the center drill is smaller than the finished size of the hole you are drilling. If it is larger, there will be a champher on the end of the blank. NOT what you want.

 

[jjjaworski]

The nice thing about center drills is the 60 degree hole it leaves is great for turning between centers or for truing up stock held in a scroll chuck using the tailstock with a 60 degree center to line things up prior to final tightening.

 

[John Den]

I drill all my blanks, after rounding between centres, on my metal lathe using a Collet chuck.
I follow the centre drill with a "Pilot" drill which just clears the web at the centre of the point of a twist drill. I usually use a #40 drill for this.
The Pilot hole keeps the final drill central ( concentric) for the first 1.5 or so inches and results in a through hole which exits on the centre of the bank beautifully.
When drilling the pilot hole watch the shank where it enters the blank and withdraw it immediately it starts to spiral as this indicates the tip is wandering due to swarf build up at the tip.
For acrylics I limit myself to 1000RPM for the pilot and 400 RPM for the final drill. I withdraw the drills every three turns of the tailstock wheel (approximately 0.2inches). I unlock the tailstock and pull the drill straight out of the blank, clear the swarf, and push it back in without stopping the lathe (the quickest way I've found) I cool the drill with Alcohol (Methylated Spirits in the UK) after each withdrawer keeping the drill cool to prevent seizing/blowouts.
Follow the pilot drill with the full diameter drill required DONT enlarge the hole in steps as this causes non-concentricity.

Hope all this helps somebody.
John

 

[jsolie]

. . . I unlock the tailstock and pull the drill straight out of the blank, . . .

Just be sure to hold onto your drill chuck as you remove the tailstock to keep the chuck IN the tailstock. I seem to remember seeing a pic here of what can happen if, during the removal process, the drill chuck comes free from the taper.

 

[Joey-Nieves]

I like to buy here High speed steel Combined Drills And Countersinks
They have drill bits, taps and dies at great prices
http://www.victornet.com/alphabetic/Center-Drills-Double-End/43.html

 

[mark james]

I cool the drill with Alcohol (Methylated Spirits in the UK) ... UK Alcohol: I thought that was warm beer ...:tongue::bananen_smilies046:

Hope all this helps somebody.
John

Oh, Your text of your procedures was excellent!

 

[Curly]

My preference is to use a spot drill. It matches the angle of the jobber drill which helps to it from wandering. One of the reasons people use centre drills is because every metal lathe operator had them at their machine. It doesn't mean it's the best for the job, just handy.

 

[John Den]

. . . I unlock the tailstock and pull the drill straight out of the blank, . . .

Just be sure to hold onto your drill chuck as you remove the tailstock to keep the chuck IN the tailstock. I seem to remember seeing a pic here of what can happen if, during the removal process, the drill chuck comes free from the taper.

Yes I do and it should have been in my post!!!!!
TOO LATE TO EDIT IT IN NOW!
Thanks,
John

 

[TurtleTom]

I'm with Curly, spot drills should precede drilling to size. The purpose of the center drill is to drill a 60 degree hole for the live center so that only the shoulder touches. But I still use it for centering holes as I haven't bought any spot drills....yet.

 

[Skie_M]

. . . I unlock the tailstock and pull the drill straight out of the blank, . . .

Just be sure to hold onto your drill chuck as you remove the tailstock to keep the chuck IN the tailstock. I seem to remember seeing a pic here of what can happen if, during the removal process, the drill chuck comes free from the taper.

Also keep in mind that the construction of some chucks contain double-ended mandrels... One mandrel fits into your tailstock morse taper, the other end fits into the back of the chuck.

If this other end comes loose AND YOU SEE NO REASON TO LEAVE IT INTERCHANGEABLE, you can just add a little superglue and push it back in. :biggrin:

The reason it can come loose in the first place is so that you can swap out the mandrel attachment for another in case of damage to the original or for porting it (the expensive tool) over to another lathe by means of just swapping the cheap attachment mandrel...


Please note: Even if you use a Draw Bar in your headstock or tailstock, most chucks on the market are NOT secured because of this double mandrel issue.

 

[John Den]

A Centre Drill is also known as a "combined" (Centre and Spot) drill -it just depends on how deep you go as to whether your spotting or forming a seat for a Centre.
The best spotting depth is less than the beginning of the first parallel section of the Centre Drill.
A "Spot" ideally should just clear the way for the web of the drill that follows.
Regards,
John

 

[mmayo]

I use mostly Colt and Fisch drills. Every once in a while I wish I had used a centering or spot drill as you all describe as I watch the bit jump slightly off center. This can be OK or could be a warning that the blank will vibrate and get cranky.

I will buy a bit as suggested and add a step to my work.

Thanks to all who helped me.