Center Bits

[Birdhunter]

I ordered a set of center bits (used to create a small depression for a standard drill bit to start in) from Amazon. They came from Accusize. There are 5 bits each of increasing size with a centering point on each end. They are packed in a foam lined plastic box.

I tested one last night chucked in a big Oneway lathe. No observable runout and appears to be very sharp. Left a clean starter hole dead center. Material appears to be stainless.

My main use will be in drilling dowels.a center bit greatly helps in getting the hole drilled dead center.

 

[Rob Z]

Hello BH

Is this what you ordered?
https://www.amazon.com/Accusize-Ind...ze+center+bit&qid=1590945546&s=hi&sr=1-1&th=1

 

[Cheese]

Material appears to be stainless.

Center drills are either HSS (high speed steel) or solid carbide to maintain edge sharpness, there may also be a few cobalt (M42) ones out there. They were originally introduced to be used for machining metals, thus the reason for the materials that were chosen for their construction.

They are used extensively in lathe work for metals.

Happily, they've since made the transition to the woodworking segment.

 

[rvieceli]

Truth be told, center drills have one real purpose to drill a hole in a workpiece to properly fit it to a lathe live or dead center. They are usually short so they don’t flex. The two step bit is designed to make the proper hole for the center. The little cutting bit at the end makes a hole deeper than the point of the center so the point of the center doesn’t bottom out. The angle of the other portion matches the angle of the center (usually 60 degrees).

They are obviously used for other things but may not be the best choice.

If you want a two step process, you might want to look for a 140 degree spotting drill. Once again they’re short to reduce flex. The 140 degree angle works with both 118 And 135 degree Drill bits. Allowing the bit to engage the workpiece at the drill point.

If your equipment is sufficiently rigid (and it probably is) you might want to invest is a set of screw machine length or stubby bit. They are short to reduce flex but don’t drill as deep because of it. You can probably confidently use them to drill your hole in a one step process if the drilling depth works for you.

Here’s a comparison shot of 3/8 and 1/2 screw machine vs jobber length.

View attachment 1

[attachimg=2]

Here are some articles you may find interesting. Wood is of course more forgiving than metal but the same principles should apply.
https://www.cnccookbook.com/when-to-use-a-spot-drill/
https://neill-lavielle.com/louisville-cutting-tools-centerdrills/
https://www.yamawa.com/Portals/0/resource/en/tips/pdf/tips-022.pdf

Ron

 

[Birdhunter]

Rob Z, the link is what I ordered.

When I chucked one up into my tail stock, there was about 1” sticking out. So, not much room for runout.