Knife-making question - boring out boltholes

[General Strike]

Hi all,

I recently bought a knife-making kit, and have ended up slightly consternated. The reason for this is that while the fittings - corby bolts and thong tube - are imperial sized (1/4 inch, with the Corby bolts necking down to 9/50 or about 4.6mm), the holes in the knife handle are actually metric (4mm and 6mm). This presents a few problems:

> The step drill bit I got with this is also imperial - 9/50 to 1/4. It comes with a pilot bit at the 9/50 diameter as well, so I could try boring out the existing holes. However, I don't know if the bits are going to cope with going through heat-treated carbon steel! It looks like both parts are HSS, so should do metal. But am I missing something? A lot of sources recommend cobalt steel for drilling hard metals. And I haven't seen a 9/50 cobalt bit anywhere on t'internet.

> Although there are Loveless bolts which are 1/4 inch with a 4mm threaded section, there's no step drill for these sizes (ie a metric-to-imperial step)

Should I go ahead and try to bore out the existing holes to the bigger and imperial diameter, or should I get the Corby bolts replaced with Loveless bolts that will go through the existing holes? If I choose the latter course of action, how do I drill through the knife and handle scales in one go, in order to make sure everything lines up?

 

[kristophish]

I personally would try and drill the tang first. its your cheapest option I think. get some lube in the hole tho (wd40 or something)

 

[HillBill]

Drill the tang with a masonary bit, that should open it out. Or if you have a dremel, use that with the diamond engraving bits you can get to do the same..

 

[FGYT]

use a 3/16" (4.75mm) or even 5mm isnt to big bit for the center would need to be cobalt drill / Tungston carbide reamer (TC drills dont do well at opening out an existing hole) masonarry drill may work you need to sharpen it to a sharp cutting edge and you will only get a 5mm one tho sharpening the sideswill bring it down a little.

Dremel as has been said with diamond or tungsten Burr
if the tang is hardened you will kill your Step drill or any HSS ones

 

[santaman2000]

Back when I was still a tin bender in the Air Force (aviation metalsmith) I used whatever bits they provided. Often regular high speed bits to drill stainless aircraft parts. It CAN be done but my preference was always cobalt bits.

Heat treated carbon steel really isn't especially hard to drill.

 

[General Strike]

Thanks for the advice, everyone! It seems like the consensus is that boring out is the way to go. Although I haven't seen any 9/50 inch cobalt drills, I have found 4.6mm which is a close as any human being could discern, so I'll invest in one of those and one at 1/4 inch to ream out the thong tube hole. However, in future I think I might stick to plain pins!

 

[spandit]

If you flatten the tip angle (127° rings a bell) you can cut harder steels more effectively but I don't know how proficient you are at sharpening drill bits

 

[dwardo]

Remember doing this my self an age ago. What i do remember is i only wanted an extra mm and it took several masonry bits, a lot of cooling and a lot of time.
Also tried various "metal" bits and nothing was as effective as the masonry.