drilling with zero clearance

S

smirnoff

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Jan 3, 2010
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Im building my first ever set of three knives, and at this point i need to drill out the holes in the handles. Im drilling 1/4" holes on a drill press and have been having trouble drilling the holes with zero clearance, the pins seem to just go in without the use of the hammer. Are there any tricks to getting the holes to be tight enough? Ive got the hole to be tighter by drilling a small pilot hole, but its still not quite zero clearance.
Thanks for any feedback in advance.
 
A bit of clearance is a good thing, when you put it together ruff up the pins a bit with sand paper then coat the scales and pins with glue.
If the holes were tight then you would wipe all the glue off the pins.

Richard
 
I agree with Tinbasher about roughing the pins up so the glue will bite. But if you need to have a tight press fit the you can go 1/64 undersize and bevel the leading edge of the pin so it takes a bit of drive to seat it. Also you can go 1/32 undersize, then ream with a carbide reamer to 1/64 under then you will seat good also. A twist drill at 1/4" will not drill a round hole.. A carbide spade or straight flute will

Zoe
http://www.zoecristknives.com
 
Drill your hole in steps to cause less wobble of the bit 1/8" - 3/32" - then 1/4".
The 1/4" will stay more centered.
Press might be an issue, too.
If still not tight, use a "D" lettered drill which is .246" - .004" under .250".
Then, if you're good enough to actually end up with a .246" hole, stick your pin in a drill press chuck and slightly reduce it with a sandpaper block.
There will be about 744 different solutions to this issue.
At least.

http://bobmay.astronomy.net/misc/drillchart.htm
 
The first thing I would do is measure the diameter of the pins. Not all stock that is sold as 1/4 inch is actually 0.250 inch. You might need to adjust your drill sizes to acomodate the diameter of the pin stock. I would have to go along with leaving enough room for a little glue. We sometimes use an F drill (.257") for the 1/4 inch thong hole tubes, depending on the diameter of the tube, so that we can get a small amount of clearance. It doesn't take much and you don't want too much because a glue line will result.
 
There is more than one way to fix your problem:

- either drill an undersize hole and sand down the pins by chucking them in a drill or lathe, sanding them to size while they are spinning

- drill undersize and then use a chucking reamer (machine reamer) to get the hole to an exact size.

I am going to assume that you don't have a lathe or precision measuring tools - you need to seriously think about getting a vernier dial caliper so that you can accurately measure your hole and pin diameter. Having the ability to measure to within 0.001" will save you a lot of future headaches and tell you what needs to change/why things aren't fitting properly.

In case you are not familiar with them, here's a wiki article on vernier calipers http://en.wikipedia.org/wiki/Caliper

In case you don't know how to use a dial caliper, there is a fairly decent explanation of it in this thread http://www.papawswrench.com/vboard/showthread.php?p=12266

Hope it helps,

Nathan

Also, questions like this should probably go in the bladesmith question and answer section of the forums, this page is more for displaying finished knives and collections than questions about methodology.
 
I use a digital and manual calipers for measurements. The pins are precisely .250" and the best diameter i can come up with with a regular cobalt bit is .2505 which is snug enough for basically no pin wobble but loose enough for me to be able to push pin through by hand. I think it will do.
Is it best to drill before or after the heat treat? Does the shrinkage after heat treat cause any significant diameter change or is it negligible? Thanks for the input!
 
smirnoff said:
I use a digital and manual calipers for measurements. The pins are precisely .250" and the best diameter i can come up with with a regular cobalt bit is .2505 which is snug enough for basically no pin wobble but loose enough for me to be able to push pin through by hand. I think it will do.
Is it best to drill before or after the heat treat? Does the shrinkage after heat treat cause any significant diameter change or is it negligible? Thanks for the input!
Click to expand...

I assumed a certain degree of ignorance in my post smirnoff, hope you were not offended.

A 0.0005" clearance is negligible, you may actually want a bit more if you are glueing the pins through handle scales. If you are putting them through bolsters or a guard, you can simply peen them and they will deform inside the hole and negate the clearance. If you really, really want an interference fit, you can drill a mil or two undersize and shrink the pin with dry ice (cryo). Interference fits are frequently done this way in industrial applications.

As for dimensional changes during heat-treat, they are also negligible. With a close tolerance fit, you will have to watch for scaling inside the hole during HT. Honing the inside of the hole by wrapping a piece of 200-400 grit sandpaper around a smaller diameter pin, will get rid of any heavy scale.

Have a good one,

Nathan
 
Last edited:
smirnoff said:
I use a digital and manual calipers for measurements. The pins are precisely .250" and the best diameter i can come up with with a regular cobalt bit is .2505 which is snug enough for basically no pin wobble but loose enough for me to be able to push pin through by hand. I think it will do.
Is it best to drill before or after the heat treat? Does the shrinkage after heat treat cause any significant diameter change or is it negligible? Thanks for the input!
Click to expand...

It's best to drill before heat treatment it will be too hard to drill after.
Richard
 
Nathan, thanks for your input and im deffinately not offended, it was a fair assumption concidering i said it was my first set of knives. Thanks for the help everyone, ill try to get a few photos after hand rubbing.
 
Definitely consider the idea of drilling undersized and reaming to final size if you are after a tight fit. A drill bit doesn't drill a round hole.
 
A .250" pin will NOT go in a .250" hole

As stated: Measure the pins

Work up to your size

Drill about .003 undersize and then ream

One problem not mentioned is your drilling machine......

Many of these are less than perfect and thus drill a hole bigger than the bit, and the chuck could magnify this problem.
 
John T Wylie Jr said:
Definitely consider the idea of drilling undersized and reaming to final size if you are after a tight fit. A drill bit doesn't drill a round hole.
Click to expand...


As a trained engineer, I was always taught by my peers that this would be the correct solution.
 
I like the idea of drilling and reaming.

For an alternative, and for hardened steel, what do all of you think about drilling with a short 0.250" carbide mill?
 
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