2 Questions to help me understand

P

PoolQs

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Feb 5, 2014
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Hi guys, I need help. First, I am making a hunting knife and drilling my holes. 4 - 1/8" and 2-1/4". I got all 6 drilled and wanted to check
and make sure that my pins all fitted correctly. I mic'd my rods and they are all dead on, .125 and .250. The pins will not fit. I was told
once that drill bits are NOT to true sizing. Since they didn't fit, I mic'd the bits; .121 and .245 ... really ???
So the pins don't fit and I am drilling one size up. Here is my issue, I use DeWalt Cobalt bits and have never had a problem drilling through
anything until tonight. From the .25 I went up to 5/16"(.312) and burned up 2 bits. I easily got the smaller bits through the steel with NO
problem. I should mention that I am using 1080 soft and not HT. I always use either type of cutting oil when drilling. I even tried a step
down bit and burned it up. Can anyone help me and tell me what I am doing wrong or what I am missing? I am using a drill press and tried
speeds from 390 up to 1100, no difference.

Second question ... why do manufactures make bits that are not true to size ?? I went through all my bits of different companies and steel,
I could NOT find a 1/4" bit that was .250 ...

I included some pixs to show the blade and the bits being used. The .312 looks like a countersink (looks the same on both side as I tried
3 different ways and bits)

photo-12.jpg
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photo-10.jpg
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photo-11.jpg
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Thank for the education and sorry about the rant !!!
Troy
 
Sounds like you might have work-hardened your steel... I'm not an expert or anything, but I've had this happen to me before on stainless, maybe it's the same thing...
 
PoolQs said:
Hi guys, I need help. First, I am making a hunting knife and drilling my holes. 4 - 1/8" and 2-1/4". I got all 6 drilled and wanted to check
and make sure that my pins all fitted correctly.

I mic'd my rods and they are all dead on, .125 and .250.
The pins will not fit. I was told once that drill bits are NOT to true sizing.
Since they didn't fit, I mic'd the bits; .121 and .245 ... really ???


So the pins don't fit and I am drilling one size up.
Here is my issue, I use DeWalt Cobalt bits and have never had a problem drilling through
anything until tonight. From the .25 I went up to 5/16"(.312) and burned up 2 bits. I easily got the smaller bits through the steel with NO
problem. I should mention that I am using 1080 soft and not HT. I always use either type of cutting oil when drilling. I even tried a step
down bit and burned it up. Can anyone help me and tell me what I am doing wrong or what I am missing?
I am using a drill press and tried speeds from 390 up to 1100, no difference.

Second question ... why do manufactures make bits that are not true to size ?? I went through all my bits of different companies and steel,
I could NOT find a 1/4" bit that was .250 ...
Click to expand...


There are several issues here.
I find your speeds may be too high, with high speed and light pressure, you may have wrk hardened that steel.




A .250 drill should measure .250 pretty darn accurately at the cutting edge, and the round body, but the fluted area will have clearances ground in.

How are you measuring, did you check zero.
I notice that both sizes are off by the same amount

If you are using a micrometer, it's possible to turn the thimble too hard.

Show us how you are doing it.





A pin that is .250 will not fit into a hole that measures .250 without being forced in.

They call that a press fit.

going up a size = by a sixteenth, won't hurt in the steel, but in the handle you need a closer fit.


Download a number letter fractional decimal drill chart

find a drill just a hair or .002 bigger

Try a #30 and a Letter F drill
use those to drill your handle holes
but now that you have drilled larger in the steel, it will be very hard to line up the handle and steel holes unless you set that distance at a measurement you remember.




Are you done putting your bevels in ?
 
I find your speeds may be too high, with high speed and light pressure, you may have wrk hardened that steel
my drill press only goes down to 390, so do I need to go back to 700 and apply more pressure?

Download a number letter fractional decimal drill chart
find a drill just a hair or .002 bigger
Box stores nor DeWalt could I find anything between .250 & .312 Where would I get # or Letter bit in Cobalt?

Are you done putting your bevels in ?
No I haven't Count. Just got back from the store and decided to drill my holes then get back to the bevels.
So now what do I need to do? put a torch on it to soften it back up?

Thanks for the info and help sir !!!
 
PoolQs said:
I find your speeds may be too high, with high speed and light pressure, you may have wrk hardened that steel
my drill press only goes down to 390, so do I need to go back to 700 and apply more pressure?

Download a number letter fractional decimal drill chart
find a drill just a hair or .002 bigger
Box stores nor DeWalt could I find anything between .250 & .312 Where would I get # or Letter bit in Cobalt?

Are you done putting your bevels in ?
No I haven't Count. Just got back from the store and decided to drill my holes then get back to the bevels.
So now what do I need to do? put a torch on it to soften it back up?

Thanks for the info and help sir !!!
Click to expand...

1. Slowest speed, more pressure, sharp bits - It takes a while to get speed and feed right... I'd keep the press on slow for most knifemaking. Press hard enough that you see curls of metal coming off the bit.

2. Check out a knifemaking supply or machinists supply like USAknifenmaker or ENCO. I use a F sized bit for a .25" tube or rod and A #31 for 1/8".

Hit those high spots (around the hole) with a sharp chamfer bit running slow then drill away.

I used a fast running drill press for many knives but a slow one is nice, I keep mine set at 150 rpm for everything but the smallest bits.
 
I have the same bit set, mine are very close to true. So I wonder if it is a problem with quality control? As far as my pins go I sand them just a bit to get a snug fit into the knife and handles before I give them a light peenning.

As I need to I have replaced my bits with the RIGID brand and they seem to last a little longer. My lowest speed on my press is 570, so I'll burn some up till I get around to doing some math and replacing pulleys.

If the holes are work hardened then I would hit it with a torch, but now I have a question. If I'm laying into a hole with a dull bit and the steel gets hot and I let it cool at room temps, wouldn't 1080 get softer and not harder? I don't see in color change in the pics so this question may not apply to these particular holes.
 
I'm a fan of screw machine length bits like this Letter F bit.. They're shorter and much more rigid. They're also split tip so they don't wander when starting a hole.

Here's a Drill Speed Chart. I'd reduce the speeds around 25% for use in a drill press. It's likely you're biggest issue was not enough pressure. You don't want to bear down so hard that you snap bits, but you want to constantly be cutting and get some nice curly chips.
 
There was a post on this Forum by Nathan The Machinest,about speeds and feeds.This article was a lot of help for me.Do a search and read it,you will be amazed at the difference in the way you go about drilling metal.
Eddie
 
Excluding gun drills and spot drills, all drill bits are tapered from the point to the shank. In the size range you are dealing with it is going to be .002-.004 inches. So if your are measuring the shank it is going to read small.

As far as drilling holes in you knife, it is very hard on drill bits to drill a hole and then go up one size. If you look at your drill bit you will see the corners burnt or broken off. Try sharpening the drill bit and finish drilling the hole from the opposite side.
 
Thank you EVERYONE for your help and advice !!!

I got a real education here on this one. I have seen and heard a lot of my mistakes and
going to use ALL of your info to make my life easier.

Got my speed chart for the drill and my letter/number chart for sizing.

Time to get some new bits and get it done right !!!

Since I use only Cobalt bits, is there a good tutorial out there to sharpen them?
I do have a Tormek wet grinder that I can buy an attachment for but its like $90.
Cheaper to buy new bits.
 
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