? for the machinists on drill bits and reamers

Robert Hankins

Robert Hankins

Joined
May 19, 2003
Messages
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Can someone explain to me why when I drill a hole with a .310 thick shank jobber bit the hole turns out to be over .313-.314?
Also seems to have a "Lip" around the hole that is smaller than the rest of the hole. IE: That which I thought was the right size hole is now a sloppy fit :mad:
Are Chucking reamers the only way to get a smooth, correct size hole?

I hava a Ryobi drill press and notice when you have a bit chucked up there is a little side play if you wiggle it...Is this normal? Can it be tightened?

What should I do to eliminate this? Buying a mill is out of the question right now, however I can do smaller equipment investments.

Any educational advice is certainly welcome and appreciated!
 
The chisel point of the drill bit walks. There isn't the proper cutting relief on drill bits to avoid that. One way to reduce it, it to drill ream. For instance, stay you want a 0.310 diameter hole. First, drill it with the proper drill for about a 0.280 diameter hole. Then follow that up with a 0.310 drill. It will still be oversized, but shouldn't be more than 0.311 if it's sharpened properly. The main thing is that you leave enough stock in the hole to properly load the cutter on the second drill bit. For most steels, 0.015 per side is sufficient.

The hole that a drill makes would have to be slightly oversized, otherwise the hole and the drill bit would be metal to metal, and there would be more drill bits stuck in the hole.

If you want a 0.310 hole, go for a 0.309 or even a 0.308 hole.

Drills make ugly holes. They aren't entirely round, they have no guarantee of perpendicularity, and the finish sucks. Reamers will help tremendously with finish and roundness, but will still follow the hole.

Play in the spindle will affect hole size, shape, and location as well. I'm not familiar with Ryobi's drill press, but I have a feeling that it can't be easily tightened.

Depending on what you need the hole for, try drill reaming first. You can also replace the second drill bit with an end mill if you have the appropriate size. If that doesn't give you the finish and control that the hole needs, then go to a reamer. Beyond that, you have cnc circular interpolation, fine hole boring, jig grinding, and edming. These last four are more expensive and require different equipment.

Jamie
 
Jamie Thanks that helps!
What size hole should I drill to effectively use a reamer?
Need this for folder making and (As you can tell) have very little machinist knowledge.
 
Blinker said:
Jamie Thanks that helps!
What size hole should I drill to effectively use a reamer?
Need this for folder making and (As you can tell) have very little machinist knowledge.
Click to expand...

For the sizes used for knives, drill 010" to .015" undersize, then ream using a tapping fluid. :cool:
 
Can someone suggest a good quality drill press that is under $300 that is tight?
OR
Would I be better off spending a little more for a Mini Mill/drill?
 
Blinker, welcome to my world. I tried to reply to this but Bladeforums crashed when I posted my reply a few days ago, so better late than never! :D I've been having some weird problems as I get more into folders, too, and here's what I've learned, which you may or may not already know:
1) Reamers are pretty much thought to be precisely made. That is, a 0.1865" reamer is probably actually 0.1865" in diameter.
2) Drill bits are not precise at all, nor do they give you round holes, as Polarbear mentioned.
3) Pivot pins and other hardware are generally all over the map. A pivot pin that is sold as 3/16" could be a few tousandths off in any direction. Unless it is precision ground, you could be getting anything.

So, the advice I've been given is to buy a few reamers in 0.001" increments in both directions of your theoretical pivot pin (or whatever hardware) size. Also buy digital calipers. Also buy lots of the hardware you are using, then using the calipers find the best/closest pivot pin and reamer combination. If your pin is, let's say, a couple thousandths larger than it should be, then you ream up to that measurement.

To make matters worse, titanium tends to shrink around the holes you drill and ream. Case in point, I am doing a framelock right now using Peter Atwood's video method. It uses a 7/32" pivot pin, in theory. Reamed up to the press fit for the 7/32" and in the Ti it was really tight. No problem, though. Reamed up to 7/32" for the show side of the knife and it was a PERFECT slip fit. Dead on. Did the same procedure in my steel, and there is a little slop. So, what probably happened is the pivot pin is a little undersized, but in the titanium is doesn't matter so much because it shrank a little to fit nicely, whereas in the steel, which won't shrink like that, there is a bit of play. Now, it's close enough that once everything is put together and the lock is engaged it'll probably be plenty solid, like any good production knife, but for that extra something you expect from a custom/handmade knife, it's crap, relatively speaking. :(
 
Blinker said:
Can someone suggest a good quality drill press that is under $300 that is tight?
OR
Would I be better off spending a little more for a Mini Mill/drill?
Click to expand...

There is no such animal as a good quality drill press for $300. The best you can do is get a Harbor Fright or Grizzly and put a good chuck on it. The next jump is up to a Clausing, which will set you back about $1800. Don't let yourself get fooled into believing a new Delta or Wilton are better machines - they are the same machine with a better name on it, and about $100 more.

Used Rockwells, Deltas, Atlas, and Clausings will set you back $500 at least.
 
Blinker said:
So it looks like I would be better served to get a $400 or so Mini Mill ehhhh!
Click to expand...

I could write a book about deflection in hole-boring using the common jobbers-length twist drills, but suffice it to say that the advice in the above posts are very good to help you make clean, precise holes. A really good way to make a decent hole from the start would be to buy yourself a set of stub-length, also known as screw-machine-length drills, at least in the sizes you will use all the time. These drills are short and stiff and never walk around on you when drilling. Armed with these, and a decent chuck, you can do a good amount of quality work even on a cheap drill press.
 
Even with a wobbly spindle, you can get a good hole on the correct location if you use a center drill to start your holes. The drill bit will pick up the center drill start and follow it.

Any drilled hole that must be on location must be started with a center drill.

:D
 
I've been watching Peter Atwood's excellent video and what Don said is in that vid, too. He starts pretty much all of the holes on his project knife with a #2 combo bit. Major difference!
 
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