Higher Speed = Straighter Holes ???

[triplefreak]

A few of you guys know I've been having problems with my drill press & being able to drill straight holes in pen blanks.
Well, yesterday I changed the drive belts & upped the speed to max.
I was drilling at 650 to 950 rpm's or so, & getting crooked holes in every pen blank. So, on a lark, I upped the speed to 3450 rpm's when I installed the new belts. Then, I marked a scrap of wood on the top & bottom, so I could estimate how far the drill bit drifted. It went thru a 2X4 sideways.
So, about 3 & 1/2", and it did not drift at all. It came out exactly on the "X" mark on the bottom, which matched the one on top.

I usually drilled metal with this press previously, which is why I had it on low speed.

Here's my question: Would simply upping the speed make the drill bore straighter? What's going on here? I used the exact same bit I was having problems with, BTW.

[sawduster]

I guess an argument could be made that with the bit spinning faster, there is less opportunity for it to flex and go off track. Only issue might be some burning of the wood at the higher speed.

[triplefreak]

Jan 27, 2010 12:29:31 GMT -6 sawduster said:

I guess an argument could be made that with the bit spinning faster, there is less opportunity for it to flex and go off track. Only issue might be some burning of the wood at the higher speed.

I sincerely could care less for what gets burned inside the pen blank.
You will never see it anyway. What I'm concerned most about is a straight hole.

[TDHofstetter]

Wood DOES LIKE to be drilled & sawn & planed & otherwise machine-shaped at very high speeds... I wouldn't think that a lower speed would make it wander more unless the feed pressure was too high, but it's possible.

[triplefreak]

Jan 27, 2010 13:47:08 GMT -6 TDHofstetter said:

Wood DOES LIKE to be drilled & sawn & planed & otherwise machine-shaped at very high speeds... I wouldn't think that a lower speed would make it wander more unless the feed pressure was too high, but it's possible.

So, you're saying when I drill wood, it should be at my max speed for my drill press?

[sawduster]

Jan 27, 2010 13:46:22 GMT -6 triplefreak said:

Jan 27, 2010 12:29:31 GMT -6 sawduster said:

I guess an argument could be made that with the bit spinning faster, there is less opportunity for it to flex and go off track. Only issue might be some burning of the wood at the higher speed.

I sincerely could care less for what gets burned inside the pen blank.
You will never see it anyway. What I'm concerned most about is a straight hole.

The glue you use to secure the tubes to the blank would prefer to bond to wood as opposed to ash (as in burnt wood), so burning is an issue to be concerned with. The trick is getting the right speed that makes for efficient cutting while not creating too much friction that will cause burning. Bit feed speed, as well, is a component of drilling without burning. Too slow a feed and you'll smoke the wood, too fast and the cutting edge can't keep up with the pressure and can cause the bit to flex, throwing the hole out of alignment.

[triplefreak]

[quote author=sawduster board=ampers thread=1543 post=14722
The glue you use to secure the tubes to the blank would prefer to bond to wood as opposed to ash (as in burnt wood), so burning is an issue to be concerned with. The trick is getting the right speed that makes for efficient cutting while not creating too much friction that will cause burning. Bit feed speed, as well, is a component of drilling without burning. Too slow a feed and you'll smoke the wood, too fast and the cutting edge can't keep up with the pressure and can cause the bit to flex, throwing the hole out of alignment.[/quote]
Thanks for your reply. Sincerely. But, when I drilled the scrap at high speed, there was no burning, & it was a piece of spruce I drilled into.
So, did I do something correctly?
Seriously, I'm trying to find out wht's going on with my drill press.

[TDHofstetter]

Jan 27, 2010 13:48:19 GMT -6 triplefreak said:

Jan 27, 2010 13:47:08 GMT -6 TDHofstetter said:

Wood DOES LIKE to be drilled & sawn & planed & otherwise machine-shaped at very high speeds... I wouldn't think that a lower speed would make it wander more unless the feed pressure was too high, but it's possible.

So, you're saying when I drill wood, it should be at my max speed for my drill press?

Yep, exactly... unless you're using a really large (like more than 2") Forstner bit. Anything smaller will want the highest speed your drill press can muster.

Aluminum's the same way - it wants the highest speed you can make. Steel, on the other hand, wants low speeds.

Come to think of it... my thinker thinks PastorPaul ran into issues with drilling a couple years back, and when he went to high speed (he had been using a very low speed) his troubles went away, too. I don't remember what his symptoms were, though.

[lexrex]

You changed something, the belts. That shouldn't matter, but you still changed something. Put it back on slow speed and do your test again. I'm just interested in eliminating that from the equation.

[sachbvn]

This reminds me I could probably up my belts several speeds on my DP - it's easy enough to do, no reason I haven't - just haver is all.

Now, the 8mm bit I have, I KNOW is a little crooked, it won't even spin right - just haven't had a chance to order a new one yet.


Zac

[mapleman]

i do not mean to hijack the thread, but i have a similar problem and might elicit some similar possibilities for solutions...

i have had a similar problem --- i have two 7mm brad point bits for pen blanks --- and BOTH has that wandering affect. it is usually small enough that it is not noticeable (but if i was using laminated blanks it would be).

so - you say quill has runout, right? well, not much. it does not some, but very very little. i put any other bit in, there is almost no wander or flop.
i use the barrel trimmer in the DP, and it shows not wobble.

can it be that i have two bent 7mm bits? and they both had that wobble before i ever put them to wood.

it could be that the small wobble at the quill is just more pronounced b/c the 7mm bits are so much longer... i dunno. the bits themselves have a lot flex to them...

thanks guys...

[TDHofstetter]

If they wobble around before they're touching wood, and if other drill bits & your barrel trimmer all run true... then yep, there's an issue with those drill bits. Any roughness or even a little nib of steel on the shank? If none, then they're a little bent.

My 7mm bradpoints aren't much, if any, longer than ordinary twist drills of the same size range. There's not much justification for longer bits. Of course, the shorter the bit the more accurate it'll tend to be.

[Ruffnek]

John, I think the problem with the 7mm brad point bits is likely with the grind on the point, especially since it wants to track with the grain in laminated woods.

On the other thread Trip had about his problem, someone noted correctly that a bent bit would drill an oversized hole but wouldn't cause the drifting issue he is seeing. Since it's rotating, the bend force would be equal all the way around.

I think a higher speed DOES help the bit drill straighter, especially when combined with light pressure. It has more time to cut the wood and is less likely to follow the grain when turning faster.

In a similar case, when drilling a tilted (dipping is the term we use) underground formation, the drill bit will attempt to walk uphill...into the tilt. The tendency can usually be overcome by increasing rotation speed and applying only light pressure to the bit. In well drilling, it's a case of giving the drill bit more time to cut the rock and also mother nature is helping with the gravitational pull trying to keep the drill string vertical.

With a woodworking drill bit, it's simply a case of giving the bit more time to remove the wood.

Trip, I've got a laminated sheet inside my drill accessories cabinet that specifies the optimum rpm for different bit sizes. With pen-drilling bits, you can spin them as fast as you want but with the bigger Forstner, spade or adjustable bits, you will want to use the correct speed.

I got the sheet from WOOD magazine but I can probably scan it and e-mail you a copy if you want one.

[sawduster]

Believe it or not, I actually got out into the shop today and cut some pen blanks (mesquite) and drilled them. On a whim, I switched the belt on my DP from the slowest speed to the middle (of five) pulley pairs, before drilling the blanks. While I am generally not overly concerned about the exits holes being off a bit from the entry hole, what I found is that these holes are seemed to exit dead center on the blanks, matching the entry holes.

I did get a little smoking but that was remediated by raising and lowering the quill to clean out the waste from the cut.