Drilling problems

[Band Saw Box]

I do my blank drilling on my lathe using a Nova g3 chuck with pen jaws. I'm getting a lot of bit wobble when I'm using a 7mm bit and with a lot of different 7mm bits. It seems to be happening with both square and round bits and the hole look to be off center a bit. Any ideas as to what might be wrong?

 

[monophoto]

Square and round bits????

Are you suggesting that the hole is oval shaped rather than circular, or is the concern that the hole doesn't remain centered on the axis of the blank?

There are several things you should check:

- make sure the bits aren't bent.

- check that your tailstock isn't moving as you are drilling. Sprinkle some sawdust on the bed ways before moving the tailstock into place. Then, after drilling a hole, look carefully at the face of the tailstock. If you see a gap between the front face of the tailstock and the edge of the sawdust, that suggests that the tailstock moved.

- make sure that the headstock and tailstock are aligned. A slight misalignment between headstock and tailstock will be amplified when you mount the Jacobs chuck in the tailstock, mount the drill bit in you tail stock Jacobs chuck, and then check the alignment of the tip of the bit with the headstock.

- you mentioned that you are using pen jaws to hold the blanks for drilling. By that do you mean two angled jaws that grip the corners of the blank, or two out of a set of four jaws that grip opposing faces of the blank? If the latter, the blank could be rotating about the point where the jaws grip the wood.

- have you tried putting the blank between centers and cutting a tenon in one end that you can grip with your jaws?

 

[Skie_M]

Also make sure that the blank isn't wobbling in the pen jaws .... you'll want to make sure your blanks are always cut perfectly square before mounting them in, and that they are stable front to back with good surface contact all the way down.

It may be possible that when you clamped down on a slightly outsized blank, you may have bent your chuck's clamping jaws ... they do stick out a good bit. Check with a known good squared piece of stock, and bend them back into shape if you can.

 

[Charlie_W]

Dan, are these bits sharp? Have you sharpened them or tried a fresh one?

Are these regular twist bits or brad point bits?

Also, since the 7mm bit is smaller, it can deflect more as it hits some hard grain.

Have you tried using a starter bit to get a centered hole for the bit to follow? This is for regular twist bits...not brad point.

Another question.... does the tailstock quill have lateral play while you are drilling? Sometimes I have just snugged the quill lock to remove some of the play but still allow me to advance the drill.

Some drill chucks have deeper jaws and can grab more bit and help prevent a bit from deflecting. Try not to use a bit that is a lot longer than you need. A long bit for a clicker pen might not be thee best for shorter blanks.

Hope this helps as well as your other suggestions.

 

[Band Saw Box]

Thanks for the help..I'm going to try chucking up a blank in just the chuck to see what happens. I was thinking about how the pen jaws set where fully closed and I think.one side was closer together then the other. I'll check that when I get home.

 

[jsolie]

I was having some problems with the cap tubes getting stuck on pens requiring a 12.5mm bit and I wasn't sure why. I suspected a slightly bent bit (and not sure how the one I was using could have become bent), and things went back to normal after replacing the bit. Maybe your 7mm bits have a slight bend in them?

 

[monophoto]

"I was thinking about how the pen jaws set where fully closed and I think.one side was closer together then the other."

What kind of jaw are you using? You used the term 'pen jaws' - that usually means two jaws that are angled and that grip the blank at its corners. The term 'pin jaws' usually refers to four narrow jaws, and when used for drilling, grip the blank on its sides (faces).

Pen jaws are designed to grip the blank in a way that prevents it from moving. But if pin jaws are used and the blank isn't perfectly square, they will grip only two faces of the blank. When that happens, the blank can twist (or rotate) about an axis that passes through the two points where the jaws grip the blank - and that rotation will result in an oval hole in the blank.

 

[Skie_M]

He may also be referring to the base part of the chuck that holds the pen jaws ... if the scrolling chuck is out of alignment, that would cause all of his issues too.


But the issue I was referring to was if, when tightening down on a pen blank that was out of square and uneven (towards the end of the jaws), you can bend the pen jaws outwards from the pressure .... thus, when you go back and put another blank in the jaws, the back is now held securely, but the front is allowed to wobble because the pressure there is less (not secure contact). Bending the pen jaws back in would solve that problem, if it exists.

 

[bobleibo]

Lots of great advice above. I would definitely make sure that nothing is wobbling around while drilling (tailstock, drill bit, blank, etc.) , the bit is not bent and be 100% sure the headstock and tailstock are in perfect alignment.

A few of things I do which works well for me
- I always use brad point bits. They don't walk on the material like regular bits. Try to use ones that have upward or tipped outboard wings on them so they go into the material slowly
- I'm not a fan of the pen jaws that only have 2 jaws, they wiggle around.
- Try chucking the blank up inside the chuck not using the jaws at all. You'll get a very strong grip and can drill right thru the center. My midi chuck handles just about any pen blank and I dislike constantly changing jaws .
- center punch the blank as close to dead center as you can before drilling, then bring the drill bit to that location before you tighten down the chuck. It makes sure the blank is aligned with the headstock and tailstock.

Hope this adds a little bit of help....
Cheers
Bob

 

[TurtleTom]

As long as the wood is tight in the chuck the wood will have a center point. (or else headstock bearings are out but that's your new lathe) You can prove this with a pencil or use the live center just barely denting the wood. Take a skew and make a cone in the center, stop the lathe, is there a small hole from the skew? It's not the chuck or the headstock if there is a small point where the skew went in. The live center could be off from a misaligned tailstock though.
So it's either your bit or your tailstock. The biggest cause for bit drift is non concentric cutting surfaces on the two wings. If your bit is not HSS, then one pass, wobbling, through a 5" blank is enough to ruin it. Try several bits, if they all give the same result the answer is the tailstock shaft is not running on center or if on center then at an angle through the workpiece.
Another test is pick one of the bits and rather than crank it through the blank, crank it about a half inch and push it the rest of the way, at a low speed, with a loose tailstock. Hang onto the chuck when you pull it back out. I have a mini Rikon too and this is what I have to do to get a round hole. I also step drill it with 3 drill although some say not to do that. It works for me though. I get very tight 7mm holes. For large holes I cheat, I use a boring bar with a carbide cutter.
When you first see a wobble, take out the chuck and put in the live center. Lock down the tailstock, loosen the chuck, advance the tailstock forcing the round hole to center on the live center with the blank against the back of the chuck, and tighten the chuck forcing the chuck to center on the live center. Pull the center out slightly and turn the chuck, does a gap go all the way around with the chuck? If so redo till it's centered, now your bit will usually go straight through.
I suspect bobleibo may be right about those chucks even though I think for it to do this would probably have it come apart.

 

[dogcatcher]

Are you using a centering bit to start your hole?

 

[Sabaharr]

Here is a problem that I once ran into that caused just what you are describing. We are all taught that putting a dead and live center in our lathes and seeing if the points touch will tell us if the alignment is true. Well yeah it is a good indication but ..... My new Jet lathe had a very minute alignment problem that didn't show until the head and tail stocks were well separated. I first realized it when I started using a mandrel saver. The mandrel end rubbed one side of the saver as it was going in and deflected just the slightest amount. When I was using a live center I didn't notice it because it slipped right in the end of the mandrel. I first thought the mandrel was bent but it turned out the headstock was mounted just slightly cocked to one side. This was causing my drilled holes to wallow out on the outward end but looked fine on the clamping end. You can spin a mandrel in the headstock and it won't wobble because it is squarely mounted but if the headstock is cocked off ever so slightly it will cause wallowed out holes to be drilled and slight off center turning which will show up mostly on the tailstock end of the mandrel, headstock end not so much. Its a longshot but worth checking and easy to do.

 

[Skie_M]

Hmm ... how do you check the alignment of the headstock to tailstock? Test bar turned to specific diameter and then flip to test how much deflection?

 

[Chasper]

Are you drilling wood or resin?
Are the flutes of the bit filling up and forcing the new shavings to go around the flutes causing the wobble? That will happen on resin but also on more oily woods.
If resin are the shaving coming our as flakes or tight worm-like coils. The worms form when the shavings are pressured and heated on their way out, forcing the bit to wobble.

 

[silent soundly]

If you want to throw money at the problem, you can get the psi Pen Drilling Chuck. It's $77.43 at amazon right now with prime shipping. Every blank that I have ever drilled has been on this. It's very stable since it contacts so much of the blank. You will still want to have a sharp straight bit of course.

PSI Woodworking Products CSCPENCHK Dedicated Pen Drilling Lathe Chuck PSI Woo... via @amazon

 

[TurtleTom]

I had the same idea as Sabaharr, and since I also use a Rikon mini lathe too I thought I'd do the best test I could find. I zeroed in a large round bar in the chuck and rigged an indicator to travel up the bar via the tailstock. (See picture)
I was expecting a bad readout on the travel but it was only 0.010" out over the 3 1/3 inch travel of the tailstock. I slid the tailstock back several times to give it a chance to get cockeyed but the error remained the same.

 

[monophoto]

I'm getting a lot of bit wobble when I'm using a 7mm bit and with a lot of different 7mm bits. It seems to be happening with both square and round bits and the hole look to be off center a bit.

Let's stop for a bit to make sure we are correctly understanding the problem. I see two things in the original message:

• wobble - I presume this to mean that the drill bit is wobbling as the blank is being drilled.
• the hole is off center - this statement is confusing - which hole is off-center, the end that the bit enters, or the end where it exits?

In my experience, bit wobble usually means that the center of the bit is being forced into the blank at a point that is not on the axis of rotation of the blank. I've seen this happen when I have engaged the tip of the bit into what I presume to be the center of the blank without first locking the tailstock down. In my experience, the best way to avoid wobble is to lock the tailstock down with the bit not touching the blank, start the lathe, and slowly advance the tailstock quill until the bit engages the wood. If the tailstock and headstock are correctly aligned, the bit will be exactly centered on the axis of rotation and won't wobble at all.



If the second issue is that the entry hole is centered, but the exit hole is not, then that generally means that the chuck jaws are not holding the blank exactly centered on the axis of rotation, and can easily happen if the blank does not have a square cross-section. And if you are using standard pin jaws (four thin jaws) to hold a blank that is not square in cross-section, only two of the jaws will actually grip the wood, allowing the blank to twist. The best way to avoid this problem is to first put the blank between centers and turn a tenon on one end that can be gripped by the pin jaws.

The PSI catalog cut that Nick showed is an example of pen jaws. PSI also sells these as aftermarket jaws that fit their Barracuda line of chucks.



And what is meant by 'square and round bits'?