Splitting back side of wood with Brad point bid...

[tom_k/mo]

Curious if anyone might have a suggestion. I was drilling some pen blanks this morning and in the process drilled my first 10mm holes. I had 3 different wood varieties, Cocobolo, Spalted Maple (stabilized) and Olive Wood. I had no problems drilling the Cocobolo, but with both the Spalted Maple and Olive Wood, the back-end of the blank split and a chunk broke out of it (ruining the blank). I was being very careful, and drilling slow, and backing the drill bit out often to cool it and remove chips, but it still broke. I tried a second set of blanks, and drilled a 7mm hole first, then chased it out with a 10mm. That worked, but I don't think that the brad point bit is made to enlarge or chase existing holes, as the bit vibrated somewhat (which it didn't when drilling a 10mm hole from scratch). Any suggestions on what I can do to lessen the chance of the back side breaking on the larger holes with this hard wood?

On another note, I didn't configure the SS as a drill press with a vise this time, I set it up as a horizontal boring machine, put the cross-cut miter gauge in backwards, adjusted the table height and locked the gauge in position. Then just butt the blank up to the fence, clamp and drill. It worked much better (and faster) in my opinion... Not only that, but with the SS configured like this, I could slide the headstock back, and couple it to the bandsaw, leaving the chuck and drill bit on the other end of the quill, and cut more blanks to length, then slide the headstock back to the table and drill more, and it stayed in alignment for the blanks.

[kalynzoo]

I often work with small blanks, however, I have not drilled a pen blank. Using a small blank, I find that a quality drill bit is of great importance. Some of my lesser quality brad point drill bits (the ones in the red box from China) tend to act more like a cutting torch, burning their way through, rather than a cutting instrument. The blank should be held tightly to a waste backing, allowing the bit to cleanly exit the blank and enter the waste wood. I often make drilling jig by notching a waste blank allowing my work to fit firmly on three sides, sort of like a tongue and groove joint. This not only give me a firm support for drilling, sanding, and gluing, but it give me a measure of safety if I'm working with a sharp power tool...even the drill, as it keeps the blank from spinning.
Hope this works for you.

[Gene Howe]

I'd imagine that your miter gauge set up is right on the money to get a perfectly centered hole. In which case, I'd drill both ends to the middle.

And, I would seriously consider Gary's advice re: quality bits.

[charlese]

In thinking about the splitting issue with small blanks, while using brad point bits, I first think of two causes.

The quality and SHARPNESS of the bit used is of importance. Also the GRAIN of the wood blank must be assessed. My suspicion is the wood split at a point where the grain exited the blank in a fairly sharp angle from the penetrating drill bit. A freshly sharpened, slowly penetrating bit will somewhat relieve this splitting issue.

Also I am guessing the dryness - hence brittleness - along with the breakdown of wood fibers in the spalting area, enhanced the chances of splitting. Maybe running a little water through a pilot hole, prior to final drilling might have the effect of softening the wood fibers and making the piece less brittle.

The drilling of a pilot hole has a certain amount of wisdom, in that the final bit does not have as much wood to hog away. However when using a brad point, the second bit has no stabilization base for the brad point. Therefore wandering/chatter/wobbling will occur.

If a center pilot hole is used, I think a forstner would be a better choice for the enlargement than a brad point. Of course there will be more heat build up.

As Nick pointed out a Spade bit is a better choice for drilling end grain because the cutting edge can be changed to a less sharp angle that will produce scraping rather than slicing.

Maybe one of these days someone will produce drill bits specially ground for end grain drilling.

[tom_k/mo]

Thanks for the feedback guys. I think my problem is probably that I didn't back-up the blank with a piece of scrap wood, and the bit drilled out the end into the air. I'll back it up with a piece of scrap next time and see if that doesn't resolve the issue. I do know the bit is a good bit and sharp.

[hew]

tom_k/mo
I have a few peices of spalted maple. I resawed 3 or 4 small slabs that I could cut pen blanks from. I would like to know about the process for stabilizing spalted maple. The natural spalted maple looks as if it maybe hazardous to work.

I had a pretty good size stack that set in the shop 4 or 5 years. I was at an auction that sold the stack of maple to a fellow where I worked. A couple of years later I ask if he had made any thing from the maple. He said he had not and was moving and need to get rid of it. If I wanted it I could come pick it, so I did. At the annual retirement party 04 or 05 I set at a table with another retiree and got to talking about woodworking. I ask him if he would like some spalted maple burl. He sure and I said come by and pick it up. This past December annual retirement party I ask if he had used the burl. He said that his wife wanted it to be gone and that he had give a few peices away to fellow making duck calls. I will ask at the next party if he is still storing the stack.

[RobertTaylor]

tom, i reccomend a backer piece and drilling with 135 degree split point bits. as far as stabilizing spaulted maple ca glue is the woodturners friend. drench the blank with thin ca glue turn a little and drench again. when you are done turning to final shape sand with micro-mesh , wax it and done. this is a spalted maple pen from last year. bad pic but good pen. fwiw the same method works well for turning corn cob pens.

[hew]

bettyt44720
Thanks for stabilizing spalted maple with ca info.

[tom_k/mo]

betty44720, thanks for the recommendation on the bit. I'll give that a try.

[markap]

When drilling my pen blanks, I use a vise with two pieces of wood with V's cut in them that support the wood down to the bottom which sits on a 3rd piece of wood. I still infrequently get some breakage with some acrylics. So, in the future, I will cut the blank longer than necessary and knot try to drill all the way through - just far enough for the tube ( and a little longer) and will then cut to near final size.