Continuing on from 10 Tips for Drilling Better Holes, Part One, Kurtz Hertzog shares his time tested methods to guarantee accuracy and quality when drilling holes.
Keep things cool
Smoke is never a good thing when drilling wood. You can drill quickly and efficiently without creating a lot of smoke. On occasion, you may get some, particularly from those species that like to burn such as cherry (Prunus spp.), but it should be rarely and only a little bit. If you’ve got smoke erupting from your drilling, regardless of your drilling method you’ve got other problems. Chances are it is one or more of these: when a drill is dull, rather than sharpen it we often just push harder and speed up the rpm. Smoke can often be caused by far too aggressive speeds and feeds. Slow things down and let the tool do the work.
Plugged flutes will also impact the drilling location and just continue to pack things in with no relief for heat or debris. Smoke is a good indicator that shows it is time to check the flutes. Lastly, even without smoke, many turners overheat their drilling. This is often true with plastics, they wonder why the holes aren’t round and can have recast plastic on the inner diameter. The short answer is speeds and feeds are too high. The longer answer involves the thermal conductivity of plastics and how being a thermal insulator traps the heat inside rather than shedding it. For plastics, it is all about being slow and easy. Once you’ve screwed it up it really is scrap at that point. Besides, removing a too hot to hold drill bit from the drill chuck is no joy. When things get hot, stop and take a rest. Let things cool and then continue.
Step up sizes
Even in a machine tool shop with speciality equipment of massive sizes they rarely go from zero to big in one step. If you have a larger sized hole to drill, begin with a pilot hole. You’ll drill that pilot hole using your starter location and all of the good practices for drilling. Once that has been accomplished, step up to a somewhat larger size and drill another hole using the smaller hole as the guide. Once that has been accomplished, do it again.
Depending on the material being used, the drilling equipment and the final size needed, you might need to only drill a pilot hole and then the final size. You might need several intermediate drillings. Don’t believe that if you go slow enough and think things are rigid enough that you can put a quality 25mm drilled hole with a twist drill into a turning on one go. It is possible with a Forstner bit, but not with a twist drill in my experience. By stepping up through intermediate sizes, you’ll be able to let things centre on the previously drilled hole and work far less since the current drilling is opening the hole.
Check your drill sizes
If you need a specific hole size, you need to do a couple of things to ensure that you get it. First, you need to check the actual twist drill you intend to use. Whatever the manufacturer marked is usually close, but on smaller drills you can’t even read it. Obviously, the slop in sizes in the index stand is no guarantee of the correct size. When you measure the drill you’re going to use, measure it across the flutes, that is where the work occurs. Even when you have that across the flutes measurement, you still don’t know what your final hole size will be. For the most part, we aren’t working in thousandths of an inch, but sometimes we are.
When I drill my custom nibs for the inkfill, my minor diameter is selected to be 1.98mm. Because my inkfill dimension is 1.90mm, I really can’t live with a no clearance fit at 1.90mm or a sloppy fit at 2.08mm. You may not care a hoot about the real dimension, but only if a mating part fits properly. Again, too small and you get press fits with no glue gap. Too big and the precision is gone, and the adhesive needs to fill the slot.
Different materials yield different size holes
If you drilled the same hole in a variety of species of woods and in different grain orientations, I think you’d be surprised and the variation in hole sizes that resulted by doing this. The end grain will drill differently than the face grain in the same species with slightly different results. Now throw in the various species and any cross grain drillings you might be doing. Plastics and metals are obviously going to have a different response.
Though not often that critical, when I need a special size or a special fit, I will test drill my hole(s). I will use the drill I intend to use and a scrap of the exact same piece of wood in the intended orientation. It lets me work out any special workholding if needed and zero in the best speeds and feeds. Once I’ve completed the practice hole(s), I can measure or test fit things to be certain they meet my needs. If there is a problem, I can easily regroup and change drill sizes, parameters or anything else that might impact my results. Upon successful completion, all is well, and I can proceed with confidence. How long does this take? Usually a minute or two at most. Is it worth it? For me, it is when the size is key.
Practice
I’m certain none of us looks forward to telling our turning mates you can’t go off with them since you are going to the ’shop to practise drilling holes. I don’t treasure it either. Like any skill, reading about drilling doesn’t perfect it. Understanding it doesn’t perfect it. Only doing it repeatedly and learning from the mistakes will you build the skills to make drilling holes a rote skill. Of course, you can continue on as you were if you are content with your current results. I would liken this to any of the skills you have or will get in the woodshop. You didn’t master the skew chisel by reading about it or understanding it. You mastered it, if you have, by spending sessions at the lathe practicing each of the cuts until you got comfortable with them.
Gradually, your quality of cuts improved, and the frequency of catches decreased, and one day you were comfortable reaching for the tool. Don’t worry about setting aside specific times to practice drilling holes. When you need to drill, spend a few minutes ahead of time practising. Make that your mode of operations and soon you’ll see the improvement. The great news is that mastering drilling will take a small fraction of the effort that mastering the skew did.
Conclusion
I view everything in this series as building blocks. Individually, they might seem inconsequential. Collectively, you’ll be surprised if you look back to see how far you might have come. Just knowing the shop equipment, workholding, processes, tools, sharpeners, techniques, good and bad practices, shortcuts and the other items should be helpful. I try to share things that will improve your skills and make your shop time more productive. Is drilling a hole that big of a deal? By mastering these basics, I shouldn’t be.