Drilling Holes
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How do I mount tools to my lathe? Here is a frequently asked question… it comes down to matching specs. If you have the manual for your lathe, it should tell you. If you don’t, I suggest you try and find one, or you will need to do some measuring. Then it comes down to matching size for size. The most common lathe mounts are the Morse Taper socket in the spindle and the threads on the outside of the spindle. Usually, if you have a #2 Morse Taper (#2MT) the threads will be 1” x 8 threads per inch (TPI) – but not always, so its always best to check so you know for sure before you buy anything. #1MT lathes are smaller than ideal, but can be made to work, but there are limited tools made in #1MT so keep that in mind if you are buying a lathe. #1MT lathe sockets usually have a ¾” spindle thread, but there seems to be less standardization as I have seen both 10 TPI and 16 TPI – ¾” threads on #1MT lathe spindles. So you will want to verify the thread count. 10 TPI accessories are less common than 16 TPI accessories. And or course there is always the chance of metric threads, odd ball SAE threads and it all depends on the manufacturer – so check it to be sure. Once you know what you have, you buy what matches it. You want a thread mount collet chuck, match the threads on the chuck to the threads on your lathe. If you’re buying a Morse Taper mounted tool, match the MT of your spindle to the MT of the tool. They do make adapter sleeves and sockets, but they have limited uses in call making because of the lack of a through hole or extended length which eats up lathe bed space you might need. Drilling Holes: Accurate holes with a drill bit are one of the hardest things to do. There are so many ways a drill bit can “go wrong” and create an oversized hole. Anything that affects alignment of the drill will affect the diameter and shape of the bore. As will any outside forces on the drill (like wood grain for example). If the drill bit is not in line with the axis of the rotating portion of the process (be it the drill in line with the spindle axis of a drill press or the drill being aligned with the axis of the spindle when drilling in the lathe) you will have additional errors in the size of the hole you are drilling. There are two areas to focus on when checking alignment of a drill, and it is most easily done with a dial indicator. Axial alignment of the drill with the rotating axis – which is more easily described with the following example: If you put a small drill bit in the drill chuck, grab the point of the bit, and bend it – you would see axial misalignment. The most common causes of axial misalignment are: low quality drill chuck, poorly mounted drill chuck on the spindle or arbor, chips in the jaws of the chuck, or a bent drill bit. The other alignment issue is radial alignment. This is generally more likely to be seen when drilling on a lathe than when using a drill press. An example of radial misalignment is: Imagine drilling a hole in a rod, off center – and then placing a drill bit in that off-center hole. When you rotate the rod, the drill could very well be aligned axially with the rod, but the entire bit has an “orbit” around the true center of the axis. This is less common in drill presses just because of the design – but it is a very common occurrence when drilling on a lathe due to a mismatch in height of the spindle in relation to the height of the tailstock. Axial misalignment causes the tip of the bit to “orbit” around the true center line, causing one edge of the drill to cut on the outer face – in turn causing an oversize hole. Generally, what will happen is the entry point of the drill will be oversized, and as the drill progresses into the hole, it slowly starts to be supported by the material causing less run-out, and the bore starts to get smaller and closer to the desired size, but usually it will still be oversized – but tapered – and this will affect how the mandrel holds the blank. Radial misalignment will do the same thing, but generally, the size of bore is less tapered and more equally oversized – though some taper will be expected. The other big contributor to tapered or oversize holes (this primarily applies to drilling on a lathe) is not starting centered. If an accurate bore is required – it is best to start the hole with a center drill or spotting drill – just enough to give the regular bit a spot to start that is accurate and centered. Drill bits will flex, but center drills and spotting drills are very short and rigid – so the flex is for the most part eliminated allowing a more accurate starting point for the regular drill. Drilling accurate holes is a difficult thing to do even with exceptional and expensive equipment… let alone a $300.00 wood lathe or drill press. Expecting a hole size within +/-.002” of the stated drill size of most larger drills (like 5/8” or ¾”) is very unlikely, in wood especially. If an accurate bore is required… for example for use with a pin style mandrel, it is strongly suggested that you drill undersize by 1/64” to 1/32” and then use a chucking reamer to enlarge the hole to size. Chucking reamers are designed to enlarge holes to an accurate size, but the also will only follow the previous hole. So if your hole “wanders” because of the wood grain, the reamer will follow it. It may lessen the extent of the “wandering” but it will still be there. The absolute most accurate way to bore a hole is to use a metal lathe with a boring bar – but that is not something most people have access to. Accurate holes are one of the more intricate things to do with limited equipment. The best thing to do if you want an accurate hole, is stack the deck in your favor… and you do that by drilling undersize and using a chucking reamer to open the hole up to size. Drilling/Reaming feeds and speeds: Slower is your friend with larger bits. Generally with 5/8” – 7/8” drills, I will run no faster than 500 RPM and you want to keep the drill moving into the material or back it out completely or it will affect your surface finish. Its hard to get a specific feed rate of the drill since its run by hand… but you want to take a decent cut when in the cut, and you want the drill out of the hole when its not drilling. Reamers follow a different rule… which I refer to as the ½ - 2x rule. Reamers usually work best when they are run at half the RPM as the drill bit of comparable size, and you want to feed them into the material at 2 times the rate you did with a comparable sized drill. That usually yields the most accurate bore size and best surface finish. Though I have found that the “half the RPM” rule is more important than the “2 times” feed – but they both play hand in hand. Collet Chucks: These are great little tools. I used to be quite skeptical of them running true, but have learned over the years, that they do center quite well as long as the threads are clean, in good shape, and the back face of the spindle is clean and flat. They have become one of my favorite tools. There is one MAJOR thing one needs to know about using collet chucks… you NEED to snap the collet into the collet nut, THEN put that assembly into the chuck body loosely, THEN put in what ever you are holding into the collet. The collet nut has an off center ring that is designed to pull the collet out when loosened… if it is not seated in the nut prior to assembly it will likely not run true. I have seen many suggest “put the collet in the chuck, thread the nut on with nothing in the collet, and then tighten down the nut all the way, and then back the nut off and insert what ever you are holding into the collet.” This MAY seat the collet in the nut, but it also collapses the collet beyond its designed range, and could very likely damage the collet. I suggest you never do this. It takes a second to snap the collet in the nut… and takes many more seconds to tighten down the nut and back it off anyway… so doing it the correct way will actually save you time and eliminate the risk of damaging the collet. One advantage of a collet chuck that mounts to the threaded spindle is when using straight shank expanding mandrel, you do not need to build a draw bar to hold the mandrel in the tapered socket as you do with a MT mount mandrel. Mandrels: There are many versions out there… from homemade to machined specifically for call making… expanding, pin type, crush type, taper length, friction fit and so on.