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| Drilling! - small holes on the mill and centre drills |
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| raynerd:
Hi Guys I need some advice if you will. I`m pretty useless at drilling but I have improved over the last year as I realised I was pushing the drill though too fast and it was causing my holes to wander. I have drilled small holes on the lathe and know to peck at the work piece. I really struggle drilling holes on the round surface of bar as of course my drill slides off. I want to drill a 0.8mm hole on a 3mm bar but with the work being so small, I can`t get in to centre punch without the punch sliding off. I`ve spoilt one part last night trying to do this, managed to get a small centre punch but it wasn`t enough and ended up chewing the surface of the bar rather than drilling the hole. Any advice welcome? While I`m on the topic, although I own a large selection of centre drills I never really know when to use them. Are they really just to get the hole started with them being rigid (or is that is that a spotting drill and how do I tell them apart?) or are they for cutting the "cone" in the work piece to accept a lathe centre? I know this is basic stuff but I`ve looked back at some of my old projects and really decided I need to think about my workmanship more, slow down with pace and eagerness to finish the project and take more time! I think it is fundamentals that are letting me down. My lathe turning is OK, my milling is getting better but it is the basics and setup inbetween that is letting me down when I move the work piece from one job to the next. Chris |
| Bluechip:
Chris The apparently simplest thing turns out to be a PITA You need to make a simple 'cross drilling jig'. Plenty of ideas on the net, pick the easiest. Dave BC |
| Gauge3:
Hi Chris, I use centre drills to make a good start on any hole I drill in the lathe, as they are more rigid than a twist drill (although you can get short 'stub' drills). They can also be used to make lathe centres as you mention. There are lots of designs for drilling jigs out there. A quick (one off) way is to clamp a small square/rectangular bit of steel on the topslide, and 'square' it to the axis (e.g clock it or grip a bit of silver steel in the chuck and use a square of steel plate or a 6" ruler to align the block with the s/s). You don't want a huge piece as the drills will wander if too thick, so you may have to pack it up with a larger block underneath. For this I'd find a bit in the scrap box about 10mm square by about 25mm long. Drill through the length of the block with the diameter of the rod you want to drill (e.g. 3mm). Then rotate the block 90 degrees (square it up again, using the chuck face this time. I have a bit of mild steel plate that I know is parallel to do this quickly and then carefully peck in your .8 mm drill (after 'dimpling' with a small centre drill - and you have just made a simple jig for this particular job. Leave the jig in the lathe after drilling it 0.8mm and shove you 3mm rod into the desired depth and then drill .8mm again. Easier to do than to describe! If you are going to do this regularly - then for small rod I think a finger plate with some simple round 'sized' guides, (easily made in the lathe as needed) is a good way to go. You can use it for lots of simple operations on small parts, so it's worth some time to get right and will last a lifetime once made. Regards. |
| 75Plus:
I use a similar method to the one posted by Gauge3 except I make mine with the drill press or mill. Take a bit of flat bar and make sure the end is square. Clamp a stop on the table and, while holding the work piece against the stop, drill the larger hole through the wide side of the bar. Rotate the work piece 90 degrees and, using the smaller drill, drill the bar again while holding it against the stop. The best part of this method is that NO measurements are necessary and can be accomplished faster than explained. Edit: The picture shows a jig I made, using this method, for placing tension pins through the center of of 1/2" ali rod. The set screw was drilled through then case hardened to act as a drill bushing. It also holds the workpiece firmly while drilling. Joe |
| wheeltapper:
Hi I see you are in the UK so you may get Model Engineers Workshop. Harold Hall described a good cross drilling jig in one of his articles. heres my take on it, it fits on the lathe in place of the toolpost. and here are two pins I crossdrilled, the pin is 6mm, the hole is 1 mm. if you are interested I'll look up the issue No. cheers Roy |
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