I have a slug of 2" diameter aluminium 4" long that I bought just to learn on and play with. Ends are not cut exactly square and when I chuck it in my 3 jaw, about 1/32" from being all the way into the chuck and bottoming out, it has 0.037 runout. I tried repositioning in the chuck but couldn't do much better on runout. I've checked other round stock and get between 0.011 and 0.015 runout, which sounds high. One piece is something I turned and the other is a piece from a tool i just bought. How do you start trueing up the slug? Could the slug be that out of wack or is it just how it is chucked?
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Where to start?
- Thread starter DiscoDan
- Start date
With 3 jaw material goes in and stays until finished.
To make true insert to almost seated and tighten 3 places gradual tighten.
Face of end then flip and seat against face of Chuck and repeat.
Toss in bin for use later...
If making something between centers then after facing center drill.
Does not matter if Chuck running exact...place material in Chuck and perform all cutting then part off.
Facing parted face last.
Sent from my SAMSUNG-SM-G930A using Tapatalk
To make true insert to almost seated and tighten 3 places gradual tighten.
Face of end then flip and seat against face of Chuck and repeat.
Toss in bin for use later...
If making something between centers then after facing center drill.
Does not matter if Chuck running exact...place material in Chuck and perform all cutting then part off.
Facing parted face last.
Sent from my SAMSUNG-SM-G930A using Tapatalk
tq60, that is exactly what I did last night except my chuck only has one pinion to tighten. I have a second chuck that I posted about last night that has 3 pinions.
Maybe a dumb question but can you use a center in the tailstock and drive with the chuck or does it have to be between centers? Reason is that I don't have the setup to do it between centers but I do have a dead center for the tailstock. If you can do it, I assume I would set the tailstock end up on the center first while the other end is being loosely held in the chuck and then tighten the chuck. Yes...No???
Maybe a dumb question but can you use a center in the tailstock and drive with the chuck or does it have to be between centers? Reason is that I don't have the setup to do it between centers but I do have a dead center for the tailstock. If you can do it, I assume I would set the tailstock end up on the center first while the other end is being loosely held in the chuck and then tighten the chuck. Yes...No???
Dan, here's some really basic stuff in no particular order that will hopefully clarify:
- A 3 jaw chuck will turn a work piece concentric with your spindle centerline as long as you don't remove it from the chuck as the other guys have told you. The work piece does not have to have a finished surface for you to turn an accurate part; an extruded surface will be fine as long as you don't take the work piece out of the chuck.
- A work piece should not extend from the chuck more than 1-1/2 to 2 times its diameter without tailstock support, that being a live or dead center. So, if its short then just face and turn it. If its long, face it, center drill it and bring up your tailstock center for support. This is so the force of the cutter doesn't rip the work piece out of the chuck or cause inaccuracies as you turn it.
- You do not have to face one end to turn a piece. The end face inside the chuck doesn't even have to bottom out in the chuck, although it is best if it does. Just close the jaws until they touch the work, then rotate the work as you tighten the jaws. This will get it close. You can then snug it down. If you want it as accurate as possible then use an alignment tool with a bearing on the end. More on that some other time. In any case, once the work is clamped in the chuck, face the end that is sticking out and have at it.
- When clamping a work piece in a 3 jaw chuck, high quality chucks are always marked on one of the three pinions. These chucks have a rated or specified accuracy level and that accuracy level is achieved only when the work is tightened with that marked pinion. The mark will be a hash mark, zero, straight line or dot. Use that pinion. It is not a good idea to tighten a 3 jaw chuck by cranking down on all three pinions; this throws the accuracy of the chuck off. If your chuck is not marked then mount a short piece of ground rod and lock it down with one pinion and check with an indicator to see what the run out is. Repeat this with each of the other pinions and mark the most accurate one. Use that one every time you use the chuck.
- Turning between centers is the most accurate way to work but it is rarely used by most of us. It requires careful work, with carefully drilled centering holes. You must use a drive dog to drive it, a dead center in the spindle to locate that end and a dead or live center on the other end. I would guess only 1% of my work is done this way. Most of the time I use a 3 jaw, sometimes a 4 jaw and a collet chuck only when appropriate.
- Most work will be done in a 3 jaw and you can use a tailstock center, a dead or live center, to support a long work piece. The chuck drives the work, the center supports the other end. So yes, you can use your dead center. You need to face the work, center drill it with a 60 degree center drill, then lube the dead center before engaging it in that hole. You apply enough pressure with the tailstock to just enable the chuck to turn freely by hand, then lock everything down. As you work, the work piece will heat up and enlarge so watch the pressure exerted by the dead center. You need to adjust it if things get too tight. Also, periodically re-apply lube to the dead center. When you tire of this, buy a live center.