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Dial test indicator question
- Thread starter fcs
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- Jun 7, 2013
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Well, I was going to wait with the big question until I had taken the diagnosis as far as I could.
This is a beginners forum and I am a beginner. I may not use all the correct words. I have a new lathe, my first and probably only lathe, a Sherline 4400. I am interested in lapping some small sleeves with an external hone, using drill blanks as slip fit mandrels, sizes mostly in the range 9/64 to 15/64. But with the Sherline 3-jaw chuck, I am getting huge runout: .005-6 at 1/2 inch from the jaws. The runout is the same using different sized drill blanks, center drills, and an end mill with a 0.5 inch shank. Also a Forstner bit. The high spot always occurs at the same spot on the chuck. Rotating the object in the jaws does not matter.
So my beginners diagnostic sense says the problem might be internal to the chuck, or in the threading of the chuck to the headstock. I disassembled the chuck, gave it a cleaning. I found a few slivers of metal from the tapping of the chuck threads, but visual inspection found nothing in the chuck spiral or the jaw teeth. I greased everything and put it back together. Runout was the same, with the high point at the same place.
I was trying to see if I could find any runout on the face of the chuck. I was having difficulty with getting the DTI positioned to do this. It SEEMED like I had more than 1.3 revolutions in the DTI at my disposal earlier, but I'm not sure. I just wanted make sure I hadn't damaged the DTI with my clumsiness. I have not been able to detect more than about .0005 variation in the chuck face, but its awkward with skipping the slots where the jaws move and the chatter caused by the laser etching.
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3-jaw chucks are for speed, 4-jaw chucks are for dialing in.
You put things in a 3-jaw with 5-thou run-out and you simply have to turn the part down by more than 5-thou and presto it is round.
If you have something that really is already round, you chuck it up in a 4-jaw, and dial it in until it is concentric; as small as you can measure.
You could find some way to applying outward tension to the 3-jaw, and then use the lathe to cue the inside of the jaws and make them round and reduce runout.
You put things in a 3-jaw with 5-thou run-out and you simply have to turn the part down by more than 5-thou and presto it is round.
If you have something that really is already round, you chuck it up in a 4-jaw, and dial it in until it is concentric; as small as you can measure.
You could find some way to applying outward tension to the 3-jaw, and then use the lathe to cue the inside of the jaws and make them round and reduce runout.
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- Jun 26, 2018
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- 1,733
Those DTI that measure that resolution don't cover much real estate. That's either a .030 or .060 version? That is, the full amount of movement that covers is .030 or.060 so it probably has 60 or 120 hash marks? I wouldn't think it travels much past one revolution, is that the case?
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- Dec 20, 2012
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I'm with Mitch. The issue is that a 3 jaw scroll chuck is always going to run out to some degree except for the first time you turn a part; then that part will be concentric with the spindle. Once you remove it from the chuck, or if you chuck up something that is either already turned or is round (like your drill blanks), the chuck will run out. This is just the nature of a scroll chuck. Even Set-tru scroll chucks behave this way. If you dial in a Set-tru scroll chuck to zero for a work piece, the minute you chuck up a piece of a different diameter the run out increases. The reason for this is that the scroll is engaging the jaws in a different spot when you change sizes. In any case, there is probably nothing wrong with your 3 jaw chuck. If you wish to confirm this, chuck up a piece of something and check the run out; it will be a lot. Then turn it down and check the run out again without disturbing it in the chuck and run out should be zero.
If you really need to minimize run out then use a 4 jaw independent chuck and dial it in or use a collet chuck and accept what run out there is from the spindle/chuck/collet/nut combination.