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Is it my turn? Anything to do with lathes, mills and other shop tools
Well, I did that and got no joy... nice concentric ring on the jaws, good die grinder (tight bearings) in a QCTP holder, fresh stone spinning at full speed and grinding the full length of the chuck jaws under slowest carriage feed speed with .001" depth of cut per pass, with last 5 passes with no further lateral (depth) adjustment. Did the whole process twice and I still have .011" to .0125" runout at chuck. Disappointing to say the least and unclear as to probable cause. Is it possible that the scroll and/or the jaw-to-scroll engagement on one jaw is worn, which no amount of grinding will fix?
Attachments
That would be my first suspect.
not trying to bust yer chops...
Have you removed the chuck and inspected the back plate/mounting, tightness, debris, damage? With the chuck off check the spindle for concentricity, that it runs true.
I have not done the leverage test
couple pieces of wood and ten seconds?
Then take the chuck apart, there's yootoob howto's
is it off center or not running parallel to the bed?
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I would not use carbid bits for grinding the chuck jaws. I would use a grinding stone.
I suspect the forces are higher with the carbid bit, since its more machining than grinding. Just my thoughts
I suspect the forces are higher with the carbid bit, since its more machining than grinding. Just my thoughts
Were you able to preload the jaws inwards like in the example?
Let's see your set up. Are the jaws the bolt on replaceable/reversible type or one piece to engage with the chuck scroll?
Hey @gggGary, no offense taken...recall, two chucks, both 6", one very large Chinesium with lots of overhang from the spindle nose and a very shallow old one with minimal overhang, believed to be original to the Logan 820. The Logan jaws are not reversible. Overhang on both noted in a previous postnot trying to bust yer chops...
Have you removed the chuck and inspected the back plate/mounting, tightness, debris, damage? With the chuck off check the spindle for concentricity, that it runs true.
I have not done the leverage test
couple pieces of wood and ten seconds?
Then take the chuck apart, there's yootoob howto's
is it off center or not running parallel to the bed?
- Chinesium chuck runout measured at .0005"
- Logan chuck runout measured at .0005"
- spindle deflection with large chuck installed = 0.000" (zero movement on my Mititoyo dial indicator)
- both chucks run true to the bed
- Logan chuck disassembled with no immediately obvious wear to the scroll or to the jaws, but considerable axial movement of the jaws when engaged on the scroll (on the bench), the closer the jaws are to being fully closed, the worse it is. Otherwise, the fit of the parts; scroll to chuck body, backplate to chuck body all very tight
- jaws are indexed to the chuck body
- the only obvious dimensional discrepancy is the comparative length of the of the nose of the jaws. Not sure that's normal; comments?
@Bjorn, the carbide just happened to be in the collet when I took the photos. I did the grinding with a new very fine cylindrical stone.
Yes, the jaws were tightened around a machined-concentric piece of steel pipe.
@RC4MAN, no pics of the setup... the jaws are not replaceable/not reversible. They are as you say one-piece to engage with the scroll and are indexed to the chuck body.
Could well be as you suspect, the chuck is too old and worn. The slots in the body the jaws fit into may allow the jaws to cock when tightened and the further away from the chuck body the worse it is. And then there's the scroll condition.
Even a new 3 jaw chuck is only going to be "so" close to .0000
I've personally found that you can't beat a 3 or 6 jaw chuck that you can dial in, but may be too expensive for your application but Chinese ones would be acceptable. Example below, you'll notice the 4 set screws around the perimeter of the body which allows you to dial it in true once the part is tightened in the 3 jaws, like having a 4 jaw chuck. You'll need a specific back plate adaptor for your head spindle.
https://www.ebay.com/itm/3135538213...4TebFQ1uyyqvFxqjQkB+9kRl4=|tkp:Bk9SR_qRkbWPZw
Even a new 3 jaw chuck is only going to be "so" close to .0000
I've personally found that you can't beat a 3 or 6 jaw chuck that you can dial in, but may be too expensive for your application but Chinese ones would be acceptable. Example below, you'll notice the 4 set screws around the perimeter of the body which allows you to dial it in true once the part is tightened in the 3 jaws, like having a 4 jaw chuck. You'll need a specific back plate adaptor for your head spindle.
https://www.ebay.com/itm/3135538213...4TebFQ1uyyqvFxqjQkB+9kRl4=|tkp:Bk9SR_qRkbWPZw
Since we are on the subject of jaw chucks, getting a self centering 4 jaw is a very interesting option most people overlook. Turns out that hexagonal stock runs absolutely true in a self centering 4 jaw. So you can clamp the most different styles of stock.
#nerdmodeout
#nerdmodeout
Before making investments if the chuck that came with the lathe is THAT worn out what about the ways?
The reason I went on an upgrade search from my Daddy's old Southbend; just too many worn out parts to make using it useful.
Two swaps laater I'm happy with the Grizzly I ended up with and recent inflation has made it a good investment too.
Next up getting my head out the gutter and learning how to machine! Tried to make an accurate spindle to help align a reamer to a valve guide bore and it didn't go well, poor surface finish and stupid big unintentional taper bit me hard! Major results; a skinny wobbly shaft and lots of springs, LOL
The reason I went on an upgrade search from my Daddy's old Southbend; just too many worn out parts to make using it useful.
Two swaps laater I'm happy with the Grizzly I ended up with and recent inflation has made it a good investment too.
Next up getting my head out the gutter and learning how to machine! Tried to make an accurate spindle to help align a reamer to a valve guide bore and it didn't go well, poor surface finish and stupid big unintentional taper bit me hard! Major results; a skinny wobbly shaft and lots of springs, LOL
I hear you and am quite conscious of the limitations and age of the lathe I have...that said, it does what I need it to do for now. I consider that most if not all of my machining needs are not super-high precision. For example, I have never tried to turn a straight shaft more than 6" long or so... meaning I have never tested to see if the ways are heavily worn close to the chuck. There are a few dings and scratches etc, so one can be sure there's wear there. I suspect the lathe will outlive me!
Deep tangent I've long thought a 6" spindle extension with a support bracket clamped on the ways to hold a new chuck moving the tool post back on "good unworn ways" would let a lot of old lathes do good work in home shops for several more decades.
Well, feck me!!! Took the Logan chuck fully apart, knocked off a burr here and there, cleaned and oiled the innards and reassembled it. Guess what? I'm absolutely tickled to say that there is now less than .001" runout on 3/4" shaft. In all honesty, I really don't think I fixed anything, except possibly the cleaning. Don't think that it had ever been fully cleaned since it was made. Persistence pays?
My shop vac sits right behind my Logan 200 and I pretty much vacuum the chuck after every use... keep my chuck running much smoother
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