The slot drill is a no-no, it's just the wrong tool for the job. The same applies to a normal drill. The most practical method is to use a boring tool. A couple of thou runout swapping ends and changing in a
3-jaw chuck would not be surprising so if concentricity is a major issue put the sleeve in a 4-jaw and clock the OD first.
Then bore the 10mm for the bearings to the required depth. You can face and if required relieve the bottom of the recess. The corner radius could be an issue so check the tool ref the bearing spec. and re-grind it if necessary
I was thinking of using a collet to hold this job at least for th boring operations. If I was working very close the the headstock (o both ends) do you think concentricity would still be an issue (assuming the collets are true!).
I can only conclude that the strips have been fitted incorrectly. Such a scale is not much use unless a precision vernier scale. Many turners favour setting the tailstock dead true and leaving it alone. Offset centre work can then be performed with a boring head fitted to the tails stock and thena centre fitted in place of the boring cutter. Adjustments to the boring head then give an calibrated offset.
I very much doubt it will be a problem. Not knowing the exact application it's a little difficult to be certain, but collets should be as near as to 'c*ck-on' unless you're being _really_ pedantic.
On or around Fri, 2 Nov 2007 15:37:45 -0500, DR_G enlightened us thusly:
drill in some
square bottom.
drill 9mm and use a 10mm reamer, if necessary reducing the lead on the end of the reamer?
I've got a 20mm reamer which I use for making accurate 20mm bores, spiral flute one and that's quite happy to go down a 3/4" hole.
as for concentricity, unless the ball races are something VERY good, I'd think that doing the same machining job from both ends, with the part held in a chuck, would serve. If you want to be posh, put it in a 4-jaw and centre it properly first. Also, make sure that the workpiece is all or mostly inside the chuck. I guess if you're machining 10mm dia inside 12mm, you don't want to be gripping the bit you're actually working inside, but don't have it sticking out more than you need to. I'm sure that's all egg-sucking, but worth saying. The further the workpiece is away from the chuck, the less accurate things get, unless you can employ a fixed 3-way steady.
In your case, it really depends on how mission-critical it is and how fast you want it to run, I think. If it's going on a spaceship and you want it to do 50,000 rpm, then you probably can't machine it too accurately... for more mundane use, it's possible to get bogged down in a quest for the last thou' or two of precision, when it's not actually needed.
On or around Sat, 03 Nov 2007 20:20:59 +0000, Richard enlightened us thusly:
wot he said.
I wasn't thinking of collets, haven't got any for mine. see my comments about what it's going to do, to be certain, we need more info...
Small boring bar is a good way of getting an accurate hole, though, as someone else said. Take it slowly and carefully, make light cuts or the bar will flex.
Quick update: managed to get the tailstock alignment test piec
diameters to 0.001" over 10" long between the 'lobes'. I don't think can get it much better than this without resorting to random trial an error adjustment of the tailstock screws. To adjust out 0.001" would b very difficult for me - it might even be the difference in "how tight i tight?" on the screws!!
I guess the closer I move the tailstock to the headstock, the wors this error will be, but there you go. I will leave the lathe set u like this and see how I go.
The best and fastest method (that assumes that the spindle is *dead* parallel to the bed) is:
Make some stiff round with a recess on one end. Onto that recess (8 or 10 mm diam.) clamp a dial indicator (the type where the point swivels*)). That round goes into the spindle (-chuck). It doesn't matter how bent the bar is or how excentric the chuck is! Put an dead centre into the tailstock. Get the dial's point in contact with the centre's cone. Now rotate the spindle and watch the dial. It will show the deviation in the horizontal and vertical plane. Adjust the tailstock.
That method can be used to adjust a lathe in *all* aspects. Alignment of the spindle relative to the bed, detect a bent or twisted bed. Align the tailstock's axis parallel to the bed, and coaxial to the spindle. Hard to explain in words, needs some show and tell. I've never seen that method being mentioned for a complete alignment, so I claim that invention for me. :-)
*) I'm talking about these. A classical dial indicator doesn't work.
but did it around the morse bore rather than with a dead centre in it ... but was wondering what effect the tailstock lock has on the barrel .. . like sometimes you use it
sometimes you don't
also .how far down the bed is the tailstock when.the measurement on the tailstock is taken
bet the barrel wears across the bottom faces of it most ......
so I'm thinking of shimming the barrel inside ....or maybe two grub screws pointing up-wards from outside too inside ......pair of ball bearings on them maybe to reduce friction..
all this rather than machine the tailstock...what do you think
Some further comments in a repeat of a 2005 post. By far the most useful bit is the P.S !!
Not too sure which method you finally used but I've had best success with a lever type dial gauge mounted by a 3 or 4 jaw chuck with the measurement tip bearing on the INSIDE of the tailstock bore.
Because the dial gauge is rotated by the chuck it uniquely defines the headstock rotation axis. This eliminates all errors from the headstock end.
Because the tip bears directly on the tailstock bore it eliminates all errors relating to the use of tailstock centres.
Best of all it shows up directly the shifts resulting from clamping the headstock to the bed or the barrel to the body. It is also easy to check the change in alignment at different extensions ofthe tailstock barrel - this can be surprisingly large!
The only real downside is that it needs a mirror to read the dial gauge when it is rotated by 180 deg.
Jim
PS If you value your dial gauge, disable the motor start switch before you start!
A lot if the bore is much bigger than the barrel. :-) You can observe this on the dial. On my EMCO, I made fine adjustments by locking the tailstock more (or less) to the bed. 8-/
If you move the tailstock along the bed, you can adjust the spindle. Of course, you have to pull out the round accordingly. If you move the tailstock's quill in and out, you can align the tailstock.
Maybe I would bore the tailstock out and re-cast the bore with Moglice. Then scrape the tailstock to be parallel again. Depends on how bad the bore really is. An other option would be to just Moglice the beginning of the bore. Or glue some bronze ring in.
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