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No HSS blanks.
Sure I can do the part on a lathe, but my question was referring to rotary table centering, not grinding lathe tools.
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Confusion With Machining A Blank On A Chuck Mounted To Rotary Table
- Thread starter Machinehead
- Start date
No HSS blanks.
Sure I can do the part on a lathe, but my question was referring to rotary table centering, not grinding lathe tools.
B
Bill Gruby
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"Billy G"
"Billy G"
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Actually, this makes me wonder if the table moves after, or while I machine the outside cylinder. If I indicate the part and set zero, machine my cylinder then go back to zero, the table (x,y zero on the DRO) could be in a different spot after the tables backlash is taken up from the cutting forces?
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I use a test dial indicator on the spindle of the mill to find the center of the rotary table sweeping the center hole of the table. Zero out the DRO at that point. The chuck for my RT is loose, screwed to a ground plate of steel. It's mounted to the RT with a couple of T-nuts/bolts to the slots in the RT. I set the chuck/mounting plate on the RT and roughly center them to the mill spindle with the T-nuts/bolts loose. I then put a 3/4" dowel pin in a collet in the mill spindle and advance it down to and an inch or so into the chuck. Then lock my mill spindle and tighten the chuck onto the dowel pin. Then tighten the bolts that clamp the chuck/mounting plate to the RT. For grins and giggles I'll sweep the dowel pin in the chuck and am never worse than 0.002" out.
If you have an RT with a chuck mounted to the spindle through an arbor, your chuck should be reasonably centered on the RT. You should be real close taking a dowel pin in the spindle collet and run it into the chuck like I do. Then tighten your RT to your mill table. You may have to do some table movement to get the mounting slots on your RT lined up with the slots on your mill table at the start.
Boy, I'd sure think if you zero'd your DRO once you found the center of the RT, backlash should be out of the picture as long as you're locking your mill's table down at 0,0 before machining. Your DRO tells you where the sliding detail of the glass slide is within the glass slide itself, not the position of your handwheels. Unless you have ball screws on the mill, you can probably chuck your table back/forth because of the slop between the table screws and table nuts. That'll show up on your DRO since the glass slide . I'd think you'd be good zeroing the DRO once you find center and make sure to lock the table before cutting.
Not to belabor it, but Tom Griffin of Tom's Techniques (google it) has a nice tutorial on centering the RT to the mill. He uses a tapered plug in his mill spindle. Advances it to the hole in his RT until it wedges, locks the spindle and bolts the RT to the mill table. I recall him showing he was within 0.0005" using that technique.
Good luck! Bruce
If you have an RT with a chuck mounted to the spindle through an arbor, your chuck should be reasonably centered on the RT. You should be real close taking a dowel pin in the spindle collet and run it into the chuck like I do. Then tighten your RT to your mill table. You may have to do some table movement to get the mounting slots on your RT lined up with the slots on your mill table at the start.
Boy, I'd sure think if you zero'd your DRO once you found the center of the RT, backlash should be out of the picture as long as you're locking your mill's table down at 0,0 before machining. Your DRO tells you where the sliding detail of the glass slide is within the glass slide itself, not the position of your handwheels. Unless you have ball screws on the mill, you can probably chuck your table back/forth because of the slop between the table screws and table nuts. That'll show up on your DRO since the glass slide . I'd think you'd be good zeroing the DRO once you find center and make sure to lock the table before cutting.
Not to belabor it, but Tom Griffin of Tom's Techniques (google it) has a nice tutorial on centering the RT to the mill. He uses a tapered plug in his mill spindle. Advances it to the hole in his RT until it wedges, locks the spindle and bolts the RT to the mill table. I recall him showing he was within 0.0005" using that technique.
Good luck! Bruce
B
Bill Gruby
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The center bore on my RT is a MT2, Last I checked it, it was within .0003 of the spindle. My mill spindle is also MT2. I just put a dead center in the mill taper and bring the table up till the dead center catches tight. Tighten the hold down bolts and you as close to "0-0" with the Spindle Center as you will ever have to be with the RT. Takes all of 30 seconds.
"Billy G"
"Billy G"
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You could grind a broken centre drill their hss, use them a lot for booring bars.
Did you indicate the rotary table then mount the chuck?
I tend to not indicate my rotary table but use a pin holder that goes in the centre hole. And put the pin in a collet. Most of my rotry work gets bolted to the table not in a chuck though ao thats less handy for you I guess.
If your cutting ally any old steel that is vaguely hard and cutter shaped will cut it in the lathe, I forgot to harden a tool steel bit once, used it for a couple of turning jobs an ally then tried to turn some steel and was confused as to where the point went
With regard to getting the hole on centre I would do the hole first then crank out to do the outside, no point trying to refind the centre or if you have to do it that way re indicate it.
Stuart
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- Dec 3, 2015
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Well then drill your hole right after you indicate the cylinder, THEN go out and run around the outside....That should resolve this issue
I just finished installing scales on the Y- and Z-axis of my own mill tonight (X-axis soon), and was initially very disappointed with poor repeatability of these I-Gauging scales. After some head scratching I figured out the problem, and then immediately thought of this thread.
What I believe he is seeing is like "backlash" between the table and the scale - there is too much flex in the brackets, allowing the scale to lag behind when the table changes direction. Verified with indicators, for me I'm getting about .005" on the Y-axis and about .012" on the Z-axis.
Solution is, as with any other backlash, to always approach from the same direction. So in this case when returning to your zero, pass it and come back from the other direction.
Better yet, improve the brackets.
B
British Steel
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What are the brackets like? When I used to fit scales and heads on machines (several times a week, but still to do it on my own!), I used to make up new brackets every time as the supplied ones were a) pretty bulky and b) multiple parts bolted together and c) looked naff.
If the scales aren't absolutely parallel with the ways, the reader head will drag and the friction will try to move them or the reader out of alignment, leading to backlash and in the worst cases, broken scales and readers...
To mount the scales I'd use a couple pieces of sturdy (e.g. 10mm) plate, tapped for the scale's fixing bolts, with counterbored holes for its fixings to the lathe/mill and threaded holes for dog-point grubscrews at the corners to a) adjust the plates parallel to the ways and b) pierce the quarter-inch of loose filler and paint found on far-eastern machinery.
When setting up, before attaching the reader head put a DTI on the carriage / table and sweep the length of the scale both vertically and horizontally aiming for (ideally) no deviation end-to-end, maximum of a few thou" - the corner grubscrews make this pretty easy to do, along with the slotted ends of the scales
For the readers, again there's no substitute for sturdy mountings, and parallelism's just as important! Leave the transit spacers in place while adjusting, and adjust the bracket to the reader, not t'other way around!
Dave H. (the other one)
If the scales aren't absolutely parallel with the ways, the reader head will drag and the friction will try to move them or the reader out of alignment, leading to backlash and in the worst cases, broken scales and readers...
To mount the scales I'd use a couple pieces of sturdy (e.g. 10mm) plate, tapped for the scale's fixing bolts, with counterbored holes for its fixings to the lathe/mill and threaded holes for dog-point grubscrews at the corners to a) adjust the plates parallel to the ways and b) pierce the quarter-inch of loose filler and paint found on far-eastern machinery.
When setting up, before attaching the reader head put a DTI on the carriage / table and sweep the length of the scale both vertically and horizontally aiming for (ideally) no deviation end-to-end, maximum of a few thou" - the corner grubscrews make this pretty easy to do, along with the slotted ends of the scales
For the readers, again there's no substitute for sturdy mountings, and parallelism's just as important! Leave the transit spacers in place while adjusting, and adjust the bracket to the reader, not t'other way around!
Dave H. (the other one)