Knee Automation - Iggy

I was thinking about your comments on knee automation and had this thought. Do you really need to CNC control the knee in order to get the positioning
you wanted except maybe for an extremely few parts? Why not just put a DRO of some type on that knee. Maybe not a fancy made for application one. Just a simple digital caliper (over sized for your ap of course) like used by a lot of the mini lathe guys on their tail stock. Or you could shop for deals until you find a fancy DRO at an auction somewhere.
I'm dealing with a lot of these same ideas on the Hurco retrofit, and I started with the concept of using an independent control just for raising and lower the knee, but then I thought, "Gee. Its not that hard to crank, and even if I do need to move it its only going to be once or twice during a fairly complex part." If it were hard to crank I could throw any old DC servo on it that's strong enough and power it from a variable voltage power supply for speed to move and slow speed to position with a DPDT spring loaded toggle switch. Maybe some diodes for protection of the switch.
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Bob La Londe wrote:

You don't even need a DRO on the knee if you're doing tool touchoff to set the tool length offset. Indeed a single touchoff of a previously measured tool after a knee reposition will give you the offset to apply to the rest of the previously measured tools. There really isn't any reason to power the knee unless you plan to lock off the quill and use the knee as your Z.
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Well, Pete, actually there is a good reason.
I don't know what Iggy does, but I do a LOT of work where I have to find the center of existing old parts to machine new features in them. Many are plastic, which means I have to use a centering indicator instead of an edge finder.
Being that my centering indicator is more than 4" taller than my longest cutting tool, that puts me in the mode of _continually_ cranking the knee up and down to make headroom for it, then going back to my usual machine Z for the cutters. It gets wearisome. I will eventually power my knee, but I see no reason for DROs and the like. I just go (as was said) for a touch-off of a known tool, and done.
LLoyd
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On Tue, 18 Jan 2011 18:54:47 -0600, "Lloyd E. Sponenburgh"

Why can't you use an edge finder on plastic? I do it all the time
Mike
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snipped-for-privacy@iname.com wrote:

....probably has one of those electrical edge finders.
--
Cats, coffee, chocolate...vices to live by

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snipped-for-privacy@iname.com fired this volley in

I'm in the fireworks business; my hearing ain't that great when there ISN'T a BP spindle running.
(yes, I have both "clickers" and electrical edge finders...) I can still hear the mechanical ones on steel, but have trouble hearing the edge on PVC or polyethylene.
LLoyd
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On Tue, 18 Jan 2011 19:57:12 -0600, "Lloyd E. Sponenburgh"

got it
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On 2011-01-19, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

Yes, as soon as the difference between tool lengths is too great, it means constantly going up and down and touching off. Gets tiring very quickly.
i
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Ignoramus5053 wrote:

No problem, just sell me your Interact with it's inadequate Z travel for a decent price, and then go find yourself something like a Mycenter 1 with longer travels, more horsepower, ATC and a footprint that isn't a lot larger :) I'll help you with the rigging and moving...
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How generous of you ;-)
I like my Interact VERY much.
i
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Bob, I am still stuck working on my 4th axis and I do not want to get into too much detail in the knee.
But I already have a nice servo ready DC gearmotor with a shaft for the encoder. All I will need to do to automate the knee is
1) Put encoder on the DC motor 2) Make a bracket to mount DC gearmotor 3) Add limit switches to the knee 4) Configure EMC
and I think that what I will get amounts to a huge value for not too much cost. The motor cost me $40 and the limit/home switch $40 IIRC.
There are very many parts where tool length differs by more than 4.5 inches, and without CNC knee, I would have to split programs into pieces to get done with what I want, plus I have to re-zero positions etc.
i
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wrote:

How accurate is the table level as a function of knee height? Are there any options for implementing the knee lock, then re-zeroing the work position?
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GOOD question! The one thing you don't want to do is work a critical piece without locking the knee, and the OTHER thing you don't want to do is start slewing that knee under CNC control while it's locked!
I definitely don't think you can count on the bed being dead-level until the knee is locked.
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

FWIW, depending on the characteristics of the knee joint, my bike has a lever that holds the front axle to the fork - the axle has the two nuts, but the one nut has a locking lever which is just an eccentric; I can release the lever, and get the wheel off by hand.
Just an idea, thinking about the knee lock.
Cheers! Rich
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"Lloyd E. Sponenburgh" wrote:

Considering that these are "knee" mills and in their manual form are intended to use the knee as the primary precision Z axis, I think you are way off base thinking that the knee needs to be locked.
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Pete, the little training I have had taught that the knee shall _always_ be locked during machining. I'm not sure why the locks would be there at all, unless they serve a functional purpose.
LLoyd
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"Lloyd E. Sponenburgh" wrote:

That's bad or misinterpreted training. The knee is your Z in normal manual machining, not the quill and you have to have it unlocked to do any machining with a Z move. What you may be misinterpreting is the recommendation that you lock and axis you aren't moving for a particular machining operation, which applies to X and Y as well. Locking any axis you aren't moving will increase rigidity by locking out the backlash in the axis, as well as protecting it from you accidentally bump the handle when reaching for something.
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handle
And your point? I do not move the knee except to get to a position. Once in that position, I lock it. Manual or CNC -- lost motion is your enemy.
And normally, one would not (say) drill with the knee crank, one would lock knee-Z at the clearance point, and peck with the spindle feed. Knee feed is for "getting there", even if the holes are deeper than the spindle extension length.
I believe _any_ axis not being moved during a cut should be locked. It would normally be quite inconvenient on a manual mill to lock X or Y unless you were only doing straight lines, but the opportunities to lock the knee gibs are often and many. FWIW, I do not guess, but know, that the table is not level and true on my old Cincy #2 until the knee locks are tight enough that you _cannot_ easily move it with the crank. Can't tell you that for sure on the R2E4, though, because I've never checked the whole table end-for-end and side-to-side for planarity.
LLoyd
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"Lloyd E. Sponenburgh" wrote:

It's a mill, not a drill press. On a manual knee mill the quill is there for quick drill type operations, while the knee is intended for use as the precision Z axis for milling operations (with the quill locked). My point is that if the knee needs to be locked to make the table level, your gibs on the knee need to be adjusted, that is not a normal condition. Since your CNC mill is based on a manual knee mill design, the same applies there as well.
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Interesting discussion. I don't think I've "ever" locked the knee.
On both my mills, I trammed in the head by using a dial indicator several inches out from the quill and adjusted till perfect in both X and Y. I always watch when using a large face mill to verify that the head in still in perfect tram. There's nothing that shows out of tram quicker than a skim cut with a large face mill.
I can see where locking the knee might change this. If you're getting good results with out locking the knee I think it would be best to never do so.
However, I bet many machines out there have more wear at the center of travel and using a face mill with the knee all the way down would produce different results than at the center of travel. In this case, always locking the knee would improve things.
My two cents
Karl
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