Messages

1481

General Mach Discussion / Re: Z AXIS KNEE

« on: November 08, 2008, 04:21:17 PM »

Gee, we seem to have an awful lot of very happy knee-drive folk here, considering what a bad idea it is!  :-)

Now that I'm getting 60+IPM out of my knee, and 300+ IPM on X & Y, I'm a VERY happy camper!

Regards,
Ray L.

1482

General Mach Discussion / Re: Z AXIS KNEE

« on: November 08, 2008, 01:05:44 PM »

I just got done re-biasing the optos on my BOB, and my knee rapid speed has gone from 25 IPM, BOB-limited, to 60 IPM, motor limited.  Not bad!

Regards,
Ray L.

1483

General Mach Discussion / Re: Z AXIS KNEE

« on: November 07, 2008, 11:36:44 PM »

Ray,

Your saying; " But for now, the knee works beautifully."
That's not what your saying on the other forums. 25 IPM.? I use higher feeds.

I have 40 taper tooling, and the extended holders are no problem, not even for roughing.
 I Only use a drill chuck for center drill. I use collet holders for drills.

Good Luck

Ed V

Ed,

   I have no idea what you're referring to.  My knee works fine, the only limitation being the relatively low speed, which is caused by a bad breakout board, not the drive.  That will be fixed.  99% of my milling time is spent moving in X and Y.  If I got the knee up to 100IPM like the other axes it would save me a few minutes a day, so who cares? Yiour original point seemed to be that moving the knee is bad, because it'll be slower than moving the quill.  For me, the difference would amount to mouse nuts.  If it doesn't save me time, or give me a better result, there's no reason for me to spend the money on it.
   If you're happy with what you've got, great.  But don't tell me your way is the only "right" way to do it.  What you do works for you, what I do works for me.  What's "right" or "best" depends on your needs and your expectations.  For me, a quill-only Z axis would be seriously limiting.  I don't have a million collets for all my drill bits, and I don't have 40 taper tooling.  Like probably 99% of the people here, I have an R8 spindle, and long holders *don't* work well in R8.

Regards,
Ray L.

1484

General Mach Discussion / Re: Z AXIS KNEE

« on: November 07, 2008, 11:02:07 PM »

Ed,

    So that would require me to have my 1/2" end mill in maybe a 6" long holder, so I can also fit the drill chuck on the machine with a large bit? That's not going to give a very good result on heavy cuts.  The whole point of endmill holders is short = stiff.  I always try to keep the quill extended as little as possible, for the same reason.  Using long holders will significantly increase flex at the tool tip, and degrade finish quality and tool life.  Doesn't sound like a very good compromise to me.
    Ultimately, I plan to have the best of both worlds, by having both the knee and the quill CNC'd and using the knee then only for tool length correction.  But for now, the knee works beautifully.  So, I don't need to invest in a lot of long holders that I won't need down the road, and don't have to compromise finish qualty.

Regards,
Ray L.

1485

General Mach Discussion / Re: Z AXIS KNEE

« on: November 07, 2008, 07:18:48 PM »

Sorry, but the knee just works fine, *with* a Gecko, and with the same servo motors that's driving X and Y.  Mine has been working flawlessly for the last month or more, and is very accurate and absolutely repeatable.  Rapids are not blindingly fast at the moment (25 IPM) but that is limited by a bad BOB, not the servo.  Adding $50 worth of gas springs has reduced the torque requirement by half, which will also help rapids.  When I get around to replacing the leadscrew and bevel gears with a ballscrew, I think it will work very nicely indeed.  And, I can still use the machine for manual drilling and tapping when I need to.  There is basically no slop in my knee.  Perhaps you're looking at poorly maintained production shop machines, or ones with many, many miles on them?  Besides, this is a hobby machine, not a production shop machine.  Even the bevel gears will probably last a good long while with the kind of use it sees.  Speed isn't everything, and you *can't* effectively totally automate a machine with only 5" of Z travel, unless all your jobs are pretty small.

I'd be real interested in hearing how you go from working with a small end mill, to drilling 1/2" holes, or working on a piece 3-4" high, with only 5" of travel.  Many of the jobs I do require going almost end to end on the knee travel.

Regards,
Ray L.

1486

General Mach Discussion / Re: Bugs in Mach 3.42.015

« on: November 06, 2008, 01:06:43 PM »

"My machine is mechanically plenty capable of making 0.0013mm moves" - Unless my calculator is broken, that is 0.00005", or 50 *millionths* of an inch.  Perhaps your machine, on paper, has that kind of resolution, but I would be surprised if it has that kind of *accuracy* in the real world, unless you're running in a very tightly temperature-controlled environment.  As you said the microstep precision alone is nowhere near that good.  And, I doubt you have any means of measuring to anywhere near that kind of resolution.  Resolution without accuracy is not good for much other than bragging rights.  Unless I'm missing something, this seems like you're trying to pick fly poop out of pepper.

Regards,
Ray L.

1487

General Mach Discussion / Re: Line Numbers in G Code

« on: November 05, 2008, 04:42:32 PM »

Graham,

   So does Mach completely ignore them?  i.e. - If they are there, but not in proper sequence, will Mach care?  My guess is no.

Regards,
Ray L.

1488

General Mach Discussion / Line Numbers in G Code

« on: November 05, 2008, 11:17:59 AM »

Do I understand correctly that G code does not require line numbers - i.e. - they can be deleted?

Does Mach pay attention to them?  Will it care it, for instance, they are out of sequence?  My post outputs line numbers, but it would sometimes be convenient to move blocks of code, to re-order operations to reduce unnecessary moves, but that would leave the numbers out of order.  I can, of course, write a simple Perl script to fix that, but I am one lazy SOB....

Regards,
Ray L.

1489

General Mach Discussion / Re: Peck Drilling

« on: November 04, 2008, 11:39:34 PM »

Graham,
    Interesting approach!  I'd like to try it, but part of my reason for wanting to minimize retracts is I've CNC'd my knee, and for now I'm going through the bevel gears.  All those short pecks and retracts woudl really hammer the poor gears.  But, when I get the ballscrew in , I'll give that a shot!

Regards,
Ray L.

1490

General Mach Discussion / Re: Peck Drilling

« on: November 04, 2008, 11:37:54 PM »

It sounds like your using the same machine as the one I use. A simple peck drilling cycle is just as you stated. Plunge, chip break, plunge, chip break, etc. However, if your hole is deep enough to cause a problem of evacuation of chips, a retract would be advisable. Plunge, chip break, plunge, chip break, plunge, retract.... or some form thereof. Yeah, 5IPM is kinda (allot) slow.

If the strings are to long, turn the feedrate up, or turn the spindle speed down.

OR lower the peck.

Sam,

    I modified my post to do 5 pecks with a 50mSec dwell between, then do a retract.  Worked much better, and I upped the feed to 15IPM - no more strings, and no clogging!
   Thanks!

Regards,
Ray L.