Messages

281

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 12, 2012, 05:24:47 PM »

Guys,

Quick video of my toolchanger.  This is being manually sequenced, so it's kinda slow.  I used my pendant to trigger the PDB, had a manually operated pneumatic valve to operate the "lift", and a microswitch to turn on the Geneva motor.

http://www.youtube.com/watch?v=QvSzfLZGH9Q

Regards,
Ray L.

282

General Mach Discussion / Re: scripter compile error ( 2 questions)

« on: October 12, 2012, 02:46:04 PM »

That problem has been around for YEARS, and I've never been able to cure it, though it appears to be harmless.  Sometimes, if you edit the file, make sure there are no "funny" characters in it, and there's a blank line at the end of the file, it will go away.  But, eventually, it will come back.

Regards,
Ray L.

283

General Mach Discussion / Re: How much stepper power do a 1-1/2 HP Bridgeport need to do a good job ?

« on: October 12, 2012, 11:31:25 AM »

Those steppers will work, but their performance, particularly in terms of rapid speed, will far well short of stellar.  Those motors are VERY high inductance, which, on it's own, severely limits top speed.  Further aggravating the problem is the fact that the power supply, at only 60V, is WELL below the ~150V required to get the best performance those motors are capable of.  My guess is you'll probably be limited to rapid speeds well under 100 IPM.

Though the drivers allow micro-stepping up to 256X, this is essentially useless.  You'll want to use the 8X, or at most 16X setting, to keep your pulse rates reasonable.

Regards,
Ray L.

Yes,  after making the adaptors I tested the maximum speed and I don't get more than 420 RPM on the steppers, so I guess the only thing one can do here is changing the pitch on the ballscrews or accept the speed that they are cabable of right...  Maybe 3 new controllers will improve on things ?

All the best to you guys.....

Leif

Changing the screws will likely not help, since faster screws will require more torque at ALL speeds.  High voltage controllers *might* help, and might not.  Your problem, as pointed out earlier, is those very high inductance motors.  Replace them, and you should get dramatically improved performance.

Regards,
Ray L.

284

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 08, 2012, 11:26:40 AM »

A 'linear' relationship means that the calculation is the same at every point in the curve.

Actually....  conventionally, a "linear relationship" means a graph of the relationship would yield a straight line.  For example, Y = 3 * X is a linear relationship, while Y = 1 / X is not.  Both *are* "linear equations", since neither contains any exponentials, logs, trig functions, or or non-linear terms.

Regards,
Ray L.

285

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 06, 2012, 07:36:44 PM »

Steve,

Is that really correct?  I would think tapers are purely a matter of friction.  If you know the material and surface finish of the inner and outer tapers, you know (or can measure) the coefficient of static friction (assuming a completely clean, dry fit, as it SHOULD always be).  Knowing the drawbar tension and taper angle, you can easily calculate the normal force.  Multiply the two, and you know the total frictional force.  Integrate that over the entire taper, and you can calculate the total torque that can be generated before the taper slips.  I can see how stretch might be factor on low-angle tapers like Jacobs, but have a hard time believing it's a factor on CAT/ISO tapers, especially given the relatively low drawbar tensions, relative to the cross-sectional areas of the toolholder tapers.

Regards,
Ray L.

286

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 06, 2012, 11:54:23 AM »

Interesting, fellas, thanks for chiming in.

So how much force are we talking about?

Thanks,
Dave

R8 requires upwards of 2500 # drawbar tension for max retention.  And, BTW, the set-screw in the slot on the side of an R8 has nothing to do with preventing the tool from slipping, except when the drawbar is being tightened.  The friction created in the taper FAR exceeds the feeble ability of that screw to prevent slippage.  Spec for 30-taper is about 1300#, 40-taper (IIRC) is about 1800#, 50-taper I'd guess upwards of 2000#.  Keys are not necessary for small machines (up to 3-5 HP), above that, the keys seem, if not necessary, at least worthwhile.

Regards,
Ray L.

287

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 03, 2012, 09:57:46 PM »

Steve,

I don't understand the black lever at the bottom of the photo.  I'm assuming this is a positive lock, that prevents the ball gripper from coming down and releasing the tool, but it's not clear how it fits.  I assume the pivot goes into the slot on the side of the housing, but where does the "tang" on the RH side go?

Regards,
Ray L.

My bad. I have the lever in the photo upside down . . or backwards, depending on the perspective. It works exactly as you surmised. The 'beak' if you will, pokes thru the hole at the top and interferes with the ball holder descending into the body, this preventing the tool release. The 'tail' reaches down to the bottom of the body and is spring loaded. The spring is not in the photo because those parts are not here yet. The spring goes in the bottom of the pivot slot just below the pivot pin (also not in the photo).

The claw engages the slot on the adapter and then in the last 1/4" or so of travel, it pushed in the tail of the lever, thereby removing the interlock and allowing the air cylinder to release the tool.

You are uber observant, so I will presume your next question will be why is there a 'tooth' on the 'beak'. The 'beak' is retracted, the plunger is then pushed in (down) by a small air cylinder. The plunger not only 'releases' the ball grip, it also physically ejects the adapter about .060". The next action in the sequence if to the arm to descend with the toolholder in-hand, so to speak.  At this pint in the sequence there are two options:

1) let the plunger up and lower the arm simultaneously and the plunger will raise all the way to the snap ring stop. It will then need to be depressed again by the air cylinder in order to return the tool

2) lower the arm first and then let the plunger up. When the claw is lowered from the pod, the lever re-opens via its own return spring and the 'beak' pokes back into the chamber. Letting the plunger up at this point results in the 'tooth' catching the top edge of the plunger and holding the gripper in the 'open' position. 

In the second configuration, the tool is returned simply by the claw raising the holder into the pod. The claw re-compresses the 'tail' as it raises the last 1/4" or so, thereby releasing the plunger and locking the holder into the pod.

Hopefully that all made sense.
 

Steve,

Makes perfect sense, and very clever.  Thanks!

Regards,
Ray L.

288

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 03, 2012, 11:53:48 AM »

Steve,

I don't understand the black lever at the bottom of the photo.  I'm assuming this is a positive lock, that prevents the ball gripper from coming down and releasing the tool, but it's not clear how it fits.  I assume the pivot goes into the slot on the side of the housing, but where does the "tang" on the RH side go?

Regards,
Ray L.

289

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 01, 2012, 11:33:47 AM »

Steve,

If it were me, I'd design the arm such that the centrifugal force during rotation *could not* allow the tool to come out.  The last link Bob provided shows one way of doing this, with the tool being inserted into the arm from the side, rather than the end.  A very simple retention device can then be used.

That same video offers an approach I'd never seen before, that could be quite attractive to many hobbyists - rather than having a full toolchanger, just a means of "queuing up" the next tool.  The mechanism in the video is very simple and elegant.  I may have to build such a device, just for grins.....

Regards,
Ray L.

290

General Mach Discussion / Re: Odd stalling or stuttering, loss of position

« on: September 30, 2012, 02:15:51 AM »

Reduce acceleration, and see if that helps.  It you were able to run 331 IPM, then CPU load is not the problem.  Acceleration is MUCH more likely to cause stalling.  Or, there may be something running that is causing jitter on the step pulses, but I doubt it.  If that were the case, you would've never reached 331 IPM.

Regards,
Ray L.