Re: MaxNC modifications

By the controller I mean the electronics that take the step and direction
signals and actually drive the motors.

OK, a few more questions. Don't know if I have an answers, but questions
seem in order!

Is the motor rated 5 amp as a unipolar or bipolar? Did I ask what the
voltage rating of the motor is?

I think your desire for 60 ipm may be a little much. 30 ipm may be a more
realistic number to shoot for. The Sherline I had with 125 in/oz motors
pooped out at about 35 ipm and 30 was pretty reliable. The Shoptask I have
now with 550 in/oz motors and ballscrews (rolled, not ground :( can achieve
about 33 ipm, but is rock solid reliable with 24 ipm as a max.

Tim
[Denver, CO]

> -----Original Message-----
> From: Jon Anderson [mailto:janders@...]
> Sent: Tuesday, June 15, 1999 10:21 PM
> To: CAD_CAM_EDM_DRO@onelist.com
> Subject: Re: [CAD_CAM_EDM_DRO] MaxNC modifications
>
>
> From: Jon Anderson <janders@...>
>
> Tim,
>
> Will have to sit down with my dad and gather up the details, but here's
> what I can tell you right now.
>
> Not sure what you mean by controller, Ah-ha communicates directly with
> the stepper drivers via a special card.
> Power supply is 40 volt more or less, unregulated, based upon the
> schematic supplied by CyberPak for their drivers. Dad built the PS, I'll
> get details from him.
> Don't recall motor specs, will have to look them up again.
> Think they are rated for 5 amps, we are running about 3 now, or so we
> think. That is based upon the current limiting resistor.
> Dad thinks we're not getting full power to the motors and tried to
> measure amp draw INTO the drivers, came up with something like .5 amps
> draw at rapid (40"/min). However, it's a chopper driver, not sure if
> he's checking properly.
> I've written little test routine programs. Single axis linear moves,
> looped and run for 5-10 minutes show no lost steps. Interpolated linear
> moves (XY) show no lost steps. Circular interpolation seems to be the
> problem, but not always.
>
> My dad machines little resistive elements for a customer of his. These
> are generally under 1" dia and we run multiples of up to 8 at a time on
> a custom pallet setup. We've tried using G92 to set offsets for each
> nest, no subroutines; G92 with subroutines; G91 with and without
> subroutines; and if a particular job is going to show lost steps, it
> doesn't seem to matter how we approach it. Some parts do not lose steps.
> Each part will show a different pattern of lost steps. The pallet base
> has a .500 dia hole that we indicate from to establish datum, all
> pallets and all programming is referenced from this hole. It's real easy
> to drop an indicator in and check for lost steps.
> For example, one particular part run in multiples of 8 parts per pallet
> might show .0013 lost in X and .0003 lost in Y every for every pallet
> load. With the tolerances on this job, Dad can let this accumulate over
> two pallets before having to rezero. This is so consistent that he
> stopped checking after every two pallets and simply would jog X.0026
> Y.0006 and rezero. After running several hundred parts, he'd check with
> the indicator after the last two pallet loads and be off exactly
> .0026/.0006. (I don't recall exactly the sign (+/-) of the error or
> corrections, but the numbers are real close to what he runs into)
> This is with a program that does not use G92, it's done with geometry in
> a subroutine, we move to a set entry point, enter the subroutine, enter
> G91 and machine features, then back to G90 and exit the subroutine.
> We lose NO steps in the Z axis.
> Motors are wired with shielded cable, grounded at one end to the motor
> PS ground. Logic lines are also shielded cable, grounded at one end to
> the computer ground. Care has been taken to keep power and logic lines
> well separated. If I didn't mention before, we've also run the MAX
> software on two different computers, a 486-33 and 486-66 with identical
> results. I'm close to getting my Cyrix P200 box done and will try
> the Ah-ha from it, but don't think that's going to solve the problem.
> Ah-ha warns about possible rounding errors and recommends programming to
> 4 decimal places. I edited a problem program to accomodate this and
> there was no change in the lost steps, so that's not likely to be the
> problem.
>
> I printed your message, when this gets back to me I'll print it as well.
> Dad will be by tomorrow and I'll give him both copies to go over and
> fill in any details I missed or don't know.
>
> We would both LOVE to solve this problem. Dad's good with basic
> electricity, but we are both stumbling in the dark on this, and it's
> getting expensive running around buying stuff trying to fix the problem.
>
> As for desired speed, would like to see 60"/minute. This was part of the
> reason I went with 16 pitch screws. I can accept the slight loss of
> accuracy, the tradeoff is that for a given linear velocity we are
> running the motors 20% slower. I may be all wet, but my seat of the
> pants guess was that we were coming out ahead over a 20 pitch screw by
> keeping the motor down in a broader part of the torque curve.
>
> I have some top quality linear rail bearings and ballscrews, and want to
> build a CNC conversion for my Hardinge. However, I have a hard time
> justifying the time and expense in finishing it with the lost steps we
> are getting. Even a single lost step per part would quickly cause major
> problems in the X axis of a lathe.
>
> Thanks,
>
> Jon
> (who btw, is highly impressed with the quality and quantity of posts to
> this list!)
>
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