Author Topic: Build-a-box option?  (Read 2365 times)

thespindoctor

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Build-a-box option?
« on: October 30, 2016, 08:09:16 AM »
Is there a build-a-box option for something like the PMDX-340?  Is one limited by the components included or is it possible to customize?

I have 2 issues at this  point.  The first is to upgrade my prototype desk-top CNC grinder from the Campbell's BOB and Cullins' encoder board to one of your BOBs and preserve as many components as possible including motors, drives, power supply, probe, limit switches and motors.  The motors are NEMA 34 600 oz/in motors like these http://machmotion.com/cnc-products/drives-motors/stepper-drive-motors/nema-34-600-ozin-stepper-motor.html that can be wired at 3.7, 5, or 7 amps.  I am using Gecko 251x drives and am not sure how I am getting away with 3.7amps using drives rated for 3.5 amps...  I hope to upgrade to Mach4 and use the same computer running Win XP 32 bit but switch from parallel port to USB.  I could downsize the motors on the prototype if absolutely necessary or use an intermediary BOB from another source and modify future machines.

So the second issue is the future machines that I will sell.  We have all the flexibility needed to change the design.  It would be great to be able to get a box from you all ready to go.  I do not understand from the pdf on the PMDX-340 what BOB is included or what drives.  A NEMA 23 3 amp motor could work and I would need a probe.  Now I am using a http://usdigital.com/products/encoders/incremental/linear/PE but find that it is no longer available!

The Z and X axis motors only move 1 inch for positioning and then the Z stops to hold while the Y axis during moves very slowly during light grinding.  These 2 could be NEMA 17 or 23.  The X axis motor does all the work, and this is where I was considering the Teknic motor.  That may be more expense and trouble than required.  The motor I am using in the prototype does fine but I believe with a spindle turning at high rpm in the 6-8k range with light grinding there will be very little torque needed so it is worthwhile to consider NEMA 23.

So glad to find excellent products and support that so many rely on!

Thanks
Keith

thespindoctor

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Re: Build-a-box option?
« Reply #1 on: October 30, 2016, 08:53:48 AM »
I did find a Linear Encoder with quadrature which is even better but not sure if it is available.  It has +A/-A, +B/-B, ZR/-ZR, +5V DC, and common.  It is called an encoder and that is why I use the terminology during our first discussion as opposed to 'probe".

Thanks
Keith

Steve Stallings

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Re: Build-a-box option?
« Reply #2 on: October 30, 2016, 04:33:56 PM »
The internal electronics of the PMDX-340 are not modular, everything
is on one large printed circuit board. Therefore customization is not
a realistic possibility.

Linear encoders, sometimes called scales, would interface in the same
fashion as rotary encoders except for two things. First is that a linear
scale is less likely to have an index signal to use for homing. The second
is that rotary encoders benefit from the resolution enhancement of the
rotary motion being converted to linear motion by the screw. You may
find it expensive to get a linear encoder with the resolution you desire.
Steve Stallings
www.PMDX.com

thespindoctor

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Re: Build-a-box option?
« Reply #3 on: October 30, 2016, 10:13:25 PM »
Ok I will continue on the path of individual components.

My encoder/probe is called a mechanical linear encoder probe.    If I find one,  can we use a mpg input to interface it like I did with Cullins board?

thespindoctor

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Re: Build-a-box option?
« Reply #4 on: October 30, 2016, 10:29:45 PM »
The probe I have now has .0005" resolution and cost about $750 and the new one has .0001 resolution so we will see what it will $$$ cost!

Steve Stallings

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Re: Build-a-box option?
« Reply #5 on: October 30, 2016, 11:02:06 PM »
What you seem to be describing is an encoder.

A probe is a device that gives one on or off signal to indicate if the
probe has touched the target object while the machine was executing
the G-code for a probe move.

If you expect to be able to read the encoder while the machine
is in motion, then you will have to write scripts to support that.

Linear scales with 0.005" resolution should cost on about $200
for a short scale. To get 0.001" resolution you will need one of
the fancy ones with an "interpolator" and those are expensive.
Steve Stallings
www.PMDX.com

thespindoctor

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Re: Build-a-box option?
« Reply #6 on: October 31, 2016, 12:02:06 PM »
Yes I have done all the programming and successfully but now have to do it in Lua...