On 6/19/20 1:34 PM, Chris Albertson wrote:
A 4:1 reduction is possible with gears. The sensor would be mounted the
same way but displaced off axis 24 mm then fitted with a 80T gear and
driven by a 20T gear that is itself driven by the drawbar. I would buy l
gears (mod. 0.5 or Pi/2 mm pitch) as printed gears are not great in that
tiny size.
I think gears are good because they can be small mod 0.5 or even smaller.
Two minutes of hunting found this
https://www.mcmaster.com/2662N31
for $3 each. This could be the "large" gear fixed to the sensor.
There is "all the space in the world" above the spindle on the mini mill
but you need to preserve a way to get a wrench on the drawbar.
The harder part is getting the encoder data into LinuxCNC/HAL. It is
easy if you have some Mesa cards. More work if the data must go in via
USB.
I am still messing with reading quadrature encoder(s) on an RPI, it can
be done. I am doing that for a few reasons, one
is for adding something like that to a benchtop mill and lathe, the
other is to track the axes of a telescope mount that I
am building.
On Fri, Jun 19, 2020 at 11:52 AM Ken Strauss <ken.stra...@gmail.com> wrote:
I would like to add rigid tapping. Those are some inexpensive encoders
except the top rated speed is 5000 rpm and I have a 10000 rpm spindle. Any
suggestions regarding suitable pulleys to reduce the speed (perhaps 5:1)?
Will normal GT2 belts survive?
-----Original Message-----
From: Chris Albertson [mailto:albertson.ch...@gmail.com]
Sent: Friday, June 19, 2020 2:02 PM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] Universal spindle speed control for $7
There is all the space I need to build an encoder for the HF mill's
spindle. The sensor will fit above the drawbar.
I'm thinking of using this sensor. The shaft would point down and
thesensor is aligned with an directly over the spindle.
ebay.com/itm/360-600P-R-Photoelectric-Incremental-Rotary-Encoder...
<https://www.ebay.com/itm/360-600P-R-Photoelectric-Incremental-Rotary-
Encoder-5V-24V-AB-Two-Phases-
Shaft/254214673272?hash=item3b30601378:g:AfUAAOSwQ0dcxosi>
There is a cover over the spindle that is held on by friction. It
looks
like the top on a can of spray paint. I can make a replacement that is
held on by magnets. Inside is the encoder that fits on top of the
drawbar.
The sensor is fitted with a 17mm "socket" that is light friction fit to
the top of the drawbar.
In use, I'd remove the new cover and stick it on the side of the mill
using
the magnet, apply the wrench to the drawbar then replace the cover.
I am trying to decide if I want a 360 line or a 600 line encoder.
Either
will send data too fast for a printer port with no Mesa card. I might
put
a microcontroller in the cover and use a serial interface. The plan is
to
get spindle speed control to run open-loop first. I figure an open-loop
servo-controlled pot is at least as accurate as a human operator can do
with his fingers while listening to the noise.
My pendant project got a huge boost when I figured out I don't need to
build any hardware. I can use an off the shelf X-box USB game
controller. I already have a few of them.
On Fri, Jun 19, 2020 at 4:11 AM Gene Heskett <ghesk...@shentel.net>
wrote:
On Friday 19 June 2020 06:10:48 Roland Jollivet wrote:
I was going to suggest this at the start of the thread, but I thought
it would be considered too Heath Robinson..
And within its limitation of available torque to keep the tap turning,
and an encoder able to track to a 5 degree accuracy, I see no reason to
totally eliminate rigid tapping from its abilities. Even the little 200
watt hf mill should be able to turn an 0-80 or maybe even a 2mm tap.
The
lack of space in the head to build a decent encoder is far more of a
limitation than a speed controller such as this. Thats the main reason
my little hf never grew the ability to tap, That controller/amplifier,
pulled out of the head and mounted in a 4x6x3" box so all the the hot
electronics was out of sight, proved to be a very high gain controller,
so high gain I was forced to rig an ammeter to tell me how hard it was
working so I could control the cost of fuses, there was otherwise no
slowdown to let the user know it was working too hard.
I eventually blew that controllers pass transistor, a simple powet
F.E.T., and in search of a suitable replacement, checked the bugs in an
out of spec pc supply from the junk box, found it was rated at 800
volts
instead of 200, 12 amps instead of 2.5, but otherwise looked the same.
So the consideration resolved to the driver transistor in the circuits
ability to switch the much higher gate capacitance that bug had to have
since switching speed is paramount. I put it in, think I had a
reservoir
of such bugs if it didn't work. I raised the fuse from 2.5 amps to 4.
That was over a decade back. I've blown the fuse 2 or 3 times since
with
the ammeter pegged, but its still there although the rest of the mill
is
in pieces, it unscrewed one of its ballnuts a year & 1/2 ago.
Somebody should make me an offer for it, its the complete controller
out
of the big head hf x1 with a pmdx-106 interface, ready to take the pwm
&
direction output of LinuxCNC from a parport bob, either manual or full
bi-directional computer control of a 200, maybe even a 400 watt motor.
Its not in service here, and probably won't ever be again as I'm
approaching the end of my ride here with a pump running at 31%
efficiency. And thats beginning to affect my giddy-up.
On Thu, 18 Jun 2020 at 20:40, Chris Albertson
<albertson.ch...@gmail.com>
wrote:
I'm making good progress on my 3D printed CNC conversion. I found
a
way to 3D print a spindle controller that should work for most
small
milling machines and small lathes. The cost is "almost nothing".
These machines' spindles are controlled by turning a potentiometer
so my new system simply uses a cheap model airplane servo to turn
the shaft of a potentiometer. The computer is 100% isolated from
any high voltage or noise.
These small mills will never be able to do things like rigid
tapping
so all they need is a simple and approximate way to control the
RPM.
This speed control can be run "open loop" if plus/minus 20% is
good
enough or used with a spindle encoder in a closed PID loop as long
as the PID is tunned not to aggressively.
For anyone who does not know about these hobby servos:
- They are not full rotation motors. They turn only through
about 250 degrees, This is a good match to the pot as pots also
rotate about this range.
- The angle of the servo shaft is controlled by a PWM signal.
- They are "dirt cheap" starting at about $5
amazon.com/4-Pack-MG996R <
https://www.amazon.com/4-Pack-MG996R-Torque-Digital-
Helicopter/dp/B0
7MFK266B/ref=sr_1_2?dchild=1&keywords=mg+servo&qid=1592502600&sr=
8-2
- They accept a 5-volt control signal, so they have a built-in
computer interface.
- They are fast (enough) and can move from full-low to full-high
on 0.6 seconds
- They really are actual "servos" and have an encoder, motor
driver, and gears all inside.
So when LinuxCNC outputs a low-value PWM spindle control, the servo
moves the pot to the low position. As the PWM signal value gets
larger the pot is moved closer to the high-speed position.
In the picture below is a cartoonish render. The green frame is
one-piece 3D printed, The red pannel and tan coupler are also 3D
printed. The motor sells on Amazon, four units for $20 and the pot
is about a buck each. Four M4 button head screws everything
together.
Here is a link to the current version CAD files and a viewer.
I'll
be updating the files after the first prototype is printed.
https://a360.co/2N95AiL
I may make a top cover to protect the pot and keep fingers off the
high voltage.
[image: Red Neck Spindle Control v6.jpg]
--
Chris Albertson
Redondo Beach, California
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Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law
respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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--
Chris Albertson
Redondo Beach, California
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