Hi,
I seem to remember a crank as in crankshaft lashup to drive the table.
Personally I think the hydraulic setup is better but harder to achieve.
The free lunch is hard to find.
Dave
On 2/4/22 9:11 AM, John Dammeyer wrote:
From: Kenneth Lerman [mailto:ler...@se-ltd.com]
The longitudinal travel is just over a foot, and it takes about 3-1/2 turns
of the crank to go that distance. I'm thinking around a second per turn
would be about the maximum. So, that's 60 RPM. I'm thinking of a 1:6 ratio
on the timing belt pulleys, so that's 360 RPM at the stepper which is
pretty slow. A full stepping rate would be 200 * 360/60 => 200 * 6 which is
only 1200 steps per second.
You won't want to run full step. A minimum should be 8 micro-steps/step to
avoid resonance and loss of position or lockup. I'd measure the torque
required to move the table by attaching a lever to the hand wheel that is say
1' long. Set it horizontal and start hanging weight onto the end to get ft-lbs
or ft-in until it turns. That's the torque required to overcome static
friction. Double that to choose your motor.
Say that is 1 ft-lb or 192 oz-in. If you choose 3:1 for your reduction ratio
you get 600 oz-in. Look at the motor torque curve (they are all different and
if the supplier can't give you that buy one somewhere else) and see where the
torque drops below 400 oz-in. Say that's 180 RPM. That's 3 RPS which
multiplied by 2000 steps per rev for micro-stepping is 6000 steps/second which
achieves your 1 RPS on the handle.
Or if you find it's 2 ft-lb or 400 oz-in choose a much larger motor like 1200
oz-in
http://www.automationtechnologiesinc.com/download/9259/
Notice the curve at 3000 half steps per second is about 3.2NM. That's 12,000
steps per second (7.5RPS) with 8 micro-steps per step well within the reach of
even a parallel port controller and 450 oz-in. That's well above the 1 RPS you
need and even just 3:1 still gives you 1600 oz-in.
My two cents...
John Dammeyer
An alternative would be to provide more gearing, but I don't think it's
practical to get more than about a six to one ratio in a single belt
reduction and I'd like to avoid mechanical complexity if I can.
Thoughts?
Ken
Kenneth Lerman
55 Main Street
Newtown, CT 06470
On Fri, Feb 4, 2022 at 7:13 AM Chris Albertson <albertson.ch...@gmail.com>
wrote:
If looking for lowest cost solution you can us the old "Atom" computer to
control the grinder as long as you do not need to run the mill and
grider at the same time. Get an Eiternet interface Mesa card for the new
machine, You need two config files, just load the one for the mill or the
one for the grinder.
Then someday you buy a second computer you only have to move the Ethernet
cable over. The best option is a newer version of the Atom. They seem to
sell for just under $200. Finally Newegg.com always has many used oe
refurb PCs Used PCs sourced locally can be a cheap as "free"
But 9ld PCs tend to burn up a lot of power. I am trying to get mone to do
"wake on LAN" so it can not use power until I need to log onto it
On Thu, Feb 3, 2022 at 6:52 PM Kenneth Lerman <ler...@se-ltd.com> wrote:
I'm considering converting a surface grinder to CNC. To start, I'll
probably just convert the longitudinal and transverse axes.
I'll go with steppers for this -- I'm thinking NEMA-42 motors.
My current Bridgeport clone uses servos and Jon Elson's hardware on a
little Intel Atom Box. I'm thinking of using a Rpi for this. It will
need a
minimal display/control panel when completed, but initially will need a
display with touchscreen or mouse and possibly a keyboard. In the long
run,
some buttons. and perhaps an mpg might be useful.
I'd like to use a raw Rpi without adding special hardware directly. That
probably means using a USB or ethernet interface to control the steppers.
I'm thinking of using Mesa hardware.
Can someone suggest the most cost effective way to do this? (Although I
have to admit, that after buying the timing belts and pulleys, the
steppers, power supply, stepper drivers, ..., it's too late to be really
cost effective.). And the surface grinder only cost me $300.
Thanks,
Ken
Kenneth Lerman
55 Main Street
Newtown, CT 06470
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Chris Albertson
Redondo Beach, California
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