We got our new servo motor and I
haven't even opened it yet. It just arrived today, it's still in the box, still sealed up and I want to get it out of here. My goal here is by the end of
this video to have that CNC machine running. I have
no idea what it's going to take to do that, but the first step is to get this box open and let's see what happens.
Hey it's Pete welcome back to the workshop. So the goal this week is to get
this new thousand watt DMM servo motor mounted on our spindle,
get it tuned and get that finalized. I need to get the
machine turned around- we still have to replace one of the
Deutsch connectors on the front, the y-axis stepper motor- I can't reach
that from where it's at right now so that never got done.
But that's a quick job, once that's done the machine should be ready to run and
if everything goes as planned this video will end with that machine
making chips. Before going forward with the install of
the 1000 watt motor I thought it might be a good idea to go
backwards just a little bit and discuss what happened to the 750
watt motor. when I started trying to tune the motor
I wasn't having much luck and I exchanged several emails back and
forth with DMM-tech they gave me a lot of good input but none of it was
really working.
So then our conversation transitioned to
talking about the motor itself and what exactly its
physical capabilities were and things like inertia. The 750 watt motor has an inertia rating of
2.45 kilogram centimeters square and that number it's not really
important for the sake of this discussion of
understanding that but uh what is important is remembering the 2.45. Now DMM-Tech says that that motor has a an inertia ratio of up to 20 times that
you can think of that as a mismatch between the
inertia of the motor itself and the machine you're trying to drive
and although it's 20 times they would prefer that it actually would be 10
times so at that point we're at 24.5 kilogram
centimeter squared so the question becomes what is actually
the inertia of the machine and we tried to do some estimating and
calculating of things but in the end I just decided that
the best way to find out was to pull the spindle and
actually measure it.
I didn't want to take the head off the machine again to
press the spindle out and I started wondering in a similar
situation what Yuchol at Woods Creek Workshop might do I decided he would probably call Randy
Richard and since I don't know Randy Richard's phone
number I just decided to whack it with a mallet I actually discovered, although just a
little bit too late, that there is a way of pushing that spindle out of there
with hydraulic pressure without actually using a mechanical press.
It's actually built into the spindle and if we ever have to pull the spindle
out of there again we'll try doing it that way. Now DMM-Tech shared a formula with me which was
half the mass of the spindle times the radius squared. putting the spindle on the scale along with a sample piece of tooling,
I came up with 3.33 kilograms coming up with the average spindle
diameter was a bit more involved I came up with an average spindle
diameter of 5.41 centimeters and again this this is still just an
estimate, it does not take into account the moving portion of the spindle bearings themselves which would be
attached to that spindle but it gets us in the ballpark So with a radius of 2.705 centimeters, and a mass of 3.33 kilograms, I ended up with an inertia calculation of
12.183 kilogram centimeters squared and if you remember back our target number we want it to be less than was
24.5 kilogram centimeter squared But that does not take into account the
pulley ratio that we're going for We have a two to one pulley ratio.
with the motor maxed out at 5000 rpm, the spindle spindle's supposed to go 10k.
But when calculating inertia it's a square so the 10k pulley setting-
we end up with an inertia calculation of 48.732 and
with the 750 watt motor that is a 19.8 times multiplier there-
and that's still within the 20 times but that does not take into account
any friction in the machine, it doesn't take into account actually having a
cutter and actually doing work it's just strictly the spindle itself so
we're right there at the upper limit of their claimed range with
nowhere to go and that's how we ended up with the
thousand watt spindle motor.
The thousand watt motor has an inertia rating of 3.7
kilogram centimeters squared we end up with an inertia mismatch there of 13.17 that's just above the 10 times that
we'd really like to have and gives us a lot of leeway there
for actually doing work. Again not wanting to take the head off the machine to press the spindle back
in, I use the jam nut that holds the step pulley
with a piece of aluminum tubing to wind the spindle up in place.
Okay that is tight The next issue I ran into was excessive
run out on the step pulley for the spindle motor. in a previous video I had a rather sketchy setup
I tried using to enlarge the bore size of the pulley bushing
to accommodate the 14 millimeter shaft on these motors. When I originally
installed the 750 watt motor I had great luck with it, it just went together but that luck seems to have run out. I cannot
get this pulley bushing to go on the new motor with any sort of
run-out that's acceptable.
I decided the only way to move forward
was to create a new pulley bushing from scratch. I started with a scrap piece of 1-5/16"
cold rolled steel and just took measurements from the original bushing There's going to be very little
commentary in this section, I will leave a time stamp
down in the video description if you want to skip past the machining of this
part and get to the actual motor installation. If you like this kind of content please
consider clicking that subscribe button it really helps the channel out. The diameter here isn't critical, it just
needed to have enough meat left for the set screws-
and it had to finish at a size that I had to collet for. I will have links down in the video
description to some of the tools I use this time around I could have tapped this hole before
removing the part from the lathe but I had to order the tap and didn't
have it on hand when I got to this point.
I also had to order in a larger slitting
blade, but I was able to use the smaller one I had on hand to get the job set up
and started. with all that done I could get back to
mounting the motor. I used a bolt down on the end of the motor shaft to
help seat the bushing before tightening the set screws. The pulley slipped onto the bushing with
a rather satisfying feel. I wanted to verify the RPM so I used an
optical tachometer. This is an old Pocket-Tach 100 made by Monarch. With 5000 RPM at the motor, the spindle was measuring within 5 RPM of the nameplate rating. I'm going to do S1000 M3 Cycle Start S2000 M3 And stop. M4 M5 Well it's taken way longer to get to
this point than I ever anticipated. There's no way at the beginning of this
video I ever would have predicted that I was
going to have to make one of these pulley bushings.
So that ate up a whole lot of time I wasn't anticipating.
Also with the y-axis stepper motor, the connector on there we need to replace-
another thing that slipped my mind is that the home switches for all three
axes have never been mounted on the machine so they all need to be mounted and wired in. And finally
I discovered that I don't have any hardware at all that'll fit the t-slots
in this table i've got no way of clamping down
a work piece to even try to do a test cut.
We've got a bit of an anniversary coming up, next week is actually the one year
anniversary of the first video that I uploaded in
this series of retrofitting the DM2800 milling
machine- retrofitting it to the Acorn control system. And I'd like to say that, uh you know, the
goal here is we're gonna get this thing done next week for the anniversary, at least phase one of the project uh obviously, there's the Ether1616 board sitting in there with all that I/O that we haven't
even touched. So there's plenty of room for expansion
and projects down the way. But at least as far as having a working
machine that's kind of my goal that I'm shooting for now. If you want to see how
the project started a year ago, click that link to the left and I'll
catch you over there..