I've had about a half dozen or so nights out imaging with my
OnStep converted G11.? My guiding has been pretty good, averaging
around .65 to .75 with the old two piece worm blocks and HP brass
worms.? After seeing a few posts here and on cloudy nights about
DIY spring loaded worm mods, I decided to give it a try myself.?
The raw materials were some 3/4 inch aluminum 90? angle stock,
1/8 thick, some 3D printed attachment points,? a 3D printed drill
jig, and some off the shelf hardware.?? Here is the aluminum angle
stock marked up for drilling.
I ordered fresh worm blocks so if this mod doesn't quite work
out, I can always go back to stock.? I already had extra
bearings.? The new blocks were drilled front and top, but only
tapped on the front side.? I tapped the top holes to match the
front, 10-24 threads.? I also had to file down the corner to get
the worm blocks to sit flat in the angle stock.? There is a tiny
radius in the extruded aluminum you need to accommodate.
Drilling into a nice mount can be a bit unnerving.? I 3D printed
up a jig to make sure I drilled straight, and got the depth right.
A 6-32 tap cuts the threads.?? The rear drill hole does go into
the worm block mounting hole, but the bolt does not protrude into
it.? No big deal.
One side done, one more to go.
The 3D printed attachment point is in place.
The finished assembly on the DEC side.? The empty outboard hole
next to the spring is for a push set screw, if I find it's needed.
And here's the RA side.
Hello little worm, I see you!? You can also see my DIY RA
extension I needed to clear the motor brackets.? I'm using 1-1/4
aluminum spacers, and a 3D printed trim ring.?? You can see I did
something similar with the DEC as well.
So far, so good.? The pivot point is the bottom worm block bolt
closest to the motor.? It's located in place with an m4 x 10mm OD
plastic washer.? It is very lightly snugged in place.?? The worm
block bolt away from the motor is the sliding side.? It's left
loose, only tight enough to keep the worm from walking upward.?
When testing the worm in the OPWB, if I snugged the stock worm
blocks into the aluminum angle stock, the worm was difficult to
turn.? It could be a burr or defect on both pieces of angle stock,
but more likely, the worm blocks / bearings are just off by a
fraction of a degree.? I found that torquing the top bolts tightly
first, then lightly snugging the front bolts allows the worm to
spin freely.
I can just barely get to the motor couplings without taking
everything apart, which is nice.? I'm using flexible couplings
attached to the belt drive brackets, courtesy of Rockmover on
Thingiverse.? I have 16:60 belt reduction, and I'm running the
0.9? stepper motors at 1/16 microsteps, which gives me 0.15
arc-sec or resolution.? Control is handled by OnStep.? Personally,
my gut feeling is that attaching the motors directly to the OPWB
is unnecessary for the microscopic amount of runout the worm
wheels have.? The flexible couplers are more than adequate for
taking up any angular error.? I could probably even get away with
a rigid coupler and rely on the shaft to flex a tiny bit.? And
that's to say nothing of all the plastic. :)
There's clouds in the foreseeable forecast, but I'm hoping
there's a break in the weather soon so I can get some testing
done.
Any thoughts, comments or criticism are both welcome and
appreciated.
-Tony
Michael Herman