This week mostly looks like more destruction.
That is, of course, not entirely true- I finished a new stepper mount (effectively identical to the one shown in the previous post) for the X axis, and tried to get it installed. It turns out the sides of my machine aren't entirely perpendicular to the X axis, so aligning it has proved to be a challenge. This is the technique I've been using- trying to reflect a laser back at its origin:
That's a laser level clamped to the X axis. You can also see the rather unexciting stepper mounting plate. Perhaps more exciting is the "mirror" I'm using to reflect the laser. Yes, that is a silicon wafer. Evidently that's easier to find than an actual mirror around here.
After unsuccessfully trying to shim the mounting plate into the correct plane, I think what we'll end up doing is is put some epoxy putty between the plate and the side of the machine, screw the plate down to perpendicular, then let it harden. At that point we should be able to screw everything down nice and tight while still having it be perpendicular.
As a side note, a bunch of tedious work isn't shown here- getting the leadnut on the X axis carriage aligned with the direction of motion. I didn't take a picture firstly because it looks pretty much the same as the Y axis (which I evidently didn't take a good picture of either... oops. This
is about the best I can do- you can (barely) see it in the upper left), and secondly because it was already mounted at the time it occurred to me to get a picture. It seemed like too much work to take it apart again
After getting my new table installed and the new leadscrew aligned with the bearing, I realized that the stepper won't stay aligned with the leadscrew. In other words, I couldn't use my new couplings, which depend on superb alignment. What's the logical thing to do? Complain. But after that, to make a new bearing clamp and stepper mount combo to ensure perfect alignment. So there went my day.
The mount was made from a chunk of ~2" solid aluminum round stock. It probably would have made more sense to have started with a thick-walled tube, but I didn't have any of that.
The left image above shows the top of the mount. The indented ring you can see is used to align the stepper, while the deeper region is to house the coupling.
The right image above shows the side and bottom of the mount. The hole in the side is used to tighten the leadscrew end of the coupling (the stepper end is tightened before it's inserted into the mount). On the left, you can see a narrower disc. This is used to align the mount with the countersunk circle etched into the back of the stepper mounting plate. The very center hole is for the leadscrew bearing.
There weren't any really novel methods used in making this- just a LOT of drilling on the lathe (for the large center hole) and careful measurements (for the stepper alignment indent and especially the bearing indent- both depth and diameter). On the up side, it fits perfectly on the machine, and the stepper and leadscrew seem to be aligned very well- at least the screw turns with no complaints.
So after a whole day of work (well, 1000~1800, so close enough), I've got one e axis that seems to be about as close to perfect as I can get it.
Most prominently the new table is bolted down. Furthermore, the T-slot table is bolted on top of that, so I can actually resume milling stuff:
You can see the front and back views (note the lovely metal roofing screws holding the back plate on- classy!) above. I've even gone so far as to level the table, since it had been remounted. It turns out it had shifted quite a bit- the outside slots haven't even been touched (they will be if I ever need to mill something that requires support that wide). Leveling took much less time with the new spindle than previously!
The new Y axis is incredibly smooth- the leadscrew is aligned just perfectly (well, pretty close at any rate), so it turns with negligible resistance. Unfortunately, somehow (despite CNCing the pattern and holes), the stepper is not perfectly aligned with the leadscrew shaft, so I'm still using the old rubber tubing coupling. On the up side, it works just fine for low-torque applications.
Always a favorite feature on axes: limit switches! Yes, I have limit switches installed on my Y axis still, except this time they're done better, with no wires trailing along the sides of the machine. They're hidden under the right side of the table- with "right" as shown in the left image above. They'd be on the left of the right-hand image.Just imagine they exist between the two images. In case you lack imagination:
There's an extra aluminum rail that runs along the bottom of the table. The switches trigger when they run off the end of it, which is good, since I don't want my table crashing into my stepper.
Finally, a little work on the Z axis. During the course of all this other work, it became apparent that the Z axis wasn't perpendicular to the XY plane- maybe a quarter inch of Y-dimension travel over the course of the Z axis, which is kind of a lot.. The simple solution was to shim the bottom of the Z axis to force it out a bit. Conveniently enough, a couple washers made it pretty darn close to perpendicular (at least as far as I can tell with my improvised right angle- aka, the old table).
It's shimmed out maybe 0.125" (I think the washers were ~0.128", but close enough). I didn't really do any tests to see if it gives a nicer finish, or cuts nicer PCB traces, but at least it appears to be much more square.
As far as replacing the axis goes, I'm so far quite satisfied. I have yet to check how close to perfectly aligned the Y axis is since bolting it down, but it at least looks good (though I realistically probably couldn't see the difference between 85° and 90°, much less 90° and 90.1°). At a minimum, it slides so much better than the previous iteration (remember how that was shimmed up to prevent it from wobbling- ie, had LOTS of friction?). I can now do rapid moves around twice as fast- actually faster, though not consistently. And by that I mean that 0-42 inches/minute works just fine, 42-66 inches/minute is kind of sketchy, then 72 inches/minute is fine again. Go figure- I've read that harmonics can creep into steppers/leadscrews and cause problems, so maybe that's the issue. In any case, I don't need to move that fast, so I just limited it to 42 inches/minute peak.
The X axis is coming up next for replacement! Or maybe getting the Y axis stepper properly aligned with the leadscrew... one of those two, in all likelihood.
Firstly, the damage:
The old table has been ripped out to make way for the new. Also ripped out is the old Y axis stepper mount, replaced by the new one you can see at the back of the machine. A rear view:
And because I (usually) don't just rip things apart for no good reason, the new table semi-installed and being aligned:
I say "semi-installed" because it's just clamped in place- not screwed down yet. That said, it is pretty well aligned (just about as well as I can get it with a tape measure)- hopefully I can keep it still while screwing/bolting it down. The Y axis stepper is currently installed (it may well come off again during the process of securing the table); I would post a picture, but it looks pretty much the same as the Z axis...
Two images today, the sum of which doesn't seem like it should have taken an entire day to complete.
First up, there's the bearing clamp all set to be screwed down to the stepper mount plate. The new progress on this front is the indent seen in the middle of the stepper mount pattern. This allows the bearing clamp (round chunk of aluminum with the bearing in it) to be properly centered, which is especially helpful when doing something like aligning leadscrews and stepper shafts for coupling.
The indent itself is CNC milled, hence it being nice and round. (You can also see lines where the end mill went around- my spindle isn't quite perpendicular to the work surface) The clamp itself (top) was done by hand. I have no clue why the finish looks as awful as it does; the lathe evidently doesn't like me today. That said, it should at least hold the bearing in place, which is what really matters.
Next up is the little rail to trigger the limit switches on the new axis. The limit switches will be mounted vertically and roll along the rail, triggering at either end where you can see the taper.
In in interest of full disclosure, I didn't do this today/this week. Actually, I didn't do it at all- my dad was kind enough to make it for me. It's definitely nice to have the help.
So if that's all that I did today, why did it take so long? Well, it's not all that I did today... there's another bearing clamp in progress, and a second stepper mounting plate (for the X axis) completed. That's at least a little more (though I would agree that it seems like I should have more to show for the number of hours of work I put in).
Two bits of progress this week, both of which can be seen in the photo below. Firstly, I got the feed nut mounted to the new Y axis table- this can be ween in approximately the center of the picture, with the leadscrew going through it. I didn't do all the work, though; my dad got the fixture properly aligned and secured after I drilled and tapped the first hole (of the four you can see immediately adjacent to the leadscrew).
The second bit of progress is the stepper mount seen on the right edge of the image. This will go across the entire back of the mill, providing extra support and rigidity for the stepper. It replaces the little cantilevered plate that can (barely) be seen at the bottom of this image
. The four small holes were started on the CNC mill, then manually drilled to size and tapped, while the larger center hole was done in the opposite way- first manually on the drill press, then milled to the proper size. In this way all the holes should be properly aligned for the stepper and leadscrew.
Only a few more things to do before the new Y axis (and leadscrew) can be installed!
The feed nut mounted to the Y axis. Yes, this is once again being shown upside-down.
Alternately, "this guy sure loves drilling holes axially in rods/bolts
". To illustrate why I say that (hopefully you can figure out where the axial drilling comes in):
This is more or less the culmination of trying to get my new leadscrews coupled to the steppers. In principle, it's a simple task- secure the screw to the bearing, turn down the end to 1/4", and connect to the stepper. I did this with the other axes, so why is it so hard now?
The issue is the acme nuts. 3/8" nut, 3/8" bearing- OK. 3/8" acme nut, 3/8" bearing- not OK. The acme nut is significantly larger than a regular nut. Of course it has to be just big enough to reach the edges of the bearing. In other words, there's no way to use the acme nut to clamp the acme rod to the bearing without interfering with the rotation of the rod. (The alternative would be to just not have the bearing secured, allowing the use of the acme nut and free rotation, but that's equally useless.)
The solution I've used is to basically create an intermediate piece to clamp to the bearing and the acme rod. This consists of a larger-diameter rod (actually a piece of a bolt) with a hole bored in one end for the acme rod and the other end stepped down to 3/8" (and threaded), then to 1/4" (for connecting to the stepper). Two set screws hold the acme rod in place. The result is basically a conversion to a standard fine-thread 3/8" bolt, which allows a normal-sized nut to be used to clamp to the bearing. Only one nut is required, since the other side of the bearing can be pressed against the shoulder. The whole setup can be seen above.
Thanks to doing just about everything on the lather, the results are very nearly perfectly axial.
I've also got holes drilled in the nut holders and angle aluminum cut to mount them to my axes. Just a few more steps before I can finally install the new leadscrews (and table!).... And yes, yes it is always "just a few more steps". That's how these things go.
Nothing terribly exciting, just that I got the rails fully mounted to my new aluminum table. Thanks to the blocks already being aligned, the rails slide smoothly along the entire range of motion (approximately 10 inches).
The sharp-eyed observer might note the screws sticking through the table... those should probably be cut down. The current plan is to mount the T-slotted table on top of this one, so the screws aren't a problem right now.
I'm finally getting around to installing the linear bearings on the Y axis. And by that I mean I've created a plate to hold the rail supports in the proper place:
On the right, you can see the top view, and on the left, the bottom. No, that is not a typo- the bearing blocks will be fixed to the bottom of the mill right under the cutting head so the workpiece is always supported where work is being done. The screws still need to be countersunk, but at least they're darn close to perfectly aligned.
The hole patterns were marked with the CNC mill to ensure alignment (I love having the machine upgrade itself), then drilled on a drill press. By "marked" I mean "shallow pilot holes were created with an end mill". The carriages are on roughly a 7" square pattern (center to center). Since the table will be ~14" wide, putting the supports at the 1/4 and 3/4 points seemed like a reasonable choice for ensuring support across the entire table.
I've also got a new chunk of aluminum to replace the old table- if I'm tearing the table and leadscrews off anyway, I might as well upgrade it.
My Z axis has given me a bit of trouble lately. Firstly, a couple nuts came loose, meaning the stepper would turn a shaft that may or may not cause the actual axis to move, depending on the current position of the nut. This caused a few days worth of headaches while trying to etch a PCB. A little thread locker and some torque fixed the problem.
Secondly, I decided to take a slightly fancier approach to etching PCBs and actually account/compensate for variations in copper-clad thickness (and clamping imperfections). I accomplished this by probing the height of the board at various places, then wrote a python script to adjust the Z coordinate when milling the boards. (More details will hopefully follow sometime in a later post). Since the boards don't vary in height all that much, the changes were pretty small- generally a few mils at most.
My old method of using a chunk of tubing and hose clamps to couple the steppers to the leadscrews thus became an issue, at least with the Z axis. The tubing would twist quite a bit before actually turning the leadscrew- definitely not accurate (or precise) enough to do the small variations required.
This led to purchasing some new couplings, shown below. For the Z axis at least, they were a drop-in replacement, and now the axis can move up and down consistently in 0.0005" increments. Much better!
Left: A comparison of the new couplings to the old ones... guess which one works better?
Right: The new coupling installed in the Z axis