Use the photographs to make, build and assemble the non-printed parts of this device.
Note that installing it requires no modification to your Replicator. All parts slide or snap into place or attach using existing bolts.
What this thing does:
â€¢ Using a sled mounted between the printer heads, the dial indicator measures the height of your heads above the build plate. Because it's permanently mounted to the extruders, you can use it in any location on your build plate, at any time and with no setup. You could even use it while printing.
â€¢ The entire device is permanently mounted to your extruders and is easily turned on and off by raising and lowering the sled by hand.
â€¢ If you use the optional sliding mass damper. that can double as a convenient lever.
â€¢ Readings are extremely accurate, and once installed, doesn't require any further setup. It's just there. It's robust and it works.
Here are some caveats:
â€¢ Because it's mounted under the print head, it becomes a little more difficult to see what's going on at the extruder heads.
â€¢ If you use plexiglass for the sled and leave it down when you print, it will need to be cleaned.
â€¢ The location of the gauge was the most difficult part to settle on. Where it is now is the result of many tries and many failures. Yes, the tightening knob is very close to the plastic guides, but it doesn't interfere with them at all... What it does do, is make positioning the dial indicator a pain in the butt. The good news is, the indicator only needs to be positioned once.
What you need are:
â€¢ Three printed parts
â€¢ One fabricated sled plate
â€¢ One 4" piece of .040 dia Stinless wire
â€¢ One Liver type dial indicator (that's not a mis-type).
â€¢ A bit of lead for weight if desired... And
â€¢ If desired: One optional sliding mass damper
Picture 3 shows the parts, laid out. You can use this to make your sled. Size isn't too important, the larger the area that rests on the build platform, the more "averaging" the reading will be. just make sure all edges are raised and rounded. After experimentation, I choose to make the sled from aluminum, to keep the measurement area small, with a bit of weight added and centered between the two extruders. The portion of the sled that touches the surface is round, so the point of contact is very small.
Pictures 4 & 5 show how the sled should be formed. A slight "S" curve will allow you to bend the sled so the lowest point will be located on the same plane as and half way between the extruders.
Pictures 6 - 11 show the various types of sleds installed on my MakerBot. Aluminum has turned out to be my material of choice.
The dial indicator mounts to the top of the extruders.
Picture 12 shows me snapping the sled hinge into place at the back of the extruder platform. It uses the shape of the plastic housing to grab onto and snap into place. No modification of the printer is necessary for the hinge or the gauge mount.
This mount is also the bonus I mention in the title. While the screw-on piece holds the gauge securely, the snap-on piece behind it holds the extruder cable rigidly in place... Much better than the OEM nylon ties.
My gauge is old and analog, which is what I prefer (analog, not old). Modify your mount to fit your gauge.
Use .040 wire to link the gauge to the sled. Bend and run the wire to fit between the heating elements. Avoid the power strips jutting out of the extruders' heating elements. I'd imagine there'd be quite a show if those were to short out. Attach the wire to the gauge at the top and the sled at the bottom. If you're afraid of shorting the elements out, put heat-shrink tubing over the center section... You can see, I didn't... But I like to live dangerously.
I'll try to answer any questions about my setup. It's really a robust, install-and-forget way to adjust your table. I've come to rely on mine, even though I usually only pay attention to it when the layers don't look right. At those times, it becomes invaluable, and like a speedometer in a car, is always working.
The stl file contains the dial indicator mount, a reliable cable clamp as an extra feature and a single print, no raft hinge. You'll need to pick up a suitable dial indicator to fit having a point with a .040 hole through the tip. You can also modify the file to fit the indicator you'll be using or modify the tip of your indicator. You'll need to make the sled from plexiglas, aluminum or other suitable material. You'll also need hard stainless, .040 wire.
Picture 7 shows me snapping the sled to the back of the extrusion carriage. The carriage is designed like it was made for this purpose.
A really neat, but unproven option... Reducing vibrations and improving resolution:
This is only an experiment, but so far, things look promising. When robotic parts go flying around at 80mm/sec, there's bound to be some stress-caused vibrations that may have something to do with rapid changes of direction.
A device, called a tuned mass damper can reduce the vibrations of an oscillating bar by vibrating out of sync with the oscillating bar. The out of sync vibrations causes the bar to "detune", reducing undesirable vibrations throughout the entire system.
The damper I use is a 3/16" steel bar cut to 3/8 gram size. I used hand-made styrene pieces to cover it and made the attachment to the pick-up pin. It slips over the pin before the wire is fed through, trapping it underneath. The damper can rotate around the pick-up pin (in practice, it only moves about .030" either way).
As a bonus, the damper adds weight to the pick-up sled, making additional weight attached directly to the sled unnecessary.
I'll continue to experimenting with and without the mass damper to determine if and how much it improves the printing. As I stated earlier, it looks promising... But qualitative observations aren't very good for making decisions... Kinda like campaigning politicians telling us how they're going to fix things. Not a quantitative statement from the bunch... But I digress.
Try this, have fun using it and please comment your experience and ideas.
I took some photos of my printer for another purpose, so it's as good a time as any to update my contraption. The original plexiglass sled wasn't very heat resistant and susceptible to picking up stray bits of hot ABS, so I've permanently replaced the plexi with an aluminum sled, added a few ounces of lead to give it some weight (the lead weight fits neatly between the extruders and covered it all with non-conductive epoxy and tape to prevent it from shorting the extruder connections. I used acrylic resin to insulate and attach the aluminum to the hinge, but should have use a good epoxy. Still, it hasn't failed in several months of use.
The pickup portion is located directly between the nozzle tips, and the lead weight helps keep the sled down and smoothing the layer being built.
Because the aluminum is heat resistant and the ABS doesn't stick to it, there's no need to clean it. ln use, the gauge needle vibrates back and forth as it runs across the plastic layers, but it does so within a well defined area of tolerance (in my case, +/- .010". It's easy to extrapolate the average distance by observing the swings. Using the gauge this way gives me a good idea how thick the layers are at any given moment.
The gauge is set to "zero" on the first layer. Depending on the direction the head is moving, the gauge reads either .27mm (.010") or "0". If these figures change as the extruders move to other areas of the plate, I simply adjust the plate on the fly.
The other thing the sled in the down position does is, it flattens many tags and inconsistencies the extruder nozzles leave on the build surface. My prints (mostly done at medium resolution) come out much better with smoother and flatter layers when the sled is lowered.
I've added a new stl file "Meter Holder 4" that works better for my setup. It makes use of the steel clamp that came with my gauge and is much, much more stable than the all-plastic one. This holder keeps the gauge completely rigid and still allows full access to the 2 bolts holding it all in place.
In my opinion, it's much better than the original version.