Thumbscrew to level bed from beneath (Page 1 of 2)

i'm interested in using a glass plate or granite tile inplace of the aluminum but i have a few questions. how do you zero out the printing table does the abd adhere well to the glass or the tile?

Manx, you might need a longer Z offset screw with a glass bed.  It will need to be able to go down an extra 2-3mm to hit the limit switch before the glass bumps the nozzle, and 10mm more to account for the thickness of granite.  I had an extra that was long enough for granite, but it was getting into the unthreaded section of the screw.  Unfortunately hardware stores here hardly stock anything in M3, and whatever they have is short.  I'm thinking it would be useful to see if I can mail order a bunch of M3 screws in assorted lengths  just to make sure I have something handy.

For glass, I use small binder clips to hold it to the aluminum.  I also use them as handles for the glass when it is still hot.  I found some at staples that have rubber coating on the handles so you can still touch them when they are hot.  I only did one small print so far with the granite.  I put a large clip on one side.  It is heavy enough, it doesn't need much help staying put.  If you are doing a very large print, you will need to be careful about the clips getting in the way.  For the back right corner, I set the clip closer to the center so the nozzle doesn't hit it when it homes.

I got threaded rod. I've run into so many situations where I need longer or custom pieces of small diameter screws, so now I just keep a couple of everything below a 1/4 inch and m6.  Binder clips have worked well for me also.  I am impressed with how much all these improvements keep improving the prints. I would think at some point soon we are going to close in on having maxed out the full capabilities of this machine.

Ian, let me know if you like the granite more or less than the glass and or why. Also, I melted the fan a little bit once when I wasn't running it. I'm wondering if it needs to be running that close to the hot end with that design. What actually happened was the part holding the magnet in loosened up and the magnet popped out. How bout threaded magnets? They would e very useful with abs.

One more comment would be that it is easier to so self thread the screw by using the hex driver in the top of the screw at the same time.

The thumbscrews work really well.  You can make fine adjustments without pushing or pulling on the bed, and watch the readout on the Dial Indicator.  If using paper, this lets you park the nozzle right on the screw since you don't need to make room for the hex driver.  I did one set in ABS before deciding to go with the fancy translucent green.  It wasn't hard to break the bond on the superglue to get them off.

I think Solidoodle should adopt these as standard.  It makes leveling much easier, and no tool required.  Now to work out a thumbwheel for the Z offset...

I also switched to a glass plate (2mm framing glass), but couldn't use these thumbscrews. because I use Lawsy's end gcode (which lowers the bed to the bottom when done printing) and I didn't want to reduce my Z height more than I had to (you never know when you need it). So I bought 6x M4 hex nuts, put two on each threaded end, held the top one in place and  fastened the bottom one. Then I made functional, yet ugly thumb screws that fit on the bottom M4 nut.

My Z-screw was long enough, so I didn't have to replace it. I did break my first glass plate within minutes, because the two center screws (I think they hold the thermistor?) were sticking out ever so slightly and the first time I hit the glass by accident it shattered. I've grinded down the screws somewhat (they wouldnt budge when I tried reseating them) and now it seems to be working just fine.

Back to the original topic, bed leveling.

I tried to print a large object (in the X/Y sense) and almost immediately, some of the initial layers began to come off.  I assumed that it was time to level the bed, that the areas that had poor adhesion were lower than the areas where the layers stuck well.

I printed Ian's dial indicator holder and three thumbscrews and tried to level the bed.  I chose four points 100 mm apart in both the X and Y scales.  While I can get the two points nearest me to be within perhaps 0.003 inches, along the back, the best I can do is 0.010 across 100 mm of travel.  Clearly the bed plate is warped somewhat.

Does anyone know how much tolerance there is?  That is, is 0.010" across the back a real problem or nothing to worry about?

Trying to see a gap of 0.010 under a straight edge is not easy.  When I put the straight edge from near left to far left, I can put a piece of paper under the straight edge and move it almost completely from front to back, so there are "lips" on the front and back edge.  That is the only thing that I can detect using your suggestion. In particular, I cannot detect the 0.010 problems across the back.

I bumped my bed temperature up from 85 to 95, and that has allowed me to get larger pieces to stick, although I believe that I am relying on the adhesion on the front, along with the structural integrity of the piece, to keep everything in place.  It looks as if the back of the parts is not sticking very well.

I'm not sure what the spec is here.  I'm also not clear whether Solidoodle tests their beds prior to shipping. I could imagine at least two different tests. In one, you would attempt to print a 125 mm x 125 mm plate, to verify that filament sticks properly across the entire bed.  In the other, you would print a grid of 20 mm x 20 mm plates all across the surface, to see if some of them fail to adhere.

Josh, could you post the thumbscrews to Thingiverse?  So many people ask for them, it would be an easy place to point them.

Yes, the printed bed adjusting screws limit my total Z height to about 145mm. Not sure I will ever need that much height. If I do I will get the SD3 then. 

I took a belt sander to mine so that they were not too tall!

thank for the new stl joosh. I've updated the wiki to point to the thingiverse link.