One other thing I was going to do along with that mod is cut the lead screws short enough so that there's no chance that the hot end could ever bang into them if it was moving about.

 

I meant to say that too! If anyone else does this mod they should either add like 50mm to the leg height or be prepared to cut the lead screws shorter. Carl's measurements give you plenty of room for a variety of hotends and carriages on a regular build (where they're out of the way) but the extra length can definitely ruin your day with them out in the "playing field" like that. I've already slammed my hotend to a lead screw at 250mm/s and it left a gouge on the fan housing. I've been trying to decide if I wanted to get two more pieces of extrusion and replace the legs with longer or just cut the screws but I'm pretty sure I'll just cut em.

 

I just planned on cutting my lead screws down from the start, no need to re-do the legs

 

I wanted a Hall effect endstop for my Z axis so I made one that is a little cube you can thread the wiring into and clamp down an A3144 unipolar hall effect sensor. The sensors are like 25 cents each from China, or as much as 70 cents from Amazon prime. They're not supposed to work on 3.3V which the Smoothieboard puts out on its endstop lines, but it does. I can just move the power to a 5V pin if I feel ambitious later. There's no cool LED though.



I'm having a hoot with this printer. The two Z axes are incredibly difficult to keep level. It sort of worked but then I put some super lube on the lead screws and now it is right f*#$ed. The lead screw nuts now don't have enough friction to hold the bed in place when the stepper current is off so one of the two sides ends up slipping down. Even if they don't slip, the slightest bed pressure (such as trying to remove a print) will trigger it. I had them positioned 220mm from the back of the printer (of 405mm arm length), although the majority of the weight was on the shorter half due to the weight of the bed. I pushed them back as far as they would go until they hit the power supply, 160mm from the back extrusion. At this point there was slightly more friction and they'd pretend to hold a little longer before slipping.

I'm going to give it one more try, moving them as far back as they can go without hitting the corner brackets and moving the power supply to the other side of the bar, but I've given up for today. It might work better with the OpenBuilds nut block, but they were out of stock when I ordered. This brass lead screw flanged nut has some play in it. I'm not sure if that's how lead screw nuts are normally as this is my first build with them.

 

Thanks for the update, I think I might have the same lead screws, if I hold one vertically with the brass nut at the top it will spiral down the screw via gravity. Ive considered pinching the brass nut to make it slightly oval.

 

Exactly how mine are too. I did come up with a completely inelegant temporary solution, which is to take a 2lb sack of bolts and tie it to a piece of fishing line, tied to the Z bar and thrown over the top bar. The boltsack acts as a counterweight and is enough to prevent the bed from easily slipping. I'm looking on eBay now for a piece of steel remnant that I can use to build a slightly better solution. I figure a 1.25" round steel bar weighs about 4.1lbs which would counteract most of the bed weight. I have some thin stainless cable in the garage from another project I can loop over the top on a pair of V-groove bearings.

Looking forward I'll probably now replace the dual Z direct drive system with a single Z motor and a belt sort of like @adamcooks Triple-C build, except with just two lead screws. That way I'd really have to go out of my way to get them out of sync. I can get 8mm bore 40T GT2 pulleys for the screws and a 5mm bore 20T GT2 pulley for the motor, which would give me a 2:1 gearing so the motor wouldn't have to work so hard and I'd get a nice even 0.02mm per full step. Can anyone see a reason why this would be a bad idea?

 

For what its worth, my build platform ain't goin' nowhere on its own accord: It spins freely when the steppers are idle (I can adjust it by hand), but not enough to actually have it travel down under its own mass. I lubed the leads-crews with the remainder of the lithium grease that came with my makerbot.

 

I didn't try moving my steppers back to Carl's original position. I didn't have the tee nuts loaded in the Z bar for it and I really didn't want to take everything apart to get them in there. Maybe that's the secret, having them attached to the Z bar ties them together more rigidly? When they steppers are out on the arms, the arm can have a little flex to it that allows the weight to be unevenly distributed and one just moves a bit. The arm on that side lowers a bit, only a portion of which is transferred as torsion to the Z bar (because there's a bit of flex at the arm joint), and only a portion of that is transferred to the opposing arm for the same reason. The whole thing sort of twists slightly.

If they're both attached to the Z bar, they only one can be lower than the other is if the Z bar tilts left or right. The wheels in the V-rail do a good job of preventing that from happening so they there's no slip.

At least that's what I'm thinking must be going on. I'd rather not attach the motors a the Z bar because with the weight of the block of aluminum bed, the whole thing can bounce like a diving board (not as flexible, but in that manner) and I'd be concerned about it moving up and down tiny amounts while printing at high speeds as the inertia of the print head shakes the whole structure. The 2lb bag-of-bolts counterweight I have on there currently seems to be working pretty well so far, but I will be upgrading that to a more permanent solution with a heavy steel rod and some V-groove bearings over the top.

I think like Carl's said, making your own problems and solving them is half the fun of building a printer!

 

I am experiencing some bounce... I'm just getting started with this thing so I can't say yet how bad it is. Once thing I've been thinking about is move one of the leads-screws to the middle of the back, and the other to the front of the bed. This seems like a great solution... we'll see if I get that far

 

Mine is a 3 screw setup and it is not too hard to rock the single screw side but it is stable under operating conditions. I only have a single wheel at each of the 4 corners. I would be very leery of just 2 screws without more wheels on each corner or a smooth rod and linear bearing arrangement to keep it from rocking. OH the thought of that is making Carl cringe. But that also asks for binding issues to exhibit themselves.

As far as the pulleys go, mine is running well (after I got it aligned correctly) on 4 36T pulleys on motor and screws, but I can see and advantage to a 2:1 gearing. The Z motor doesn't work very hard anyway since it is one small step at a time - unless u home from full down. Then, I also have 76 oz-in motors.

 

Thanks, @AK Eric and @ruggb for the input on your designs. Everyone is so friendly and collaborative in this thread, it definitely helps.

Those 1-start screws would probably have been the best to start with for the simplest design, not so much for the torque but because the angle of the thread would divert the downward force enough to prevent them from auto-turning. I think I'm going to prefer having both lead screws linked though, because once they're locked together at equal heights, they'll stay that way forever. My current i3, one side of the Z very slowly gets out of whack. Like on the order of 0.01mm per 4 hours of print time so every few days I have to grab the motor and give it a little turn to keep it at the same height. I'm hoping with this new C-Bot that I'll never have to do this again-- that things that are level will stay that way until there's a disaster.

My belt loops (got a couple sizes) and GT2 gears are coming from robotdigg in China so I guess I'm going to be quiet for the a few weeks. Thanks for the help, guys!

 

Does anyone have a sketchup or an stl model file of a v1.2 endstop switch?

 

See if this helps.
I've converted the Endstop Switch to .stl
Was taken from here --> Gadgets3D Starter Pack RAMPS 1.4 - Elettronics for 3D Printers

Cheers

 

I know there are a few prusa i3's around with a belt coupled a axis.

Wow, been away for a few weeks switching sides of the country and quite a few new printers popping up. Did finally get my shop setup, made the mistake of modifying my tempered glass build plate. I found out that tempered glass explodes with tremendous force.

 

Thanks for the upload of the endstop files!

I couldn't resist doing a preliminary dry fit build while I wait for my MrMetric hardware to arrive. I didn't have a banana for scale so I used an egg. Going with an 8"x12" bed with 12" build height. Parts are being printed on a Robo3D.


For anyone looking for a good cutting method for the rails I had some great success with this $25 blade, it gave perfect burr free clean cuts of the v-slot with a miter saw:
http://www.amazon.com/Concord-Blade...=1436882538&sr=8-3&keywords=non+ferrous+blade

 

8mm lead screws

 

Yeah lookin' good @trublu832! I linked the same blade a couple of pages ago, except the 80 tooth version which was $1.50 cheaper at the time. 80 teeth was still sufficient for me to cut without needing any cleanup on the edges of the parts, and I cut through all 4x 2040 legs at the same time no problem.

I am still waiting on my belts and GT2 gears, but my bed heater finally showed up. It is that 120V 750W Keenovo silicone heater with integrated 100K thermistor. For reference it heats up my aluminum build plate (12 x 12 x 1/4, 3.5lbs) from 25C to 100C in under 3 minutes. I measured the temperature at the top and it lags by about 5-10C, but in under 5 minutes it is fully and evenly heated edge to edge. To maintain the temp the PWM runs at ~15% power (40 of 255, or 117W). The cheapo "fotek" 30A SSR I had removed from another project doesn't even get warm during the heatup, but it is clamped to the extrusion so it is effectively heatsunk if it does generate any heat.

 

What are the dimensions for the bearings that go in the v wheels (625ZZ bearings)? It looks like the OD needs to be 10mm to fit in the wheels and ID has to be 5mm to fit on the M5 bolts, but I can't find any bearings with these dimensions. Am I doing something wrong?

 

5mm ID 10mm OD 4mm thick is what I'm using, I bought the wheels and bearings separate. Here are the bearings I used http://www.ebay.com/itm/291206716216

 

I'm making progress on my build slowly but surely. I'm now collecting the electronics as i'm nearly ready to start installing it all.
Question:
Fans - what type/sizes, how many & for what purposes are you all using?
Any guidelines on airflow/cfm?

 

Just an update: First 'really big' print. 20" tall, 11" diameter, just over 3 hours with the 1mm Volcano nozzle @ 500 micron.

http://www.akeric.com/blog/?p=3300
Very happy withe the printer so far