D-Bot 3D Printer

[Gina]

I have mine held together with 3D printed framing clips.

[Stub Mandrel]

@tekkydave I noticed this in your sig:

DIY Bahtinov mask (Cardboard based ° )

Try printing this for your Nexstar, you'll need two M6 nylon screws to poke through it as supports.

130P-DS mask.STL

[tekkydave]

2 hours ago, Stub Mandrel said:

@tekkydave I noticed this in your sig:

DIY Bahtinov mask (Cardboard based ° )

Try printing this for your Nexstar, you'll need two M6 nylon screws to poke through it as supports.

130P-DS mask.STL

Thanks for that

To be honest I haven't even touched my scope for a couple of years now <shame>. I seem to have been completely taken over by the 3D printer bug.

[Stub Mandrel]

LOL! print yourself some accessories and get an excuse to combine the two interests.

[Gina]

My 3D printer bug has just been taken over by an Ha solar telescope   But with my grasshopper mind who knows what I shall feel like doing tomorrow

[tekkydave]

I have drilled the mounting holes in the bed plate and countersunk them so a glass plate will go over the top. Today I attached the heat pad to the plate and fitted it to the printer. I cut some PTFE spacers from some bowden tube to keep the metal mounting screws and springs away from the cut corners of the heat pad. I'm sure the heater wires are still about 5mm from the cut edge but you can't take any chances with mains voltages.

I needed to adjust the positions of the z motors, bed mountings and z carriage 'arms' to accomodate the larger bed. I also moved the z motors forward as the centre of gravity of the combined bed assembly had moved forward significantly. I should have removed the entire assembly from the printer and found the balance point manually but I think I have it in approximately the right place. I intend to upgrade to three lead screws with a single motor at some stage so it will all get rearranged at that point anyway.

I have connected the bed thermistor up to the RAMPS and updated the necessary Marlin configuration, moved the endstops etc.

Next step is to wire up the heat pad to 220V via the SSR. I will also be ensuring the metal parts are all grounded and the bed supply is also fused.

 

[tekkydave]

I've also ordered a piece of 300x300mm borosilicate glass from Ooznest to give a nice build surface.

[Stub Mandrel]

Looks smashing Dave.

[tekkydave]

I have temporarily connected up the heat pad via the SSR to test it. The bed now heats from room temp (21C) to 65C in about 30 seconds. Should be fast enough . No picture as I dont want to encourage exposed mains voltages 

I did add a grounding point to the metal part of the bed for safety.

 

The glass arrived today so I installed that and did a PID tune for the full shebang. I discovered that the thermistor types used in a lot of these beds needs to be set up as type 75 in Marlin

#define TEMP_SENSOR_BED	75

One thing that is now happening is due to the weight of the bed it now sinks down the leadscrews under its own weight when the motor power is off! Maybe some anti-backlash nuts might help, I'm not sure.

 

Edited September 2, 2017 by tekkydave

[Chriske]

12 hours ago, tekkydave said:

 

I did add a grounding point to the metal part of the bed for safety.

 

 

 

 

 

Did it to, good work..!

[Stub Mandrel]

28 minutes ago, tekkydave said:

One thing that is now happening is due to the weight of the bed it now sinks down the leadscrews under its own weight when the motor power is off! Maybe some anti-backlash nuts might help, I'm not sure.

If you fit ballscrews it will drop right down with the power off, on machine tools they are generally only used for CNC where a motor gold the position.

Anti-backlash would be pretty pointless as the weight you have will take up any backlash (TBH they are pointless on any 3D printer as the carriage only moves one way...) A few 3D printer things are snake oil, like bearings on top of z-axis screws, although I fitted a pair just to look neat...

[tekkydave]

Yes, I thought ABL would not be relevant. Maybe some kind of braking mechanism is needed or keep the z motors energised. In a normal printing situation its not an issue as they are permanently energised during the print.

[Stub Mandrel]

I can see dropping being a PITA, perhaps a counterweight on a wire/string over a pulley? Works very well for milling machines and unlike various combinations of springs and levers it gives a constant force (just doesn't feel as high-tech...).

[tekkydave]

I've ordered some single-start T8 lead screws. These will have a pitch and lead of 1mm as opposed to the 8mm lead my current ones have. This should stop the sagging (hopefully). I've ordered 3 so I can upgrade to a triple drive system at some point.

[Stub Mandrel]

13 hours ago, tekkydave said:

I've ordered some single-start T8 lead screws. These will have a pitch and lead of 1mm as opposed to the 8mm lead my current ones have. This should stop the sagging (hopefully). I've ordered 3 so I can upgrade to a triple drive system at some point.

Certainly should. It will also give you much better z-axis resolution and precision and load the motors much less, at the expense of speed.

[Gina]

Sounds good Dave   I never did think those 4-start ones were suitable - too coarse.  Well done on finding single start ones - when I looked I couldn't find any.  I think using three would be a good idea.  Maintaining the bed at the same level throughout the Z range is difficult with wheels and rails, even with these superb V-slot rails and wheels though I have to say I have conquered it with my Titan printer.  But for my new printers I'm going to use three cords/strings for the Z axis and a simplified guiding system on two V-slot rails, one either side of the bed.  These then only have to guide the bed in the XY plane, the height and levelness being taken care of by the cords.

[tekkydave]

The new leadscrews arrived this p.m. They look pretty good quality with nicely finished ends.

These are 8mm dia, pitch 1mm, lead 1mm, single start. For some reason I ordered 500mm length, but I need 400mm for the D-Bot. I'm not sure how easy they will be to cut. I'll have a go with a hacksaw or maybe my angle grinder. The narrowest metal-cutting disc I have is 2.8mm. Maybe a 1mm would be better.

[Gina]

They look nice   I'm sticking with cord for my printers.  Just finished the 4 cord drive on my "GinaRep Mini" printer.

[tekkydave]

I've also been busy designing and printing an enclosure for the IEC C14 inlet and Solid State Relay.

The plan is to keep all the mains voltage wiring together and separate from the rest. A mains feed from the box will feed the power supply. The SSR will have 12V input from the RAMPS and mains output to the silicone heat pad.

 

[tekkydave]

3 minutes ago, Gina said:

They look nice   I'm sticking with cord for my printers.  Just finished the 4 cord drive on my "GinaRep Mini" printer.

Ooo, another printer topic. I'll pop across and read up so far

 

[tekkydave]

I took a trip to B&Q the other day and picked up some 1mm thick discs for my angle grinder. Today I shortened the new lead screws to 410mm. I ground an approximate 45deg finish on the cut ends to avoid any nasty burrs. I didn't bother trying to clear the threads as the cut ends will be in the flexible couplings. I fitted them to the D-Bot and they work very well. The bed doesn't back-drive the motors now and move down under it's own weight

I temporarily changed the Z steps_per_mm to 3200 using M92 for testing:

M92 Z3200

I need to make this permanent in the firmware and also adjust some of the speeds as the movement is far too fast for these screws, especially the Z homing speed which tends to stall the motors.

I have a 3rd screw and a spare motor so I'll be trying to add it in at some point to give better support to the heavy bed.

 

[Dave_D]

must be some weight to the print bed for it to do that...  :|

[Dr_Ju_ju]

I was finding that the bed would 'droop' front to back and give some jerky movements. So I ordered another bed cross beam (as per the back one) and fitted it up with 3-way Delrin wheels etc. Stripped the whole lot down & made sure the bed framework ran true & 'clean' top to bottom, then with the motors re-connected & using Ooznest's anti-backlash nuts, I don't get the bed sinking unless I push down hard. 

[tekkydave]

Yes, I was considering doing that myself. The D-Bot is designed for light PCB style heated beds not the 6mm Ali like I'm using. The cantilever is not really up to holding the weight without a bit of droop. Some use 3 lead screws which is what I'll try first as it is easy to implement but I may end up going the way you have. I may do it as a general upgrade to 3-wheeled carriages all round.

[tekkydave]

12 hours ago, Dave_D said:

must be some weight to the print bed for it to do that...  :|

Yep. 300x300x6mm ecocast Ali adds a bit of weight. It's not too bad if you get it balanced but a bit fiddly. To be fair I used to get backdriving on my Prusa using the 4-start screws. They are not really suitable - 2 start would be a good compromise between speed and accuracy I think.