SoliForum - 3D Printing Community — SD4 - why does the bed move?

Re: SD4 - why does the bed move?

null@example.com (eflyguy) — Mon, 08 Sep 2014 01:00:07 +0000

I think a single additional z rod on the front would help a lot.

Re: SD4 - why does the bed move?

null@example.com (grob) — Sun, 07 Sep 2014 23:55:03 +0000

I had exactly the same - they hadn't loosened I think, they were like that when I got it. Drilling them out and replacing with bolts did help a lot. I'd recommend it to anyone if you notice the joints are loose as you describe; although a lot of disassembly is required to get the bed out to drill out those rivets.

There's still quite a lot of wobble in the flexing of the z rods that I'd like to get rid of!

Re: SD4 - why does the bed move?

null@example.com (slowjoe) — Fri, 05 Sep 2014 19:39:10 +0000

Hi, I have an SD3 and it bothered me that my bed had developed a lot of up/down and side to side wobble, but it seemed to print fine, so I never really bothered to look into it. Then one day when I had a day off and was looking for a project I decided to fiddle with it. I found that the pop rivets that attached the bed frame to the z-bolt frame had loosened up in the holes and were causing a lot of the wobble in the bed. I drilled all of the rivets through, removed them, and replaced them with cap screws with locking nuts and it made the connection much sturdier. I didn't realize how much the bed was sagging forward due to the egging out of the holes by the loose rivets until i tried a print and saw how much bed re-leveling I had to do to get it adjusted right again. I was very careful to cover up the area where I drilled so that no shavings got into anything. As for the Z stop screw, you can get a longer cap screw at any Hobby shop that sells R/C cars and planes.

Joe

Re: SD4 - why does the bed move?

null@example.com (grob) — Wed, 03 Sep 2014 02:59:32 +0000

eflyguy wrote:

Back to the bed shake - There's so much flex in the Z carriage bracket, but wouldn't another vertical guide rod on the front, like the two at the back, easily solve that?

That's my plan - people already seem to build things that run up and down the sides of the case, but I figured I could just redesign the y idler brackets to fit a vertical 8mm shaft, and do one on each side, with a brace that connects them to the middle of the front of the bed. Bottom end would be a printed spigot bolted to the bottom of the case (so I can adjust them to be parallel; don't trust my ability to spot a hole in the SM accurately enough! ).

Re: SD4 - why does the bed move?

null@example.com (eflyguy) — Wed, 03 Sep 2014 02:38:52 +0000

Sounds like I need to look at the firmware options. I'd like to get the mechanical side as good as practical first. Yes, it's x/y issues I'm talking about, and I have a digital dial indicator. I am printing the Lawsey carriage upgrades that uses the LM8 bearings, I've not seen the belt upgrade thread - might as well look at that while I'm rebuilding it.

Back to the bed shake - There's so much flex in the Z carriage bracket, but wouldn't another vertical guide rod on the front, like the two at the back, easily solve that?

Re: SD4 - why does the bed move?

null@example.com (grob) — Wed, 03 Sep 2014 00:43:22 +0000

If you can get your hands on a dial gauge, and put the lawsy/adrian firmware on the board (which has the hysteresis fix), you can measure backlash in the z axis and have the board compensate for it with M99 in your start code. This made a huge difference to my first couple of layers (mine dragged quite badly). I'd see it as one of the more effective solutions for z backlash - even given I'm a mechanical engineer and appreciate a good mechanical solution!

Re wobbling - yup, it's in the design, and it's pretty annoying... I've been meaning to stabilise the front of the bed for a while now, i'm pretty sure most of the ghosting on my prints is the bed moving. It's not affecting my overall accuracy by much though, it's just ugly in the wrong lighting!

Your distortion due to backlash is in the x-y right? You can consider the hysteresis fix method to improve this too if you don't want to get too crazy with the mechanical mods. I went all-out mechanically: bearings on all the driveshafts and bearing idlers, direct-drive y axis (motor sticks waaay out the left of the case), GT2 belts - the result is I can press skate bearings into a 22mm circular hole kind of perfectly (I haven't actually measured the residual backlash recently), but looking back I have a sinking feeling I could have got here just with a firmware tweak...

Re: SD4 - why does the bed move?

null@example.com (eflyguy) — Wed, 03 Sep 2014 00:13:24 +0000

Head is not banging the print and, even if it was, that would be a 1st-layer-only issue, wouldn't it? The bed wiggles all the time.

I'm also getting great prints now except for the little bit of distortion from backlash. I'm printing new carriage parts now, and looking for the quickest z-axis solution.

Re: SD4 - why does the bed move?

null@example.com (lueman) — Sun, 31 Aug 2014 20:56:44 +0000

I'm not sure what glass bed you added but mine is about 4mm high I just tightened my level screws a little without adjusting the z height limit switch. if your head is banging against the print you either haven't calibrated the height and/or your level is off. My procedure is to use a single edge razor & I take off the safety end so I have a very flat surface. A single edge razor is a precision instrument with a height of about 0.22 mm. I home my Z axis then adjust the back screw so the razor smoothly glides underneath, then I adjust the left & right front screws, I repeat the process just in case. Finally I set my slicr3 z offset to .19 this allows some give for the hot filament. but your adjustment depends on your desired extrusion width... I always get very accurate prints and very rarely have failed prints.

Re: SD4 - why does the bed move?

null@example.com (eflyguy) — Fri, 29 Aug 2014 21:03:56 +0000

Yeah, I changed that when I added the glass, that's why it's 'maxed out' and hitting the cutout in the case.

Have not seen the sig mandatory thread but added my info. Thx!

Re: SD4 - why does the bed move?

null@example.com (n2ri) — Fri, 29 Aug 2014 19:59:08 +0000

put your printer info in your signature like others (see mandatory signature topic) have to help get better replies. from other posts it seems you added a glass bed plate which requires mod to the Z switch adjuster (like done on SD2 & SD3). but dont tighten springs down tight as that is for allowing movement from extruder bumps or when removing prints etc. thats far as I can help with no SD4 exp

SD4 - why does the bed move?

null@example.com (eflyguy) — Fri, 29 Aug 2014 19:16:00 +0000

I know what causes it, but why isn't the bed more stable? That *has* to affect print quality?

Should I crank the adjustment screws down as much as possible to reduce the movement? I'm wary of that because my z-axis adjuster (on the back) is already contacting the case cutout, which means if I lower the bed on the carriage, the adjuster will need to go even higher (which it can't without cutting the case opening)..