Saturday, 25 June 2011

The OverSized bed.

So i over sized my print area by increasing the length of the bed and rails. these ended up being 16mm mild steel rods that i center drilled M5 threads to the ends for mounting. i also cleaned the rails with emery paper to make the rails smoother..

 i then saw a mate that once mentioned he uses lots of plastic round off cuts, and soon i was in possession of  various pieces of 50mm round blocks. some 25mm round blocks and some 75mm blocks. i took the 25mm blocks and drilled a hole 16mm in the center of them then reamed them so they slid on the rails nice.. i made four of these bushes one for each corner of the bed.

the bed was a made by gluing with 5min epoxy these bushes to a piece of perspex that had the four M4 screws mounted in them for the sprint loaded adjusters. the glass bed then had some small perspex lugs made and glued to it.. these lugs had oversized holes and springs glued in place. the lugs were then held down with nuts and washers to allow me to square each corner.

 now this worked great was easy to adjust and was i was happy, now being an impatient  ass i wanted to make something print, as i failed to get the bed up to 110'c i tried the masking tape, this worked quiet well, up to about the 3hour of a 7 hour print of a 40mm cube! then i had to hold it inplace while it finished printing 

Tip: Don't try and print a 40mm cube as a first test, not @100% not @25%... it takes too long..

the result :-
 it has a rounded bottom where it rolled back and forth for hours...
the shorter one on the left was the result when the printer just stopped for an unknown reason.. this gave me hope to try again and got the big full cube out.. this has been the thorn in my side ever since.. all the problems i have had, i look at that sitting on the bench and think why wont it just do that again, at least it was something...

Oh the Glass only bed had a NASTY NASTY ring to it, my Y rails are screwed directly to the bench not actually attached to the A frame, so the bed moving back and forth created a nasty resonance to is, lucky my neighbors cant here it, thank god for double brick interior walls... being in that room made your head hurt.. 

So since this the bed has changed quite a lot.. i sh!ts with the glass only solution and decided to use some of the stepper motor's potential lets make a metal heatbed that will spread the heat evenly, as opposed to the spotty results of the glass only bed..

so i calls up a few mates and i now has  slab of aluminum  6mm thick 480mm x 380mm, on the way home i stop at bunnings hardware and buy me a hacksaw a small bench vice and various bits of aluminum and screws. 

i took the slab and cut some angle so run the length and 3 straps to hold them in place, this then supported the 10mm diameter springs that i found, they were a bit weak so i placed two there to support the weight of the slab. i then cut some PFTE blocks to keep the heat away from the bed itself. i then drilled four M4 holes one in each corner and locked 4 M4 bolts to the lower frame with nuts and loctite, dropped the springs and PFTE blocks over the top then the bed and finally two nuts on top.

this frame was then attached to the nylon bushes that ran on the rails, it was attached with hose clamps (turns out to be a very bad choice of macguyver technology) these worked well for a while, it was a little tight sliding back and forth so out with some oil to lube things up (castor oil from the hobby shop bought in little drip dispenser ), oiled up it ran nice.. so i then attached this to the lead screw  that ran between the two 16mm rails, the leadscrew had two nuts with a spring between them to reduce the backlash, these nuts were then attached to the center strap under the bed. i used spacer blocks to make up the height difference.. this worked  really nice it even cut the noise down by about 200% it was now bearable to be in that room while it was printing...

 the nylon bushes over time became really tight, i believe it was due to the oils and grease that i used to lube it up, that coupled with lots of heat and a hose clamp around it made the hole in the middle far far too tight on the rails. these had to go... see my post about roller bearing runners.

So i still haven't sorted out the heating, this was a problem i started armed with all the learnings i got from trying to heat the glass bed up that i just have far far too much thermal mass to heat up this slab of metal and a sheet of glass on top of that too!! so i visited my mate who works at a appliance repair shop and tells him my tale of woe with cooking resistors and my fingerprints off several times and he told me he has the solution for me... a 2400 Watt mains Grill element!.. Well my eyes light up when i walked into the room that has all the elements on the wall and started looking around and me being me i picked the worst one.. it was the only one they had, didn't know what it was from, where to get more etc etc, so he picked me the cheapest one they have as they sell these by the box load they will always be avail and would have only been $20 if i didn't know him :) yay... so off to jaycar to buy me a opto coupler and a triac and a little metal box to put it in, as i do i doubled the order expecting to fry at least one of these parts..  and i ended up making a nice little control box that could switch up a total of 2400 watts per channel that could be driven off a 5v logic signal and had it wired up to the heater element, mounted it all up on the desk and was ready to cook steaks at least.. this heated bed has better heat control than my stove ( they are on or off )....
this slab o aluminum is topped off with the same piece of glass that was my glass only bed.

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