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So, whilst working on another project (more to follow in a month or so) I nearly destroyed my Mendel printer by trying to print a part which was too high. Of course, this was the one time I wasn't in the garage keeping an eye on things and I came back to a twisted printer, over stressed belts and a huge mass of spagetti plastic. My first thought was a four letter word, my second was OK, how am I going to build the part I need? I then re-architected the part so I can split it in to 2, but this then just bugged me since I really didn't need much more height to be able to print my part in one.
So I did what any good engineer does (and what I also try to do !!) and looked to see if I could improve the Z height without having to do much work.
The solution was extremely simple, and suprised me that the original Mendal was not designed according to my idea. If you look at the Mendel Z travel the biggest issue is that the belt hits the frame and feed motor before anything else gets even close to the ends of their travel. If the frame M8 threaded bar is moved to the outside of the frame then about 50mm more clearance is available for the Z travel !!!
Not wanting to completely dismantle the printer I realized it would be possible to build extenders to move the M8 threaded bars on to the outside of the horizontal bars and would not even require different bars since the extenders would be parallel.
Read the entire instructions first, and check the pictures. Everything will become clear after that hopefully.
What I printed are four extenders clips (2 for the left and 2 for the right) which simply slip over the existing rear plastic brackets and can be glued in place allowing the M8 bar to be removed and re-inserted on the outside of the frame.
Again, being a lazy engineer (or efficient, you decide) I did not want to have to re-tune everything so I did actually buy a new M8 threaded bar from Home Depot and cut it so that I could clip, glue and set the new bars in place before removing the original ones, thus would not need to re-measure anything. Then simply removed the original bars. I recommend this since it was REALLY easy and everything remained perfectly aligned, plumb and square. You could optimize this a little by only buying enough bar for one side then as you populate each new support simply use the old bar for the next new support.
Once you have printed 4 extenders check that they fit snug over the existing brackets. then check that the M8 holes allow the threaded bar to be inserted without too much slack or stress. You do not want them slack but you do not want to have to force the bar through.
Note, you do not need to replace all 4 supports since it is the belt which causes the issue and it only exists on the back side.
Loosen the extruder mount brackets from the M8 bar and top frame mount and gently place the extruder on the build plate.
Next, bolt one of the extenders to one end of the bar with 2 washers and 2 bolts. Next, on the opposite end put a bolt, washer, extender, washer then bolt on but do not tighten them. Snap the 2 extenders over the upper and lower Mendel frame brackets on either the left or right side but towards the belt and make sure they are snug, straight and not twisted. Finger tighten the bolts around the loose extender so there is not forced distortion on the frame. Then with 2 sets of pliers, wrenches or whatever tighten both bolts at the same time so that the extender is not forced out of alignment with its natural position.
Now, pop everything off. If you have excessive M8 bar length cut it off. Alternatively you could have marked the bar length before assembling and cut it first. Your choice :-) After cutting check that everything snaps back in to place and is still aligned and straight. Apply a generous coating of gel based super glue to the inside edges of the extenders then carefully align both extenders with the upper and lower frame brackets before pushing them firmly back in to position. Do this in one motion since super glue has a tendancy to cure pretty quick once contact is made. You will not be able to move anything after about 3 seconds of contact!!! Don't glue your fingers to the frame, it makes printing difficult.
Next, loosen the bolts on the original M8 bar, then remove the bar.
Repeat the process for the opposite side.
Using the original plastic extruder mount bar clip re-attach the extruder to the new M8 bar. Note, the top mounting support will no longer fit but I don't think it is necessary. Try to make sure that the extruder is somewhat aligned with the new M8 bar and does not interfere with the new extended Z travel area. If it does simply adjust it and tighted the bar clamp so tht extruder does not move easily. (I will design a new upper clamp some day)
At this point you can now check your extended height.
If you really want to get the absolute max height you can also move the clamps that hold the Z drive motors to the threaded Z bar as far up on the threaded Z bar as possible whilst still clamping to the bar, then cut the excess rubber tube off the threaded bar, allowing the Z carriage to travel slightly further up before hitting the top.
After this procedure I managed to increase my build height from 92mm to 130mm, an increase of 40% !!!
There have been some recent changes to the Mendel printer frame and my printer is about 8 months old, so make sure you have a close look at your printer to make sure that this modification will work. Looking at the new model I don't think my update will help much since the carriage is now rotated and the belt is no longer the limitating factor for Z height.
Owners of the older model might also be interested in my filament cooling fan accesory.
Mendel 3D printer Z extender, get an extra 40% build height by SteveDC is licensed under the Creative Commons - Attribution - Share Alike license.
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