The rods are a standard length so I would have to make the machine taller, which make the Dibond more expensive as I would get less out of a sheet.
On the other hand homing towards the bed simply doesn’t work unless the X or Y travel allows the nozzle to be past the edge of it. Again that would require the machine to be bigger.
I have never managed to print PLA on cold glass so I always use a heated bed.
actually the machine would not have to be any taller to do this, simply increase the height of the nut relative to the rod. I.E the top of the linear bearing and nut are about the same now, if you increase the height 5-10 mm(edit: of the nut relative to the bearing ) when the printer hit the top it would unthread.
The printrbot simple does not move outside of the print area, but it homes at the bottom. The way you handle this is to over thread the adjustable screw to its deepest setting then slowly lower the head while homing, when a feeler gauge barely fits it is perfect. much like your current method you make it miss until you have it perfect.
The problem is if the nozzle has any cold plastic attached to it then it can’t get to zero so can’t trigger a switch at 0. That would mean you would need to have Z =0 slightly above the bed which makes no sense to me.
or heat then zero, where zeroing at the bottom doesn’t make sense to you, zeroing at the top does have some negative aspects as well, and to me these negatives out way the positives. but the beauty of opensource is that it is easy to make those changes
If you heat at the top the nozzle oozes and then you need to re-prime it and wipe it. My ooze free unattended start procedure requires it to heat at the bottom: http://hydraraptor.blogspot.co.uk/2012/04/ooze-free-unattended-start.html.
The way I operate my machines there are no downsides to homing at the top, only advantages.
@nop_head Maybe i will come to agree, bed leveling with the z home at the top is not very fun however.
Yeah, i don’t know how you live with the z home at the top. i have yet to get a good print out of this setup due to z height calibration issues. the bed is level. I know they are completely different, but i have never had this type of issue on the simple i am running.
Are you following the instructions in the manual for bed levelling and Z calibration? What issues are you having, it should be straight forward?
The first print worked great, now the head is dragging again. I did check to make sure it is moving the proper about in the z direction.I don’t know how it is out of z cal, but it is.
@nop_head I think I am going to flip it anyway, there is no benefit the way I do printing. Modifying the g code so the travel time is useful would work fine if you print the same gcode over and over, I almost never print the same object twice. Forked the Mendel 90 repo and will modify the z parts to work without potential damage and allow for z at the bottom. It would not require any additional parts as the stepper Screws should be long enough to make this work. I understand how this could work, but the its like Porsche putting the motor in the back of the 911, it can work and there are some benefits, but it brings in other problems.
I don’t modify the gcode. I configure the slicer to have the correct start sequence so it works exactly the same for one off parts. My print procedure is switch machine on, select file, print, go away and leave it. When it has finished I remove the object and clean the bed while the axis is at the top. It is then ready to print again. It doesn’t get any quicker or easer than that. With that work flow there really are no downsides to homing at the top.
Except bed leveling and calibration. I feel like it is a solution looking for a problem.
It does take 3-5 minutes to change the Z height using this method, It takes 2 seconds to change it using the standard method.
Also if for some reason there is a short on the limit switch, you are intentionally running it into the top. Potentially damaging your z axis, i would argue that with the the leads on the switch being upright it is quite possible that a screw or something short out these pins.