I'm puzzled...

Summary:

How do I adjust my build plate for a glass build surface mounted on top... And make it permanent? No matter what I've tried, the aluminum build plate refuses to lower the 1/8" required to allow the glass plate to rest on top.

I'm puzzled...

Bruce Kinsey 24 Aug 2012 01:19

I've read about the joys of using PLA and heated glass build plates (the one that comes with the Replicator is only rough tooled. I've flattened it is much as I can, but the uneveness is more work than I want to put into it.

Enter plate glass. I'm all set to start printing with a sheet of glass mounted to the top surface of my aluminum build plate, with a layer of Kapton between. Glass is an excellent conductor of heat, so the inconsistent temperature of the aluminum should even out as it travels through the glass.

That requires me to re-set the z axis zero point.

The problem I'm having is; no matter what I've changed in ReplicatorG or the control panel, the changes never make it to the print. If I were to leave the glass in, the heads would go crashing into it. What am I doing wrong? How do I make changes to the z axis that will be permanent?

I suspect I'm missing something basic and once I know what it is, I'll be able to slap my forehead and get back to printing neat stuff… In PLA.

Thanx

Last edited on 24 Aug 2012 03:04 by Bruce Kinsey Show more

Re: I'm puzzled...

Jetguy 24 Aug 2012 04:55

re-run the calibration script in the bot. The motherboard stores the offsets. Basically we use the method of the far endstop and then count back (read the gcode, that's what the recall the offsets does). Since it's your start gcode, nothing you do in rep-g other than running the calibration script will fix it.
http://www.makerbot.com/docs/replicator/fre/

I know it says level but it also does the height.

Next, glass works great for PLA, glass has not worked as well for ABS. ABS in general has a massive contraction problem when it cools, thus for big builds, it's not always the best choice. PLA is a much better plastic for large object and for it, blue painters tape on top of glass is best.

Last edited on 24 Aug 2012 11:51 by Jetguy Show more

Re: I'm puzzled...

Bruce Kinsey 24 Aug 2012 13:24

Thanks Jetguy.

I don't think I can slap my forehead on that. Being lazy, I'll have to come up with a work-around. It may be as simple as a mechanical spacer for the endstop. Pull it out for ABS, push it in for PLA.

I'll explore the back side of the machine, come up with as elegant a solution as possible, test it out and post my results on Thingiverse. My bed is all laid out for the glass, which I cut, polished and set up yesterday with corner blocks bolted around the OEM bed (notched for the heads in the home position for when the glass is not being used, of course). So with the exception of that z axis issue, I'm all ready to print. I have a 4x Dial Tool Indicator permanently mounted to the extrusion truck, so I can adjust the height on the fly while the machine is printing (the aluminum plate really is pretty bad and leveling it is hit or miss). When I have half a day free, I'll pull it off again and work on it more. Once it's flat, and if I'm lucky, one leveling might handle both setups.

Re: I'm puzzled...

Jetguy 24 Aug 2012 13:38

Update, I don't have a replicator so I'm going off of what I know about the firmware structure and solid assumptions from past reading when the machine came out. I looked at getting one an decided to pass it up for the price.

SO do yourself a favor and connect to the bot with Rep-g first, then open "Onboard Preferences" under the machine menu. THe homing tab has the offsets so write them down.
This way, you have the X and Y offsets and a ballpark idea of what Z was.

Then, in replicator-G under the file menu>scripts> calibration>THe Replicator Calibration code.

Open it, and run it.
Basically, just like the TOM, you move the heads to the center of the build platform, then use the card to put the nozzles just above the surface. The script writes the offsets to the motherboard.

Point being, go back and check the x and Y offsets and see how far they are off from the ones originally. You can just make them the original number and hit commit changes.

Understand that for z it homes far away and then counts distance back, so a a taller bed should be a lower number, the exact thickness of the glass.

Last edited on 24 Aug 2012 13:40 by Jetguy Show more

Re: I'm puzzled...

Jetguy 24 Aug 2012 13:42

(* This script will guide you through *)
(* calibrating the start position on *)
(* your Makerbot Replicator *)
G21 (Use Millimeters as Units)
G90 (Absolute Positioning)
M18 (Disable stepper motors)
M70 P10 (Move carriage to center of plate)
M01 (Move the extruder carriage until it lies in the dead center of the build plate, then press yes to continue.)
M70 P10 (Check distance from nozzle to plate)
M01 (Check the distance between the extruder nozzles and the build plate. They should be about one business card thickness apart. )
G92 X0 Y0 Z0 A0 B0 (Declare the current position to be (0,0,0,0,0))
G161 Z F1000 (Home Z axis minimum; go until reaching the end stop.)
(G92 Z0.0 (Set Z to 0)
G162 X Y F4000 (Home X and Y axis maximum; go until reaching the end stop.)
M131 X Y (record the current coordinates to the motherboard)
M70 P10 (Calibration complete)
M01 (Your coordinates are now saved! To adjust them, use the 'Machine Onboard Preferences' dialog in the Machine menu to change the Axis Offsets.)

Re: I'm puzzled...

Bruce Kinsey 26 Aug 2012 17:04

Hi Jetguy:

Thanks for all the information. Unfortunately, it's all way too complicated for me to remember and far too much work for my lazy attitude to accept.

I've created a solution which you may find interesting:

thingiverse 29214 (I'd put the link in, but I can't because, evidently I'm a "low karma" user… What the hell is a low karma user?)

Anyway, it works perfectly.

If my experiment with PLA works out, I'll most likely stop using the aluminum surface all together. Blue tape holds well to glass and ABS slurry spread on top holds ABS down with no warping and if what you say is true, then PLA will be my material of choice.

Check out my work-around and leave a comment.

Thanks for your help. I hope my solution is able to help others who aren't that proficient with code either.

Re: I'm puzzled...

Jetguy 27 Aug 2012 05:08

It's not about typing code, it's built into the replicator-g application. Just open it and hit print. It's there for a reason.

Nothing technically wrong with doing it mechanically, but I being that it's stored in the eprom, you MIGHT want to know how to set it when the day a new firmware comes down and wipes it out. The you have no choice, there's no offest to adjust too with your mechanical system you MUST run the script. Better to learn now, and know how it works than be in the dark on a day when you cannot print.

Thanks for the alternate fix. It is nice.

Re: I'm puzzled...

dnewman 07 Sep 2012 20:48

Another way of dealing with this might be to use SF's Bottom plugin. For the Replicator & SF 50, Bottom is off by default. That "Altitude (mm)" field is a measurement which SF adds to the initial starting altitude in the gcode. So, instead of starting at a z-height of 0.15 mm the print will start at an altitude of 0.15 + alt where "alt" is the starting altitude. So, if your plate is 2.0 mm thick, you could enable the Bottom plugin and set the starting altitude to 2.0mm.

Dan