Build table calibration experiment

Successful prints based on Model construction, supports, material selection & printer settings.
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Robert Howle
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Build table calibration experiment

Post#1 » Sat Jan 11, 2014 4:41 pm

Have a solid steel bench block that measures 2.25 inches x 2.25 inches x.75 inches and weighs 570 grams. I tested the pressure I usually use in the center of the build table with my hand on a large flat scale. The pressure, best approximation is between 700 and 1000 grams of downward force. This block slides right on top of the build table. This will eliminate variations in pressure at the corners, etc. Will be using it on my next calibration. Will let everyone know if this is enough pressure to assure parallel position of the table. This would eliminate guessing about the amount of pressure u need when performing the calibration and also eliminate uneven and inconsistent pressures. These blocks are available from all jewelry tool suppliers. They run about 15 dollars. I'm sure any piece of scrap steel that is not to tall, or too heavy, (I think there is a limit to the weight that should be used). As long as it fits on the top of the build table and is easy to center. My idea is this or something like it will give us a standard to work with and eliminate the variations in technique that I think maybe causing problems for some users.

Any feedback is welcome.

Robert
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cl2635
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Build table calibration experiment

Post#2 » Sat Jan 11, 2014 5:00 pm

I think it all depends on your PDMS application... if the PDMS surface is extremely flat, you don't even need to apply any pressure. I just hold the 4 corners with four of my fingers to make sure they're all touching the floor.. no pressure whatsoever. Applying pressure seems to jam my motor during the first VAT cycle.

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Robert Howle
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Build table calibration experiment

Post#3 » Sat Jan 11, 2014 5:19 pm

Never had a jammed motor so I wouldn't know about that. Just trying to find a way to standardize some of the procedures that seem to be causing problems for some users. I did assume in my post that the user can mix and pour and cure a proper PDMS layer. Prob should have mentioned that that step is also critical.

This is not for users like yourself that are not having issues, it's for the others that are having problems with technique. Not all users have the same level of dexterity as others. I also assert that the table itself which weighs approx. 60 grams does put some pressure on the PDMS along with whatever added pressure your fingers add. The weight I am going to use may be heavier than is necessary, I don't know yet. Again I am only trying to help users that are having issues. Table calibration, z axis binding, and proper PDMS replacement are 3 of the main ones I see on the forum. Anything that helps to standardize a procedure just makes helping diagnose problems easier.
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form
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Build table calibration experiment

Post#4 » Sat Jan 11, 2014 7:51 pm

Quote "Anything that helps to standardize a procedure just makes helping diagnose problems easier"

Absolutely agree with this.
Reducing variables is the quickest way to consistent results and this is one of the ways (providing it works).

Good of you to do this Robert. These are the sorts of things that make this a very good forum to belong to.

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tim.yoshi
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Build table calibration experiment

Post#5 » Mon Jan 13, 2014 7:22 am

awesome idea. I'll try it next time, if I'll find such a block :)
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akgold
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Build table calibration experiment

Post#6 » Mon Jan 13, 2014 1:15 pm

This is very crude and quick I just drew something that would give you an idea in matrix.
I figured I read enough about the failures and accomplishments I thought I could just go with the flow and print one right off.
Wrong!!
I spent a good part of Friday just focusing the print in 50. Figured if I am going to start printing now I might as well start where I want to be. Using cherry red alone. guess I need to get a bottle of the other and do the 1:1 mix I have yet to get anymore than the base and some supports up to about .5 mm high much like others are running into. I swear the z is not moving up. seems like the vat just moves back and forth.

anyways here is what I am perusing later as a downward pressure for the build table it is a quick crude matrix model on a picture of a table. but you get the idea. have one on each side using two fingers to just move levers towards the center thus putting down pressure on the table evenly in the center and the cantilever on the bottom is opposite each other so you just need two fingers then tighten screws, going to change those to thumb screws as well.

I am using the brand new vat that came with the unasssembled machine I have only removed the vat 3 times and already there are cracks that formed on the ends where the screws go to batten it down. I only tightened them very lightly enough to hold in place no more but what I noticed is I was putting downward pressure on the table to make sure it is flat that I could see the vat flexing down to the surface of the plate it is on as it is not exactly flat. there is inconsistency in either the plate it sets on or the vat itself is slightly warped. the vat came to me with the PDM already on it. I haven't exposed it to any undo heat but I would think after reading the fast curing in ovens that this too would affect the plastic and warp it as well.
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Robert Howle
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Build table calibration experiment

Post#7 » Wed Jan 22, 2014 9:10 am

I tried the 2.5 inch x 2.5inch by 3/4 inch steel block as a weight in the middle of the build table so I did not have to press at all. The calibration was dead on and I am printing. This removes the problem of having only one hand free and what ever dexterity problems might exist. Even though the block weighs 500 grams that is spread out over more than 14 sq inches. around 30 grams per sq inch. Im sure a lighter weight will work. This was only done as an exercise to eliminate the manual leveling (making parallel to build table) technique. To give somewhat of a standard that would eliminate human error. This is also assuming that PDMS coating is done correctly. The whole purpose is even pressure across the entire build table. No guessing and not slipping (tilting). Remove the block after first time screws are tightened, then remove from PDMS and do final tightening. There is over time a buildup of resin on the build table screws that may cause the table not to "float" as loosely as in the cleaner assembly. The added weight also helps with this. I had one assembly I had to take apart and clean the screw threads and tapped openings.

Suggested for newbs to eliminate one possible reason for no first layers sticking. Table not parallel to PDMS.

This also made the turning of the screws much easier because now u have two hands free at all times. I for one am going to do it each time I calibrate because I want consistent repeatable pressure with regards to the table and PDMS contact.
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Robert Howle
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Build table calibration experiment

Post#8 » Wed Jan 22, 2014 9:13 am

Some pics
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Robert Howle
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Build table calibration experiment

Post#9 » Wed Jan 22, 2014 9:15 am

Does it make sense now. I slide it in after the calibration step that lowers to the PDMS (screws loose) before the first tightening. I just didn't want to drop it into the vat. I'm sure u can add it after u put in the thumb screw securing it to the Z axis arm (screws loose).

Jewelers bench block all suppliers should have them. Also scrap steel. Be careful of the thickness this is 3/4 of an inch.
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zanderscreations
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Build table calibration experiment

Post#10 » Wed Jan 22, 2014 7:43 pm

hmm I am not sure i FULLY understand the issue really, which may explain why some of my prints have odd problems.... maybe something i havent noticed yet...

So instead of like in the calibration steps it sais to loosen the 4 screws so when the build platform hits the PDMS it pushes the black thing down towards the red platform as far as the Z goes down, this block keeps the black part all the way extended or at least evenly?(im bad with words sorry haha)
this makes sure the black part and red platform are even with eachother yes?

I always just let the platform push down the black part as far as it would go then I tighten it, I didnt know you should apply pressure i was afraid of it breaking the VAT or causing other problems with PDMS or something.

Would you do this if you have trouble leveling the VAT when applying PDMS? I had to build a box with leveling screws and some lights for heat on mine. It works pretty good but is a pain to level.

I should have one of those blocks somewhere in my house

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Robert Howle
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Build table calibration experiment

Post#11 » Thu Jan 30, 2014 10:03 am

Have done 4 calibrations with the block to give even slight pressure and all have been good. I will continue to use the block so that the pressure on the PDMS is consistent. This will, at the very least, eliminate one variable when it comes to calibrating the build table. I really do enjoy the change of being able to use both hands when tightening the screws. Still wish those screws were thumb screws so didn't need the allen wrench.

Robert
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perpetual_dreamer
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Build table calibration experiment

Post#12 » Thu Jan 30, 2014 10:10 am

^ yeah.. i think the build table calibration is one of the hardest tasks on the B9 - handling the allen wrench and trying to apply even pressure using hands, one can't be certain if it was calibrated properly until they've run a print so any process to ease it welcome ^^

KNSCi
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Build table calibration experiment

Post#13 » Thu Jan 30, 2014 6:52 pm

I'm wondering is table calibration is the issue with my Cherry attempts washing away on the first layer. Today I put in a fresh vat and pushed down with some pressure before tightening the table screws, printing coming up after I check some other posts here.
Is there a spring and locking lever device of some sort, lets say conceptually like vise-grip pliers, that could be applied to this? something where spring tension is applied to lock in a consistent pressure, that would accommodate varying pdms heights? I'm not a mechanical engineer, just an idea...
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Robert Howle
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Build table calibration experiment

Post#14 » Thu Jan 30, 2014 7:06 pm

Just put a weight on it for now, u will get consistent results.
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perpetual_dreamer
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Build table calibration experiment

Post#15 » Thu Jan 30, 2014 9:42 pm

KNSCI - if your PDMS was applied properly and flat, you do not need to put any pressure on your bulidtable, just make sure the 4 corners are sitting on the PDMS well. If your PDMS is uneven, then you will likely need to apply some pressure to make sure its sitting flat on PDMS.

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