Mhackney's Rostock Max

[dbarrans]

I had the very same thought last night, about using shorter spacers to lower the hot end, but it was to let me see the workpiece better during a print.

- dan

[mhackney]

Dan, that was one of the reasons I want to lower the nozzle too, it is tough to see under there!

[mhackney]

My new borosilicate glass is due to arrive from SeeMeCNC in a couple of days. So, I'm doing some prep work for it. The Onyx is a great heated bed but like all heated beds, it isn't perfect. I have been plagued by 2 problems.

1) The center is a lot hotter than the perimeter. Even after letting the bed warm up for extended time, there is a pronounced temperature gradient. Many heated beds have this issue. The nichrome bed I made for my H-1 especially since it has a fairly short coil of nichrome. I solved the even heat problem with an aluminum (1/16" on the H-1) plate between the heated bed and glass.

2) My Onyx bed warps at high temp. The center pops up because the edges are held in place and thermal expansion wins. This may have contributed to the demise of my original window glass plate. In any case, it makes it a bugger to get the first layer or even 2 right - especially on larger prints.

So, I am going to kill 2 problems with one aluminum plate! The idea is to fasten a 1/8" thick aluminum plate over the heated bed. I decided to go with thicker aluminum for its structural strength over the 1/16". Here's a picture ready to install:

[img]http://mhackney.zenfolio.com/img/s3/v7/ ... 7498-4.jpg[/img]

It is 12 3/16" diameter with a flat and cutout for the electrical connections at the back.

[img]http://mhackney.zenfolio.com/img/s8/v81 ... 4304-4.jpg[/img]

This cutout will also allow the full circle borosilicate plate to rest on top and not interfere with the electronics (I can bend the LED back out of the way).

I need to get some longer 4-40 flat head screws to mount through the aluminum, Onyx, melamine, and spacers!

[Eaglezsoar]

May I ask how you cut the aluminum so perfect?

[mhackney]

The outer perimeter was cut on my 12" metal bandsaw. I cut A LOT of metal so I'm pretty good at free handing! the cutout for the back was done on one of my milling machines by hand. It's pretty simple.

[cjdavis618]

Hey MHackney, your link from CNC zone led me here. Thanks for that.


I've got to get a table before my rostock gets here. Like a kid waiting for Santa with this kit .

Could you tell what the outer dimensions are for this thing? Didn't see it on the SeemeCNC specs page.

[mhackney]

The MAX is 17 1/2" diameter and 37 1/2" tall - this does not include the extruder / filament spool arm that hangs off the side.

The Onyx heated plate is about 12 1/8" diameter.

cheers,
Michael

[mhackney]

Well, this is stupid...

The "Oh Rats" part
When I was test fitting the aluminum sub-plate I had my Rostock connected to Repetier and plugged in. Nothing was on and the heaters were off. The aluminum contacted the electrical pad in the back and I got a little spark. So I immediately shut things down - I didn't realize I had it on actually.

Then when I hooked things up for a dry run I noticed the heated bed temp was 174°C! "That's not good" thought I and indeed it was not good. I measured the resistance of the thermistor and it was fine. I plugged the bed thermistor into the hot end jack and it was fine. I plugged the hot end thermistor into the heated bed jack and got an off the wall temp. So, it looks like I blew something on the RAMBo - probably the little capacitor. This is not a fused circuit.

The "Thank Heavens" part
The RAMBo has 4 heat control circuits. Two are for hotends and thermistors, one for the heated bed and there is an extra. So, a quick look at the RAMBo Development turned up the pin assignments. Pin 3 is the original pin assignment for the heated bed thermistor. Pin 7 is the thermistor input for the 4th thermistor connector on the RAMBo board. So, I edited Pins.h to:

#define HEATER_BED_PIN 3
//#define TEMP_BED_PIN 2
// I popped the thermistor input on my RAMBo so I'm using the 4th thermistor connector on the board.
#define TEMP_BED_PIN 7

Recompile, upload and all is well again.

[Highcooley]

Luckey you

Another thing I am a bit reluctant to are the PCB through holes on the onyx board. Did you insulate them with some Kapton tape in order not to short over the aluminium plate?

[mhackney]

I have a version 2 Onyx and there are no electrical traces out where the holes are so it is safe to mount directly.

As for the little holes and thermistor hole, I am thinking about using some capton tape over those. I have some very thin tape that I was experimenting with on an unrelated project, It should be just right.

[Highcooley]

I have a version 2 Onyx and there are no electrical traces out where the holes are so it is safe to mount directly.

As for the little holes and thermistor hole, I am thinking about using some capton tape over those. I have some very thin tape that I was experimenting with on an unrelated project, It should be just right.

That's the holes I meant. So capton it is.

I'm thinking about the opposite of a thick aluminium plate. I am wondering if thick aluminium foil could already do the job, as I don't want to make the whole sandwitch bigger.

[Eaglezsoar]

The outer perimeter was cut on my 12" metal bandsaw. I cut A LOT of metal so I'm pretty good at free handing! the cutout for the back was done on one of my milling machines by hand. It's pretty simple.

I can get a 5/32" x 12" aluminum circle on Ebay for about $20. Do you think that it work just to place the aluminum over the heat bed without screwing it down?
I just noticed that the borasilic glass Seemecnc sells is just a little smaller than the heat bed and would cover up the led area if it is centered, I guess you are supposed to let it hang over the edge of the bed?
You would think the glass would be the size of the white circle, 280mm but the glass is 300 mm. Weird that they would do that.

[mhackney]

@highcooley - Foil should work fine for spreading the heat. Do you have trouble with your Onyx warping or does your glass surface stay flat? I'm probably overkilling a bit!

@Eaglezsoar - that is just a scooch over 1/8" and should be fine. You will probably be able to drill and countersink holes in the edge to mount if you wanted.

If SeeMeCNC made the plate the size of the white circle you would sacrifice build surface with mounting clips. I guess most folks do hang them over the front. A better solution would be to cut a flat like I did on my original glass plate to clear the electronic area. If you do that with the aluminum plate, it acts as a spacer so a round glass plate will fit on top and cover over the electrical area. That's what I'll do.

[Eaglezsoar]

@highcooley - Foil should work fine for spreading the heat. Do you have trouble with your Onyx warping or does your glass surface stay flat? I'm probably overkilling a bit!

@Eaglezsoar - that is just a scooch over 1/8" and should be fine. You will probably be able to drill and countersink holes in the edge to mount if you wanted.

If SeeMeCNC made the plate the size of the white circle you would sacrifice build surface with mounting clips. I guess most folks do hang them over the front. A better solution would be to cut a flat like I did on my original glass plate to clear the electronic area. If you do that with the aluminum plate, it acts as a spacer so a round glass plate will fit on top and cover over the electrical area. That's what I'll do.

You are full of great ideas, I didn't think about the aluminum acting as a spacer so the glass fits the way it should. I'm ordering the aluminum circle. Thanks again for the great tip, I sure am glad that you are on this forum!

[mhackney]

So I did put some little strips of thin capton tape over the several groups of little holes and the thermistor hole on the Onyx. I also had a scrape through where my nozzle gouged through the tape into the paint on the Onyx. The tape is thinner than the silkscreened writing.

All of my local hardware stores are closed for the holiday this evening so I didn't get the longer screws that I need. So, to do a quick test I eliminated the melamine snowflake spacer and just used little standoffs (I have some aluminum ones about the size of the plastic ones in the kit). I won't run like this since I think the Snowflake will help prevent bowing and provides some insulation.

Here's the cool part (actually, "hot" part!) the temperature across the entire build surface only varies by 5°D at 80°C! This is without a glass plate on top. I'll let it equilibrate for 15 minutes and check again. But, this definitely distributes the heat evenly! The aluminum plate all the way to the edge is hot!

[mhackney]

Thanks Eaglezsoar, you can cut out a little section in the back with a copying saw, hacksaw or drill it out and file smooth. It really is easy to work and the dimensions are not critical.

I just posted my first test run a minute ago, you will be VERY happy you are adding this plate!

[Eaglezsoar]

So I did put some little strips of thin capton tape over the several groups of little holes and the thermistor hole on the Onyx. I also had a scrape through where my nozzle gouged through the tape into the paint on the Onyx. The tape is thinner than the silkscreened writing.

All of my local hardware stores are closed for the holiday this evening so I didn't get the longer screws that I need. So, to do a quick test I eliminated the melamine snowflake spacer and just used little standoffs (I have some aluminum ones about the size of the plastic ones in the kit). I won't run like this since I think the Snowflake will help prevent bowing and provides some insulation.

Here's the cool part (actually, "hot" part!) the temperature across the entire build surface only varies by 5°D at 80°C! This is without a glass plate on top. I'll let it equilibrate for 15 minutes and check again. But, this definitely distributes the heat evenly! The aluminum plate all the way to the edge is hot!

Good job! Now I know it works. Seemecnc should add the aluminum circles to their items for sale.

[mhackney]

And now the temperature is within 3° across the entire plate, very nice. I measured in 12 spots with a thermocouple. Even the edge of the aluminum is only 5°C cooler than the center. Plus, there is no warping, so it is performing both tasks well. I think once the glass is on the temperature will be even more even.

[geneb]

No they won't fit, just multiply all the numbers by 7/9 that should fit.
Any scale will retain the points in a circle which is what matters.

Um, that doesn't make any sense. Multiply them by 7 divided by 9?

g.

[mhackney]

Basically, he is suggesting scaling the values by seven ninths - 7/9ths. That will make the circle smaller and presumably small enough to fit on the smaller heated bed. Make sense?

[Polygonhell]

No they won't fit, just multiply all the numbers by 7/9 that should fit.
Any scale will retain the points in a circle which is what matters.

Um, that doesn't make any sense. Multiply them by 7 divided by 9?

g.

You just need to scale the numbers to fit multiplying by 7/9 means that the the 90mm radius of the original numbers becomes 70mm which should fit on the Phebe bed.

[dbarrans]

Hmmm. I wonder what a 12" diameter x 1/8" copper disk would cost.
Hmmm again. Maybe a magnetic stainless steel disk with an induction heater, forget about the Onyx. Bet that would heat up quicker.

- dan

[Highcooley]

@highcooley - Foil should work fine for spreading the heat. Do you have trouble with your Onyx warping or does your glass surface stay flat? I'm probably overkilling a bit!

Reason 1 for aluminium: The filament won't stick on the outer parts of the glass bed @ 40 °C. Reason two: The glass bed warps about 0.3 mm. While it was easy to adjust the convex warping by adjusting delta radius, there is a non concentric warping which isn't. I was able to adjust the following four points to +/- 0.03 mm:
- X0 Y0
- X0 Y120
- X-112.6 Y-65
- X112.6 Y-65

But X-112.6 Y65 and X112.6 Y65 are still -0.3 mm off.

[mhackney]

Copper is MUCH more expensive than aluminum and doesn't offer any significant advantages. As I showed, 1/8" aluminum dissipates the heat as nicely as you could ask. My Onyx heats up like a champ (less than 5 minutes to 100°C) but that is probably due to the power supply I'm using. An induction heater would be quite expensive too and a SS disk 12" in diameter would'n be cheap either.

The Onyx with an 1/8" aluminum plate and borosilicate build surface should provide even and reliable heating and be cost effective. The Onyx now ships with the Rostock Max so you only need the aluminum and the glass. You can get a 12" square of aluminum .125" thick on OnlineMetals for $14.53. Draw a circle and cut it out with a saber saw or by hand. You would be surprised at how good it will turn out. This is exactly how I teach people to make fly fishing reels in my book without using machine tools! The Onyx build surface is $32.00. So for $46.53 plus shipping you have a really nice, evenly heated build platform for a $1000 machine. Not a bad deal at all!

If there is interest, I would consider machining and selling these aluminum plates with the mounting holes drilled and countersunk.

EDIT/UPDATE - I checked with my metal supplier this morning and a 12" x 12" x 1/8" copper sheet would cost $97.00!

[dbarrans]

Yeah, I was kidding about copper or stainless w/induction heating. I knew the cost wouldn't make sense, but copper moves heat much better than aluminum does. For that reason, I was considering copper foil for the hot end resistors, but I decided to try out aluminum foil anyway, after failing to keep Arctic Silver under control.

How do you heat up your Onyx that fast? It takes forever for mine to get up to 70 degrees C. I'm using the PS as supplied by SeeMeCNC, and 12 gauge stranded wire to feed the Onyx.

- dan