Gettin ready to make some changes, help me

I am getting ready to order some stuff to upgrade my heated bed / build platform and replace my smooth rods with metric ones but I have a few questions...

Right now I have a slightly over sized i2 sae prusa from makerfarm.com kit (MK headbed which is small for the room I have, 5/16 smooth rods). I have already replaced the Z axis - 5/16 threaded rod with 1/4 acme(2 nuts each side w/spring) & flex couplers and thrust bearings (had to make a z motor lift plates for the couplers and thrust bearings to fit in, which also was used to fix the alignment problem with my Z screw and Z linear). I put a layer of insulation under the MK heatbed (but it still takes forever to heat up). Replaced all belts with GT2 and 32t pulleys.

My new attack is on the heatbed/build platform and 5/16 smooth rods...
Smooth rods: I didn’t notice it at first but these LM8UU bearings from the kit have a bit of slop on 5/16 drill rod (should a just bought the 8mm to begin with (oops). I think replacing these will solve some of my quality issues. I just hope 8mm will fit in my X-ends??
I will be ordering:
McMaster - 3x - A2 Tool Steel Tight-Tolerance Metric Rod 8 mm Diameter, 3' Length

Build Platform: This one takes too long to heat up, its lexan upper and lower so it warps (re-leveled constantly) & I have plenty of room for a bigger envelope. I want to use some of the extra space I gained from building the frame bigger. I can get 10.5" of X travel and 12.5" of Y but to stay on the safe side and keep weight down I think max bed size should be 10"x10". I think I am going to get a silicone heater and some aluminum to rebuild this part but as far as the electronics go (relays and heat pad) I'm a little lost.
I was thinking like:
McMaster - 1x - 6" X 6" Sheet, HI Watts/SQ Inch
(Will this be large enough to heat up a 10"x10"x1/4" chunk of aluminum and the glass above that?)
What relay will I need? I am running a Printrboard, so I have no idea what I should be looking for. If someone could help me out here that would be fantastic.

All of the Aluminum was going to be ordered from onlinemetals.com since I have no place local to get it & they will cut it.
Onlinemetals - 1x - 10"x10"x0.25" MIC6
Onlinemetals - 1x - 10"x5"x0.25" 6061 plate

any help would be wonderful, thanks everyone

That silicone heater runs on AC. You can use this setup to control that mat.

And don't bother with the 6x6. Probably too small to heat effectively ~ 360W is not that much more than your current MK I heated bed. Try 9x9, it's only $10 more, and has way more output ~ 800W.

As far as the aluminum, try discountsteel.com - they are pretty cheap.

Edited 1 time(s). Last edit at 08/21/2012 01:31PM by akhlut.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

akhlut Wrote:
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> That silicone heater runs on AC. You can use this
> setup to control that mat.

So as long as its a 3-32vdc control and 24-480vac 25a output I should be fine? For easy install, panel mount.

>
> And don't bother with the 6x6. Probably too small
> to heat effectively ~ 360W is not that much more
> than your current MK I heated bed. Try 9x9, it's
> only $10 more, and has way more output ~ 800W.

thats what I was afraid of, ok 9x9 it will be!

>
> As far as the aluminum, try discountsteel.com -
> they are pretty cheap.

OMG they are alot cheaper.. wish I had known about them 10 projects ago...

6of1 Wrote:
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> > And don't bother with the 6x6. Probably too
> small
> > to heat effectively ~ 360W is not that much
> more
> > than your current MK I heated bed. Try 9x9,
> it's
> > only $10 more, and has way more output ~ 800W.
>
> thats what I was afraid of, ok 9x9 it will be!

360W is far more than the MK1 bed uses. The MK1 barely draws over 100W. My current heated bed, which is about 300mm x 300mm (about 12x12in) draws 300W of AC current and heats up far faster than an MK1 heated bed does. 800W is overkill, I would be very careful because if the thermistor comes off the bed, it would heat up to dangerous temperatures very quickly.

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OK, I was off on the PCB power consumption. But the MK I PCB has very little mass, making 100W of power a feasible amount to get up to 100C.

What did you make your heated bed out of? Aluminum? How thick?

And what heating element did you use?

And you are correct! This is not a safe option. A thermal cut-off switch should be incorporated into the design to prevent a possible runaway condition.

And an inexpensive SSR can be found here. Don't forget the heatsink!

Edited 2 time(s). Last edit at 08/21/2012 03:23PM by akhlut.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

I have an 1/8 inch thick aluminum bed (a bit over 3mm) and 10 5Ohm 25Watt aluminum-clad power resistors wired in series bolted to it, giving a total resistance of 50Ohms. At 120VAC that gives 2.4Amps current draw for 288 watts total power.

BTW, that SSR shouldn't need a heatsink if run at a reasonable power level, say less than 5 amps. The SSR I am using doesn't even get a few degrees above room temperature.

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ok so I did a lil bit of looking around for info on thermal cut-offs. Now remember I can wire it up if I have a little direction but that doesnt mean I know what I just did, lol..

From what I found (please correct me if I'm wrong) Thermal Fuses & Thermal Cut-offs are one in the same? If triggered they have no reset, Replacement is the only way to get up and running again. Is there anything that could be reset instead of replacement? links please

Edited 1 time(s). Last edit at 08/21/2012 10:34PM by 6of1.

That 9x9 silicone mat pulls nearly 7 amps. The SSR needs a heatsink if it passes 8amps - better to be safe than sorry.

I'd still say go with the 9x9 vs the 6x6. I know aluminum conducts heat very well, but I'm not too certain that it would evenly spread the heat from the 6x6 element to a 10x10 plate.

I wish I could have found some 1/8" cast aluminum...wound up using 1/4".

As far as the thermal cutoffs, a bimetal disc thermostats 3L11-250 should do the trick. It will open the circuit at 124C and close it at 118C. For that extra level of safety add a true thermal cutoff as well.

Check the wiki for construction.

Edited 2 time(s). Last edit at 08/22/2012 03:43AM by akhlut.

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

As long as you have a thermal cutoff I don't see an issue with using that 9x9 element. At 7 amps, a heatsink on the SSR is probably a good idea.

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Hi:

I used 1/4" aluminum for my heated bed and somewhat regret it. I have to keep travel speeds fairly low (<30mm/sec) or the y axis (that moves the plate) will skip steps.

john

Well I got together a parts/price list quick. The weather here in SW Florida isn't looking to good for the begining of next week so I'm going to have to hold off. Once the storm has passed (or misses us entirely I hope) I'll start ordering. According to my wife having the money to help myself and family if the worst happens is more important then a 3d print, I hate when shes right If you happen to be in the "Cone of Uncertainty" good luck.

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Discountsteel.com
10"x10"x1/4" MIC 6 Plate - $26.62
10"x5"x1/8 6061 Sheet - $12.88

SubTotal $39.50
S & H $13.78
Total $53.28
=============
McMaster
9"x9" Heat pad - 35765K429 - $56.16

SubTotal $56.16
S & H ????
Total ????
=============
Newark
WHITE RODGERS, 3L11-250, DISC THERMO - $ 6.56
NTE ELECTRONICS, NTE8149, FUSE, THERM - $ 1.68

SubTotal $ 8.24
S & H ????
Total ????
=============
auberins.com
25A SSR, Model: MGR-1D4825 - $15.00
Heat Sink for 25A SSR, Model: HS25 - $ 9.65

SubTotal $24.65
S & H $ 6.42
Total $30.07
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The only caution I might offer is that you are adding quite a bit of weight to your print bed. The MIC6 plate is almost 3lbs and the lower sheet is nearly a pound. Print bed weight can be an issue and can affect print speed. I know this from experience. I had a similar setup on my MendelMax (1/4" thick sheet, 1/8" MDF lower sheet) and the weight from the print bed caused my y-stepper to miss steps. I had to ramp up the power from the driver and even then was having issues. Only after halving my acceleration speeds in Marlin could I get an accurate print but the speeds were terrible.

Now, full disclosure, the cheap LM8UU's I have on the y-axis aren't super smooth and there is quite a bit of drag. You may have a smoother y-axis which avoids these issues. You will still wind up with a pretty heavy print bed and the inertia might be more than your stepper can handle at high speeds.

The engineers at TrinityLabs had a very similar setup for thier MendelMax kits which they have recently scrapped in favor of a linear guide bearing and glass print bed. Take a look at their kit that they sell. While it isn't a bolt on addition for a Prusa, it can be adapted. I like the glass print surface and large kapton heater. I would also definitely recommend linear guide rails! They are smoother than you can possibly imagine. They can be expensive but IGUS makes a line which is very affordable ($60 for a rail and carriage). Like I said it might take some engineering to adapt it to a Prusa, but hey, thats what these printers are all about. Good luck out there!

Thanks for mentioning weight, It completely slipped my mind when planning all this out.. I think weight will become a problem for me b/c right now I have the 2 lexan, MK1 bed & 8x8x1/4" mirror glass and it was skipping / jittering when I added the glass. When I pull the machine apart to change out my 5/16 rods for 8mm rods I will find a way to weigh it.

Is there anyplace that sells 1/8" MIC-6 Tool Plate? Should only weight 1.5lbs for 10"x10".

just an update..

I'm a little more worried about weight now.. I started to get my 8mm rods swap started, pulled the whole Y axis, moving parts (lm8uu bearings and mounts x4, upper and lower lexan, mk1 heatbed, 8x8 mirror glass trivet from craft store & spriings/hardware). I put it on a kitchen scale and it was 2.5lbs.. With this setup i had to lower my speeds to keep it from skipping/missing on small rapid infils.

That 2.5lbs tells me I can not put a 3lbs upper platform, plus aluminum lower and then thin glass without major issues (meaning I will have to reduce speed again). not to mention the fact that 8mm rods will have a little more friction then the 5/16 rods in the lm8uu's and i havent even factored in the weight of the silicone heat pad..

I guess back to the drawing board...

Edited 1 time(s). Last edit at 08/29/2012 02:43AM by 6of1.

Another update... lol

Well I got the 5/16" smooth rods swapped out with 8mm rods... My print quality has improved sorta. I have allot less wobble in the prints because the bed doesn’t shake side to side like it was before. On the 5/16" you can feel the slop in the LM8UU bearings, 8mm there is none that I can tell. This is where the good news ends...

With my 2.5lbs bed assembly & 8mm rods I had to decrease my speeds again and I’m still getting Y axis missing steps. I thought I slowed it down enough but as I was typing this it missed again... ugh!

These LM8UUs are just a little bit stiffer on the 8mm rods plus my heavy glass is causing the missed steps. It moves easy, just not easy enough I guess. I have tried tightening the belt, readjusting the rods & bearing mounts. I need to find some thinner glass I think. The last piece of glass I had was so thin when it heated up it would warp in the middle and this one was all I could find around 7:30 at night.

I’m also wondering about a redo of the lower lexan with 3 bearings instead of 4 (less friction). I have looked at HD and Lowes and cant find anything resembling Dibond so IDK...

Go check your nearest sign shop for the dibond. Hell, they might even give you some gratis.

Also, have you lubricated the LM8UU's? Personally I use tri-flow, It's relatively cheap and easy to find locally. Try a bike shop.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

akhlut Wrote:
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> Go check your nearest sign shop for the dibond.
> Hell, they might even give you some gratis.
>
well I called a sign shop and spoke to the shop foreman. I described what I was looking for as Dibond, and Its plastic with aluminum on both sides and he said he thinks he knows what I'm looking for. He described it is about 1/8" thick and flexible / bendy (o.0) I didn't think it was the right stuff but told him I will stop by tomorrow to take a look. Is it "bendy"? that just didn't sound like a good base to me..

> Also, have you lubricated the LM8UU's?
>
Yes, I lube the rods/bearings, I don't have any of the stuff you were talkin about but I use "3-in-1" I think its called, comes in a metal can with like a dropper..

There is some concern about the 3-in-1 oil. Read this thread.

And dibond should be pretty stiff.

It should look like this.

Edited 2 time(s). Last edit at 09/12/2012 04:41PM by akhlut.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]