SD Press - Mark II (Modifications Breakdown) (Page 2 of 7)

105C for ABS (It could probably do it at a lower temp. Never tested. Just tried 105 and it stuck)

0.07 ~ 0.09

You can get it here: https://github.com/ymilord/Solidoodle-P … rts/Bowden

One of the things I've noticed is the bed is drooping slightly. From front to rear is now a 3.188mm. When I first got the Press is was 2.101mm. The long term repair is replace the plastic mount that is attaching to the acme nut to the bed. It seems that the tapped screw holes on the side are deforming. In the short term, I've increased the Z Offset probe count from 9 to 16. With the higher density probing it seems to have completely corrected the odd lifting issues I was getting with prints in the upper area of any print. (And this is due to the fact that visually it looked that the bead of filament was contacting the bed, but over time it would slightly curl upwards. As great as PEI is, The filament has to be contacting the bed for it to work.)

On the bed rebuild, I plan on using a short piece of 2020 with the two acme nut's captured within it and a spring to act as a anti-backlash. As usual, Once completed I'll upload pictures and plans on how to do it.

You'll love the MK2a. Super fast heat up times. And nice and even.

Jonzerb, what are you planning for powering the new bed? A stock Press can't handle the 190W Mk2a/b. (vs. the 90W stock heater pad). My apologies if you and MacGyverX discussed this already.

Well, I grabbed 3-3.4ohms @ 24v from a random supplier's* MK2b web page. Is that atypical?  3 Ohms is 8A@24v. or 190W**.
I don't see how 190W fiits into a 125W budget, or how 8A fits in a 7.5A supply.

Also, cheap brick power supplies are spec'd somewhat optimistically, and tend to have short lives at the limit of their output, so you might want to downrate that 125W budget.

The stock heater is stamped 90W, so you're doubling+ current in the heat bed path with MK2. Could be SD built 100%+ margin into that path, but probably only if the cheapest parts dictated it. I haven't looked there, but I would be unsurprised if you needed to beef up the traces, add a heat sink the FET (or ugrade the FET), or ugrade the heat bed connector to be reliable.

I don't doubt you when you say it works for you, but I'm not sure how reliable it will be unless you've done due diligence on the engineering end.

*http://www.reprapdiscount.com/electroni … d-bed.html
**A little less, due to the voltage drop across the FET. But pretty close.
*** 3 ohms is probably the cold rush resistance, and will be higher as the bed warms.

how do you change the number of probe points?

So if your FET is putting out 23.2v like mine, that's a cold resistance of 3.7 Ohms. Anyone following in your footsteps will hopefully get a bed more like yours than the strongest of reprapdiscount's beds (3 ohm).

I don't blame you on that frustration. Mine tops out at abput 100C, depending on the room temp, so it takes a very long time to get printing. Seems strange that some people report getting 110C in 10-12 minutes, while others poke along.

Just of of curiosity, has anyone tried insulating the underside of the heat bed? (Definitely not as cool as amping up the bed, but it might help.)

BTW, thanks for measuring out what your printer is doing and sharing your hacks. It's all very interesting. I wouldn't be surprised if eventually expired Presses start showing up on your doorstep hoping for a new lease on life.

So my plan with the new bed was to stick some PEI to it and be done. But if the bed is 8x8 and that's the size of the print area, thus the size of the PEI. How are you screwing the bed the the carriage?

Sorry I missed this. You don't have to drill anything. I used the old hardware.

I took the four screws and the spacers. I threaded the screws in the bottom. Pass the them thru the spacer. In my case I cut some FR6 (PCB boards) in to small squares. Then tighten the screws till they make contact to the bottom of the FR6 which then makes contact to the Mk2b. So the screws push up to the mk2b which then presses the PEI (Which is backed with a sheet of 468MP) to the side hooks. I used a bubble level to square it up.

Currently not at home. But I'll make a diagram of what I mean if my description sucks.