MK2 Heatbed on standard Mendel?

Hi! I have a quick question for you. I want a Heatbed on my new Standard Mendel build, but I am not sure if it is for Prusa Mendel only of for both Mendel. Here is the website I want to order from : [mixshop.com]. Also, I would like to know what exactly is the use for the dent in the front of the Standard Mendel tick sheet? Thanks!

from what I know that is usually where the hotend of the extruder goes to when heating up and pre-purge the nozzle. Correct me if Im wrong I would like to know as well.

Yes. that was the original intent of that notch or dump zone. But it's obsolete and it's better not to have it. Skeinforge has the Skirt feature that works well to purge the nozzle just before printing the part.

Ok! So then the Heated Bed would work?

I use the same type of heated bed under the same type of aluminum build plate with a notch and it works fine. The one I got by Prusa is slightly wider to clear the mounting holes on the Sells Mendel bed. So, I put notches on them with a drill bit and then I cut a nylon washer of similar thickness to the heated bed so that the bed springs would seat level. This holds together well without additional hardware or holes on the build plate. I started out with the printed springs but after one broke due to a head crash, I switched to metal springs. Some insulation under the PCB is good.

Note, it works better to have the bed with the circuit traces down and the printed labels upwards. This way it makes a concave shape and it presses on the builld plate when it's hot.

Edited 1 time(s). Last edit at 11/02/2011 07:55AM by brnrd.

I too have a prusa heat bed that I want to install on my standard (Sells) Mendel.
I don't have a clear picture of what you did brnrd.. You cut notches on what? What is the pcb screwed into? How did the washers help?

Are you saying you had nylon washers wide enough that you cut a second offcenter hole in them for the mounting screws heads that go down to your frog?
Any chance of posting a picture?

I'd love to do this without tearing apart my Y axis and replacing everything. If I could use the original MDF bed that I have on there now, that'd be great (even if I have to cut slots in it to allow bulldog clips to hold it to glass above). But the heads of the bolts on that bed get in the way.. (I used those bolt heads as guides for the removable 2nd layer of MDF before the heatbed).

Working on it today - I'll figure something out if you don't see this by then, but I'd love to see what has been successful for other Sells Mendel owners with prusa pcb heatbeds.

..Jeff

---

--Jeff Keegan (Just Another RepRap blog)

If you clamp the PCB in position on top of your build plate, then you can mark the PCB where the 4 bed mounting holes are located. Then you can use a 4 mm drill to put the notch on left and right edges of the PCB. This way, you can put the 4 x 4mm bolts to hold the PCB on top of your MDF build plate. You may be able to do this even without the washer. You can then clamp a glass or aluminum plate on top of the PCB with bulldog clips. I had my PCB mounted this way on an acrylic plate and it worked well for PLA but the acrylic didn't hold up when I increased the temperature for ABS. I think MDF would do better. After that, I went back to the aluminum build plate with the PCB underneath as I described. I don't know if I have a good picture that shows the aluminum build plate configuration. Perhaps I can just draw a diagram.

Edited 1 time(s). Last edit at 11/05/2011 07:43PM by brnrd.

Ok, so you're talking about cutting semicircle notches into the PCB itself so it can be dropped in between the existing mounting screw heads that are already there - right? (or next to the bolt shafts and then unscrew the bolts to make the heads higher, I suppose, which would involve less notch-cutting).

So then are you not using the PCB mounting holes at all, and instead you're just holding down the PCB with nylon washers over the newly cut notches in the PCB on the original bolts? (I think I'd make something similar out of PTFE rod).

Does that mean you have the board resting flat against the wood? Or do you have a gap? Prusa's blog showed him leaving a washer's height gap, mounted with mounting holes, on his prusa bed. His claim seems to be that if the bed is bolted down from those corners, the bed will warp up slightly, right into the glass. He has wood, a washer-height air gap, the bed, then glass.

With your suggestion I could see either:
1) PCB flat on bed, held down via nylon/PTFE around the original M4 bolts of the bed (just above newly cut notches), and glass slid on top between bolt heads and bulldog clipped down
or
2) PTFE/nylon "washers" around original M4 bolt heads, PCB on top of that (snug against M4 bolt shafts in notches), more PTFE/nylon washers above that, then the bolt heads.
Glass slid between those and held down with bulldog clips.

#2 sounds better but I'm all ears.

Also, how many bulldog clips are necessary to hold down the glass? I use four with MDF on MDF. Prusa's blog shows his bulldog clip at a place where the
MDF was cut away (which looks suspiciously like the original purge point on the standard Mendel bed). That seems to let him clip the glass to the PCB without having to have MDF and an air gap in the clip too. I'd like to be lazy and not have to cut 3 more notches on my bed, but I will if it makes sense.

Thanks for the data!
..Jeff, all ears

---

--Jeff Keegan (Just Another RepRap blog)

Here's what I mean about using a cut washer to hold the Prusa PCB heat bed under the aluminum build plate on the Mendel viewed from the bottom. Another washer and a bed spring (printed or metal) would press against the cut washer and PCB. Pick a nylon washer that's about the same thickness as the PCB.

Edited 1 time(s). Last edit at 11/05/2011 09:32PM by brnrd.

Thank you for your advice! I cut notches in the PCB for the M4 bolts (so I could still level the bed). I cut eight m4-holed PTFE washers on my lathe - 4 that were .100" thick, and 4 that were .220" thick (I usually do everything in metric, but here I rounded to 1000ths of an inch to make it easier to measure them on my lathe).

I have the .220" washers beneath the PCB, around the 4mm bolts. Then above the PCB I have the 0.100" washers that I later cut to be D shaped, just like the ones you show above. The glass sits on the PCB, between the top cut washers.

Then I actually put in the m3 bolts too, coming up from the bottom (got that idea from my friend Chris), so the m3 bolt heads are below, then a washer, then the MDF, then a washer, nut, nut, washer, then the PCB, then another washer and a nut.

The .220" PTFE M4 washer is the same size as m3washer m3nut m3nut and m3washer stacked.

That leaves space for a bulldog clip below the PCB and above the glass, but above the MDF (no square notches).

I'll post pictures/video here soon. Thanks!

..Jeff

---

--Jeff Keegan (Just Another RepRap blog)

I make my own heated beds to suit whatever I'm building, mostly Prusa's or should that be Prusi? What is the plural of Prusa anyway?

I don't have any holes for purging as it would be a waste since I put Glass on my beds as a print surface anyway

---

__________________________________________________________________________
Experimenting in 3D in New Zealand