Prusa Mendel Build

[LeeWay]

Thanks for that link, Hoss.
I will definitely pick some up. I like that is comes sealed and dried already.

I'll have to pull out enough for a single project and reseal it. It's not humid in the house.

I found another type of tape that works pretty well on the glass that I have been testing.
It is the green masking tape used with powder coating. Quite a bit cheaper than the gold kapton.
McMaster-Carr

Seems to be working well with a heated bed. It does have the same issues w with trapping air bubbles, but using a rubber roller to apply should help with that. Still testing.

Oh, I have to replace my acrylic under bed. It warps when I heat the bed up. This does crazy stuff with my Z zero settings.
I am going to try some phenolic that I have on hand.

[LeeWay]

A little more on the progress so far.

I managed to do away with the limit switch holder for X. End stops are what they call those I think.
I just used some zipties to secure the opto between the X end carriage. Perfect spot for those.
I also designed an adjustable opto holder for the Z. This makes is nicer to get just right. This and the table leveling rosettes make that a simple thing now. Without these it was a big fuss adjusting the Z home and table level.
I also designed a carrier for the filament on top of the machine.
Works pretty well considering it was a thin quick and dirty print. (= fast.)

I want to rework that file though. Make it a little thicker and print heavier to support 2.2 pond spools. The rod is just PVC conduit and a cut down elbow for the ends.
It works great in that position.

[LeeWay]

Forgot to mention what I used for the bed after the great acrylic bed melt down. I simply replaced the acrylic with some black 3/16" paper based phenolic that I have on hand. It stays pretty flat. Then I added a simple layer of aluminum foil for a heat resist on the phenolic. I turned my bed heater upside down so printed letter are down. They say the hottest side is the circuit side rather than the solid sheet side, so this should help with heating the glass. I bought a 9" by 9" piece of high temp glass from McMaster Carr. Not cheap by any means. $28.46.
Hoss linked to a cheap place where he bought his 10" by 10" glass. That link is here.

The width of my machine is just a bit narrower than Hoss's. I could have and should have made it a bit wider, but I have exactly 10" between the threaded rod. As it is, I still get 216 mm usable printing in X. This is with the 9" glass.
My glass actually sits on top of the cap screws in the corners of the bed and get clamps to the circuit board for now. This is not ideal. i'll probably get some silicone covers for the cap screws and bigger clamps to stay off the CB. This high temp glass is apparently not tempered. One corner had a chip in it when I unpacked it. It was packed pretty well, so no telling when that was done. It doesn't effect anything though, so I am running with it.


Just an FYI on another useful tool for pulling off parts that are PLA on a cold bed with the blue tape.
They can stick pretty well, so I use some wide jawed "Vise Grips" that are designed for sheet metal.
Like these in the image.
It allows a pretty fair grip on the parts and they snap off pretty easily then.



That is how I print in PLA with good results.
I am now doing some testing with ABS. Love to be able to print it on a cold bed, but that is doubtful from the looks of it so far. I have some pet tape here and some Kapton tape coming to throw in the mix. I'll let you know the results.

[LeeWay]

Okay, changed the table again. The center table part. It seems the phenolic that I was using @3/16" was just not good enough. It did show some minor warping. It would probably have held up though, but I checked the temp on the bed at one point and it was nearly 160 C. Now that is too hot. I was told it would hover around 110 C with no temp control on 12 VDC, but that isn't the case. I did order a couple MK138 kits last week. I knew I would want them at some point. Need one sooner than anticipated now.
With the bed temp that high, my ABS printing was like it was on jello. Not good. You really want it semi rigid through the print after it has welded together. That is where the accuracy of a part comes in.

I was looking through some stuff and was going to make a sheet steel bed when I spotted an old table off one of my metal bandsaws. HF variety. This table actually came off the red model, but this is because I used the beefed up bed from the green model I wore out. It's a little smaller than the red one. Anyway, it looks to be about 14 gage steel and has several bends to help keep it flat. It was the perfect size for this app as well.
I'll add a picture or two later.

I also intend to make a new lower table that is actually the Y carriage. Narrow it down to 4" like Hoss did. Gives a bit more extra travel.


There is no doubt about there being a learning curve and some trial and error on these, but that is why I wanted to get into them at this point. There is still some stuff that can be figured out and even stuff that we can design to make them work better.

A little tip I have found when designing parts for these. I am using Turbocad. I have found that the machine like to cut straights better than curves and radius figures. What would look nice and work well in a machined part isn't necessarily what will work best in a printed part. Stay away from camphers and rounded edges. Raw part geometry is more desirable when possible. It increases speed in which the parts slice and load as well as print.

The image in the first picture has an STL file size of 345 KB.
Second is about 2500 KB. Nearly identical parts. Little variation, but nothing major. Big difference in part processing and printing. Second one would have taken over 7 hours. I haven't yet printed the first one. Still tweaking it.

[LeeWay]

This is an image of the band saw bed.