My H-1 Build and Mods

[mhackney]

I'll try to post some photos tomorrow but Wow, print quality has gone way up with the idler bearings and properly tensioned belts.

Cheers,
Michael

[mhackney]

So, here is the problem I was fighting after installing my hot bed.

[img]http://mhackney.zenfolio.com/img/s3/v43 ... 4763-3.jpg[/img]

Even though the hot bed is insulted underneath and sat above the H-1 stock table on 1/8" standoffs, there was enough heat to warp the table. The "backlash" problem I had on my Y was due to this:

[img]http://mhackney.zenfolio.com/img/s3/v42 ... 7159-3.jpg[/img]

See how the posts on the left have bent? That is towards the back of the machine. As the machine was printing, that post slowly bent backwards causing a shift in the Y direction. Here is a closeup of that post:

[img]http://mhackney.zenfolio.com/img/s3/v44/p23399837-3.jpg[/img]

It got so hot that it actually melted the table in that area.

I've now taken the hot bed and table off and looking at alternative for mounting. I don't think insulation is going to be enough. I think the underside of the hot table needs to be insulated but it also needs to be in the open air to dissipate heat. I think the heat was getting trapped between the hot bed and the H-1 table, causing the warping, etc.

I'll probably mill an aluminum cross bar similar to Dave's that is about 4 1/2" wide and spans the bearing blocks left to right. The table will mount to this on standoffs and/or springs like I've seen on some of the RepRaps.

Michael

[michaellatif]

WOW! That thing will never be flat again!

I used springs and about 3/8"" of air to keep the bed from melting. Also I sandwiched a piece of birch plywood and 1/32 aluminum plate under the heated bed to add as insulation/dissipation.
So far that has worked like a charm, I get the heated bed to 140C without issue.

Edit: Meant 140C slight difference!

[Leeway]

I had the 1/4" acrylic on the Prusa bed warp bad as well. I wasn't using insulation though. I am now using some steel. It's actually an old table from a HF metal cutting bandsaw. It has some bends in it that helps keep it flat. Perfect size for Prusa, so I think I can get away with no insulation.

[mhackney]

Only 140°F on your hot bed Michael? I run mine at 200°F doe ABS.

I just made the aluminum cross brace to replace the table. It is 7" long and about 3 1/2" wide. It attaches directly to the bearing blocks. The lower part of my hot bed is phenolic and that is mounted to this cross brace on 1/8" standoffs for further isolation. The aluminum table with the nichrome heater is then mounted on the phenolic with 1/8" standoffs to provide a gap between for the nichrome. There is enough room for insulation in there so I am looking at alternatives for that. Another advantage of this configuration is that it will be a lot easier to level the table.

Cheers,
Michael

[mhackney]

Ok, I made the new table mount. This is the cross brace that the table will mount to. The screw sort of in the middle is the mount for the Y belt tensioner as you'll see below.

[img]http://mhackney.zenfolio.com/img/s3/v40 ... 7694-3.jpg[/img]

Here is the underside. The belt mount is that screw I mentioned in the previous photo, with a 1/4" standoff and a nut.

[img]http://mhackney.zenfolio.com/img/s3/v41 ... 1328-3.jpg[/img]

And here is how the belt and tensioner are mounted to the post.

[img]http://mhackney.zenfolio.com/img/s3/v39 ... 2658-3.jpg[/img]

I've mounted the table and it is printing now. Seems to be working fine.

Cheers,
Michael

[michaellatif]

Only 140°F on your hot bed Michael? I run mine at 200°F doe ABS.

I just made the aluminum cross brace to replace the table. It is 7" long and about 3 1/2" wide. It attaches directly to the bearing blocks. The lower part of my hot bed is phenolic and that is mounted to this cross brace on 1/8" standoffs for further isolation. The aluminum table with the nichrome heater is then mounted on the phenolic with 1/8" standoffs to provide a gap between for the nichrome. There is enough room for insulation in there so I am looking at alternatives for that. Another advantage of this configuration is that it will be a lot easier to level the table.

Cheers,
Michael

Yeah, typo on my part, I run my heated bed at 80C - 100C, I have run it up to 140C without issue.