Welcome to the SeeMeCNC Community

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

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

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!

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.

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

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

mhackney wrote: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.