My H-1 Build and Mods

[Leeway]

I don't have that type. Mine is a Prusa with the typical big red circuit board for heat bed. It definitely warps acrylic and even some 3/16" phenolic that I used. Just paper based stuff, so not as high temp as you can get phenolic in. I will say though that I was running the board without the MK138 at the time and it got to nearly 160 C. Way too hot for a heat bed.
I haven't hooked in the Velleman board yet, but will eventually, so your findings on your design are still interesting.
I am slowly working on my own design that will have about 16" x 16" x 8" print area hopefully, so I will need either a larger solution or 4 of those circuit boards. It seems your solution might be more cost effective for sure.

[mhackney]

Thanks Lee. My goal is to create an expandable, inexpensive and low profile hot bed. I also plan to make a larger machine, probably something like 18" x 10" x 8" so being able to make a hot bed for any size table would be needed.

Cheers,
Michael

[Chris Muncy]

OK Michael,

Remember when I said that I was 99.9% sure everything was stock? Well I found the .01%

R5 was shorted out on the bottom of the circuit board and since I have a mount for it, I didn't see it until I dismounted the MK138.

SO...

If you want to use the MK138 with it's included thermister to control a heated bed, short out R5 to get higher temps.

[mhackney]

Mystery solved, thanks Chris! I was starting to question the very foundation of existence (and physics) in this universe.

It all makes sense again now.

cheers,
Michael

[mhackney]

While I am waiting for some silicone to cure on my homebrew hot bed, I got motivated to cleanup my machine and electronics. I decided to build a short box that the machine will sit on with the power supply and electronics underneath. I plan to make a front panel with the pots for the hot end and hot bed thermostats, on/off switches for the thermostats, LED display for the thermostats, on/off for the fan, power on/off and an e-stop. The box is made of 3/8" Baltic birch so it is strong and light weight. It is 20" wide, 16" deep and 3 3/4" tall:

[img]http://mhackney.zenfolio.com/img/s3/v41 ... 1773-3.jpg[/img]

[img]http://mhackney.zenfolio.com/img/s3/v45 ... 3152-4.jpg[/img]

I grabbed a really nice little 20A 12 volt power supply from eBay.

I'll mount it on short standoffs to allow air flow.

This should keep everything neat and organized and very easy to move around. Simply disconnect the parallel cord, unplug and go.

Cheers,
Michael

[JTCUSTOMS]

Looks good Michael! I am actually buttoning mine up as well, I had a decent size plastic enclosure here so I hacked it up, and will use it as a base for the printer as well. Not as pretty as my enclosure for the mill and lathe but it's functional.

I am cleaning up my wiring on the printer this morning but after that I am at a standstill until I get my filament and other goodies I ordered a couple of days ago.

I set up the hot end last night but have not powered it up. I cant find any 18k resistors for R5 locally, and I dont want to wait for another delivery!
I have wired through a 6pin trailer plug (hillbilly, yes I know) but it makes for easy removal for maintenance. The steppers are also running through some XLR connectors which will make it easier to move around as well.

Anyway keep up the good work!

[mhackney]

I love XLR connectors. I used them for the steppers and relay outs on my G0704 mill and am updating my minimill to provide relay out as well using them. This is my weekend to cleanup all those "almost" finished projects.

Do you have a RadioShack? Anything in the range of 10K to 20k will work and you can run 2 (or more) in series if you can only find lower value. Just add enough together to get up to 15k or so.

cheers,
Michael

[JTCUSTOMS]

Ya, that's what I had planned. I have some 10k and 4.7k resistors, I just wanted it to not look hacked up but no one will ever see it I guess.

I am pretty disappointed with Radio Shacks selection and expertise, they should be called Cell Phone Shack now, but I did see they were starting to carry arduino stuff as well as several velleman kits just no MK138's. I asked them if they could order the MK138 and they said no. WTFarley they already carry 15-20 of their products!

[mhackney]

My new hot bed is working great! It warms up to 200 deg F in less than 10 minutes and the aluminum provides a nice level surface. I mounted it on 1/8" standoffs above the H-1 table to help keep it cool. I found that clipping a piece of 1/4" acrylic on top to print on resulted in the acrylic warping. So I removed it and put blue tape right on the aluminum. That works really well and gives a great surface finish.

Now that the prototype is done and working, I'm doing drawings and directions for others to make their own. What's nice is the hot bed can be made to fit a variety of machines. I am ordering some Teflon coated nichrome - that will reduce the overall thickness of the hot bed for an even thinner profile.

Cheers,
Michael

[JTCUSTOMS]

Come on now Michael, why didn't you tell me that before I bought one haha
Nice seeing someone putting the time into finding another alternative than off the shelf solutions, good on ya!

BTW more pics of mine coming shortly

[mhackney]

Here's a photo of the front right corner of the table and hot bed.

[img]http://mhackney.zenfolio.com/img/s3/v45 ... 0529-4.jpg[/img]

You can see the 1/4" acrylic on top clipped on has warped due to the heat. Then the aluminum (.1") plate, a 1/8" spacer, then the phenolic. There is a 1/8" spacer between the phenolic and the H-1 table. Even with the spacer, the reflective aluminum foil you see on the phenolic and the insulation, the H-1 table still warped. That caused the pillars that the Y timing belt are mounted on to spread apart and loosen up my belt (read "backlash"). I used a small hose clamp and mounted it to the same post as the fixed end of the belt. Now I can adjust the tension.

I am going to remove the H-1 table and mount the phenolic bottom board directly to the bearing blocks. I'll probably keep the 1/8" spacers or maybe fiber washers between the phenolic and the bearing block too for insulation.

Otherwise, the bed gets up to temp quickly and works great. I now print on blue tape right on the aluminum and that works perfectly. Haven't had a peel off or warp yet.

cheers,
Michael

[mhackney]

you misplace something that you've been looking at for weeks?! Now that I am actually printing some nice looking parts I wanted to print the bushings and install the skate bearings on the idlers. With everything tuned in, I am now seeing the backlash from the belts being a little sloppy. So, I printed the bushings (they turned out great) and wouldn't you know it, I can only find 2 of the 8 skate bearings I had. I pulled them out several weeks ago and they were on the table with the H-1. But, I underwent a major shop clean out and reorganization last week and now I can only find the two!

But, I printed the fan bracket, idler bushings, and two Velleman thermostat bases. That's something at least!

cheers,
Michael

[mhackney]

I decided to do my idler bearing and belt tensioner mods at the same time - they sort of go hand in hand. Here is the X axis belt tensioner made from a small hose clamp. I forget who on the Yahoo group posted this but it is a simple and very functional mod.

[img]http://mhackney.zenfolio.com/img/s3/v43 ... 9535-3.jpg[/img]

I cut the strap about 1" from the clam (the side that is fixed to the clamp). I drilled a 1/8" hole in the end of it and in the other end of the now "free" strap. The clamp side is screwed to the end of the X timing belt, I used a washer on each side:

[img]http://mhackney.zenfolio.com/img/s3/v42 ... 4829-3.jpg[/img]

The "free" strap is screwed to the bearing mount where the belt was originally attached, using the same screw and a washer:

[img]http://mhackney.zenfolio.com/img/s8/v9/p964633839-3.jpg[/img]

This arrangement puts the slotted screw facing out so you can reach it to tighten the belt.

Cheers,
Michael

[mhackney]

And I finally got rid of my wire fan brace! Here's the brace I made from Chris' (cquinby) great design:

[img]http://mhackney.zenfolio.com/img/s11/v3 ... 1407-3.jpg[/img]

Works like a champ. I mounted mine on the back side of the machine.

cheers,
Michael

[mhackney]

Ok, I got some more skate bearings - I am sure I'll find the missing ones now! Finished off the X and Z idlers. Those are easy since you can reach them. The Y idlers (1 on front, 2 on back) are trickier. The front one is easy, you can disassemble the old one still attached to the machine. The 2 on the back require some disassembly. I figured out that you only need to remove one of the all-thread cross braces:

[img]http://mhackney.zenfolio.com/img/s3/v26 ... 4423-3.jpg[/img]

(the lower one)

Then you can finigle and finagle to get the idlers out. The upper idler uses one of the printed sleeves. The lower one is on the all-thread and needs a very thin bushing. You can get brass tubing at the hobby shop with a 1/4" bore and thin walls that works just right.

Now I have bearings on all idlers and tensioning devices on all axis. Life is good, minimal backlash and much cleaner looking prints.

cheers,
Michael

[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.