Beginners questions
December 14, 2010 02:59AM
Greetings all, I'm currently building a Mendel for my final project in highschool. I have almost all of the RP parts printed on our school's dimension 3d printer, and a hardware kit is on the way.

There have been a few questions I've had that I haven't seen directly answered on the wiki, and I finally decided it would be easier to ask you guys. Sorry if they are answered on there, perhaps I just suck at searching. I know how annoying it is to have people ask the same questions again and again tongue sticking out smiley

1. The thick and thin sheets: how much does the thickness matter? I operate my schools cnc plasma cutter, and I have some scrap 3/8" aluminum that is the perfect size for the "frog", and none of the metal we have is measured in metric (Imperial system sad smiley). Can the additional thickness be calibrated out easily?

Might just be that I don't understand how you initially set up the opto-endstops, specifically for the Z axis. How does the machine know how/how do you adjust how far down the nozzle will go before it crashes into the bed? is this easy to adjust?

2. Are there any .dxf files out there for the think and thin sheets that are drawn in imperial/inches scale? the plasma cutter I'll be using to cut out the pieces has no option for metric, so the frog alone is several times the entire build area. I can convert them, but it would save me a lot of time if somebody had a link to pre-made imperial drawings.

3. Extruders. I was initially planning on using Wade's extruder, but now I'm questioning this choice. Is there any other "better" extrusion system developed so far, and would a direct-drive system be more desirable in any way? the motors I have for my Mendel are about 5 times the minimum holding torque requirement, so I'm thinking that wouldn't be a problem.

4. How many people, if any, have multiple extrusion heads that can be used for the same print? i.e. multiple materials/support material. Are there any repraps using support material? I thought I read the other day about somebody using some sort of water-soluble PLA material.

5. Is there any reason why the reprap cannot be easily scaled up in size? Would this even require firmware modification, would moving the opto-endstops be enough?

6. I understand that 3 opto-endstops are the minimum to function effectively, but what are the advantages of using 6 (3 for home, 3 for limit)? what systems are in place to prevent the machine from trying to move outside it's build area and destroying parts of itself, if any?

It's really exciting to finally be building one of these machines, I've been following reprap loosely since Darwin, but finally got interested in it again.

Thanks for any help you can offer, once I get this running I hope to be an active community member experimenting with methods of/materials to extrude.
Re: Beginners questions
December 14, 2010 05:36AM
Cain Wrote:
-------------------------------------------------------
> 1. The thick and thin sheets: how much does the
> thickness matter? I operate my schools cnc plasma
> cutter, and I have some scrap 3/8" aluminum that
> is the perfect size for the "frog", and none of
> the metal we have is measured in metric (Imperial
> system sad smiley). Can the additional thickness be
> calibrated out easily?

The bed doesn't matter too much, as you can adjust the springs and the Z opto height to get it correct. You still don't want it too thick, especially if you want to heat it. Thicker = more thermal mass = harder to heat and/or keep the temp consistent.

If anything, the frog is the one to watch. If it's too thick, the belt may rub on the underside of the frog. This isn't a real show-stopper, but it may be better to err on the slightly thinner side vs the slightly thicker side.

That said, 3/8" = 9.525mm, which is way too big. You want 3/16" or 5/32" really (4-5mm thick).

Definitely don't want more than 5mm for the aluminium bed, from a heating perspective.

> Might just be that I don't understand how you
> initially set up the opto-endstops, specifically
> for the Z axis. How does the machine know how/how
> do you adjust how far down the nozzle will go
> before it crashes into the bed? is this easy to
> adjust?

The Opto boards sit on a plastic spring, so you can adjust their height. You can also bend the opto flag if required.

> 3. Extruders. I was initially planning on using
> Wade's extruder, but now I'm questioning this
> choice. Is there any other "better" extrusion
> system developed so far, and would a direct-drive
> system be more desirable in any way? the motors I
> have for my Mendel are about 5 times the minimum
> holding torque requirement, so I'm thinking that
> wouldn't be a problem.

I'd go with either a Wades or Adrians geared extruder. The difference is in how the nozzle mounts. Wades by default can't take the new extruder hot end design (no bolt holes for the PEEK block).

> 4. How many people, if any, have multiple
> extrusion heads that can be used for the same
> print? i.e. multiple materials/support material.
> Are there any repraps using support material? I
> thought I read the other day about somebody using
> some sort of water-soluble PLA material.

Not many, but expect that to change. A number of compact extruders are appearing that allow multiple heads in a small space. The people who have been playing with multiple extruders, (using different materials) are the "IFeel beta" guys. [www.ifeelbeta.de]

> 5. Is there any reason why the reprap cannot be
> easily scaled up in size? Would this even require
> firmware modification, would moving the
> opto-endstops be enough?

Depends on your definition of scaled up.

If you mean larger print areas, this has been done. The problem is speed, and that is dependent on how thick your filament is, which affects the resolution of corners on parts.

If you mean multiple sizes of filament so that you can fill print large objects with thick filament at a high rate, while small features get printed with thin filament, I've not seen it done. It's something I'd love to see.

> 6. I understand that 3 opto-endstops are the
> minimum to function effectively, but what are the
> advantages of using 6 (3 for home, 3 for limit)?
> what systems are in place to prevent the machine
> from trying to move outside it's build area and
> destroying parts of itself, if any?

Depends on what hits what as to whether it'll destroy anything.

A note: The default way a Wades sits on the X carriage allows it to hit the angled bars of the triangle vertices on each side of the build area. Adrians doesn't suffer from this. That said, it's possible to print a bracket to reorientate the Wades at 90 degrees so this isn't an issue.

PS: I'm sure others will answer the rest of your questions, or add in info on my answers.
Re: Beginners questions
December 14, 2010 12:19PM
Wow, your high school has a dimension 3d printer? Excellent!

I keep forgetting that the Z-opto-endstop is mounted on a spring.. I don't think even once I've adjusted it via screw - I've been bending the flag each time.. WAY better idea to adjust it via screw. (hopefully my mentioning this here will help me cement that in my own mind, as well as yours). smiling smiley

You do NOT want to mess with a direct-drive extruder. Wade's or Adrian's is the way to go. I have a Wade's extruder now (which works wonderfully) - but be sure you print Tony Buser's sideways mount for it - that makes mounting and unmounting it far easier, it allows the big gear to come off far easier, and it grants you more vertical height for printing.

..the downside, as Cefiar mentioned, is that there's no place to mount the PEEK block that Adrian's extruder has, so it's possible for the heater barrel to push out of the PTFE insulator (which just happened to me, again.. That's happened at LEAST 4-5 times for me over the past year). That's why I'm looking forward to also trying an Adrian's extruder - but you need access to a metal lathe to make his extruder nozzle. Wade's extruder is smaller too, but you have to knurl a bolt. That's not too hard though (although my first try certainly wasn't perfect - yet it works).

I'd worry about one head first, then you can print out replacement carriages that support multiple heads later (my $0.02).

3 endstops are fine (and normal), because you'll almost never move the head all the way to the other side, and if you do, it doesn't really hurt anything.. The software never spontaneously acts crazy or anything. Unless you were printing something extremely tall, it wouldn't matter.. (and I believe you can set the upper limits of your machine in RepRap Host and replicatorg, so printing too tall of an object shouldn't create a problem either). There isn't any well defined place to even mount the other 3.

Welcome! And good luck!

p.s. Oh yeah - from the beginning, blog everything you're doing. At the VERY least it's a great diary for you to look back on later when you don't remember some aspect of what you did.


--Jeff Keegan (Just Another RepRap blog)
Re: Beginners questions
December 14, 2010 02:26PM
Thank you two very much, I'm looking for some thinner aluminum now to make the thick/thin sheets out of...

So, I am to understand that wade's extruder doesn't have the mounting holes for the v4 hotend PEEK block? Wouldn't it be simple to drill the holes in the plastic, or is there too much in the way? I thought the one I printed out would be fine as it appears to have the mounting holes. Ah well, time will tell. I have a few ideas in my mind for different (Smaller/simpler) mounting methods once I have it built anyways.

I'll probably start a blog on this soon, I've been documenting my progress in the DIY forum on [www.totse.info]

So, I can't seem to find any drawings of the thick/thin sheet in inches. How precise do they need to be? It looks like I can get the dimensions pretty close by opening autocad and scaling everything to .0393700787 (1 mm in inches).
Re: Beginners questions
December 14, 2010 04:01PM
There isn't any place for the bolts to go on the Wades. It was designed just before Adrian came up with the V4 hotend design.

However, it should be possible to modify Tony Buser's sideways mount to have the necessary holes for a V4 hotend. I'm intending to look at this soon, but other things on my plate at the moment. If someone else has ideas, it'd be good to see a design from someone!
Re: Beginners questions
January 02, 2011 10:09AM
I love the idea of the multihead (yeah, your plasma background shows through. Also works for waterjets)
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