some question about prusa

I recently saw the prusa mendel and its simpler design, and decided to have a go at building one . But before i begin id like to have some question answered. Also im a newbie when it comes to electronic components so keep that in mind.

1.Which electronics would be the best/mostUserFriendly ? Im thinking Gen6 cause i assume i wont have to solder a thing, and its just one board.

2.Which type or extruder hot end would be the least error prone , and give the best results? nichrome or resistor ?

3.What if any, are the benefits of using nema 23's over 17' , and what degree/step would be best ?

4.Should i invest in a heated bed right from the start or is it something easily added? Will the electronics used have to be changed to work with the new bed?

5.Anything else you think i should know.

Thanks for your time.

Edited 3 time(s). Last edit at 03/08/2011 12:29AM by Rooski.

I'm almost finished building a Mendel Prusa SAE version.

The extruder is Wade's. The hot end, I made from a brass air hose coupling and a 0.023" MIG Welder Tip. To this, I clamped an aluminum block with a wire-wound resistor embedded on one side.

While I'm still waiting for stepper drivers (I'm using RAMPS electronics), I connected the extruder to a LAM Tech stepper driver, and tested the extruder up to 220C.

1. Don't know much about the Gen6, but I have to say that the RAMPS ability to plug in driver modules appeals to me, having fried drivers in the past.

2. I think the resistor hot end is less hassle than winding Ni-chrome. The resulting hot end is much more compact and clean looking.

3. Unless you have a modified set of RR parts, I do not believe NEMA 23 steppers will fit the Mendel Prusa. NEMA 17 is plenty strong enough for any job there.

4. The heat bed only requires that you have a wooden base, instead of acrylic, or some other material that might warp when heated. It can be added later, and the RAMPS (and the Gen6, I believe) has built-in support.

5. One thing that you might need to do is to place the Y-axis platform mostly to the left side. On my extruder, the nozzle moves farther to the left, than to the right. About 2cm more. Placing the platform off center allows me to use the entire surface of the platform

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1.Which electronics would be the best/mostUserFriendly ? Im thinking Gen6 cause i assume i wont have to solder a thing, and its just one board.

I would recommend RAMPS, as it is very compact and gives you plenty of expansion room. However, it can be hard to get a hold of the pololu stepper drivers as they are in short supply. Gen6 would work perfectly fine though.

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2.Which type or extruder hot end would be the least error prone , and give the best results? nichrome or resistor ?

Resistor is the easiest by far. Both will give you good results. I personally use a MakerGear hotend, which is very nice and compact, but slightly expensive at $70 or so.

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3.What if any, are the benefits of using nema 23's over 17' , and what degree/step would be best ?

NEMA 23's won't fit a Mendel, and as jcabrer said, the 17's are plenty powerful enough. Just make sure you get a really strong one for the extruder, something around 3 - 4 kg*cm. The degrees per step isn't a big deal, either 1.8 or 0.9 would work. The micro-stepping of the stepper controllers will give you plenty of accuracy either way.

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4.Should i invest in a heated bed right from the start or is it something easily added? Will the electronics used have to be changed to work with the new bed?

I would recommend printing with PLA from the start, which does not require a heated bed or even printing rafts. That's what I did, and you can always move to ABS as well at a later point if you wish.

Edited 1 time(s). Last edit at 03/08/2011 12:01PM by NewPerfection.

thanks for the replies , when i get everything together and start building ill be back to ask more questions. also doesn't 5/16 threaded/smooth rod seem kind of flimsy , i was at lowes yesterday looking at some and thought for sure mendel used at least 3/8.

Edited 1 time(s). Last edit at 03/09/2011 03:15PM by Rooski.

The plastic vertices are the weak point, and they're not all that weak. 5/16 is plenty.

A long length of rod will seem flimsy as it's supporting the entire weight of the rod, and not just the lengths you'll need.

The other part to remember is that you assemble these into triangular and square shapes, and that these shapes share the load and allow you to build far stronger objects.

I personally prefer to use stainless steel as generally it's harder, which means it's less likely to bend (particularly before you get your hands on it). Unfortunately it costs more.

PS: Avoid bent rod where possible, especially for the threaded drive.

Cefiar Wrote:
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> PS: Avoid bent rod where possible, especially for
> the threaded drive.


The threaded rod at Lowes is really straight , its the smooth rod that is bent. I guess ill order some of that from a local machineshop.

I've got another question .

I've bought SAE reprap prusa parts , and on the wiki it says only difference from the metric version is that it uses 5/16 rods , and only 1 type of bolt. In the parts needed it says the bolt is a #6 . But it the size seems to vary by brand , some are 3.3mm some 3.5mm and others 4mm so I'm kind of confused which I should get.

Edited 2 time(s). Last edit at 03/13/2011 09:29PM by Rooski.

I think you might be referring to the #6 screws. The bolts are of course 5/16 also. As for the screws, I found that one size is not enough due to the steppers needing one length, the bed needing another, etc.

Also, you will need to go to a sports shop where you can pick up skate board ball bearings (608s). There is only one size for skate boards, get the cheapest ones.

jcabrer Wrote:
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> 4. The heat bed only requires that you have a
> wooden base, instead of acrylic, or some other
> material that might warp when heated. It can be
> added later, and the RAMPS (and the Gen6, I
> believe) has built-in support.

There's no built-in support for a heated bed on Gen6. I have one on the way and failed to check that before I ordered. Options are hooking up via RS485 (some extruder controller board, eg, or custom) or bodging a connection to a couple of the spare pins. The schematic shows at least one free analog (for the thermistor) and free digital (for the FET drive) on the AVR.

BenJackson Wrote:
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> bodging a connection to a couple of the
> spare pins.

Guess thats what im going to have to do , got a link to more info?

and i ordered my board like an hour before reading this. (need a facepalm smiley)