A word to the wise regarding the pressure bearing arm.

You wanted to print the pressure arm in an upright position, so you won't have to use any supports.  While the rotated version I provided will let you print the part without supports, I'm not so sure it would be strong enough.

This part is designed to put pressure on the filament, and is always under compression.  Because of the way this part is layered, there is a chance that it can split along one of the layer lines.  So I would still try to print the part as it was originally oriented for strength.

+1 just cracked an unrelated 4hr print trying to push a bearing in at an inopportune angle... Interlayer will be your downfall!

You wanted to print the pressure arm in an upright position, so you won't have to use any supports.  While the rotated version I provided will let you print the part without supports, I'm not so sure it would be strong enough.

This part is designed to put pressure on the filament, and is always under compression.  Because of the way this part is layered, there is a chance that it can split along one of the layer lines.  So I would still try to print the part as it was originally oriented for strength.

•    Is there a reason you went to a single adjustment point on the X-carriage?  It uses a threaded screw like the stock carriage instead of double nut traps like Lawsy’s design.  I like to be able to adjust from both ends.

I assume you're referring to the belt adjustment.  I basically duplicated the functionality of the original screw adjustment, so I can reuse the same belt.  One end is permanently attached, the other end is adjustable

•    I think it could use some more material around the screw holes on the platform and bearing holders.  I’m only getting a single wall when I print the platform in 0.3 mm layers.  Also, the holes for screw heads are not big enough to hold the heads of the M3 screws I am using (identical to the stock socket cap M3 screws.  If I tried to get a nut in there, it would be way too small.
The screw holes in the bearing holders are OK.  There should be at least 3 layers of wall. 

It's the recess holes for the screw heads that end up with a single layer wall.  I didn't have any problem with them myself, but the best solution would be to remove the hole recess altogether (fill it in).  The screw socket head would then simply be on top.  This is not meant to use nuts, the holes are undersized so the 3mm screw simply threads itself into the plastic.

•    Is there anyway you can add the spring block as another stl, rotated to print correctly?  I had to print it on its side because, similar to the bearing arm, it doesn’t seem to have a perfectly flat bottom when you rotate it in repetier.  When printing like this, it seems to have a very then wall towards the edge and it did not come out very well.
The surfaces are all flat, I think you're just having a problem rotating it to where the surface rests flat.  Anyway, I attached the rotated STL.

•    I might consider adding a screw hole or flat edge on the x-carriage so it has a better surface to hit the X end stop with.  It doesn’t look like it was designed to hit the end stop and a screw here is another useful adjustment point.  I can send a pic if this is not clear.
Actually it hits the end stop switch just fine.  As I mentioned earlier, I'm using Lawsy's carriage replacements.  Here is how it looks on mine.

•    The front bearing holder has a very thin edge where the extruder mount is supposed to get glued on.  I won’t know how strong it is until I try it, but it seems there is plenty of room to make this mating surface a lot bigger.
I will be very strong if you use Acetone type cement.  As for making it larger, it's not really feasible becuase of the size of the E3D fins.  Here is a section through the assembly showing how little clearance there really is.

Just a few more general questions: have you had a problem with your spring working itself loose and going flying off?  It seems like it could happen with all the extruder movement.  A small screw thru the bottom of the piece might stabilize it.
I've been using mine for a while now, and I haven't had the spring move at all.  The depth of the spring pockets plus the tension is more than enough to hold in place.

•    Is there a reason you went to a single adjustment point on the X-carriage?  It uses a threaded screw like the stock carriage instead of double nut traps like Lawsy’s design.  I like to be able to adjust from both ends.

•    I think it could use some more material around the screw holes on the platform and bearing holders.  I’m only getting a single wall when I print the platform in 0.3 mm layers.  Also, the holes for screw heads are not big enough to hold the heads of the M3 screws I am using (identical to the stock socket cap M3 screws.  If I tried to get a nut in there, it would be way too small.

•    Is there anyway you can add the spring block as another stl, rotated to print correctly?  I had to print it on its side because, similar to the bearing arm, it doesn’t seem to have a perfectly flat bottom when you rotate it in repetier.  When printing like this, it seems to have a very then wall towards the edge and it did not come out very well.

•    I might consider adding a screw hole or flat edge on the x-carriage so it has a better surface to hit the X end stop with.  It doesn’t look like it was designed to hit the end stop and a screw here is another useful adjustment point.  I can send a pic if this is not clear.

•    The front bearing holder has a very thin edge where the extruder mount is supposed to get glued on.  I won’t know how strong it is until I try it, but it seems there is plenty of room to make this mating surface a lot bigger

Just a few more general questions: have you had a problem with your spring working itself loose and going flying off?  It seems like it could happen with all the extruder movement.  A small screw thru the bottom of the piece might stabilize it.

Thanks again for the design.  I’m looking forward to getting it up and running.  I really want a highly secure way to hold my hot end and this looks like it will do it.

The bearing arm did not seem to have a perfectly flat surface across the back.  I would have rotated it that way to print a smaller overhang but then it would have needed supports, just like a slight raft for 1 layer under about half the part.  So I printed it with the holes closer to the bed. 

I am waiting on some connectors to come in for my extruder and heater wires, then I will install those on the wires so it can be easily removed and I will do this mod at the same time.  Hopefully by this time next week I will have it done.

Has anyone printed it yet?

Second, to answer mdrVB6 question, the bump just on the front of the bearing block (where the horizontal platform screws in, is what hits the end stop on mine.  I'm currently using the Lawsy carriage replacements. 

I can also post the individual STL files (later this evening).   You can always use NetFabb Basic to separate all the pieces.

In fact it all started as a single model, then I imported it into NetFabb, where I separated the individual parts.  Then I imported all the parts into Repetier, rotated them and arranged them to create the current layout, then saved the whole thing as a single STL. 

You can always use NetFabb Basic to separate all the pieces.

Edit: is there anyway you can make the pieces available as separate .stl's?  If you did this in sketchup you could send me the file and I will do it for you.  I want to print the tension arm on its "back" so that I can do it without supports but I need to rotate it but I can't do that with them all in once file.  Thanks.

I use something called Acrylic Cement from Tap Plastics which is a highly concentrated form of acetone.  Using this, glue joints are stronger than the surrounding material.  Once you have this, everything else goes together with screws, no more gluing. 

Other Assembly Notes:
The rear bearing block is held in place by a single screw, you don't want to overtightened it, you want it to be able "float", this way it doesn't bind during fast moves, it sort of "follows" along because it can pivot slightly.

Depending on how accurate your printer is, the holes for the LM8UU bearings might be a bit loose or tight, In my case they were near perfect, but after a little use the bearing started to partially come out after long prints, so I took them out, wrapped them in a couple of layers of Kapton, put them back, and they never came out since.

The Spring is something I bought at the hardware store.  I bought one of those bags of 100 springs for $4, and there were about 4 like springs that fit perfectly.  The "cups" the springs sit in, are 8mm diameter.  and the spring, uncompressed, is about 20mm long.

The little block the spring presses against can be adjusted slightly to apply more pressure on the spring.  Simply turn it counter clockwise a few degrees to compress the sring more, then tighten the screw.

The hole at the bottom (leading to the hot end is 4mm and it's designed to take a piece of PTFE tubing (4mm OD x 2mm ID).  At the top, in the spring loaded arm, the hole is actually a slot, and it's meant to stay open, this way it gives the filament a chance to move bit while it centers itself in the drive gear groove.

All the screw holes are for M3 screws.  I recommend using washers on all the screws.  The pressure bearing arm uses a M5 screw for the bearing.  Just reuse the bearing and screw from the original extruder.

That's about all I can think of for the moment.  Let me know if you have any problems.

PS.  I don't know where the temp zones are on the E3D, perhaps Elmoret can chime in.  So I'm not sure if the E3D will affect any of the surrounding areas.  Especially if you consider the E3D can be cranked up really high to print nylon.  Speaking of which I would like to get this printed in Nylon.

Also, is that a particular size spring, or whatever you can find at the hardware store?

I will probably drill out the hole at the top so that it is big enough to get the PTFE tube from the top of the hot end sink sink to very close beneath the drive gear.

Here is what it would look like fully assembled (I didn't show the LM8UU bearings).

The original design was covering most of the got end body.  When the hot end got up to temperature, it softened up the plastic enough to distort it.  After the first use, though the whole thing stabilized and never got any worse,  and the hot end was still solidly held in place. 

When I eventually opened the assembly, it turned out that only part of the hot end body got hot enough to affect the plastic around it.  So this time around I cut back the hot end holder to the first flange.

I've also changed the bearing pressure arm to a quick release type.  This requires a 8mm OD spring.

The STL is a layout of all the parts.  If you prefer the STL of the complete unit, I can post that as well.

NOTE:  The version above is for the original SD3 hot end.  I'm currently working on a modified version for the E3D hot end.  I should have it done in later today.