Fine tuning RapMan 3.2 - Hot End clearance

The RapMan gives us several tools to raise and lower the hot end relative to the bed.

The first, and most basic, way to set the distance between the hot end and the bed is a long screw that hangs down from the extruder assembly.  Each time we select the bed height option on the console, the printer homes the machine so that this bolt can activate a switch and then the printer uses that position to move to the center of the bed and lower the hot end to the position called for the bolt's length.

The manual calls for adjusting the hot end so that it barely touches the bed.  "Barely" is the operative term.  I'd like something a little more measurable.  To get the most precise setting, I decided to use a mechanic's tappet gauge.  So, I started with the 0.102mm leaf on the mechanic's gauge to get the hot end as close as I am able to measure. But, through trial and error, I found that my particular printer responded best (laying down an undistorted raft) at 0.254 for PLA.

Here are the steps I use.

1. Press the Z-Height Selection
2. Make sure the Z-Height Offset is 0
3. Try the 0.254 leaf of the gauge under the hot end.
4. If there is a lot of clearance, tighten the adjustment bolt.
5. If there is no clearance, loosen the adjustment bolt.
6. Exit Z-Height adjustment

Repeat the above steps until the gauge just slips under the hot end.  Do NOT make changes to the Z-Height offset.  You are setting the base point and will use the offset to further fine tune for different situations or special cases.

I understand the critical nature of getting the hot end (Z-Axis) height right for the raft.  But, it's still unclear to me that it makes much of a difference in subsequent layers as the Z-Axis increments should take care of itself in spite of the starting height as long as the height was sufficient to create a starting raft.

And, the optimal height for any given printer with any given material might be a bit different.  That is because the setting you end up using is the setting that is able to lay down a nice raft without tearing it or distorting it.

The point is that we can get more precise in by using tools, like a mechanic's tappet gauge, we are better able to control our printing environment on a repeatable basis.

Follow the Directions!

I have good news and bad news.  First, the bad news.

The Bad News.

My precariously built hot end has failed.  It has clogged.

The Good News

The good news is that the failure had nothing to do with the quality or reliability of the RapMan kit.  It was all me.  And, the reason why that is good news is that, hopefully, I can help other new builders avoid the mistakes that I have made.

Mistake #1 - Cutting the PTFE insulator too short.

The directions call for cutting a small slice off the end of the PTFE insulator.  The operative word here is SMALL.  I sliced off a tad bit too much and, from my research about clogging problems, this is DEFINITELY not a good thing.  It apparently allows melted plastic to rise up and cool, clogging the hot end assembly.

I am ordering a new pre-built hot end.  But, I am also ordering a non-built hot end kit so that I can demonstrate the RIGHT way to do it.  At least the RIGHT way is the plan.  LOL!

But, for now, make sure you cut just enough of the material to square the end, taking off as little as possible.  Put that squared off end into the PEEK insulator leaving you enough room to cut it again when you assemble the wooden MDF plate.

The directions were absolutely clear.  I wasn't!

Mistake #2 - Not paying attention to the material type before taking it from the box.

In taking out the material I've been using for the duck tests, I failed to pay attention to whether it was PLA or ABS.  I simply made the assumption that it was ABS.

That meant that I was selecting a test model that was built for ABS, which requires a hotter temperature than PLA.  This overheating also probably contributed to the results I'd been seeing and the ultimate clogging of the hot end.

The type is not printed on the reel.  It is only printed on the box in which it is shipped.

I usually toss boxes immediately.  But, fortunately, I had not tossed it yet.  So, I was able to correctly identify the correct material type.

I'm learning that a perfect build is all about paying attention!  Fortunately for me, Bits From Bytes makes a very high quality product, has anticipated people with my building skills and makes a pre-built hot end available on their store! :)