Dennis Brown: Replacement bed clips - psmay/mpmd-notes GitHub Wiki

Source

The original version of this came from https://www.facebook.com/groups/mpminideltaowners/permalink/2134979383184203/, written by Dennis Brown, as it was 2021-03-30. Refer to that post for updated information and comments. Some reformatting has been applied (its correctness is not guaranteed).

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This is the most critical part upgrade for good bed leveling on the MPMD.

This post is part of my overall MPMD essential upgrades and alignments here:

Dennis Brown: My printer tune up and alignment process and needed upgrades

EDIT: I have changed some of the hardware pieces around so that they can be ordered in a small quantity from BoltDepot.com for under $6 including shipping for a set of 4 clips worth of metal hardware. The 2 binder clips can most likely be found at an office supply store (or in your desk drawer), in small quantities.

This is a replacement bed hold down clip that is much more stable and is also adjustable to fine tune the auto level with the G29 command. My previous design was to help stabilize the existing bed hold down clips, but this one is a complete replacement made from OTS parts and a printable part. The design goals were:

  1. Complete replacement using the current 5mm hole.

  2. Installed from the top only.

  3. Printed part out of PETG or PLA.

  4. No plastic parts in contact with the heated bed.

  5. Adjustable height with a hex key wrench.

  6. Swings out of the way for bed removal.

  7. Does not interfere with a 5" glass mirror.

There are two main features. The first is the use of 3-48 screw and hex nut that can be slipped into the 5mm hole sideways, but can not fit through the hole straight on. The second is the use of a small binder clip bent wire handle that actually bridges between the bed (touching at one point), and the printed part. It acts as the heat break and also allows for a 4-40 button head screw to set the height.

One option I considered is the use of a small O-ring and flat washer to apply tension to the mounting screw nut, but allow the clip to rotate away from the bed. However, it is more stable to have the clip fixed solid so it can not rotate out of the way without loosening the mounting screw, so I have abandoned that option.

The pictures show my parts printed in PETG, all the tools used to install with the piece parts, and the clips installed on my printer. The SCAD part design is also in the pictures. I printed the part as a solid piece on a raft. I tweaked the hole dimensions in my model so that I did not need to clean up the holes with a drill. Just sand the bottom of the part (which came off a raft), run a 4-40 screw through one hole to roll the threads, and start assembling it. I can not guarantee that your printer/filament will not need some minor tweaks to the 4-40 hole to have the threads come out just right, without too much friction. Only you will know for sure. There are good captions in the pictures.

Parts List: Note many of these parts are sold in much higher quantities than needed for just 3 clips. However, the special screws and nuts can be purchased from www.boltdepot.com in any quantity with a single shipping charge ($4.95), so that is where I have sourced these.

You may wonder why no metric screws? I tried, but the metric sizes did not fit the requirement of head size for the adjustment screw. The 4-40 is half way between an M2.5 and M3. Also the 3-48 nut size was perfect to fit the 5mm hole. It just worked out that way.

(3) Print hold down clips out of PETG or PLA.

The text for the SCAD model is in a reply to this post if you want to get to the source. It is also in a screenshot in the pictures.

MPMD_BinderBedClip scad (Source: https://www.facebook.com/groups/mpminideltaowners/permalink/2134979383184203/?comment_id=2136028969745911)

The .stl file is in the files section. Slice it with a raft and 0.14mm layer height. No infill. 6mm wall thickness will make sure it is a solid part. Print one part first and make sure the hole sizes are good:

(Source: https://www.facebook.com/groups/mpminideltaowners/2136026146412860/)

Here is the Cura profile I used:

BinderBedClip.curaprofile (Source: https://www.facebook.com/groups/mpminideltaowners/2136109069737901/)

You can also print it from a .gcode file that I already sliced to make good parts. You will have to edit the file text with the temperature for the hot end and bed and the type of G29 you currently use on your machine to get good prints. You could also just replace the startup gcode with the startup gcode you use on your current slicer. The .gcode file prints slow, so it takes 30 minutes per print:

(Source: https://www.facebook.com/groups/mpminideltaowners/2136024293079712/)

(2) Binder clips (remove 3 wire handles). They are sprung too wide for this application. I squeezed them together at the neck with some chain nose pliers and that set them just about perfect. You want them to be just a little bit wider than the space between the ribs where they go.

Amazon part is 144 clips of correct size for reference, but you may find smaller quantities at a office supply store or in your desk drawer (like me). The parts I used had "STAPLES" stamped into them. The critical dimension is the approximate 1 inch length of the handle:

https://www.amazon.com/AmazonBasics-Binder-Clips-Small-12-Pack/dp/B074XTRX7G/ref=sr_1_1_sspa?s=office-products&ie=UTF8&qid=1522636467&sr=1-1-spons&keywords=small%20binder%20clips&psc=1&fbclid=IwAR0R_6jBWdiz-W6555jf1vubBmqFru28nXUgZOmUDWmz989rO57eJcyAqMA

(3) 4-40 x 1/4" SS hex button head screw. This screw head is short so it will not bump into the hot end fan housing. 1/16" hex key.

Bolt Depot #5462:

https://www.boltdepot.com/Product-Details.aspx?product=5462

(3) 3-48 x 3/8" SS hex button head screw. 1/16" hex key.

Bolt Depot #21163:

https://www.boltdepot.com/Product-Details.aspx?product=21163

(3) 3-48 SS hex nut (must be 1/16" thick and less than 5mm across flats).

Bolt Depot #11911:

https://www.boltdepot.com/Product-Details.aspx?product=11911

EDIT: For those asking for a metric equivalent, the closest metric screws would be M3 x 6mm for the 4-40 and M2.5 x 10mm for the 3-48. The M2.5 nut may be a little big to get in from the top side, it may have to be assembled from the bottom of the plate. I have not tried this yet, it is all by measurements only. You should still use the same hex button head type. You may have to adjust the plastic part holes and countersinks slightly depending on the exact dimension of the screws you locate.

BED SHIMMING ALIGNMENT (optional):

For most printers this step is not required to get satisfactory results. If you just want to take a chance that your bed is "good enough", and plow ahead with the rest of the alignments, then skip this step. If things do not work well later on, you may have to revisit this step.

For the best alignments, the vertical carriage rails should be parallel to each other and the bed should be perpendicular to the carriage rails. This is not easy to measure with "hobby" tools, so we have to make some assumptions and improvise. The first assumption is that the the factory properly aligned the vertical rods to be parallel to each other (This was not the case for my machine, but we have to start somewhere).

The second assumption is that the steel plate that supports the bed, switches and bed clips is perpendicular to the vertical rods.

[Edit: this turned out to be a bad assumption. My machine baseplate was out of square to the rails by over a mm, so I had to come up with a different measurement method.]

[Edit: The post for my top of bed switches describe the alignment process and also point to making the speed square fixture. The difference is that with my top of bed switches that alignment is with a screw adjustment rather than a shim.]

Dennis Brown: Top side bed switches

[Edit: Shimming the bed without top of bed switches is tedious.

First remove all the bed hold down clips.

Then with a square tool against the rails (it helps if you have a flat plate to bridge between a pair of rials), identify which of the 3 rails has the highest top of bed (don't rock the bed by pushing down on it with the square). The highest tower will not get a shim.

Insert paper shims between bed and switches on the other two until the bed looks equally square on all three.

Take out the paper shim stacks and measure them. That is the 2 different shim sizes that you will need.

Use a mix of index card or paper to make a small shim stack (about 10mm wide), of the appropriate thickness and affix it to the bottom side of the bed with a single layer of aluminum HVAC tape.

Careful that when turning the bed upside down you do not lose orientation of which shim goes where. You might want to make 1, 2, or 3 dots on the edge of the bed next to the bed clip area and also mark your towers, so you can put things back in the correct orientation.

Put a single layer of HVAC tape also on the non-shimmed switch to balance all three switches.]

BED CLIP ASSEMBLY:

The pictures can help with the assembly.

  1. I use reasonable cleanup on the printed part, sanding the bottom flat (bumps from the raft), and cleaning up any strings in the holes. The 4-40 screw hole should be pre threaded before assembly. If it is too tight it will be hard to adjust. If it is too loose, it will not hold the adjustment and should be reprinted with more flow (e-steps calibration). I poke the wire ends of the binder clip handle from the outside through its holes to clear them. The 6-32 set screw hole at the back of the part can be ignored. It is for an alternative design.

  2. Insert the binder clip into the part. The binder clip should be squeezed with chain nose pliers at the neck all the way. The back end should be just a little wider then the inside space (7mm), so that when installed it has just a little spring tension left in it. It takes a bit of effort to get that binder clip installed. Just work at it until it pops in. Then swing it up and down until it seems well seated and friction free. When down, it should want to rise up off the bottom a bit.

  3. Insert the 3-48 SS hex button head screw through the part. Next thread the SS hex nut onto the screw. I think it is helpful to screw the hex nut all the way down and cinch it up tight with the hex key once to seat the head. Then back off the nut to the end.

  4. Lower the binder clip handle and install the 4-40 flat head screw. Use a 1/16 inch hex key to screw it down until the binder clip can move up no more than 1/32 inch. This will help hold the 3-48 screw in place during assembly.

  5. Remove the existing bed hold down clip if you have not already done that. You have to pull out the plastic pin and then pry it up.

  6. Unscrew the 3-48 nut so that it is all the way out to the end of the screw (and maybe even one thread beyond). Now position the clip so that it can roll over the beveled side and cause the nut to slide sideways down into the 5mm hole. You will have to align the nut so the flat sides are parallel to the hole (one point straight up). You may have to wiggle it a bit and push pretty hard to get it to go in. once in, you can position the clip upright. With the clip upright, the nut will not be able to come back out the hole.

I explain it again a little differently in this comment:

(Source: https://www.facebook.com/photo.php?fbid=1656895247756878&set=p.1656895247756878&type=3)

In case you are having trouble with the instructions for how to install the clips, here it is explained another way.

I designed it so that you can do the assembly completely from the top side without taking the printer apart (though, taking the printer apart is an option).

If you unscrew the nut to the very, very end of the screw, but not remove it completely from the assembly in your picture, you can push the nut through the hole sidewise (see photo). Then straighten out the clip and pull up and spin the screw with the hex wrench. The nut will stay on the underside of the plate. This is sort of like the way you put hollow wall anchors (toggle bolts), through a wall for hanging things on a wall.

You might have to rotate the clip partially sideways a bit to get the nut to catch in the hole so it will not rotate while spinning the screw with the hex wrench. Once it is almost tight it will catch on its own.

When first trying to get the nut through the hole, you will need to make sure the flats of the nut are on the sides (point of the hex nut is up), to get it through the hole. You may have to use a bit of force to get it through the hole (a very small flat blade screwdriver can help apply pressure right at the nut). The closer the nut is to the end of the screw, the easier it is to get it to go in.

If you are not careful, the nut can rotate off the end of the screw and drop inside the bottom of the printer. If that happens, put another nut on the screw and try again. Any nut that falls into the bottom can be retrieved later by taking off the bottom plate.

  1. Use the 1/16 inch hex key is small enough to fit between the binder clip wires to screw the 3-48 screw. You will have to pull up on the clip or angle it a bit to get the nut to catch enough to thread it up the screw. keep screwing until it is very slightly tight (the clip should not yet be over the bed).

  2. Repeat the installation on the other bed clip locations.

  3. Back off the 4-40 screw to give some play to the clip. Swing the clip over the bed and tighten the 3-48 screw snug (don't over-tighten and strip the hex key).

BED CLIP ALIGNMENT:

  1. Screw the 4-40 in until the clip just touches the bed on all 3 clips.

  2. Power on the printer so the bed switches activate the single button light. It helps if the head is homed.

  3. Slip a 0.24mm shim (110# index card stock), between the bed and one clip. Adjust the 4-40 screw until it is right at the point of actuating the switch then back it off a hair so the switch is off, but actuates if a not much more than a feather touches the bed. You may have to go back and forth a couple of times to get it just right. When adjusting the 4-40 screw with the hex key, you should not have to hold onto the bed clip to keep it from rotating. If it does, then either you did not get the clip tightened enough, or your 4-40 thread hole is too tight.

Also put the short end of the hex key into the screw so that you have the long arm to give more leverage and control over the angle, since it only takes a couple of degrees motion to make the final adjustment.

  1. Do the alignment step on the other two clips one at a time, then go back around the bed double checking that none of the adjustments moved. Readjust as needed.

You now have a precision aligned bed/switch combination that will make it much easier to get repeatable first layers on your prints with G29 auto leveling.

The G29 command in your slicer startup G-code can now be changed to G29 P5 option to give the best results. P5 will level all the way out to the full print diameter.

MAINTENANCE:

It is easy to check the bed clip alignments periodically with your shim. It only takes a minute or two before you begin a printing session. With new parts, they might seat in after some hours or days. You may also have to retighten the 3-48 screw if it feels loose. If you retighten it, check the alignments again.

NEXT STEPS

Getting the home sensors aligned can now take place.

Images

  1. 30264359_1609112449201825_1835878371901308928_n.jpg Clip is printed on a raft. https://www.facebook.com/photo?fbid=1609112445868492&set=pcb.2134979383184203
  2. 30729770_1619322088180861_5452197868280479744_n.jpg Clips all installed. https://www.facebook.com/photo?fbid=1619322081514195&set=pcb.2134979383184203
  3. 30723825_1619321884847548_8731691885980024832_n.jpg All parts and tools needed for a clip. https://www.facebook.com/photo/?fbid=1619321871514216&set=pcb.2134979383184203
  4. 30705170_1619321894847547_1811063339355209728_n.jpg All parts and tools needed for a clip. https://www.facebook.com/photo?fbid=1619321874847549&set=pcb.2134979383184203
  5. 30714833_1619321861514217_6525291169398652928_n.jpg Clip top view (focus!). Both screws accessible with 1/16" hex key https://www.facebook.com/photo/?fbid=1619321854847551&set=pcb.2134979383184203
  6. 30726067_1619322018180868_8737689859348496384_n.jpg Side view, ready to install. https://www.facebook.com/photo?fbid=1619322011514202&set=pcb.2134979383184203
  7. 30738148_1619322054847531_7691662024790507520_n.jpg Assembled! https://www.facebook.com/photo?fbid=1619322051514198&set=pcb.2134979383184203
  8. 30726191_1619322104847526_3857555938105884672_n.jpg Bottom view. https://www.facebook.com/photo?fbid=1619322098180860&set=pcb.2134979383184203
  9. 30729618_1619322278180842_4628720047701884928_n.jpg Roll clip on beveled side into hole. It is a tight fit to get it in and may require some convincing. Note, pointed side of hex nut is up. It will not go in with flat side up. https://www.facebook.com/photo?fbid=1619322271514176&set=pcb.2134979383184203
  10. 30728881_1619322251514178_5335146364353380352_n.jpg Clip is tightened up with hex wrench like this, so not too much leverage and over-tightened. Loosen 4-40 screw first so it will not press down on the bed while tightening the mounting screw. https://www.facebook.com/photo?fbid=1619322248180845&set=pcb.2134979383184203
  11. 30713356_1619322201514183_7931031676161884160_n.jpg Clip is fine adjusted with hex key like this, so more control over adjustment. https://www.facebook.com/photo?fbid=1619322198180850&set=pcb.2134979383184203
  12. 30711894_1619322144847522_4473285112540168192_n.jpg Clip in adjusted position. It only touches bed at one point. Bed must not touch the end of the clip and must move freely. If it does touch, adjust screw position or sand a little off front of clip.]https://www.facebook.com/photo?fbid=1619322138180856&set=pcb.2134979383184203
  13. 30710335_1619321951514208_5345250639989440512_n.jpg Full OpenSCAD program model. https://www.facebook.com/photo?fbid=1619321944847542&set=pcb.2134979383184203
  14. 30707049_1619321984847538_6834884472362500096_n.jpg Cura 3.3b Layer view and Shell settings. https://www.facebook.com/photo?fbid=1619321981514205&set=pcb.2134979383184203