Idea for quick switch bed: feedback requested

[brvdboss]

Hello all,

There have been a number of designs and ideas for easily changing between the different tool heads. But not really for the bed itself. Personally I don’t have that much of a problem with switching the tool heads (just 4 screws) but I don’t like to change the bed which is a lot more work than the tool head.

The only idea I know of (so far) is the use of magnetic strips like posted here: Easy way to switch build plates
But I’m not sure that would work good enough for CNC. I had some concerns about how “flat” it would be in the case of 3d printing, but that would be just a matter of creating a slot in the build plate with the cnc so the magnets are countersunk/flush with the buildplate.

My ideal solution would be something like:

• prepare a “premounted” board for all toolplates. so one for the printbed, a cnc wasteboard that can actually be wasted and one with the laser plates mounted.
• “click” that prepared plate in place and just go.

Before trying to build something myself I thought I’d first try and pitch my ideas here and get some feedback.

What have I tried already:
Mill flat the cnc wasteboard and put my printbed on top of that to get a surface as flat as possible. I was a little bit concerned about the heat so I had put a heat resistant silicone mat in between which actually had the nice side-effect I could use the screws to “squish” the mat to finetune the flatness of the bed even more. I didn’t take a good picture of that but you can more or less see it on this one:

I did use the totally wrong type of wood for this, which started bending really bad MDF would have been the far better choice as that is much more resistant to changes in humidity and temperature. And then I probably wouldn’t have had to “finetune” the leveling at all. Lesson learned. Another disadvantage is that it’s even more work to mount/unmount the bed as I did it with longer screws all the way through and the different layers weren’t fixed together.

So new and (hopefully improved) idea:

• keep a cnc wasteboard permanently mounted on the carriage and use that as the easy attachment layer: This should allow to use something else than the screws to connect it to the carriage and provide more flexibility
• have a piece of MDF to which all buildplates can be mounted. For CNC I actually already have been screwing a sacrificial plate between the wasteboard and my workpiece. Although that was mostly because I needed peg holes for double sided milling. See below*. The peg holes did provide a lot of “fixation power” to the workpiece which gave me the idea.
• the above premounted MDF board could use carriage bolts (completely countersunk obviously) which go all the way through. 4 should be sufficient.
• these could be tightened from the bottom with just 4 wing-nuts. Or if I wanted to do it more fancy things like these threaded cam levers: https://www.wdscomponents.com/en-us/cam-lever-cam-clamp-female-thread-red-aluminum-handle-wds-369/c-400/p-2097. Or maybe the combination of magnets and 4 peg holes with steel pieces of steel bar that I used for my cnc project would already be sufficient. but I’m a bit worried that those might be more susceptible to wear and would get loose over time. Hence I would put a bolt through that can be tightened from the bottom. And by using carriage bolts, they won’t spin and lock in place.

I’m having some problems so far finding a supplier for those fancy lever clamps, but it should be possible to make those myself by using some barrel nuts and 3D printing the rest of it, and glue a washer to the bottom of the wasteboard to make it easier to flip them.

Advantages:

• “easy” mounting with only 4 screws/wing nuts/clamps from the bottom.
• always flat surface, only once to mill the base plate flat and from then on, no more worries.

Disadvantage:

• some work to make all this
• you lose some build-height.
• Some extra weight on the carriage, but that shouldn’t be a problem

I would love to hear some feedback on this.

* I needed to do double sided milling to create a tablet wallmount. Needed to cut parts from the back as well for the cabling). (Tip: use painterstape on your plate and workpiece and superglue to connect those together, works really well!)
Front: (cutout is for a magnet to fix the tablet in place)

back:

finished product after painting and mounting:

The tablet can be removed and is “attached” by the magnet in the wallmount (and sticker on the tablet). Charging is done with a magnet charging cable that connects/disconnects as you mount/unmount the tablet.

[StumbleRunner]

How much elevation do you figure you’re going to lose by adding the toolplate mount?

[brvdboss]

That would depend a bit on the thickness of the MDF used.

• The SM wasteboard which I milled flat is approximately 10mm. (12mm new out of the box).
• the MDF plate I have laying around is 18mm thick.

Adding those two together results in 28mm extra when 3D printing or the laser bed.
18mm is the more or less standard thickness every home improvement type store here has on stock for the water resistant MDF. You can find it in 9/12/15/18/22/25/30mm if you look around, but 18mm is most common around here. The non water resistant version is usually more easily found in the thinner versions.

But I do want it to be sufficiently rigid. So I personally would prefer to have it 5mm thicker than necessary than to have it too thin.

I’m trying to make some sketches of it, will upload when finished.

[brvdboss]

As promised an update with a first “sketch”

STL-version if you want to have a look and rotate the model: mountingplates.stl (3.4 MB)
What do you see in this picture:

• bottom plate: this is the waste board, or a new custom waste board.
  • it has the holes needed for mounting it to the carriage; there are 4 “crosses” These could be 3d printed and are used to "fix/align the bed
  • it has 4 through holes for the carriage bolts
  • the screws to mount it to the carriage (and the carriage itself) are not visualized in these images!
• 4 crosses as a fixture:
  • these can help to keep the bed in place/aligned
  • I think that for 3D printing and lasering it might not be needed to use the bolts as the forces on the bed are rather limited, so I don’t see it jumping out easily, depends on speed and how tight it can fit.
• middle plate: on this the bed is mounted so it has the same mounting holes as the carriage which should be threaded inserts so it’s a drop in replacement for the carriage.
  • This one also has the countersunk holes for the carriage bolts
  • On the bottom it has the same “crosses” for attaching it to the bottom plate
• then floating there are the carriage bolts
• the actual top plate: this represents the 3D print bed or the laser bed.
  • For CNC there wouldn’t be a reason to add an additional layer on top. So in that case it would also need to have holes for inserts to use for clamping

I’m not sure if the crosses are good enough on their own. They need a tight fit and a high risk of wear over time making them unusable. The carriage bolts on their own should be good enough.

To be clear, all top layers are intended to be mounted to each other and stay that way. Only thing needed would to put it on top of the bottom plate and tighten the carriage bolts from below. This part should be stable and MDF should be flat enough.
The bottom plate is then milled flat to make sure it’s completely parallel to the x-axis guaranteeing a flat mount every time.

Some things to add/to do:

• the bottom plate should have some notches in them so you can grab the plate on top and easily remove it.
• double check I’m not running the bolts into the y-module or carriage. I now more or less guestimated a potential place without measuring I might just have pierced the y-modules in the current drawing
• for the 3D print plate, there must be a small part milled out from the center for the temperature sensor
• for the cnc plate it’s an opportunity to choose a different grid size for the threaded inserts to offer more flexibility (why not 4x4 cm in stead of 5x5 now)
• the more I think of it, the more I think the 4 crosses should just be ditched completely

But overall, I think this might actually work.

Important: This is only a concept! Has not yet been tried and measurements might still be off! Only published here to gather feedback and trying to improve the design before I actually have a go at his!

Any feedback welcome!

[brvdboss]

Some items scratched off from the todo list:

• notches created in the bottom plate: check
• put bolts in a place where they do no harm.: check It might even still be compatible with the new carriage referenced in the manual (just noticed that one here: SM2 Bed Leveling 101
• separate mounting plate for print, laser & cnc: check (laser & print are basically the same except for the cutout of the temp-sensor
• I finally did keep the cross-things in place. Maybe it would work, maybe not, but I think I’ll try anyway. I think it could be just fine for laser & 3d printing. if it doesn’t work that good, they do no harm. I’ve designed them to be a through hole in the platform so it can be milled from a single side.
• used a different grid for the cnc plate (spaced 3cm apart in stead of 5 11x12 grid)

It should be possible to mill everything from one side (2 sided milling can be a challenge, so let’s avoid it) Only to countersink the threaded inserts for the cnc that won’t work. But that could be done manually with a drill, the accuracy of the bigger hole to countersink is less important.

todo’s:

• I should probably make the cnc plate compatible with the clamps I designed earlier (Printed CNC clamps (sideways): feedback welcome)
• check the measurements of the carriage bolts (need to get some first)
• actually make it
• publish it on github/thingiverse

screenshot:

(stl is too big to include in the post)

[opdehoek]

I agree the bed change is the most time consuming, toolhead changes is not.
But i was thinking of puting a metal plate under the CNC-bed so it could be hold by the headbed magnets. Also the laser bed could be mounted on a metalplate.
Changing beds is then very easy.

[brvdboss]

Thanks for the feedback. I highly appreciate it!

part of my reasoning for this approach:

• I didn’t want to put it on the heated bead to avoid unintentionally breaking it. For example the top coat of mine is already somewhat scratched exposing the copper of the heating element (still works, nevertheless, it’s not that difficult to damage it)
• In my cnc projects I’ve already had some unintentional mistakes where the bit broke, or ran the head in the workpiece. If it was in place with only magnets, I would have needed to restart from scratch because I’m sure it would have moved and would be very difficult to position it correctly again with the required accuracy. Hence I want a mechanical element of keeping it in place. I think magnets are a good solution for printing & laser, but not necessarily for cnc. But it could be a good solution to embed magnets (or metal) to have the printbed on the bottom plate directly without the need for th intermediate plate. But I think it would be more difficult to get it flat. This is also more or less the approach of the topic I referenced in my opening post.

A metal plate could be challenging as it might increase the time it takes to heat the bed. Basically, you’re making the entire printer a large heatsink which is not necessarily what you want. In my experience using the wooden base plate actually acts as a form of insulation to speed up the heating and making it more stable.

[brvdboss]

I kept thinking about your reply. The laser has these cutouts where the screws go. What if we glue in some magnets there. The base board can incorporate cutouts for some metal pieces that can be glued in place and then that might be enough to keep those in place.

To increase friction some cutouts for a rubber strip could also be foreseen. That might then also be sufficient for the printbed. This does mean incorporating more and more materials and keeping it all perfectly flat becomes more of a challenge again.

It would make mounting the printbed and laser plates completely toolless though… Just snap it on there.

I still wouldn’t trust it for the cnc. (depends on what type of work you’re doing on the cnc)

Always too much ideas…

[StumbleRunner]

I guess for the CNC you just remove all the stuff above the base plate/waste board.

[brent113]

Not to completely derail all the progress that’s been made on this so far, just offering up a shower thought I just had:

What if instead of magnets as a retaining mechanism it was a cam lock and slots, here would be on the right of the diagram which I imagine would be the front of the machine:

Something like a bed frame quick release:

Or even a sliding locking mechanism:

There’s got to be a simple, elegant way of inserting the rear of the work table into a locking mechanism, then latching the front so it’s secure for even CNC.

[ITmaze]

I’ve been thinking along slightly different lines for a while. Not only for bed-holding, but also tool and work-holding.

• https://www.mcmaster.com/threaded-dowel-pins/headless-alloy-steel-precision-shoulder-screws/

The idea is that you use existing threads in build-plates, tools, etc. and use the stud or dowel to repeatedly place the item in the exact location.

Clamping becomes a separate issue using the above “alignment”.

o

[MooseJuice]

Another off the rail idea… I don’t know if you’ve ever seen these snap together “hook and loop” substitutes before, but they are in credibly strong.

The adhesive would give before the snappers would, so maybe making some kind of frame / brackets out of sheet metal that binds it to the bottom plate, then a recessed 2nd plate which has the table you wish to use to clear the frame.

I love this stuff.

The rolls of this appear to come in up to 3" from mcmaster, perhaps you can get wider rolls from a different distributor who might specialize in this sort of thing. I am pretty sure these are made in wider rolls then cut to size. most things like this are anyhow.

i think i might fiddle around with this a bit.

[brvdboss]

@StumbleRunner

I guess for the CNC you just remove all the stuff above the base plate/waste board.

That could be an option, but then it would be better to also add the inserts in the base plate so you can use those to clamp your workpiece.

As I want the base-plate to be my flat reference. and just want to mount it once and never touch it again, my intention was to put a wasteboard above for which it isn’t a problem that it gets damaged. And potentially in a slightly softer version of MDF.

@brent113

Not to completely derail all the progress that’s been made on this so far, just offering up a shower thought I just had:

That’s why I wanted to create a topic to collect different ideas before spending hours making stuff and see someone else come up with a much more elegant solution

I do like the idea of the slots and actually it was on my mind too. Not in the tilted way you described (which is quite fool-proof) but with tradtional t-slots. And then a lever on the side to lock it. 2 slots front to back and 2 levers on the front and on the back would be enough I think.

Or a catching latch (not sure about the terminology here ). Basically like a dowel pin sticking out of the base, from the side a “hook” type latch that catches it and as you close it also tightens it.
Something along the lines of this (but also pulling it closed, not just latching):

Another variant is like a “chest-lock” or the type of spring locks you have on a spring-form used for backing. like this:

But with both of those options I was struggling as where to attach those. For the box lock I was thinking underneath the base plate and have them pull down on the front and back, but you don’t have that much space at the bottom to put these.

@ITmaze

The idea is that you use existing threads in build-plates, tools, etc. and use the stud or dowel to repeatedly place the item in the exact location.

Yes! That’s where the inspiration for the cross-shaped cut-outs came from!
Why not just use round dowels? The projects I’ve done with two sided milling have learned me that if you just put them in wood, the holes will start to show some wear and they will get loose, so i wanted to use the cross shaped section to make it less susceptible to this. (because there is friction in all directions. Another solution would be to make the holes a bit bigger and insert a piece of tube to avoid that wear.

Your idea is also along the lines of what @brent113 mentioned in this post: New quick toolhead change print - #15 by brent113

That was my first idea in combination with the box-locks, but I failed at finding a good place to attach those.

@MooseJuice

Another off the rail idea… I don’t know if you’ve ever seen these snap together “hook and loop” substitutes before, but they are in credibly strong.

So should I consider this to be like a sort of velcro on steroids? Or does it also help to align the two connecting pieces?

Finally some updates from my side:
I have been tweaking the model a bit more and cleaning up the openscad code a bit. I intend to have it online on github soon. Mostly to make sure I do proper version tracking for myself as well

It came out pretty well (on the right hand side you can see that the toolhead doesn’t reach far enough to make the cutout of the handle. Left and back work out just fine. The front just falls short but you can easily break out the remaining piece.

The good news is that all holes align up perfectly (yay!). I did do a quick test by running a calibration with the 3d print heat and just the sheet on top of the wood and it looks pretty good. There is still a deviationm but the surface is flat, just tilted. (hence the idea of machining it flat. Or this board could just be shimmed.

I modified the through holes for the carriage bolt so I can fix those to the build plates with a washer and nut from the bottom as well. (in stead of just having the hole there. Should make installing easier.

And as they say: measure once, cut twice (or how exactly did that go? )

The location of those through holes is actually ok. It’s about 7mm away from the carriage. Which is ok for a normal bolt, ok for the type of clamps I first intended to use there but not for the wing nut I wanted to use for initial testing.

Nevertheless, good enough for a first iteration and doing some more testing with it.

But because magnets are fun, and it would cooler if I didn’t need screws/clamps at all, I finally did order these (pot magnets):

25mm diameter and supposedly 18kg of pulling force.

I chose those with the threaded barrel so they can easily be adjusted in height if needed. (and to prevent having them glued in place and just ripping them out every time because the magnet is stronger than the glue.

combined with these:

because they have a small border, that will prevent them from sliding away.

I figure that 3 or 4 of those magnets in the base plate should be enough to keep it in place.
Or maybe even already impossible to remove without a crowbar

I’ll be trying out some more stuff later this week, so if you think I should try something else as well, do let me know!

[brent113]

I think this is essentially what I’m thinking of - a thin flush mount bracket:

Extra-Thin Flush Mount Brackets, 1-1/2'' x 1-7/8''

A pair of those on each of the corners, maybe one in the middle too for 5 pairs, carefully located so they are a snug fit (maybe counter rotated 2 degrees), would hold well in all directions except 1 (the direction you insert from). You could drawbore a pin/bolt to keep the table in tension against the hardware.

Edit:
Yes I was thinking these would be countersunk so the pieces are in contact. The one in the middle I guess would resist bending of the wood for seasonal movement if it tried to lift up. Nothing is really holding it down.

And yea, your latch previously, or any other number of solutions would work in lieu of the pin. I think it’s important to be kept in tension or compression, a simple bolt from top to bottom I don’t think would be adequate. It needs to have spring pressure to preload the hardware.

I guess if the way they are flush mounted is done just right, maybe mounted at a downward angle so the brackets are really snug and get tighter as they are inserted, then a light tap would “seat” them in tension against the friction of the 2 surfaces in contact. Then a simple bolt would secure to make sure it doesn’t loosen.

[brvdboss]

This does look very simple and nice indeed.

It might be good to countersink them so the two plates are directly flat against eachother. To avoid the empty space between them and eliminate any wobble. In that case I don’t think you would need the one in the middle.

Alternatively to the pin the the bottom, plate could also be a bit longer or have a small extrusion in the front big enough for a hole something like a cam-lock type of latch to keep it in place.

The elegance is in the simplicity definitely. I like your idea very much.

[brent113]

I have used those brackets before and there is a bit of slop in them - to get them to work in this zero backlash way I think is possible, but will require careful design and CNC so that inserting them puts them in increasing tension and pulls the work table snugly onto the base. I put some additional notes above.

I think you’re definitely capable of doing that and I think the tolerances would be looser than what you’ve already done with the X inserts.

There may be a clever way of countersinking them just slightly too deep and using the attachment screws (and maybe shims) to control the tension. Getting adjustability into this, without introducing something that will loosen over time, will be interesting.

If this is expected to last a long time and maintain adjustability I’d be concerned about the wood screws provided in MDF - it will chowder out the screw hole eventually. If this was my build I’d use threaded inserts from the back (T nuts probably) with thread locker and a machine thread - at least on the base since it is “permanent” and will see more wear than each tool plate.

Dialing in the adjustment, in my head, would look like roughing in the height with shims under the brackets and repeatedly test fitting the work board, adjusting the base screws and shims until it’s perfect. Then, since the shims under the brackets control the height, apply threadlocker and tighten the screws down.

[brvdboss]

The slop sounds like something a hammer could fix but doing the mounting carefully could probably eliminate most of the issues.

It could also be an option to place them in a circular orientation, so that you turn them in place. Similar to what some light fixtures use. As you turn, it pushes both sides closer together That might help as well to get the tolerances in the fit to be less of an issue. Last weekend I struggled a lot to get it loose from one of my wireless access points

It’s a snap fit, so it’s a bit loose at the end, but the “snap” part isn’t necessarily needed here. Although I’m not sure if it would add that much value and I’m just overengineering again.

@brent113

If this was my build I’d use threaded inserts from the back (T nuts probably)

Exactly. That’s also the reason why I’m using the carriage bolts in the initial idea; to keep them locked better (and obviously avoid them to turn around as they are tightened from below.

Now my main challenge is to find the correct name in Dutch for these things to find a local store/supplier where I can get these things

The dowel/pin part aren’t the perfect solution as you would need access from above (and the having everything premounted is kind of moot). But maybe the box lock type of latch could be used somehow.

Edit:
An extra advantage is that you can just hang the plates you’re not using on the wall so they are out of the way!

[brvdboss]

These might be an alternative for the rockwell brackets as well. As they connect there seems to be a slope so that they are actually pulled together. They are significantly thicker though:
https://www.amazon.nl/gp/product/B07R4N2STK/

But they do look sturdy and like they would last.

[brvdboss]

I quickly created a small 3d model of these to test the concept before I put in an order. (not an exact replica, but similar design) That should give a good idea if it could work. A3d printed model might even be good enough if if it is countersunk in the plate and all snug in there. (model created with a tolerance of 0.1mm for) Not yet tested/printed. That will be for another day.
preview:
slide-connectors-hook.stl (409.1 KB) slide-connectors-sink.stl (305.9 KB)
(to be printed standing up for optimal strength)

[ITmaze]

I’ve noticed that there’s no discussion on using T-slots on an extruded aluminium bed like many CNC machines seem to have.

Here’s an example:

https://makezine.com/projects/add-t-slot-bed-to-x-carve/

Is there any reason that this doesn’t seem to be considered?