Some things I don't understand about the TopsCNC Heavy 🇬🇧

Tension of the wheels should be accounted for in the clamping of the top and bottom pieces of the mounts (I believe). 

Eccentric nuts for the wheels are a great idea, I have considered putting them in my design. Will have to see if they can fit. Considered that a final touch. 

My design is made to dont need excentric nut. With the top and bottom part screwed together, the more you tight screws, the more you press V Wheel in the Aluminium profil.

Edit : yes the middle wheel of 3 wheels are sometime not spinning because the 80mm screws tend to bend juuuust a little so the center wheel sometime slide on rail

Yes the Z axis height is a problem and thats why i made this standoff, you just need to do a 5cm thick waste board.

In my case in need to 3D carve in 10cm thick polystyren plate, so i use standoff for little part like aluminium.

Last night I imported the mesh files into Fusion360 and started converting them to solid bodies...  I think just tensioning the parts together will compromise the rigidity. Maybe having fully rigid parts would be better, so I am going to experiment with adding eccentric nuts into the design.

Also, I think I have an idea for the Z Axis height issue - something along the lines of a base like the Lead CNC from openbuilds to raise the spoilboard up by 40mm that the Y rail can just mount to...

I will try to post some pics of the concepts later today.

@Dustin, if you wouldn't mind sharing some more details about your modifications - I think we would all appreciate it.  I'm going to keep the design the same for the most part with NEMA 17's, but I would just like to increase rigidity as much as possible.  I am mostly planning on cutting wood, with the occasional aluminum.

@Criticaldistance, I agree fully solid Parts for the main components would be great. But remember too this has to fit on a printer. I have a 400mm x 400mm build plate so I am not worried but others might see a issue with it. With that being said if I get eccentric bolts into my design I will merge together the assemblies for rigidity. 

The design is far from finished and I keep updating little bits by day. It will become cumbersome to keep updating the files every day and reuploading them (I work in Solidworks). Hopefully can sit down and work on it this weekend. Was hoping for more progress than I have gotten this week. 

You should try it before say that the rigidity is compromise ^^ I havent any rigity issue due to this tensioning system, it's very robust.

I have rigity issue due to some other point, like 8mm smooth rode which are a bit to small, maybe use 10 or 12mm smooth rod can be the solution.

Maybe you can create a topic for idea to improve the cnc ?

@Topsie, I only said I think the rigidity may be compromised - of course I don't know for sure and I'm probably overthinking it.  Please don't take offense, your design is excellent and probably the best of 3d printed CNC's currently out right now :)

@Dustin - I only have an Ender 3 so I will be keeping the parts separate as originally designed by Topsie - what I meant by fully solid was actually bolting the parts together firmly then having a little wiggle room to tension the wheels.  Not sure if my point is getting across, let me know and I can put together a crude visual to demonstrate...

No problem i don't take offense ahah, I just said, their is more important point to re-enforce before the tighten system ^^

Like Z axis, I think I have to re-enforce it before all

@Criticaldistance, I see what you mean there. I haven't begun to print the design yet either, so all my design modifications are merely speculation. Granted, my initial modifications were just NEMA23 and T12 Leadscrews, I am now using a large 2.2kw spindle which translated into a new and possibly more robust gantry design with 10mm rods and bearings, with a larger plate for the spindle to mount on. Its been transitioning to a full redesign since moving stuff around for the motors and leadscrews changes a good amount of dimensions. Not to mention converting the files over from STL's was a pain but past that stage now. 

But back to your concern of strength of clamping. I see your side of not having two surfaces fully mate and can cause rigidity issues. The concern I see with adding the eccentric spacers into this is you need a metal surface for the spacers to deflect off of. If you deflect them off of plastic I think you will have a worse time getting them to hold their positioning before the plastic begins to deform. Something to keep in mind. 

Secondly I need to see how well the original design clamps down the wheels and how much space is left over. If you can print it and find there is space and fill it with a printed shim (Similar to what Topsie did with the z-axis clamp) then that isn't much different. Thats been my ideal approach as of now to avoid the complexity just for the sake of eccentric spacers. 

Now, if you are set on the using the eccentric spacers you have options. My idea would be to set a hole large enough for a tube to go into the Y-axis mounts, and the ID is the mounting OD of the eccentric spacer. A lot of surface area to spread the load. Or use a large flat washer on the inner surfaces of the Y-axis mount and the ID of that be the OD of the eccentric spacer. This method would require supports when you print the part though so it could be a poor surface for the washer to mate to. 

So much to think about! I may just grab some beer and design all night! :)

Yeah my initial idea for the eccentrics was to just use a counterbored m7 flat washer as the bearing surface.  I put that into my design and it looks like it should work.  My printer is about as well tuned as it can be as far as getting exact dimensions out of it, but I am planning some manual machining on these parts after they are printed for things like counterbores and flat bearing surfaces (should be easily accomplished with the woodworking tools I have and some creative slicing with modifiers for solid infills around features like holes and pockets).

I second your sentiments about not really knowing what we are getting into without having the parts already printed and assembled to make modifications off of  - it's really a shot in the dark, but a great man once said "if you can't make it perfect, at least make it adjustable" :)  That being said, I did print a few parts already, but those are ones I will not be modifying, still, not enough to have a working assembly in front of me that I can play with.

Here are a couple pics of my base idea to raise the spoil board up by 40mm and also help stiffen up and square the frame, any thoughts would be welcome..

Cant wait to see your work @Dustin !

Yeah @criticaldistance I think make a upper waste board on 40mm aluminium profil it's a good idea.

And you know what ? I will order some 2040 profil with same size as my X axis working size ( 110cm), put them paralelle and screw on a 110x90cm 18mm thick MDF board !

Thanks for the idea, surely better than my 3D printed clamp for the larger plank to cut