[peteeng]

Hi SA - If you land the columns on top of the cars how do you screw to the cars? Do not use foaming adhesive. Its really strong but will expand for some time and can move things around I have found. I always have high Z machines with around 300mm under the gantry. Thats because I do boxes and moulds that are tall. If you can get gal steel in 1.6mm go with that for your laminates. As you say cheaper then Al if you can cut it easily and its stiffer. All your concept sketches are fine the devil is in the detail. Peter

[routalot]

How are you planning to attach the rails to the gantry?If bolts are the answer then access holes will be necessary or plates internally tht you can drill and tap.The ends of the rails in this version may make it difficult to slide the assembled gantry onto the rails.
I'm sure others would agree that you need to add all the details before cutting or assembling a single part.Mistakes are much cheaper on a monitor than in the workshop.

[SweetAs]

I went away last night and looked at a whole bunch of products and you are both right, I need to spend a little time on getting this design right before I go start work.

Torsion Box - I have an idea of how I am going to build this. I did look to see if there is some sort of formula/calculator used when assessing the thickness of the internal structure material, external face material and the spread of the internal structure (every 150mm/200mm etc) but was unable to find anything. Do you have any suggestions or just to over-engineer it?

In terms of mounting gantry onto the rails, I think I have a few options.



A - Mounting a wooden bracket, mortised into the vertical side plates. Not sure how this would work with a wooden type bracket mortised into the main torsion box. I would probably just be better off creating a metal bracket. I guess the big issue with that would be if Im making a torsion box for the side plates, the bracket would need a good amount of meat around the bracket and for the fixings to bite into, Im not sure how I would accomplish that short of framing that into the torsion box itself.

B - Mount a plate on the bottom of the Vertical section and into the top of the carriage. This would make that side of it easier but then Ive got no overhang to mount to for the R&P underneath and then I worry about the forces on the carriages.

C - I think this is probably the best option, I can bolt through the vertical torsion box and spread the load.

Any suggestions on the thickness of the Steel plate I should be looking at for the brackets? I have some 6mm mild steel plate in the workshop that I could use. I do have a friend who runs a metal fabrication place if I need something bending and we do have a supplier who is able to waterjet/laser cut steel plate. Maybe Ally would be an easier option but it is expensive in the UK. I should probably look at adding some triangles to the sides of the brackets for additional strength. I have a cheapo 100A MIG welder so that should work for welding them. I wonder though, has anyone used metal epoxy for creating something like this? I wonder how well it would hold up.

My main concern with these designs are the twisting forces, is that something that the supported round rails will be able to take easily? Am I right in thinking that the force would be equalized because of the same type but opposite on the other side?

Ballscrew - I just read another post, one that you both commented on where the OP was asking about using 16mm ballscrews and the importance of the different pitches. Makes sense but I didn't realize it. Now I think that I want to be looking for a 1610/1616 instead of a 1605 for the X gantry...I think that's right?

Please bear with me, I do a lot of conceptual type work with designers, architects, and engineers in the workshop. This means that a lot of the time we have an idea of how it needs to be built or look but we don't really know how to assemble it or what materials to use at the outset. We tend to make a rough plan, just get on with things, and deal with issues as they arise. I understand that could make an expensive mistake here with the machine so I am trying to get all my ducks in a row before I get at it so apologies for my enthusiasm.

Best get back to work and earn some actual money for the build lol

[peteeng]

Hi SA - Ballscrews for a router are best at 10mm pitch or more. 5mm is good for the Z axis to give it lots of force and the Z axis does not move fast. I think you need to move along and not get bogged in details at the moment. There are many issues to solve and you won't get a good idea about these until you have a full general arrangement done of the machine so you can look at the big picture. Don't worry about laminates just block geometry to understand the big relationships, especially how things will be bolted together. The Z axis and saddle is especially complex and you will spend a lot of time in this area. Perhaps a heavy aluminium angle is the go for the column car mounts. If you use round rails there is no local bending moment so webs are not needed to support the bracket. Relationships between drives and rails and motors etc will be difficult and only once you get the GA done can you figure these out. Keep at it. In general you are trying to minimise parts to minimise interfaces as these are inefficient. So your carriage bracket would be better if it was one aluminium or steel bracket vs many bits. or none at all - see machine attached just rotate bearing 90degs....

Maybe find a muse machine that gives you some guidance for solutions. May save you100's of hours of thought. Peter

Heres a neat ply machine that you could scale up. He made the mdf one then used that to make the ply one.

[peteeng]

Hi - Densified wood has very good properties. About the same stiffness as UHPC (review that below, its not real stiff) but much stronger and easier to machine. I have vacuum impregnated lots of timbers and MDF to use as tooling board or interesting objects. Densification requires large presses... But I think aluminium laminated with plywood is stiffer and just as easy to work with and you can make this yourself. I used to get MDF dust from a cabinetmaker and vacuum cast it into blocks as tooling board for a client. Had to sort out getting all the moisture out of it before epoxy infusing it... Interesting stuff. Peter

edit - I agree getting the design into CAD is really important and unless you design it at least 20x you have not refined it enough and best to use up CAD time than real time... Reality sucks and mistakes are difficult to fix.... but CAD mistakes are very easy to fix.

Jabroc data attached. Its only 15GPa in flexure much less than I expected. So aluminium laminate much, much betterer...