[JayneV]

When I said solutions, I was referring to the solution for the final tool path calculated by the MC. And yes, that solution would depend on the parameters for each machine. Does that explanation sound more accurate?

Have fun making sawdust with your new baby.

Jayne

[peteeng]

Hi Jayne -

Machine controller (MACH , UCCNC etc) talks to the motion controller (in this case a UC100) , the BOB (break out board) breaks out all the signals to the other components including external components like spindle speed, air on off etc. (PORTS) have fun. Peter

[JayneV]

Thank you for the explanation and labelled photo, got it.

[mactec54]

I understand now. The motion controller takes care of all the critical timing and signals to the motors. It also optimises the gcode to create the actual real life path followed by the tool based on user settings for desired tolerance and speed. The computer is basically the user interface for the machine and keeps the buffer memory topped up for the motion controller to use. So as long as that buffer doesn’t become empty, the motion controller will happily continue to do its thing. This seems like a superior arrangement than one where the computer performs the role of motion controller as well. Does that all sound about right?

Peter, I read a little about path tolerance in the LinuxCNC manual. I’m sure the concept is the same across all controllers. I assume this is how machine limitations are handled when transferring from the ideal CAD/CAM world to the real world, like the acceleration limits of the machine. And different machines would have different solutions to the same problem?

Mactec54, is the UC100 the motion controller hardware used by Mach3 or is it a hardware interface to connect a computer to various brand motion controllers?

Thank you everyone for all of your help. It is all so very helpful to help me have a better understanding of CNC machine construction and their controlling electronics.

Jayne

You have a good understanding of how everything works, the UC100 can work with UCCNC control software as well as Mach3, I only know of these ( 2 ) that work with it

[JayneV]

You have a good understanding of how everything works, the UC100 can work with UCCNC control software as well as Mach3, I only know of these ( 2 ) that work with it

Thank you

[JayneV]

Hello everyone,

I did a little more tweaking with the CAD model to follow through a little more with the raised sidewalls idea. Not sure if this is a path I want to continue following or just stick with the original design. The gantry assembly now has a mass of about 45kg according to Fusion, assuming I have assigned correct material properties to each component. I have no idea what a reasonable mass should be for a gantry but 45kg seems like a lot. The large SHS section (125x125x4mm) is steel, which accounts for almost half the mass.

I also added aluminium flat bar (shown in green) between the Y axis linear rail and the RHS in an attempt to provided a better mating surface for the rail. I forgot to move the rail to the edge of the section so is still shown in the centre.

[peteeng]

Morning Jayne,
Some gantries are 100's of kg depends on how stiff you need. 125x125x3 is about the same stiffness as YaG so it will be quite stiff. But you have mounted the rails directly to the SHS. 3mm thick SHS will not be flat or straight and square rails will jam. 10mm pitch ballscrews and a large N23 motor will push 200kgf easily so don't worry about weight yet. Plus the gantry is on rails and you are only working against friction. The real enemy is acceleration and inertial loads in this case. So low accelerations require low forces... eg you can easily push a 1T car on a flat surface, slowly. Remove the bits that stick out the sides at the base they are chewing into your footprint and serve no purpose... Are you going to glue the aluminium to the SHS? Peter

[JayneV]

Good morning,

The SHS is 125x125x4mm (not 3mm). That was a typo, sorry. Inertia and acceleration are what I am mostly concerned about with the gantry weight. I’m planning on using two N23 3Nm motors for the Y axis. The second motor would be driven by a 4th channel of the controller. And the ballscrews for the Y axis would be 2010 or 2005. I haven’t yet tried to figure out the best pitch for the ballscrews. Something tells me 5mm might be too fine and the motors would fall off the back of their peak torque curve if I try to spin them fast enough to keep the machine acceleration from being too slow.

The bits sticking out the side of the base are there to bolt down the sidewall assembly. The connections between components haven’t been modelled in CAD. What I’m thinking of doing is to weld the wall assembly together and then use the angle sections at the bottom to bolt to the base to avoid welding. I figured I’d have a better chance of getting the walls perpendicular to the base by bolting those parts together and shimming where necessary. If when I start welding I find that I am able to maintain reasonable accuracy, I could delete the angles and the side protrusions and just weld everything together. Please excuse the crude sketches attached, they were marked up on my phone using my finger.

I don’t know anything about glueing metals together or what products are best suited for the job. I’m open to suggestions. The way I’ve been planning to secure the aluminium flat bar to the RHS is bolting from the underside through access holes drilled through the bottom wall of the steel section. See attached image. The bolts would have a cap head so an Allen key could be poked through the hole to screw them in. The blue circles in the image are meant to represent the hole in the bottom of the RHS. There would be bolts along the whole length of the flat bar spaced around 100mm apart and staggered between left and right locations to avoid removing too much material in the same location of the RHS. The flat bar is 20mm thick. I could do a similar arrangement for the gantry X axis rails so that they are not mounted directly to the SHS. Is there some kind of glue/filler product that can be applied between the AL flat bar and steel SHS that could act as shimming material to fill any gaps between the two surfaces?

[peteeng]

Hi Jayne - two N23 with a 10mm pitch is the go. 5mm will give you very large force but low velocity. I haven't tuned YaG yet but its getting 6000mm/min rapids at half current (16mmx10mm lead ballscrews). The Z uses a 5mm pitch as you need lots of grunt for plunging...

I'd use something like this for the adhesive Techniglue R15 - ATL Composites if you bolt hard you will pull the aluminium and steel into some sort of curve. You need to be able to snug them together so the Al stays flat. Use the epoxy as a filler vs an adhesive, wax the surfaces & bolts so they can be released in the future or if something goes wrong. Set up a master side and shim or grind as needed to get it flat and level. Then set up secondary side and use a level to "shot" across and get as close as possible. Then set the master side with epoxy checking back to the secondary as you go. Check and if happy proceed to secondary same manner. Use master to level from.... If the AL plate is predrilled and machined then you also have to register the LHS and RHS so they are correct in space. If left plain they can be post drilled so they align. Either way care is needed. Peter

One way around the wobbly SHS is to use round rail. I know I'll cope flack for this but 1) its your first machine and you want to use simple structures 2) round is compliant and will accept variations. Square will not. Since your not aiming at a uber stiff machine to cut aluminium all day, round will be fully acceptable and half the price. There are many machines with round cutting Al. The issue is that next machine you will go up to square and if you use the same sections they will jam... and you will wonder why.. Peter

[peteeng]

Hi Jayne - I think your wall design is a bity complex and combines the wrong elements. Think of how your planes are built. Would Boeing, Cessna or others weld RHS together and have bits sticking out etc? I suggest you simplify the design to attached or similiar. 1) The envelope of a structure is what needs to be built for max stiffness and minimum weight. Using RHS and frame work is not efficient and does not suit bolted construction. 2) I also suggest you speak to local laser cutters. Their price on flat cut stuff is really good and accurate 3) you can have things cut with slots and tabs and weld the back of the tabs resulting in minimal distortion 4) You can design so bolting is convenient and effective, you can have thick and thin bits as needed by laminating or doubling parts 5) cross bracing can be added as bolted or welded elements 6) It will be easier and more effective then the hollow section path... 7) if you make it in Alum and your keen you can cut the parts yourself with a jig saw and hand router the edges (ganged) so they all match.... Peter

[JayneV]

Hi Peter,
You confirmed what I suspected regarding the ballscrew pitch. 10mm for X and Y axis and 5mm for Z sounds like a plan.

I had a look at the Techniglue website and like the glue you mentioned. One of their distributors is only a couple of suburbs away and I've already sent them an email enquiry. Using the product as a filler is what I had in mind, thank you for the tips on how to do it.

I agree with you that my wall design is overly complex and not the best use of hollow sections. These sections were chosen in an attempt to make use of what I already have but I am realising this may be a false economy. I feel like I'm chasing my tail using the hollow sections and the design is starting to get away from me. Might be time to take a step back and have another rethink about the materials I would like to use in the construction. Getting the parts laser cut with slots and tabs is a good idea but I am really liking the diy approach with a jigsaw and router. That is right up my alley of challenging myself to build something using tools and materials already at my disposal. I haven't tried cutting aluminium with a router before except for once accidentally pushing the router into the frame of a planning jig made of aluminium. Now I am keen to try cutting the parts myself this way, thank you for the idea.

Jayne

[peteeng]

Hi Jayne - so you are going to weld the aluminium? If its thick 12mm plus then you can edge bolt it and glue it with same glue.... a 12mm fillet each side and its a very strong joint.... Peter

[JayneV]

Hi Peter,
No I don't have the equipment or any previous experience welding aluminium. With the laser cut route, I imagine the mating joints would be good enough for brazing, so that is a possibility, but bolting together would be my preference.

[mactec54]

Hi Peter,
No I don't have the equipment or any previous experience welding aluminium. With the laser cut route, I imagine the mating joints would be good enough for brazing, so that is a possibility, but bolting together would be my preference.

You don't want to be brazing anything on a build like you are planning, Tig, Mig or Stick for a build like this, you then Stress Relive the Frame, and machine the important mounting faces, if you can't do this then not much point in building a steel frame like this, your only other option is to bolt it together, like an aluminum extrusion machine, and this is a lot of work to bolt a machine this big in steel to give it any structural integrity

3mm wall thickness is also not very good unless you plan on filling the tubes with something, normally 5mm is the minimum wall thickness, for a machine build like this.

You could make the sides using 75x75x5 top and bottom and the same material for the bottom to top spacers, a steel bar welded on top and angle iron pieces on the bottom inside face, your sides will both be made the same, when complete these could be Stress Relieved and machined, the center table supports would have matching plates on the ends that could be bolted into the 2 main frames, this would be quite a simple build done like this

[peteeng]

Hi Jayne - If bolted then use the angles from the construction aluminium systems and profiled plates as needed. Edge bolting has issues, they have to be square and flat. Best achieved on a mill. But the angles will allow some wiggle room. Can also use std angle extrusion as a joiner. That would also give you good surface area for bonding. So after assembly and squaring it could be epoxy set together. Peter

[awerby]

I don't think brazing works with aluminum; the brass won't stick, and its melting point is too high. It's also difficult to get aluminum to hold threads well, especially if the metal's fairly thin. Adhesives might be the way to go. But you don't need to use aluminum for any parts that don't move; steel is both stronger and cheaper.

[peteeng]

Hi Andrew - If your good with oxy/acytyelene brazing Al is very good method. An aluminium brazing alloy is used not brass. Typically 4047 a high silicon alloy. Its very good for joining thick to thin elements with little distortion. Here's some examples I have done in the past. As aluminium does not change colour you have to watch the flux as when it melts you are close. It can be flow brazed or braze welded. But I think a bolted and epoxied build would be easier. There are some high magnesium alloy sheets/plates that don't like brazing....Peter

[peteeng]

Hi All - I do like the asthetics of hot rivets - Wallace and Gromit esky (esque) .. Peter

Machine parts are blunt instruments when it comes to structure, not much elegance to them. Welding is used because its convenient and 100% efficient. But then the resulting distortion has to be dealt with. Rivets are used on aircraft and bridges because they have to be assembled and maintained. High strength bolts can be preloaded to a higher grip then hot or cold rivets therefore provide more friction then rivets. The microfriction effects in a friction joint make it damper then a welded joint. In structural design a welded joint is considered to have no damping whereas a rivet or bolt is considered to have 2% damping. That's the same as cast iron. So a bolted construction has many advantages to be taken advantage of.... and I think jayne wants to use her kawasaki personal assembly robot to build this thing.. Peter

by the way that kwaka robot can lift 1.5T and drill titanium!! and its bolted together

[mactec54]

by the way that kwaka robot can lift 1.5T and drill titanium!! and its bolted together

If you are referring to the robot in the photo, that is not bolted together, yes rivets are cool, but not very practical for a simple build like this

Robots can do anything a router can do, and more

[JayneV]

Hi Mactec, I think I'm going to abandon the idea of trying to use the hollow sections. Most of the sections I have are 3mm wall thickness which is giving me a headache figuring out how to assemble it all. I've been working on a redesign to removed the hollow sections, see attached image.

Hi Peter, The redesign is made from flat bar and flat profiled parts. Most of the parts are edge bolted on this first version of the revised model. LOL, how did you know I had one of those assembly robots hidden in my garage?

Hi Andrew, I once tried to braze aluminium using the only brazing rod I had on hand (for copper pipe) and not surprisingly it didn't work. Could helicoils be used to strengthen a threaded hole in aluminium?