[Zorbit]

I'd want the envelope to be 1220mm plus clearance either side for at least a 12.7mm tool.

[peteeng]

Hi Zorbit -Thats 1220+13+13=1246mm (or 1220+13=1233 CtoC) and its now 1263mm CtoC so alls good... Peter

[Zorbit]

On the X axis, it would be nice to have enough "overshoot" to machine the edge of a vertically mounted board or to retro-fit toolchanger stations. I haven't seen a machine in this class that is able to mount an aggregate head, to drill / mill edges of boards at 90 or 45 degrees. I know it's not the design brief, just thinking aloud.

[peteeng]

Hi Zorbit - The bed has an apron for doing edge work. If you can point me in the direction of an economy supplier of ATC, or aggregates I'll see what's needed. But at this level of machine these would be unheard of but maybe thats a good thing to consider.

Just remember its a Maker, DIY, Fabber, grade machine with no machined mating surfaces so it will not achieve "commercial" class accuracy (ie machined fit parts) but it would be good to have an ATC for large scale Maker projects. Its in the Avid CNC & Shopbot class...

Peter

[peteeng]

Hi All out there? Been beavering at the dwgs and more dwg checks. The column assm looks quite nice.

Working on a machine at the moment that is too big for thermal stress relief so they are shaking it. But to give people out there some sense of what happens when you heat treat a steel table see the chart attached. Metals have a "hot strength" as the temp rises its strength decreases. Stress relief is done at cherry red which is about 1200deg F or 650deg C. At this temp it has nearly zero strength. That's why a blacksmith can bend large sections easily and steel buildings fall down in fires. So if the structure has internal stresses of which a welded structure has heaps, these can now pull and push the structure until they equilibrate. Consequently the max stress in the structure becomes the hot strength of the steel at the heat treat temp. The general rule is about 1hr per inch soak time.

https://www.youtube.com/watch?v=G60llMJepZI heres some hot metal working for some fun...Peter

The other thing to consider when stress relieving is the expansion of the metal. If you have a 8ft long table it expands over 1/2" at 600degC temp (see calc attached) . So if it is constrained in any way during the process it will buckle and be useless when it comes out of the oven.

[ger21]

I think you need a pretty big spindle to even be able to use an aggregate head on it, and the heads tend to start in the $7500 range, and go up from there. Then add the fact that they hang pretty far out the end of the spindle, so the forces are much higher. You're really talking about an entirely different class of machine.

[peteeng]

Hi Gerry - I agree an aggregate adds a level of complexity beyond the intent of this machine. But into the future it's good to get an understanding of them so maybe it could be an option. I might even design my own aggregates.. that's a project. NEWS FLASH - sent 12Mb of stuff off for its first quote. So now I wait and do the mechanical parts detailing, like dwgs for the drive screws and couplings (and N&B's) to get away for quote... Soon start adding up the $$$$

https://www.youtube.com/watch?v=h_51HU9ppxk thats familiar I just fixed my kitchen cupboard bifold!!

https://www.youtube.com/watch?v=hKLCqMGUAXE

Regards to all out there - Peter

[peteeng]

Hi All- ARRGGHH I've got trouble with my nuts!! I decided to start setting up P5 for its full contact analysis so brought it into simsolid and went thru the usual workflow. But it didn't like my nuts and refused to accept them as NUTS. This meant I couldn't preload them. All the bolts with holes where fine but the nuts remained an issue. So I backed down and just modelled the Z axis, same thing, so backed down further and modelled a small test coupon with all the size nuts I use. Again no good, so went and looked at a N&B tutorial no news there but I did notice that their nuts had sharp corners whereas my nuts I model with a small flat on the corners like real nuts have. So I changed my nuts to true hexes and bingo they became nuts, yeh!!

So once modelled correctly simsolid will calculate if the connection opens up or closes (see opening image, shows the corner of the connection opening 0.12mm) , it calculates the effective zone the fastener is operating on (see the traction image, the traction area is greatest with the 8mm bolt as its preload is greater therefore its friction and contact area is greatest) and can show how far the connection has slipped. In this case there is no slippage. The nut image shows that the nuts have been identified as nuts. It also calculates the shear load and tensile load in the bolt so you can check its sized right.

So now the plan is to go back to P5 as the nuts will have been updated when I open the file, and analyse the structural loops and figure out how each one is contributing to the deflection. First thing to do is model all the connections as bonded to establish the perfect minimum deflection then work all the connections to friction and bolted ones to compare to the bonded connections. Then it will be time to wrap up and finalise. May have to change something once the benders look at the parts... we wait for their $$$ and their comments. Peter

[peteeng]

Hi All - This mornings exercise was to get the Z Axis bolts working. Here's the result. Current design is about 60% efficient. Looking at the joints they are not slipping which is good (at 100kgf applied load at the spindle clamp) the rail is opening and the top cap is opening slightly when "pushed" when pulled the screws are in compression. Will need to drill into the info a bit more to determine what exactly to do (if anything can be done that is) to improve the deflection in this loop. I've always assumed bolted assemblies to be 50% efficient if no analysis done. I definitely will place an extra screw down the sides and change from M5 to M6. More work to do. Peter

edit - Further investigation shows the main improvement can be made by adding more bolts to the sides. So next round here we come. Peter

[peteeng]

Hi All & Sundry - I've included the second structural loop and it contributes 0.01mm to the deflection vs the Z axis' 0.07mm (bonded connections 0.08mm total) . So I need to look at the Z axis as this is the major deflection. I'll convert this one to a bolted model asap. I also included and deleted the extra support bearing and it did not change the deflection of the spindle. It did stop the z drive warping very slightly so I expect no support bearing is the go. Peter

[peteeng]

Hi All- I've run the full machine bonded so now we know the relative stiffness of the three loops. The total deflection at 100kgf push and pull is 0.16mm. Our target was 10N per um. Currently the bonded machine is at 6.25N/um and will drop off as I convert it to bolted joints (maybe) . Say to 6.25*.7 = 4.3N/um which is still very stiff for a router. We shall see.

So the 0.16mm is made up of 0.07mm the Z Axis, 0.01mm the drive plate and 0.08mm the gantry and columns. Will look at the gantry when its converted to bolted to see how we can improve that. Cheers Peter

[davida1234]

Hi Peter,

Is all your modeling assuming that there is no "play" in the linear bearing blocks?

[peteeng]

Hello David - There is no play in medium or heavy preload bearings. In the simulations the bearing stiffness is modelled in critical models. Bearing manufacturers publish the stiffness of their bearings, I'm currently using 600N/0.001mm stiffness for the bearing contact. Regards Peter S

[peteeng]

Hello David - The modelling of the bearings also includes allowing them to slide on the rails which makes it less stiff as well and allows correct load transfer from the carriage to the rail in terms of moments & forces. Peter

[davida1234]

Hello Peter, I am certain you are aware of it but wanted to still bring it to your attention.

You have something like a 4.5 - 5 x cantilever on the Z to the tip of the tool.

[peteeng]

Hello David - That ratio really doesn't matter. Target static stiffness for the machine is 10N/0.001mm and all through the last 4 months I have been analysing and working towards that stiffness. There are lots of routers and mills with far greater cantilevers then this one. Once the Z axis travel and gantry clearance heights are specified it becomes an engineering exercise to achieve those specs and remain stiff. This machine has achieved nearly all of my design features so far. I must say however that it looks like I won't get the +10N/0.001mm so this machine may become the Maximus-M. In the last round I had to make several parts that where 8mm thick 6mm thick due to bending constraints and I have lost a bit of stiffness through that process. This one was to be Max-HD which would have a more economy maker grade cousin the Max-M but this one maybe the M. Not sure until its fully resolved, tested and costed.

I do know how to get to the 10N/um through this exercise so designing Maximus-HD will be easier once I resolve the Maximus concept to a commercial level. Even if Maximus-M is +5N/um it will be stiffer than a few small mills so I'm happy with that.

I'm very interested in people testing & quoting their routers for their static stiffness so the community gets an idea of what the machine stiffness range is out there. It's a commonly asked question in this forum and yet we do not have a database of machine stiffness yet. Seems the only people that put this on paper are the very large mill people. Large mills run from 25-600N/0.001mm. Cheers Peter

Edit - Hi David to give you an idea of how stiff the Z axis tube could be, I've calculated the equivalent thickness in steel. Its equivalent to a 72mm thick solid steel plate 194mm wide. This is quite a bit thicker than the usual bearing plate arrangement, so its very very stiff... Peter

[peteeng]

Hi Al - Found an article on measuring a machine centres stiffness. It was 167N/um so we have a long way to go to get to that!! Peter

[peteeng]

Hi All - Been away for a couple of days. Took the drawings with me and have worked thru them looking for errors or improvements. Can see a couple of improvements so will do these as I rework the stack. No major errors so far...Otherwise waiting for quotes which I'm told are about 7 days away. waiting waiting... Peter

I'm into composites and Have been looking for quite a while for an acrylic resin to do various things with. Have a look at this stuff if you need a water thin resin that cures fast. https://www.turntex.com/

[peteeng]

Hi Sundry and Others - Back onto updating the drawings. Found an error, in that I started the design with plain M15 bearing cars and when I moved to flanged M15 bearings I assumed the screw size would be the same M4. But no its M5 so have to go through all the parts and update the holes (and bolts) that are associated with the flanged bearings. That mistake has been buried for quite some time. Waiting for quotes patiently. Peter

EDIT - While waiting for the computer to figure out an answer for me today I cut another wax stamp sample on Brevis for a friend. I've just put on a 400W 48V DC spindle to see how it goes. Very quiet and cuts very well for a cheap item. I've ordered some 1/4" ER11 collets so I can give it a better test with some bigger tools. It's also about time to pull Brevis No1 down and get it painted. Once I cut the actual stamp in aluminium I shall do that.

Edit - By the way I want to set up a good power laser on a machine anyone have a good source for laser stuff? 30-50W?

[peteeng]

Hi out there - No news about maximus quotes but I have been reading about s-curve toolpaths. Problem is I can't find what the "S" stands for? smooth, sine, sigmoid, spline??? Anybody know? see https://www.sciencedirect.com/scienc...15000536#bib11 for a good explaination about how to do it but not what the S stands for. Peter