[stuarttaylor00]

Thanks for the detailed write up Pete, It has given me much to think about for my router design.

Whats your target price for the Maximus? and what is your planned level of assembly? i.e completely assembled, box of parts etc

[peteeng]

Hi Stuart and Sundries - Until I get the mechanical parts quote back I don't know. This will be published here when available in the next 2 weeks. Tetra Motions business model is to sell individual mechanical parts in model groups. Models are currently Brevis and Maximus. Each part is available individually and a shopping list of standard parts is included in the model documentation. A complete model BOM and cost is available for Brevis. Brevis is a benchtop carver, 3D printer, drag knife platform, soft material router. In this way the full cost of the machine can be estimated and then adjusted by the Maker using parts available to them. eg motors, controllers, bearings are all std parts. The Maker can buy economy bearings or expensive, up to their performance requirement and budget. I get enquiries from people who have already bought bits and pieces but are stumped for a gantry or a bearing plate etc. So I changed from selling "kits" to parts to allow people to pick what they need.

Tetra Motion sells mechanical parts that are not readily available eg gantries, motor mounts, Z assembly parts etc. Tetra will also quote for bespoke parts if you have a napkin sketch with a coffee stain (bent plate, billet cnc or composite). Maximus is much more substantial than first envisaged due to my changed intent to make it as stiff as a small mill. This thread is a concept /design exercise that goes from the napkin to the build.

Once the part costs are in I'll balance the parts costs against its performance and the total machine cost so it makes sense. Tetra Motion sells parts but some enquiries want partly assembled machines so I have to figure out those on a quotation basis. Tetra also does not intend to make stands or benches as these can usually be made by the Maker as freight on large objects is big. Plans for stands will be available.eg Maximus' plywood bench is available as a plan set. And I'll probably design an extrusion based bench for it as well. Tetra Motions website will go live in the next couple of weeks.
cncrouterkits.com.au stay tuned

Tetra Motions next project is a small kit mill, called Rollo I'm looking fwd to that one. Or maybe a moulded composite gantry assembly, been on the list for awhile

Happy to answer commercial and technical questions. Peter

I've attached Brevis' info as an example. Any comments on this format would be appreciated.

[ger21]

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

If I had to guess, I think it looks like an "S" shape when graphed.
The article you linked even calls it "S" shape.

[peteeng]

Hi all - So I suppose it's an industry term as I can't find a suitable curve except the sigmoid . The only time the toolpath is an "S" shape is when it swerves between two parallel paths. Plus the velocity has to be fixed (for good machining) and the blend curve has to be "jerk" limited. All other changes in paths are not S shaped. eg at a 90deg corner a G3 or G4 curvature curve will be a smooth motion. I suppose the S term is used in roughing cycles where the paths are parallel vs a stop and sidestep. It's the same problem as changing lanes on the hwy smoothly. Its roughing where the most gains can be made with this strategy. Cheers Peter

For people interested in this stuff:
Continuity descriptions | Rhino 3-D modeling
https://www.augi.com/articles/detail...ace-continuity

if you look at the curves image. G0 is a linear change in direction. The small purple circles indicate infinite acceleration (and therefore infinite jerk) points called inflections. This is bad for machining. G1 is an arc which has the same problems and it has an inflection mid path. G2 is tangent at the ends but smooth in the middle, a bit better. G3 is curvature continuous at the ends and is quite smooth. G4 is even smoother. Once the motion controller figures out a path it gets descretised into small linear steps, then turned into Gcode. If you have an s-curve controller you spec the jerk max (just like accel max) and the controller figures out the trajectory that achieves this jerk. It may change lane in 20mm or 50mm depending on the jerk spec. Acceleration is the derivative of velocity , jerk is the derivative of acceleration and is used for cam design so followers don't jump off cams and you do it automatically if your a good driver when changing lanes. Peter

[ger21]

The acceleration rate is "S" shaped, when starting from zero velocity in a straight line.
http://www.ni.com/cms/images/devzone...ce058d1a95.gif

[peteeng]

Hi Gerry - Thats a velocity vs time chart not a path chart but I get the picture. The velocity profiles in the chart is a trap shape and an S shape. So the velocity is changing as it rises to its max velocity ie its accelerating and it could be jerky as well. Then the vel changes to a constant so its an inflection with infinite accel and infinite jerk. Same on the other side as it slows down.

But we are interested in the toolpath. An ideal toolpath has constant velocity for its entire path (except when it starts and stops) to maintain a constant chipload. Even though the velocity is constant it still has accelerations and jerk when it changes direction. Accelerations are not a big issue as these generate inertial forces which should be overcome by the machine stiffness. Its the jerk that produces the vibration or stutter in the tool that is the problem. Plus its also the way the path is descretised. If too coarse then lots of accelerations and jerk, if too fine the path is slow to execute and not worthwhile to do. Interesting stuff, I'll leave it to the controller developers, better mathematicians then me. Peter

[ger21]

I'd never heard of S Curve Toolpaths, and thought you were talking about S Curve acceleration.

[peteeng]

Hi Gerry - Sorry this can get complicated. Yes the industry talks about S curve acceleration which minimises jerk. But the accelerations and jerk are created by the path shape and how that path is descretised and moved along. So it starts with the path and the path is created to ultimately minimise jerk. If the tool accelerated and slowed smoothly we would not care. But Jerk creates a stutter on the tool that creates chatter that is the root of the problem. Not sure if this is good enough explanation.. Peter

I reread the article quoted in #341 and I think the researcher got it wrong. The whole idea of constant velocity toolpathing is to achieve maximum material removal rate via a constant and optimal chipload. His feed velocity goes up and down severely in his test paths. He does decrease some accelerations but that's about it.

[peteeng]

Hi All- No news on quotes yet... will send to second supplier tomorrow as well. I came across this while sorting some files. Its about gantry design and selecting materials. Someone may find it interesting. Peter

[Sterob]

Thanks Peter....very interesting.

[peteeng]

Hi All - I've decided to start work on the BOM so I can get costs together. The atomic BOM has 93 items on it across 3 pages. This does not include the electronics. So I'll work through the costs I know and be ready when the metal quotes arrive. Cheers Peter S

[peteeng]

Hi Al;l out there - still waiting for quotes.... waiting waiting waiting.... Peter

[mactec54]

Hi Al;l out there - still waiting for quotes.... waiting waiting waiting.... Peter

If they have not given you a quote within 2 to 3 days move on as they are not interested in your work

[peteeng]

Hi All- Off topic but fun. I'm analysing a big (12m diameter) underwater blow up bag and during the stress plotting It grinned at me!! still waiting...Peter

[mactec54]

Hi All- Off topic but fun. I'm analysing a big (12m diameter) underwater blow up bag and during the stress plotting It grinned at me!! still waiting...Peter

How cool is that , it is trying to tell you something though

[Sterob]

Its not wincing, is it Peter?....lol

[peteeng]

Hi All- One of them looked like it was crying, didn't screen capture that one. I did do some video capture but they are too big to put up here. Here's some snaps. Peter

[peteeng]

constant chipload machining article - very interesting. maybe next week I'll get some $$$... https://www.mmsonline.com/articles/b...load-machining Peter

[davida1234]

Hi Peter, just visited your nice website. Good luck with your (new) business.

[mactec54]

constant chipload machining article - very interesting. maybe next week I'll get some $$$... https://www.mmsonline.com/articles/b...load-machining Peter

Look up Volumill have been doing this for over 10years plus do a better job here is one of the web links

VoluMill | Because it works