Jason

Drifting off topic a bit here.

Its not a case of actually feeling the need for a traditional mill head on a gantry style machine more a case of considering what is reasonably possible at an affordable price with a (potentially) viable target market. Given the absence of HSM machining strategies with current model engineer level CNC controls something more rigid than a router style head is needed to handle conventional cuts. Mix and match from components already in production is also a lot more economical than design from scratch. Especially when you aren't sure which way the market will develop. An alternative to the conventional ME small CNC machine based on manual mill components.

The uprated, fixed gantry, router style machine has to be considered as the subtractive machining equivalent to a 3D printer and would be used in the same way. Control strategy inherently HSM, probably much closer to 3D printing running "backwards" than conventional CNC. Reasonable CAD has to be taken as a given for folk starting out to do own design components now.

It will be interesting to see where the whole MakerSpace thing goes in the next few years as its now, in principle, possible to go straight to CNC subtractive machining without learning to drive manual machines first. But the equipment doesn't really seem out there as a coherent yet. Waiting for the Rep-Rap equivalent methinks.

But maybe someone knows differently which is why I started this hare running.

Hobby / ME affordable technology generally seem to run about 20-30 years behind industry and straight to CNC has been a norm for a fair few years now.

Clive

Edited By JasonB on 28/08/2020 13:04:43

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These Societe Genevoise jig borers did good work for many years so gantry style is not a new format, but they weren't designed to remove huge amounts of material quickly, more about accuracy, so the duty can be likened to a cnc 3D mill but that's a heavy old table to keep moving around at a high feedrate.

Emgee

Good video here outlines the advantages of this kind of toolpath.

Thanks for the move Jason. That hare took off a lot faster and further than I intended! I just wanted to "look at things from the other side of the fence". Which can be very useful tactic when discussions start to bog down in "I think I'd like, maybe, well I'm not sure (and how the heck can I afford it)" land.

Barrie

By straight to CNC I meant trained machinists going straight to CNC machines and learning how to exploit them rather than learning to cut metal on manual machines first. (The perils of editing and not being able to proof read what you actually wrote!)

I knew that Fusion was growing HSM strategies but I'd always thought that conventional hobby level machines wouldn't have the speed to exploit them. Especially as they are G-Code based and I have my reservations about G-Code (see below).

Jason

Yep, pretty much my thoughts but there is a historical background.

In 2004 the MoD made me redundant from my job as a Scientist / R&D Engineer / Proof of Concepts guy so I was looking for something to preserve my money and tide me over until I had to go into full time carer / house person mode. Back in the day I'd built a multi-axis motion system for evaluating certain aspects of optical performance for a rather hair-brained idea that worked at lab scale but …. . This thing was basically a 3 (or more) D vector path following drive which I reckoned could easily have been made to run a (small) milling machine at constant tooth load and constant cut velocity. Not complicated to implement once you have the Eureka moment!

I figured that commercial exploitation might be possible using a benchtop plano-mill machine something like the modern, kit built, fixed side router but better engineered and more sturdy. Using things like the extruded X format alloy rails used in optical lab gear for the cross bar and VMC style head with linear rails under the table et al. A proper cast iron machine would have been completely unaffordable but, although still not cheap back then, a build up of that style could have been viable. Stiffness should have been sufficient for a work volume up to maybe 2 ft x 18" x 1 ft at the low cutter loads I envisaged. Cutter costs then were one of my bigger worries as to the viability of the whole thing.

I bought a Taig CNC machine to test out the proposed commercial application. Took me about an hour to conclude that the folks who implemented 3D G code were smoking whacky baccy. Also concluded that Mach is both an amazing tour de force of programming and completely the wrong way to go about driving a small mill from a standard PC. I know why G code is the way it is but I learned my control strategies on guided weapons so naturally think in terms of curves of pursuit, error reduction and vectors not point to point. I also discovered that some of the computer programs I was going to need didn't exist and never would exist as the way thing's were done was different to what I expected.

Then MoD said come back as a consultant for £££ lots so I dropped the whole thing.

Fast forward to 2020 and thanks to smartphones and 3D printing all the extra computer programming bits I'd need exist. Albeit in rather different form. The mechanics are cheaper. The engineering remains viable for a limited range of bench top sizes and carbide cutters are affordable. If I were 10 years younger I'd give it a proper go but, at 66 I've got to ration the good years I have left.

Clive

PS I initially learned programming on a hybrid digital-analogue computer!

Clive;

FYI: About a decade ago, at SIGGRAPH, a 3d gantry-style router was presented, called "DIYLILCNC", and plans were available by download.

It used a Dremel for the spindle, and could do aluminum. This was when 3D printing was really doing well with home-built machines; a group thought that "subtractive machining" was something that might fly with those without tons of money for the then-current CNC mills. It used LinuxCNC if I remember correctly, so was certainly within the price range of the youngsters.

The guys seemed to be there for a couple of years, but faded out.

Maybe they were before their time, or maybe the Chinese routers are where it's at.

John.

That's because high speed is a misnomer. It's not necessarily about higher spindle speeds or feedrates. What they try and do is keep the cutter engagement constant so feeds and speeds can be maximised. The outcome is the the overall machining time is reduced – hence high speed. In contrast a simple 2D path might use a given stepover, but depending upon the geometry may decide to do a full width cut over a short period. In that case the speeds and feeds (and DOC) are determined by the full width cut, not the majority of the machining. So overall time might be slower. Another bonus of constant engagement is less chance of chatter due to short term large engagements.

Andrew

John

DIYLILCNC still seems to be around but it's very low end "look what I made" device. Current version seems to be made, mostly, of plywood. I've no doubt that in careful hands it can do surprisingly good work.

But a long step from a commercially viable offering.

As I found out hitting a sensible price / performance ratio for something novel that folk are willing to shell out lots of beer tokens for to do useful work and earn a wage from is hard. Especially if production is small workshop based with bought in components rather than having factory resources behind it.

I have a sneaky feeling that even if I'd got mine up and running the spindle costs would probably have tipped it over the viable price / performance ratio. My target was 3 (or at most 4) times the price of a CNC Taig with significantly larger work envelope. Beyond that the whole commerciaisation thing wasn't going to fly. Big difference between a "credit card" cost range machine and one needing a proper Cap-Ex process however informal.

Clive

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Andrew

Thanks very much for clarifying what HSM means in the real world. Hafta admit that I sort of knew what it was but wasn't fully clear on the details of implementation.

The simple vector following system that I would have built just innately controls tooth load and cut velocity with a fixed step over and fix maximum depth of cut so much more basic. The analysis algorithm to verify the presets looks as if it could have been "interesting" but I never got that far.

Barrie

I know where you are coming from on the G-Code tweaking thing. A lot of my living depended on doing that sort of thing in my field.

But in my view a decently sophisticated system should be fire and forget not needing that sort of thing except for real edge cases. Mature G-Code on a mature controller should be sufficiently sophisticated for all normal use without editing. Lewis Hamilton makes his living by being uber good at tweaking his car to be just so for the track and getting the best out of it. I expect to just jump in my P38 Range Rover, fire up the V8 and go just about anywhere sane with no worries or extra effort.

Certainly the sort of market I was potentially aiming for had to be fire and forget.

I'd disagree that subtractive manufacturing has to remain a lot more specialised than 3D printing or laser cutting. In principle structure avoidance isn't an issue with true vector path systems. Basically every part of the machine has its own easily derivable path so the no go area where machine or cutter intersects a structure is computable. A trivial task for an analogue-digital hybrid, dunno about a pure digital computer but it oughtn't be that hard.

For materials and finishes you simply run an appropriate good quality cutter, whose loads are within the capability of the machine, as the maker advises. Complain if it doesn't do what it says on the tin.

Two steps down from a small Hass really! (The Hass Desktop training mill is, in mechanical layout at least, a main line machine makers version of the concept I had.) Not comparable to the big industrial boys in speed or capability but for a lot of work the job gets done without operator fiddling about or gotchas. Just slower and less than half the investment. A step or two up from a Tormach is the niche I guess.

Clive

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