Freesteel Blog » Unreriable road of borrocks

Unreriable road of borrocks

Monday, February 1st, 2016 at 5:57 pm Written by:

Well, at least I sorted out the metal supplies by cycling to Scimitar Steels in Bootle at the furthest public limit of the dock road and persuaded him to cut me the most pitifully small piece of mild steel anyone has ever ordered from him. Couldn’t even be bothered to charge me. I think he said the substance was “080A15 EM32B” steel, which according to kvsteel is:

General purpose steel bars for machining, suitable for lightly stressed components including studs, bolts, gears and shafts. Often specified where weldability is a requirement. Can be case-hardened to improve wear resistance. Available in bright rounds, squares and flats, and hot rolled rounds. Can be supplied in sawn blanks, and bespoke size blocks.

Sounds like the correct stuff to me.


Then, as I was fetching my bike, I spotted a picture of a milling cutter on the side of a Lloyd&Jones Engineering truck parked outside the shop, and went in. I didn’t see any on display, so I had to check their website to find out about their sensibly priced 2 flute solid carbide tian coated end mills among their limited selection. It’s 2 flute so I don’t need to run it so fast according to the feeds and speeds calculations.

Back home on the machine it proved rather good for facing off, being as I could run the spindle at 7000rpm instead of the near-stalling at the minimum of 2400 owing to the fact that the mill cutting speed surface ft/min should be 350 with carbide cutters as opposed to 70 (for “steel 4140”, whatever that is).

I got everything sorted out, probed, position and then gouged.

What happened here is one of the drivers decided to give up and go into an error state, and the other one carried on going back and forth in its arc as though it was still following the rectangle. Luckily it was only a test cut of 0.2mm deep.

This problem means it’s not reliable enough to do the whole job without a proper gouge. We need to put a feedback from the servo driver to the controller to cut everything when one of the axes trips out like this.

I reset it (by power cycling) ran it again far enough to where the linking motions came into play. I’d dialed for a toolpath with the maximum staydown and no retracts — which was a feature I spent a whole year working on.

It’s rubbish. It takes so long to retrace its steps back round the metal instead of nipping over the top. Now I understand why Mr Denmark kept referring to this as a “perception thing” when he urged me to work on this feature, because he knew (even if I didn’t) that it was a waste of time because it made a slower toolpath. But like a know-nothing that I was, I had to try it to believe it. And until you try it, you will want it. But you only need to use it once to be satisfied.

This reminded me of Adrian taking apart a cheap toy car remote control unit the other week and discovering that the aerial poking out the top wasn’t attached to anything. The circuit board didn’t need it, but since most customers believed it should have an aerial, the designers put a pretend one in for them to extend and retract to keep them happy because it was a whole lot easier than attempting to educate them about it.

I was only going for 2D Adaptive clearing here, because I am intending to control the depth with G92 settings to reposition the Z, and so be able to try different depths of cuts. This meant that the retract plane has to be high enough so it works for my lowest cuts, which is not efficient.

I’m pretty sure now that linking motions should totally be calculated by the controller, and not be done in the CAM system. It knows where the material is (and could laser scan it if necessary). That way we wouldn’t have these overly high retract planes, and it could work out its own rounded trajectories, knowing its own kinematics. That should be its job.


Meantime, I found this very detailed video blog of someone systematically testing out four different 3D printer software slicers to see how they performed on the same printer. I watched both episodes last night.

I’ve put this here to tell you that reviewing of CAM software is a thing. In this case it’s just for the extrusion 3D printers by one guy who gets the idea. You can see the core developer teams for the different products being able to use this information to direct their work, as well as for users to be informed about which is the best software to use.

In all my experience, this thing — independent benchmarking and reviewing of CAM software with an admirable degree of curiosity for the benefit of users — has never happened for 3axis machining software. Even though such software costs many thousands of dollars, runs on machines that cost hundreds of thousands of dollars, and has been around in various states of development for decades.

The problem is that customers, who are almost always professional engineering firms, are not curious and don’t go looking for stuff. Instead they’re busy earning money and working all the time. So they don’t do anything until a salesmen comes to them personally to sell them software products for them to consider. This massively inflates the prices (to cover the cost of the salesman) and guarantees that the only information they receive is biased and not even generated. By that I mean that the salesman probably won’t even know what’s the best performing software on the market. It’s difficult to find out, and he doesn’t care, because his commission comes from sales of this product only. This is a business after all. Nobody is paid to care about getting things right.

If a detailed independent review of the 3axis CAM software on the market ever took place, it should to discover which of the different products are actually using the same machining kernels under the hood. That would be a minimum outcome.

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