Freesteel Blog » Steel cutting of shapes

Steel cutting of shapes

Monday, January 25th, 2016 at 1:42 pm Written by:

Here’s a quick offering from the “Well it’s better than nothing video editing department”. This is the result of 2 days of cutting from short videos taken with my camera. (I’ve got no talent with video editing.)

I learnt one heck of a lot in the process.

  1. Steel is really difficult to work with
  2. Small 3mm cutters are easy to snap
  3. The spindle is under-powered
  4. Big 6mm cutters can handle being bent when the spindle stalls if you hit stop soon enough
  5. You can drop the feedrate briefly to stop the spindle stalling
  6. Multiple cutters with rest machining are essential
  7. 0.1mm stepovers are a better than 0.2mm
  8. I probably need a tapered cutter to create a draft angle
  9. Clamps are a real hassle; I’m going to get a vice
  10. The noise of the machine sounds terrible, but nobody has complained yet because it doesn’t seem to carry into the hallway
  11. My 3D printed ductwork for automatically hoovering out the chips was a failure; I need to prod in the nozzle by hand to remove the chips

I was using the Adaptive Clearing toolpaths in Autodesk Fusion, which I had spent 10 years developing before and after it got sold to AD.

It sucked in several ways that I did not know about, because I’d never used it myself to get something I wanted to get done. I always said I ought to have been put on the job of using CAM software to cut steel on a machine in a factory for a couple of months at some point in my career before being allowed to continue writing software that didn’t quite do stuff right. People get into positions like I was, and seem to do pretty well, but should get the opportunity to go back and fill in some gaping holes in their experience.

The problems I found were:

1) Adaptive takes too long time to calculate small stepovers when clearing around a tongue of material and it has to turn right towards the material to stay in contact. This is probably because the sample rate has to go very small in order to maintain engagement when it does its straight line forward samples. It should detect these situations and do its initial step forward with a curve to the right so that begins with being engaged on the first sample and doesn’t need to resample backwards blindly until it makes contact again.

2) The helix ramp down pitch was not linked to the tiny stepover I was setting and I couldn’t see how to change it. I had to hack the G-code directly.

3) In spite of claims to the contrary and it being mathematically accurate, I am sure that the load going into the corners is higher than when the flank cutting is on the straight. I can hear the spindle being slowed down. This could be because the chip length is longer for the same chip width. The chip length is the distance around the circumference of the cutter that is tearing off the metal, and it can approach a semicircle in a tight corner, or be insignificant when it first engages with the 90degree outer corner of the stock.

Now a real machine tool probably has so much angular momentum in the spindle that no one is going to notice this, but on some underpowered low-spec experimental device, such as this, it becomes apparent. That’s why future innovations would happen here, and are unlikely on the big machines where you don’t notice the flaws.

I can now pretty much see how companies like IBM missed the first wave of the PC, which were toy devices in comparison to the big mainframes they were playing with. Nobody was ever going to do any real work on those barely-up-to-scratch microcontroller-based computers with deplorable amounts of RAM, audio cassette tapes for backup, a complete joke parody of an operating system from Microsoft, and a lack of customers able to pay big bucks. Most of the professional engineers in the world (software and hardware) had all the access they needed to mainframe computers in their workplace or university institutions to do fluid dynamics or graphics or simulations. I’m sure when some overly keen teenager came along with their toy machine he’d soldered together, they put him in his place with a back-of-the-envelope calculation of how many centuries it would take that Apple2 to do something real, like predict tomorrow’s weather, which was something they could do with their latest cool CrayXMP super-computer machines. PCs were obviously an utter waste of time, and because was clear where the cutting edge was if you wanted to actually get stuff done.

Sure, you could say this left a huge gap in the economy for new tech billionaires to emerge and for IBM to eventually become an embarrassment, but think about the wasted capital and precious engineering time of talented people who should have been deployed to make this microcomputer tech good from the beginning. MS/DOS and MSWord might not have existed in the horrible no-good forms they did had it not been left only to people who didn’t know what they were doing and had to learn as they went along, thus locked in their anti-productive design mistakes into the way this tech worked for the next 30 years.

Meanwhile I’ve no idea what I am doing. Should I spray WD-40 onto the metal while it is cutting?


  • 1. Greg H. replies at 26th January 2016, 1:00 pm :

    You took the words from my mouth. I have been posting on the HSMWorks forum for a long time that development should run machines with the code they develop. Or development should hire seasoned machinists to run the code. Relying on customer feed back is the lazy way out and not very productive.

    As for coolant you want a coolant that is for cutting steel. WD-40 is OK for non-ferrous materials like alum, brass, copper. It is better than nothing at all on steel. I’m sure there is a machine shop near by, they will loan you some for the steel. Your machine seems a bit flimsy.

    Have a good one!

  • 2. Graeme replies at 7th February 2016, 2:38 pm :

    Your right about choosing CAM systems.

    I use machining strategist because when it was depocam we used depo cutters, Visi because it was better that NC graphics cad offering at the time and Edgecam because daewoo recommended it and the posts when we bought Puma MX machines.
    Now that we have anything between 10 and 20 years of existing work its impossible to sell a change.
    Trying to improve the software via customer feedback is like talking to a brick wall. Adaptive clearance paths show great promise cutter super alloys on a lathe. All it would take is a bit more control on the lead on and off and the ability to split the path up with cut length to change the insert.
    I would highly recommended anyone involved with CAM cuts some metal. Getting a tie in with a sub con machine shop shouldn’t be that hard.

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