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Messages - BluePinnacle

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General Mach Discussion / Re: I had stroke!
« on: November 25, 2015, 03:16:17 PM »
Good thing you spotted it for what it was, the FAST checklist is taught to all first-aiders here but still not everyone knows about it. Hope you're feeling better soon.

Good news! Happy perforating.

General Mach Discussion / Re: safe z
« on: November 18, 2015, 05:33:01 PM »
A safe Z value should be positive with the top of the workpiece as Z=0. As to height, it should clear any clamps and fixtures. It is entirely dependent on setup and will vary according to workpiece, jigging and tool length.

The parts will be easy, it'd just be microswitches or inductive proximity sensors or whatever suits from RS or Farnell or any of the others. The code will be the important part. You could use relay logic for some of it depending on construction, it's a good robust crash proof way of handling things. Got pictures of the ATC?

General Mach Discussion / Re: Velocity in Gcode G0
« on: November 01, 2015, 04:40:12 PM »
G0 is for rapid positioning only. It's not for cutting. Still read the manual though.

Thanks all :)

The motors are actually fairly small, I can't find the specs for these just now but they are about the size of 2 tuna cans, and standard 200 steps/rev. They are very strong though, magnets have improved since my mill was built. They are each geared down 4:1 to a 5tpi 25mm ballscrew.

The bearing blocks, rails and ballscrews are all from HiWin. The stepper driver is a RoutOut unit similar to the one on my mill. It didn't need to move quickly, just steadily and accurately.

The wood stuffed under the rail was to damp a vibration which occured periodically as turning progressed. The setup lacked rigidity and if I was to do it again I'd fabricate a rail based on some of the 20" hot finished steel CHS we use here, and probably filled it with concrete. We also experienced resonance in the tool and were forced to adjust the spindle speed to dial it out. It was quite a job. I needed a good long sleep afterwards.

Afterwards we removed 600kg of swarf from the pit.

Chrisjh - Both techniques are still in use, we spin ours but larger sizes are hydroformed here and in the US. Stretch forming is also widely used, it works for the bigger segmented reflectors. Composites are also widely used but they have problems all of their own.

General Mach Discussion / Re: Hi Newbie question
« on: October 30, 2015, 01:21:45 PM »
Been using Mach3 for about 8 years now.

I'd avoid this as well. Unless your home switches are absolutely spot on you will almost certainly shift a little on re-homing and turn out a bad job, or at worst you could end up with a busted tool, or a damaged machine.

I concur with bfgstew, plan your day to allow complete cycles.

That said, welcome, and enjoy :)

This is the story of how we built one of the largest spinning tools you are ever likely to see. This is a parabolic spinning tool for making aluminium reflectors for satellite antennas and weather radar systems. It weighs around 2.5 tons. We had a 3.0m tool which was bought as part of a factory closure. it had originally been the centre of a 4.5m tool, but the outer segments had been scrapped. so we had to remake them. It was no small job.

fig.1. The 3.0m tool

Fig. 2 After making a pattern and having the new segments cast, the machining references were milled and holes tapped for fixturing. They were milled on a large 3-axis machine, tilted as they would be in service to allow the sides to come parallel when assembled.

Fig. 3. Assembling the tool for finish turning

Fig. 4. The tool in position on the lathe headstock where it will be used, driven at around 60RPM using a 20hp motor. Note the pit needed to clear the tool to put the axis at a workable height.

Fig. 5. Turning the tool. The 2-axis slide is not at 90 degrees to the machine axis as this would require too much slide movement, Instead a minimal Y axis moving only 300mm or so is used, and an angular offset applied. The software is used in mill configuration using the radius of the lathe tool tip as an offset.

Fig. 6. The finished tool With its eventual operator for scale.

Programming was simple since a parabolic curve is simply defined mathematically, so parametrics are used to recalculate the next pair of X and Y coordinates based on a subroutine that runs several times a second to change the value of two parameters which are then translated to X and Y before movement. The program as it was run was about 30 lines long. This and the angular offset made the programming easy.

Turning took six days, day and night. This was a long job and the first I've seen where the job was bigger than the machine! a number of visitors called their friends and just said "get down here. You've got to see this". As far as we know this is the largest metallic spinning tool in europe - and it was made using Mach3.

Show"N"Tell ( Your Machines) / Re: Zero gravity Z
« on: December 08, 2013, 10:23:41 AM »
I can see the problem now, the weight of the head is backdriving the stepper when it is unpowered. Took a while to see whay that could be, it's not a problem a regular mill would suffer from as it's just the weight of the quill against a fairly highly geared ballscrew. I certainly can't backdrive any of my axes  :D

The air cylinder looks as good a solution as any that doesn't add mass to the arrangement like a counterweight. Gas struts also for the same reason.

^ That's how I've always done it on every sort of equipment I've worked on. For tidiness, pop a bit of self-adhesive heat shrink over the transition between the braid and the insulated wire tail ;)

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