Adding in some more specs for the machine.
Needs to be moveable by two men or forklift/pallet truck. Forklift needs space for tines
Welded steel frame with self leveling epoxy mounts for the rails and ballscrew bearings.
£1000 rebuild cost.
40w laser tube.
belt driven X axis, ballscrew driven y axis (single )
Thinking about using igus drylin for the fast moving X axis.
There needs to be some way of tramming the X axis so it is level and square to the table.
Servos would be nice but they would blow the budget so I'm thinking about using a hybrid stepper with encoder for the X axis as this would be the axis to most likely lose position when rastering an image.
shields for the laser, the gantry design makes it difficult to fully enclose the machine.
Found these nice modular parts for laser cutters. Thought it was worth a share as they look very well designed, the only neagtive would be the high mass of the laser cutting head.
I ended up buying the setup advertised on Aliexpress. It arrived today and I very pleased with the quality of the parts. It certainly beats the build quality of the countless cheap lasers I have used in various fablab around the UK, not as nice as the American stuff as I would say the parts on the mjunit stuff are a little heavy, I think a laser should be fast and light but I hope this will do me just fine, time will tell.
One thing that annoyed me was the customs guys slashing open one of my boxes and then just making a crap job of sealing it back up. Cutting the box destroyed its strength and the delivery guy had it slung over one of his shoulders and it was bent like a banana, I feared the worst but the rails look straight.
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Next job is to weld up a frame to hold the rails and mount the electronics onto. Then I need to source some nema 23 steppers or servos. What do you think about these chinese servos
The reason I was thinking about servos or closed loop steppers is mainly for the faster rastering axis. At fast engraving speeds the quick change of direction may cause a stepper to lose position. These chinese servos look cheap but are they any good, I haven't seen anyone use them before?
Rebuild costs so far £750 leaving me £750 to complete.
One turn of the linear actuator shaft moves the carriage roughly 70mm
There is a reduction of 3:1 on the motor so one spin of the motor will move the carriage 70/3 = 23.33 mm
The advertised top speed for the units is 1.5 m/s to achieve this the motor will have to spin at what rpm?
Change 1.5m/s to mm/min = 90,000mm/min
90,000/23.33 = 3857.69 rpm
I have been looking at the leadshine closed loop stepper units. In particular the nema 23 2nm unit. They advertise the ability to run at 3,000rpm but the torque seen at these high rpms is very low just like most steppers in fact the torque curve stops at 2000rpm?. I guess this is why the high end laser cutters use small servo motors. Leadshine also make a nema 23 frame servo which is almost the same price as their closed loop steppers, for some reason I haven't seen a sole use them on any project. The same could be said for the steppers.
Last edited by gavztheouch; 14-12-2014 at 02:22 PM.
Why do you think you want 1.5m/s?
If you wanted speed why are you planning to reduce the motor rpm 3:1?
The manufacture of the slides suggest a max speed of 1.5m/s so I was just looking to see what rpm I would need to hit the max. In reality I think the laser head is too heavy to run at 1.5/ms so I would be backing off the speed until it looks about right.
The 3:1 reducer is part of the kit so I prefer to leave it in, I think the reduction also helps with the sudden changes in direction the xy is subject too.
Is it possible to keep everything static and just move a mirror accurately to reflect the beam around the tool path ? the strength of the beam would need to be continuously adjusted to compensate for distance changes I think ?
Last edited by EddyCurrent; 15-12-2014 at 10:28 AM.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
Presumably you would only go for engraving speed on the lightest axis, call it X? Making it fast will make it heavy so you will need a different motor and much lower target speed for the Y. In my day if you wanted enormous speed and acceleration then you used a pancake motor, is that what the Trotec uses?
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