Wedg1e
They call me Mr. Bodge-angles
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- Thread starter AdrianH
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Wedg1e
They call me Mr. Bodge-angles
- Messages
- 7,867
- Location
- Teesside, England
OK, in for a penny, in case anyone's still reading... 
This is the view along the tank:
The Y- and Z-axis covers...
...and the Z-axis with its fancy knickers pulled off
The mast is an inch diameter length of stainless tube, for scale (no builder's mug to hand) Just visible at top right of next pic is a Huco coupler joining the stepper to the leadscrew, to accommodate any 'production errors' in their alignment
And yes, the orange ball is the float of a toilet cistern ballcock
This is the view along the tank:
The Y- and Z-axis covers...
...and the Z-axis with its fancy knickers pulled off
The mast is an inch diameter length of stainless tube, for scale (no builder's mug to hand
) Just visible at top right of next pic is a Huco coupler joining the stepper to the leadscrew, to accommodate any 'production errors' in their alignmentAnd yes, the orange ball is the float of a toilet cistern ballcock
Wedg1e
They call me Mr. Bodge-angles
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- Teesside, England
?? Nope, you've lost me there
First time I've ever built something this complicated (although it isn't really, it's just a lot of design and engineering). It's deciding what spec., how big, what ratio, how fast etc. etc. that sort of determines how much it'll cost; as I said someone else was paying so if I got the odd bit wrong there was scope to try again. So far, so good...
skotl
Forum Supporter
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?? Nope, you've lost me there
Ah - sorry
On Dragons' Den, when they decide not to deal with the guy trying to sell them something they say "I'm out".
I was thinking of hacking together a plasma table then I saw yours and realised I didn't have a hope in hell of competing with that, hence "I'm out"
Wedg1e
They call me Mr. Bodge-angles
- Messages
- 7,867
- Location
- Teesside, England
Ah - sorry
On Dragons' Den, when they decide not to deal with the guy trying to sell them something they say "I'm out".
I was thinking of hacking together a plasma table then I saw yours and realised I didn't have a hope in hell of competing with that, hence "I'm out"
Ah right... but you'll be building down to a price, not up to a client's expectations... I'd be pinching the pennies and cutting up old bedsteads myself if it was for me
Don't worry skotl, I'll start posting a few more on this thread and get it back to ultra cheap and simple, if it works will be a different matter. Just waiting for some 9mm OD 6mm ID 5 mm long spacers or bronze bushes to arrive and I will start the next bit.
Just found my receipt for the 7.5 metres of 50 x 25 x 3 RHS that I had cut up £19.50.
Cheap Voltmeter and amp meter combined for 30 Volts and 50 Amps about £12, all to go in a box I have rescued from the scrap bin to house the PSU (was electrical waste) and Stepper controller (ebay). Mains filter also rescued from some old gear.
Collecting bits still
Adrian
Just found my receipt for the 7.5 metres of 50 x 25 x 3 RHS that I had cut up £19.50.
Cheap Voltmeter and amp meter combined for 30 Volts and 50 Amps about £12, all to go in a box I have rescued from the scrap bin to house the PSU (was electrical waste) and Stepper controller (ebay). Mains filter also rescued from some old gear.
Collecting bits still
Adrian
Oh well dream on.A stepper motor generally has no positional feedback, so if it gets stuck the program does not know, servo motors have to have feedback , generally optical sensors so that it can tell if it has moved or not. so if it is stuck it could keep trying or at least have a failsafe to stop the program, flash lights etc.
You drive the servo motor and count the sensor outputs to give position.
On a stepper you change the motor inputs and hope it moves as expected.
It is possible to stick optical sensors on steppers but generally cheaper not to.
Adrian
You drive the servo motor and count the sensor outputs to give position.
On a stepper you change the motor inputs and hope it moves as expected.
It is possible to stick optical sensors on steppers but generally cheaper not to.
Adrian
is he actually making a plasma table or nuclear machine??Ah - sorry
On Dragons' Den, when they decide not to deal with the guy trying to sell them something they say "I'm out".
I was thinking of hacking together a plasma table then I saw yours and realised I didn't have a hope in hell of competing with that, hence "I'm out"
Maker
Most folk just call me; Orange Joe
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What kind of driver do you need for DC servo motors? I ask because I have one I've been saving for something good and (if I ever get it working) it would be cool to use it to CNCify my milling machine.
I'll dig it out tomorrow, I think it's missing it's encoder.
http://en.wikipedia.org/wiki/Servomotor is your friend. basically It can be most types of motor.
Adrian
Adrian
Wedg1e
They call me Mr. Bodge-angles
- Messages
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- Teesside, England
I found you can't start a stepper at full speed with any load on it, it has to ramp up (otherwise it'll just sit there and oscillate). With the inspection tank unit we found there was a limit to how fast we could make it move, about 6kHz was the highest pulse frequency we could poke into the stepper controllers before the motors threw a hissy fit and stalled. With the 20: 1 reduction and a pinion gear about 60mm diameter that translated to an X-axis linear travel of about a metre every 15 seconds (as I recall) - this effctively told us the maximum 'fast traverse' speed we could have (i.e. when it returns the carriage from the end of an inspection run).
Steppers are supposed to be torquey but I doubt the X-axis beam would have moved at all if I hadn't included the reduction boxes. As it is you can lean on it and it'll take you along for the ride - it deliberately runs with a clearance above the tank side rails so that you can't get a hand stuck under it.
If I was going to build a CNC bed for myself I'd aim to make it universal so it could carry a plasma torch, router or whatever (maybe even a MIG torch
)Consider how to make the linear rails adjustable for parallel, level and longitudinal skew as a frame DIY-welded from box, angle or channel is unlikely to be perfectly square - the supported round rails are more tolerant of being twisted along their length as the carriages can rotate around the rail where the 'square' profile ones can't. There's also a good area under the alloy rail carrier to slip shims in if the bed is anything but flat.
On the square rails it is not necessary to use every single bolt holt to secure it
- in fact you have to be bloody accurate at drilling and tapping that many holes, otherwise either the bolts won't go in or they start fighting each other and pull the rail out of shape.If using square rails in parallel, check for friction in the carriages as you tighten the screws holding whatever beam arrangement ties them together. If the beam's bowed at all it will try to twist the carriages on the rail and they'll wear faster. You'll also feel the carriages get stiffer if the rails aren't absolutely parallel.
Oh, another thing: consider the exposure of the linear rails and whatever drive system. If you have a shufty at the inspection tank you can't see the X-axis linear rails or the rack & pinion because they're underneath the two RSJs that make up the tank side rails (hidden by those stainless covers
).The original designer had the whole lot stuck on top of the RSJs, I vetoed it because some of the lengths of bar that will be tested in the tank will weigh 90Kg, the slightest tap from one of those swinging about on a crane would write off the drive train.
On a plasma bed I'd be concerned about hot splattery bits getting onto the linear rails, into leadscrew threads or burning through belt drives...
Sorry, not meant to be a lecture, I've just been reliving assorted nightmares...
Maker
Most folk just call me; Orange Joe
- Messages
- 10,667
- Location
- Keeler crater
Do it and run some 3D printer software(maybe even a MIG torch
.
T0rnado69
DIY nut !!
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and realised I didn't have a hope in hell of competing with that, hence "I'm out"
skotl, i dunno if you are a member of http://www.mycncuk.com/
but if not join up and take a read of the build logs.
so much info and pics of cnc builds....
great load of info. and help for building your on cnc.
