Changing threaded Z rod

Hi
I am lucky enough to have aquired some linear rails and carraiges so I am thinking of building a bigger printer


If I want to use a larger diameter threaded Z rod to lift the Z axis , lets say for arguments sake an 8mm diameter then the pitch of the thread is different to our normal 5mm thread
for a normal 5mm rod the pitch is 0.8mm
for an 8mm rod the pitch is 1.25mm

So obviously the number of steps sent to the Z stepper will need to be different for the same amount of lift

How would I go about changing this , is there a G code to go into config.g to set this and if so
is there a way of calculating the required figure rather than keep adjusting and measuring untill the movement comes out to the correct amount

Don

There is an M code in the config.g file. I'm sure someone else will know off the top of their head which code. It might be M92.

Quote
jy_oc_hx
There is an M code in the config.g file. I'm sure someone else will know off the top of their head which code. It might be M92.

Yes, it's M92. The command M92 Z2560 should be correct for 1.25mm pitch.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

If you are rebuilding, you might want to consider this type of motor [www.ebay.co.uk]

Dave

RepRapPro has the math for steps per axis spelled out here, [reprappro.com]

steps for leadscrew (Z axis) = ( motor steps per revolution * microstepping ) / thread pitch

M5 leadscrew = (200 x 16) / 0.8 = 4000

M8 leadscrew = (200 x 16) / 1.25 = 2560


Keep in mind that using a non-metric threaded rod would result in a non-whole number for steps/mm which is probably less than ideal.

thats really helpful
Just what I was looking for
Thanks everyone for your input


Don

Don.

You may want to consider changing the gearing unless you are going direct drive. I just went to an M6 threaded rod and changed the ratio to suit. This way you don't loose any resolution or run into any non full step issues.

Thats a good point and I had not considered using gearing before

when I finally get around to building a bigger machine I already have bigger stepper motors and seperate MSD542 stepper drivers which give me a large range of micro
stepping sizes , right up to 25000 micro steps , so I am sure with both gearing and the right choice of step size I could get around non full step issues

I was planning on lifting the Z axis from both sides of the machine but dont know yet whether to use a separate stepper on each side or use one stepper and join
the threaded Z rods on each side with a timing belt and pulleys
two motors sounds the easier way but I worry what would happen if one motor started missing steps as both sides would then be at different heights

does any one have experience of this that could give an opinion

Don

On many other 3D printers (like Mendel and Huxley) there are two steppers for the two separate Z screws. It seems to work alright, and unless you have your machine "crash" (by going too far in either Z direction) you shouldn't have the steppers skip. And in such a situation, you may also have a belt skip.

One problem I've experienced with a Huxley was that if you were doing something with the machine when it was "off" (as in no current through the steppers), you could accidentally turn one of the steppers and have it misaligned. Not too hard to fix (zero z on one end, then move X carriage to the other side and adjust the other z rod to match), but it took a minute or two.

It should work having a belt and pulley to run the second Z rod, but it wouldn't be significantly cheaper (cost of stepper motor + driver compared to belt and pulleys), more difficult to "zero" (make both Z rods on the same level), and it would be mechanically tricky to get the belt past where all the Y axis stuff is unless you mount it on the top of the printer. It would also have to be an endless belt loop, which probably means having an idler to tension it. In all, it's just more complicated than a second stepper motor.

If I were building a large format printer, I would be tempted to use three Z stepper motors, driven independently by the electronics. Then the firmware could use the Z probe to do 3-point bed levelling by driving the motors independently, as opposed to the bed compensation that we use on the Ormerod. Of course, this would require firmware changes.

Edited 1 time(s). Last edit at 03/28/2015 06:31PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
If I were building a large format printer, I would be tempted to use three Z stepper motors, driven independently by the electronics. Then the firmware could use the Z probe to do 3-point bed levelling by driving the motors independently, as opposed to the bed compensation that we use on the Ormerod. Of course, this would require firmware changes.

oo er this could be interesting.

How difficult would it be to do this Dave as I intend to drive my bed on the CoreXY with 3 trapezoidal leadscrews in the Z axis was going to use a single Nema23 and a closed loop belt but this idea sounds like it may be a better solution?

It would mean using a Duet + Duex rather than a Duet + Shield so I could get 2 extruder's

erm interesting idea!

Doug

Quote
dc42
If I were building a large format printer, I would be tempted to use three Z stepper motors, driven independently by the electronics. Then the firmware could use the Z probe to do 3-point bed levelling by driving the motors independently, as opposed to the bed compensation that we use on the Ormerod. Of course, this would require firmware changes.

I cant visualise how that would work . I am assuming you mean one motor at each end and one in the middle
If you then used the middle motor to compensate in bed leveling surely that would have to make the x axis bend ?

where am I missing the point ?

Quote
Don Recardo

Quote
dc42
If I were building a large format printer, I would be tempted to use three Z stepper motors, driven independently by the electronics. Then the firmware could use the Z probe to do 3-point bed levelling by driving the motors independently, as opposed to the bed compensation that we use on the Ormerod. Of course, this would require firmware changes.

I cant visualise how that would work . I am assuming you mean one motor at each end and one in the middle
If you then used the middle motor to compensate in bed leveling surely that would have to make the x axis bend ?

where am I missing the point ?

Three stepper motors in a triangle. Think of the 3-point bed mounting of an Ormerod 2, or an Ormerod 1 with DaveK's bed support upgrade, with a stepper motor driving the screw at each mounting point. Except that the stepper motors also serve to raise and lower the whole bed.

For a really large printer, the bed might not be stiff enough to prevent twisting by a significant amount, and 4 stepper motors (one at each corner) might be better.

Quote
dougal1957
How difficult would it be to do this Dave as I intend to drive my bed on the CoreXY with 3 trapezoidal leadscrews in the Z axis was going to use a single Nema23 and a closed loop belt but this idea sounds like it may be a better solution?

It would mean using a Duet + Duex rather than a Duet + Shield so I could get 2 extruder's

This is what I envisage would need doing, but I may have forgotten something:

1. Design and implement a new gcode for describing multiple Z motors. Probably just need to specify which drives (as well as the standard Z drive) are additional Z drives.

2. Modify the movement code to step all Z drives together during normal moves. Should be very simple

3. Design and implement a modification to G32 to specify that we are probing over each motor, and the motors need to be adjusted at the end. I already have the code in place to so different sorts of bed probing, because I needed it to allow G32 to do both delta calibration and bed compensation. So this should not be difficult.

4. There will be some additional consequences, e.g. M906 to set the Z motor current must set the current for all Z motors, and the mapping between extruders and drives will change.

Edited 1 time(s). Last edit at 03/29/2015 09:08AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42


Three stepper motors in a triangle. Think of the 3-point bed mounting of an Ormerod 2, or an Ormerod 1 with DaveK's bed support upgrade, with a stepper motor driving the screw at each mounting point. Except that the stepper motors also serve to raise and lower the whole bed.

For a really large printer, the bed might not be stiff enough to prevent twisting by a significant amount, and 4 stepper motors (one at each corner) might be better.

Thanks for the explanation , it makes sense to me now

Quote
dc42

Quote
Don Recardo

Quote
dc42
If I were building a large format printer, I would be tempted to use three Z stepper motors, driven independently by the electronics. Then the firmware could use the Z probe to do 3-point bed levelling by driving the motors independently, as opposed to the bed compensation that we use on the Ormerod. Of course, this would require firmware changes.

I cant visualise how that would work . I am assuming you mean one motor at each end and one in the middle
If you then used the middle motor to compensate in bed leveling surely that would have to make the x axis bend ?

where am I missing the point ?

Three stepper motors in a triangle. Think of the 3-point bed mounting of an Ormerod 2, or an Ormerod 1 with DaveK's bed support upgrade, with a stepper motor driving the screw at each mounting point. Except that the stepper motors also serve to raise and lower the whole bed.

For a really large printer, the bed might not be stiff enough to prevent twisting by a significant amount, and 4 stepper motors (one at each corner) might be better.

Quote
dougal1957
How difficult would it be to do this Dave as I intend to drive my bed on the CoreXY with 3 trapezoidal leadscrews in the Z axis was going to use a single Nema23 and a closed loop belt but this idea sounds like it may be a better solution?

It would mean using a Duet + Duex rather than a Duet + Shield so I could get 2 extruder's

This is what I envisage would need doing, but I may have forgotten something:

1. Design and implement a new gcode for describing multiple Z motors. Probably just need to specify which drives (as well as the standard Z drive) are additional Z drives.

2. Modify the movement code to step all Z drives together during normal moves. Should be very simple

3. Design and implement a modification to G32 to specify that we are probing over each motor, and the motors need to be adjusted at the end. I already have the code in place to so different sorts of bed probing, because I needed it to allow G32 to do both delta calibration and bed compensation. So this should not be difficult.

4. There will be some additional consequences, e.g. M906 to set the Z motor current must set the current for all Z motors, and the mapping between extruders and drives will change.

Dave

If you want a guinea pig for this I am more than willing I haven't done my Z on the coreXY further than getting the parts together I will be using 3 TR10x2 Leadscrews and I have enough motors as well and the Bed will be plenty stiff enough (Frame of 20x20 extrusion 3 mm ally sheet underneath and bed is 6mm thick engineering plate so it is quite heavy.

Doug

DC/guys.

I was thinking about something like this for my big build.

I wasn't really thinking about software too much, more building around what is already in place.

I was also going to use a closed loop belt and just 1 bigger stepper, so as to use only 1 stepper output.

After thinking about it some more, thinking that 3 separate steppers was a better option and split the single output into 3 via transistors and a 12v rail. Thinking even more, I figure you could use an arduino to offer some tweaking while I was at it. In fact, just using a ramps setup with some simple code and a display/encoder should do the job.

At least that's how it would work in my head.

I'm currently working on a 300 x 400 X ??? With the bed moving in Y like the ormerod, but I know this won't be ideal

Automatic bed levelling using 3 or 4 Z motors is not straightforward unless you can probe extremely close to the Z drive points, because a change in height of one Z motor will affect the height of the probing position near another motor, so you either need to put in a maths routine to account for that or will need to probe each point several times in a round-robin fashion to get the bed level by successive approximation.

Dave

Quote
dmould
Automatic bed levelling using 3 or 4 Z motors is not straightforward unless you can probe extremely close to the Z drive points, because a change in height of one Z motor will affect the height of the probing position near another motor, so you either need to put in a maths routine to account for that or will need to probe each point several times in a round-robin fashion to get the bed level by successive approximation.

Agreed. However, this is easier than the maths that is needed on a delta printer to do endstop + delta radius adjustments, as my firmware fork does, so not very difficult to implement. I have it down to 2 iterations to get an accurate result.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].