4th axis as lathe spindle: question about index
15 Oct 2014 03:25 #52106
by akb1212
Replied by akb1212 on topic 4th axis as lathe spindle: question about index
We can only hope you get a 4th axis built soon then 
I came to think of a couple of things about this..... LinuxCNC have a lathe mode. I'm not to familiar with what the difference is compared to milling mode since I haven't looked at it. But I assume the tool shape and such things are implemented differently in lathe mode.
It would possibly also be a good idea to make the preview window change to lathe view, or even better, make a new view that is adapted to millturn. I haven't seen how this is handled by the commercial controls, but I imagine some of you guys know how this is normally done.
DaBit,
What are your plans/thoughts on speed range on your 4th axis? Available torque will obviously have to be compromised in regards to max RPM on your lathe. Are you thinking of using two (or more) gears like Simpson36 are using? His setup require a manual gear change. This will obviously make you loose position when you change gear. If you don't apply the brake on the spindle while you make the gear change that is.
Nevertheless, a manual gear change isn't ideal. But space and size might limit automatic gear changes and make it impractical and difficult to make.
Anyway, if a gear is implemented in any way on the 4th axis this will have to be considered when using this module. And the gear range and the way it's changed will most likely be different from gear change on the main mill spindle. In particular since the lowest speed you want for 4th axis to have is a lot lower than you would want you main milling spindle to have.
Most of these things aren't problems that will be handled directly by the new component you are making. Although they will have to be dealt with since the gearing of the main spindle will change as a result of using this new component. At least with mode 2.
There are probably also other side effects of mode 2 that will have to be considered. We would most definitely want a spindle brake on the 4th axis.
Come to think of it, it would probably also be a good idea to install a spindle brake on the main milling spindle as well if the lathe tooling is to be held in it. It might be a good idea to attach them elsewhere on the spindle head like Simpson36 have done on his mill (which is in fact quite clever and makes it possible to have many tools available in an efficient manner). But I imagine its a good idea to be able to have the lathe tools in the main spindle too. And I know my mill will have to have a spindle brake to be able to handle that. And since I have an ATC it makes more sense to use the main milling spindle as main lathe tool holder as well. Then I will be able to use the ATC for lathe operations as well.
Anyway, the spindle brake logic could possibly be implemented in to the milturn helper component? There need to be some logic to handle this as the axes are swapped.
Sorry for this rambling. But there are loads of details that comes up when I start to think of how to implement all of this.
But thanks again for sharing this. There are so many possibilities that opens up with this....
Anders
I came to think of a couple of things about this..... LinuxCNC have a lathe mode. I'm not to familiar with what the difference is compared to milling mode since I haven't looked at it. But I assume the tool shape and such things are implemented differently in lathe mode.
It would possibly also be a good idea to make the preview window change to lathe view, or even better, make a new view that is adapted to millturn. I haven't seen how this is handled by the commercial controls, but I imagine some of you guys know how this is normally done.
DaBit,
What are your plans/thoughts on speed range on your 4th axis? Available torque will obviously have to be compromised in regards to max RPM on your lathe. Are you thinking of using two (or more) gears like Simpson36 are using? His setup require a manual gear change. This will obviously make you loose position when you change gear. If you don't apply the brake on the spindle while you make the gear change that is.
Nevertheless, a manual gear change isn't ideal. But space and size might limit automatic gear changes and make it impractical and difficult to make.
Anyway, if a gear is implemented in any way on the 4th axis this will have to be considered when using this module. And the gear range and the way it's changed will most likely be different from gear change on the main mill spindle. In particular since the lowest speed you want for 4th axis to have is a lot lower than you would want you main milling spindle to have.
Most of these things aren't problems that will be handled directly by the new component you are making. Although they will have to be dealt with since the gearing of the main spindle will change as a result of using this new component. At least with mode 2.
There are probably also other side effects of mode 2 that will have to be considered. We would most definitely want a spindle brake on the 4th axis.
Come to think of it, it would probably also be a good idea to install a spindle brake on the main milling spindle as well if the lathe tooling is to be held in it. It might be a good idea to attach them elsewhere on the spindle head like Simpson36 have done on his mill (which is in fact quite clever and makes it possible to have many tools available in an efficient manner). But I imagine its a good idea to be able to have the lathe tools in the main spindle too. And I know my mill will have to have a spindle brake to be able to handle that. And since I have an ATC it makes more sense to use the main milling spindle as main lathe tool holder as well. Then I will be able to use the ATC for lathe operations as well.
Anyway, the spindle brake logic could possibly be implemented in to the milturn helper component? There need to be some logic to handle this as the axes are swapped.
Sorry for this rambling. But there are loads of details that comes up when I start to think of how to implement all of this.
But thanks again for sharing this. There are so many possibilities that opens up with this....
Anders
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15 Oct 2014 04:50 #52107
by DaBit
Replied by DaBit on topic 4th axis as lathe spindle: question about index
First I'll have to finish the mill itself 
It spent the last two evenings milling the work area flat (and it is not even done yet). I do this very slowly by taking a pass and waiting a few minutes; if the temperature of the surface rises while the bottom is still cold it will warp. Until now there are not many surprises, which is a good thing. After that I have a couple of other jobs to do to, but then I will continue with the 4th axis.
For that 4th axis I have a 1.1kW/3000rpm servo motor with 2500 lines encoder. In positioning mode it can do 3000rpm, but in (analog) velocity mode it should be capable of doing a bit more with loss of torque; I can set the maximum velocity up to 5000rpm. I am thinking of gearing it down 1:3 or 1:4 using a wide steel-reinforced toothed belt with large pulleys. That way I can do ~1250rpm or ~14Nm of torque. Should be sufficient; most of my turning needs involve POM, aluminium and brass or small diameter steel. I also need a fairly large/heavy chuck to match the inertia of the chuck to the servo. Even then I think positioning is not stiff enough for 4-axis milling (there must be a reason why everybody gears down that 4th axis 1:100 or so), but since most 4-axis milling can be done using simple indexing, a brake should take care of that.
But I suppose that leaving a little space for a second set of pulleys and an encoder on the main spindle is not such a bad idea
I intend to mount the lathe tooling to the Z-axis column itself, not in the spindle. I drilled a bunch of holes in the bottom plate just for the 'I want to hang something on the column, now where do I attach it?':
I think that handling the brakes is best left to one or more external components instead of one big monolithic millturn-helper component. That allows easier tailoring to a certain situation.
Having LinuxCNC swap display modes and possibly the meaning of the X and Z axes when the component is activated is also not very high on my priority list. Personally I don't need it when using mixed mode since the NGC code for that is most likely handcrafted anyway. And if I intend to do turning only I might as well start another configuration.
It spent the last two evenings milling the work area flat (and it is not even done yet). I do this very slowly by taking a pass and waiting a few minutes; if the temperature of the surface rises while the bottom is still cold it will warp. Until now there are not many surprises, which is a good thing. After that I have a couple of other jobs to do to, but then I will continue with the 4th axis.
For that 4th axis I have a 1.1kW/3000rpm servo motor with 2500 lines encoder. In positioning mode it can do 3000rpm, but in (analog) velocity mode it should be capable of doing a bit more with loss of torque; I can set the maximum velocity up to 5000rpm. I am thinking of gearing it down 1:3 or 1:4 using a wide steel-reinforced toothed belt with large pulleys. That way I can do ~1250rpm or ~14Nm of torque. Should be sufficient; most of my turning needs involve POM, aluminium and brass or small diameter steel. I also need a fairly large/heavy chuck to match the inertia of the chuck to the servo. Even then I think positioning is not stiff enough for 4-axis milling (there must be a reason why everybody gears down that 4th axis 1:100 or so), but since most 4-axis milling can be done using simple indexing, a brake should take care of that.
But I suppose that leaving a little space for a second set of pulleys and an encoder on the main spindle is not such a bad idea
I intend to mount the lathe tooling to the Z-axis column itself, not in the spindle. I drilled a bunch of holes in the bottom plate just for the 'I want to hang something on the column, now where do I attach it?':
I think that handling the brakes is best left to one or more external components instead of one big monolithic millturn-helper component. That allows easier tailoring to a certain situation.
Having LinuxCNC swap display modes and possibly the meaning of the X and Z axes when the component is activated is also not very high on my priority list. Personally I don't need it when using mixed mode since the NGC code for that is most likely handcrafted anyway. And if I intend to do turning only I might as well start another configuration.
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