Re: [Emc-users] Pivot mill
Yea, being on the other side of the planet from McMaster Carr has got to suck... As for using feedscrews to drive the arms that adds another part to the position calculation as the amount of rotation changes with the angles as well as the amount of force required to do said work. Keep us posted John On 5 Dec 2007 at 9:15, [EMAIL PROTECTED] wrote: Thanks for all the informative replies. I'll pursue the references. Sounds like it's doable, but the time/effort spent on software development will exceed the material savings. Unless of course, a few thousand were to be made. I would not use gears to drive the arms, but feedscrews, forming a triangle, much like a mechanical shovel. I did not draw that all in as it was getting real late. Again, my target is an entry level CNC mill, for milling of plastics, PCB, foam... And it's a pity I'm on the other side of the planet(South Africa), because I'd be happy to supply a prototype to someone who's keen on working on the software, which is not my forte' Thanks for the prices John. I'll look into it. Freight is always a killer. Regards Roland - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
Hi All Thanks for all the informative replies. I'll pursue the references. Sounds like it's doable, but the time/effort spent on software development will exceed the material savings. Unless of course, a few thousand were to be made. I would not use gears to drive the arms, but feedscrews, forming a triangle, much like a mechanical shovel. I did not draw that all in as it was getting real late. Again, my target is an entry level CNC mill, for milling of plastics, PCB, foam... And it's a pity I'm on the other side of the planet(South Africa), because I'd be happy to supply a prototype to someone who's keen on working on the software, which is not my forte' Thanks for the prices John. I'll look into it. Freight is always a killer. Regards Roland On 05/12/2007, John Thornton [EMAIL PROTECTED] wrote: On 4 Dec 2007 at 16:51, [EMAIL PROTECTED] wrote: This is a very interesting and quite challenging project... The cost to drive each joint of the pivot mill would far exceed the cost of Dremil size slides. While the concept is sound the mechanics of the gears would be the killer. You are designing a robot. The gears would need to be planetary perhaps double reduction to get enough torque to drive the arms. Of course you can't buy them off the shelf they would have to be custom made or purchased from an OEM . I would make the first joint also be the Z axis drop the links to the Z that way your tool position is constant as the Z axis moves. If you do pursue this path please keep us posted as to your progress it is very interesting... and a challenging project... I would look at the options like using 80/20 with their slides and acme threaded rods and nuts if your not needing super tight precision. I'm building a plasma cutter with that as we speed and it is super simple to work with. For a load capacity of 315 lbs each from McMaster Carr you can get slides for $34 each and the rail is $0.09/mm and come in 500mm and 1000mm lengths So for $226 you would have 4 slides and 2 rails with about 16 of travel... Part# 9867K1 and 9867K11 for the rail if you want to look it up. 3/8 acme precision threaded rods are only $28 for 36 and the nuts $22 Part# 95072A124 and 99030A326 So for less than $600 you could have the the mechanics for a 16 x 16 table... And then there is always FleaBay that sometimes has bargains for rails and such... http://cgi.ebay.com/Wafer-Handler-Automation-Robot-21-arm-10- range_W0QQitemZ180186126744QQihZ008QQcategoryZ45044QQssPageNameZ WDVWQQrdZ1QQcmdZViewItem John I believe that the greatest hurdle in constructing a small CNC machine is the cost of the linear slides, - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
On Wednesday 05 December 2007, Anders Wallin wrote: John Thornton wrote: Yea, being on the other side of the planet from McMaster Carr has got to suck... It gets worse. McMaster Carr will currently not sell anything to non-US customers. I tried ordering something a while ago and back came a 5-line answer about increasingly complex export rules etc. etc. With the cheap dollar I'd think US companies would export like crazy right now And that, to quote a friend, Joanne Dow, Sucks dead toads through soda straws. Is there not some Finnish importer who can supply this stuff? Or some Euro based company making equ's? -- Cheers, Gene There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order. -Ed Howdershelt (Author) 1 1 was a race-horse, 2 2 was 1 2. When 1 1 1 1 race, 2 2 1 1 2. - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
I like the idea of rotary joints to eliminate linear bearings. But you are now forced into a complicated drive mechanisim at each rotary joint. It's hard to beat lead screws for simplicity.- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
On Wed, 5 Dec 2007, Roland Jollivet wrote: I would not use gears to drive the arms, but feedscrews, forming a triangle, much like a mechanical shovel. I did not draw that all in as it was getting real late. once you start making triangles out of feedscrews, the madness sets in... http://en.wikipedia.org/wiki/Stewart_platform - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] Pivot mill
Hi I believe that the greatest hurdle in constructing a small CNC machine is the cost of the linear slides, and I've been trying to think of a way to alleviate this, and come up with a 'Pivot Mill'. While this is robotic in configuration, it is for all intensive purposes intended to supplant a conventional 3 axis machine. (X,Y,Z) Bearings are relatively cheap, and construction of the mechanics fairly simple. I have drawn and uploaded a concept picture here, of what I have in mind. http://www.fotothing.com/CAONgallery/photo/9e62959f5230b6745b40b5285739b62c/ There are still three axis, but they are mathematical functions of each other, essentially transparent to the user, and where Z is the most complex interaction. Also notice that the tool will stay vertical during motion due to the dual strut. The servo's are not shown, and would typically introduce a further non-linear relationship since they would act indirectly, or at an angle . To control something like this, from what I've read here, sounds like a task for EMC. So, how difficult would it be to implement this inter-relation between the axis? As far as the user is concerned, the machine must still execute linear moves with normal G-code, as in G1 X200. So the machine has ROTARY AXIS, but executes LINEAR MOTION. A JOG in the Z axis will cause all three joints to move, but the tool will only move vertically Of course, there are always rigidity issues, but it's easy to beef up a pivot arm, and this is only intended to be of the calibre of 'dremel' type, benchtop, CNC machines. There are other appealing factors like the inherent extended reach, for tool changing, and if the machine were placed centrally on a table, it could serve four work areas, as quadrants. (assuming here a 360deg. central column) So, is this worth pursuing? Is the functionality required already a sub-set of EMC, or is it a huge re-work? Regards Roland Jollivet - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
A few thoughts... Isn't the Z axis the easiest? Instead of the dual strut you could use a pantograph, which would keep the Z motion linear instead of radial. It would still be a sine conversion, but it simplifies the conversion significantly. The conversion itself is different matter. Others can speak better than I as to how easy it would be to add something to EMC to provide polar coordinate outputs, but that is what you need for X and Y. On the other hand, by the time you build it stiff enough to do anything more than light duty work it might be cheaper to just use linear ways. For the light duty work you are describing you can probably get by with steel shafting and bronze bearings and have the same precision you would get with the pivot system. Javid - Original Message - From: Roland Jollivet To: Enhanced Machine Controller (EMC) Sent: Tuesday, December 04, 2007 6:50 PM Subject: [Emc-users] Pivot mill Hi I believe that the greatest hurdle in constructing a small CNC machine is the cost of the linear slides, and I've been trying to think of a way to alleviate this, and come up with a 'Pivot Mill'. While this is robotic in configuration, it is for all intensive purposes intended to supplant a conventional 3 axis machine. (X,Y,Z) Bearings are relatively cheap, and construction of the mechanics fairly simple. I have drawn and uploaded a concept picture here, of what I have in mind. http://www.fotothing.com/CAONgallery/photo/9e62959f5230b6745b40b5285739b62c/ There are still three axis, but they are mathematical functions of each other, essentially transparent to the user, and where Z is the most complex interaction. Also notice that the tool will stay vertical during motion due to the dual strut. The servo's are not shown, and would typically introduce a further non-linear relationship since they would act indirectly, or at an angle . To control something like this, from what I've read here, sounds like a task for EMC. So, how difficult would it be to implement this inter-relation between the axis? As far as the user is concerned, the machine must still execute linear moves with normal G-code, as in G1 X200. So the machine has ROTARY AXIS, but executes LINEAR MOTION. A JOG in the Z axis will cause all three joints to move, but the tool will only move vertically Of course, there are always rigidity issues, but it's easy to beef up a pivot arm, and this is only intended to be of the calibre of 'dremel' type, benchtop, CNC machines. There are other appealing factors like the inherent extended reach, for tool changing, and if the machine were placed centrally on a table, it could serve four work areas, as quadrants. (assuming here a 360deg. central column) So, is this worth pursuing? Is the functionality required already a sub-set of EMC, or is it a huge re-work? Regards Roland Jollivet -- - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
What an interesting looking machine. We have a demo of a similar type of machine, called SCARA. In emc 2.2.2, you can run the sample configuration scara/scara.ini and see a visualization of this machine on your desktop. Screenshot here: http://axis.unpy.net/01170693566 In emc, the process of converting from the XYZ coordinate system to the motor positions of a particular machine (and back again) is called kinematics. You can view the source code for the scara kinematics online, to get an idea of the complexity: http://cvs.linuxcnc.org/cvs/emc2/src/emc/kinematics/scarakins.c?rev=1.5 There is also documentation on writing a new kinematics type: http://linuxcnc.org/docs/2.2/html/motion_kinematics.html It is possible to build new kinematics types as a part of emc, or add them to an existing emc installation -- install emc2-dev and build-essential, then use comp --install yourkins.c to compile and install a new kinematics module. The kinematics module is typically specified at the very top of the first .hal file used for machine configuration. emc has some shortcomings for nontrivial machines. * How to specify and enforce joint limits for acceleration and velocity (at present, only cartesian limits are enforced) * How to specify the working volume of the machine however, there are a number of people interested in improving these items, so it's possible that we'll find solutions during the current development cycle. Jeff - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
I think the hardest part (other than creating the kins) is dealing with backlash. Creating rotory motion without backlash, to me, would be a lot harder than with linear.. Spring load them all one way? double sets of gears forced against each other? very cool though. sam - Original Message - From: Jeff Epler [EMAIL PROTECTED] To: Enhanced Machine Controller (EMC) emc-users@lists.sourceforge.net Sent: Tuesday, December 04, 2007 8:26 PM Subject: Re: [Emc-users] Pivot mill What an interesting looking machine. We have a demo of a similar type of machine, called SCARA. In emc 2.2.2, you can run the sample configuration scara/scara.ini and see a visualization of this machine on your desktop. Screenshot here: http://axis.unpy.net/01170693566 In emc, the process of converting from the XYZ coordinate system to the motor positions of a particular machine (and back again) is called kinematics. You can view the source code for the scara kinematics online, to get an idea of the complexity: http://cvs.linuxcnc.org/cvs/emc2/src/emc/kinematics/scarakins.c?rev=1.5 There is also documentation on writing a new kinematics type: http://linuxcnc.org/docs/2.2/html/motion_kinematics.html It is possible to build new kinematics types as a part of emc, or add them to an existing emc installation -- install emc2-dev and build-essential, then use comp --install yourkins.c to compile and install a new kinematics module. The kinematics module is typically specified at the very top of the first .hal file used for machine configuration. emc has some shortcomings for nontrivial machines. * How to specify and enforce joint limits for acceleration and velocity (at present, only cartesian limits are enforced) * How to specify the working volume of the machine however, there are a number of people interested in improving these items, so it's possible that we'll find solutions during the current development cycle. Jeff - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.503 / Virus Database: 269.16.13/1170 - Release Date: 12/4/2007 10:52 AM - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
It's a SCARA. They are very common for pic-and-place machines but one of our guys a few years ago wrote a thesis while building one and testing it for stiffness. I believe the guys was from India. The current SCARA kinematic files are based on his work. Shouldn't be much of a problem to control the electrics with EMC. Rayh On Wed, 2007-12-05 at 02:50 +0200, Roland Jollivet wrote: Hi I believe that the greatest hurdle in constructing a small CNC machine is the cost of the linear slides, and I've been trying to think of a way to alleviate this, and come up with a 'Pivot Mill'. While this is robotic in configuration, it is for all intensive purposes intended to supplant a conventional 3 axis machine. (X,Y,Z) Bearings are relatively cheap, and construction of the mechanics fairly simple. I have drawn and uploaded a concept picture here, of what I have in mind. http://www.fotothing.com/CAONgallery/photo/9e62959f5230b6745b40b5285739b62c/ There are still three axis, but they are mathematical functions of each other, essentially transparent to the user, and where Z is the most complex interaction. Also notice that the tool will stay vertical during motion due to the dual strut. The servo's are not shown, and would typically introduce a further non-linear relationship since they would act indirectly, or at an angle . To control something like this, from what I've read here, sounds like a task for EMC. So, how difficult would it be to implement this inter-relation between the axis? As far as the user is concerned, the machine must still execute linear moves with normal G-code, as in G1 X200. So the machine has ROTARY AXIS, but executes LINEAR MOTION. A JOG in the Z axis will cause all three joints to move, but the tool will only move vertically Of course, there are always rigidity issues, but it's easy to beef up a pivot arm, and this is only intended to be of the calibre of 'dremel' type, benchtop, CNC machines. There are other appealing factors like the inherent extended reach, for tool changing, and if the machine were placed centrally on a table, it could serve four work areas, as quadrants. (assuming here a 360deg. central column) So, is this worth pursuing? Is the functionality required already a sub-set of EMC, or is it a huge re-work? Regards Roland Jollivet - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Pivot mill
Oops. One additional thought, while the tool will always be perpendicular to the work surface, the z kinematics are not trivial either. But in that case I think you can use an Angular definition for that axis. You'd just have to work out the motion in and out along the axis of the forearm depending on how far down in z the tip is. Rayh On Wed, 2007-12-05 at 02:50 +0200, Roland Jollivet wrote: Hi I believe that the greatest hurdle in constructing a small CNC machine is the cost of the linear slides, and I've been trying to think of a way to alleviate this, and come up with a 'Pivot Mill'. While this is robotic in configuration, it is for all intensive purposes intended to supplant a conventional 3 axis machine. (X,Y,Z) Bearings are relatively cheap, and construction of the mechanics fairly simple. - SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
