> > ------------------------------ > > Message: 10 > Date: Sat, 06 Oct 2007 13:27:05 -0400 > From: Dale <[EMAIL PROTECTED]> > Subject: Re: [Emc-users] machine geometry compensation > To: "Enhanced Machine Controller (EMC)" > <[email protected]> > Message-ID: <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=us-ascii; format=flowed > > I see this idea come up every now and then. If the Machine is not square > then you square up the machine. If the ways are worn then you refinish > them, and If the lead screws ar worn you replace them.
This is the exact reason I commented I am not concerned with roll, pitch and yaw. These are a different issue. >You're right it > is impossible to build a perfect tilting rotary table, or anything else > no matter how small the error may be. I have used tilting rotary tables > to inspect parts and you'd need to look damn hard to find the > inaccuracies in those tables. I know from working with machinery fo 34 > years that unless you have some instrument that can measure in micro > inches you can't acheive micro inch precision. In order to compensate > more all the machine and tooling inaccuracies you first have to be able > to measure them. In manufacturing every dimension has a tolerance > appropriate for each and every feature of the part to be machined. Not > everything needs to be perfect. It's not difficult to align tooling of > any kind on a machine including a tilting rotary table. Besides the > ability to measure accurately there are thermal factors. Rigidity of the > machine and tool holders is not constant. The longer you have to reach > the more deflection you will encounter. The amount of deflection also > changes as the cutting tool wears as well as with feeds and speeds. You > are talking about a huge battle to get software to compensate for what > is part of a machinsts job. If the machine is not up to the task I would > consider it a loosing battle. Before taking on such a challenge I'd > strongly suggest that the machine and tooling is up to specs in order to > even have a chance at a successfull implemantation. Like it's been > said, "You can't make a silk purse out of a sow's ear". I have now been machining for 30 years. I do not wish to try to make a silk purse from a sow's ear. I can measure .002/.003 inch of inaccuracy for each of the rotary axis intersections on my machine. This is in each of the rotary axes mounted on the end of the Z axis ram of a bridge mill. This machine has +- 120 degrees of B movement and C has slip rings to make it infinite. It is not truly infinite as the Fanuc control has an 8 place register for the C axis. I can rotate the C axis 9999.999 degrees before the control says you can go no more. This flexible motion allows the machine to cut features on one side of the part using the B axis in each of two positions and the C axis in each of two positions. Taking the axis intersection accuracy into account allows the machine to misposition the tool tip. This should be just additive (I think) but sometimes the frustration level causes me to thing it is geometric or exponential. My CAM system will allow me to put the inaccuracies in a table and it will calculate the corrections and include the corrections in the program furnished to the machine. If the machinist uses the jog wheel the inaccuracy is not accounted for. I would also like to develop a probe routine to calculate the inaccuracies and write them into a table for the machine control to use. I am not shooting for microns. I would like to be able to position the tool tip to +- .002. This should be easily doable. > > I wish you the best of luck and do hope you keep us all informed as to > your progress and successes/failures. I have reported my success and failures of my EMC endeavors. I have had egg on my face but my machine is running very good. >To have EMC compensate for > inaccuracies in the machine alignment would be a great asset. I agree wholeheartedly. This is the reason to have this dialog. >If I > should ever find the room to contine building my second (larger) > machine. It sure would be nice, there are limits as to just how accurate > I can build and align a machine in my garage. With this method of compensation you would only have to worry about straight and square. The position errors would be compensated for. With roll pitch and yaw compensation you would be able to overcome many (BUT NOT ALL) manufacturing inaccuracies. > > Dale > > thanks Stuart ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
