Messages

1

General Mach Discussion / Re: Engine Cam Grinding

« on: November 18, 2013, 10:14:18 AM »

Great information.  The measurement probe the same radius as the grinding wheel is what I also came up with for a easy solution also.  If you have the formula for the follower calculation I would love to see it.  I have some text books with the information but if you  had a formula that worked for you that would be great. 

I can write a program in Labview to use the encoder of the rotary axis to get my degree's and then measure with a very high resolution linear displacement sensor to get the lift at the given points.  So if I had a 2000pulse/rev or more output on my encoder (with gear reduction) and took a linear measurement at every point I could get a pretty accurate profile.

I could then use this program to replicate the profile but I worry about the smoothness of the servo control.  At 2000+ points I don't know if it matters as long as I hit the points the interpolation between them may not matter much.

Was sheet cam able to generate the G code for you? Do you have any details on that?

2

General Mach Discussion / Re: Engine Cam Grinding

« on: November 17, 2013, 10:09:23 PM »

Hi Terry, I was hoping you would speak up on this.  I read some of your previous posts on what you had to say, figured the engine in the title would suck you in.....LOL.

I have to look closer at the wheel to cam interface and how much it changes with the angle of the lobe as it rotates.  Didn't really think of that.  I will lay it out it cad.  It seems the bigger the wheel the worse this would be.

What did you use to measure the cams?  I was hoping to use the stand to measure the cams with a linear sensor and at least dublicate lobes.

I could write the software myself but would much rather use Mach for its proven motion control.  So sheet cam was able to generate the code for you?  Including the rotary axis?  Did you generate the code off of a dxf?  Maybe you could PM me and we could discuss this.  Thanks.....

3

General Mach Discussion / Engine Cam Grinding

« on: November 17, 2013, 02:07:40 PM »

Hi Guys,

I was looking for thoughts on a concept of a cnc cam grinder.  The purpose would be for small engines but the concept would be universal to cam grinding.

I would like to make a two axis machine.  One axis would be a rotary the other would be Y (I think) that would move in and out on a plane parallel to the base of the grinder.  I am picturing about an 8in wheel.  The cam would be held parallel to the ground by  a rotating collet driven by the rotary servo on one side and a live center on the other.

The rotary axis would be servo driven with an encoder and have high resolution.  The Y axis would be driven linear slide supported and ballscrew driven in and out with a servo also.  By design this would be made to be very accurate and rigid.

The rotary axis would turn like a 4th axis in degrees at a relatively slow speed.  The Y axis would then move in and out to replicate the cam profile.

This is the concept.  I am open for other ideas.  I have a cnc converted Bridgeport that I could put the cam in vertically and use a grinding wheel to go around the profile but my mill can only hold +/-.0005 and this would not be good enough for performance cams.

The problem I have is generating the code for the machine.  It would be easy if the cam was vertical and the table moved in both axis's around the cam like described with cutting it in a bridgeport.  I feel this way looses too much rigidity.  Though this way it could use x and y or polar cooridence.

In this case though I don't know how to generate the code to have the rotary axis in degree's and the Y axis in inches and then output the code to Mach.  This is virtually a cnc lathe that has the ability to cut eccentrics.  Don't know much about cnc lathes, maybe most do this??? Maybe none do.

Thoughts?

Thanks

4

General Mach Discussion / Re: backlash comp creates follow error

« on: October 31, 2013, 02:56:30 PM »

Thanks.  But why does the % of feed speed setting in the backlash comp dialog have no effect on the speed of the slack take up.  That makes no sense to me.  This value is used to slow it down but seems to do nothing.  I am only looking to take up about .0005" so no matter what the move it is not like it is trying to move the table, but rather just take the flex out of the components.

This may sound picky but I do a lot of hole interpolation that if this was working would give me really good results.

5

General Mach Discussion / backlash comp creates follow error

« on: October 31, 2013, 02:21:38 AM »

OK guys I can't figure this one out myself and am hoping that someone can shine some light on it for me. I have a bridge port mill converted with DC servos.  Spent money and got good ballscrews. The backlash I have in the system is just the flexing of the related components. About .001.  When I enable the backlash comp I get a follow error at the drive at the direction change.  If I keep the bl comp low enough it doesn't error out right away.  This is because it doesn't go outside the follow error setting of the gecko drive.  What I can see is that no matter how slow I have the percent of feed option set it still snaps the comp move at a speed that the servo can't do which is where my error is coming from. So if I put in even just .001in of comp on direction change I get an instant error. Even with the feed percent at 1.

Do I have a setting wrong or am I missing something? Thanks