Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: cliveastro on March 25, 2010, 07:44:47 AM
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I am doing a project where I need to turn an eccentric on a shaft.
Being a little idle and not wishing to set up a 4 jaw chuck I wondered if anyone had a written a wizard?
Clive
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Never seen one but i'd be interested too. Wouldn't milling on a 4th axis be better for that?
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The tool cuts concentricaly about the lathe center, so you need to shift the work.
Thus no wizards.
RICH
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I am doing a project where I need to turn an eccentric on a shaft.
You would need a hell of a fast X axis on your lathe for doing that I would think.
Hood
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You say that it would have to be very fast in X but is it not similar to the way a copy lathe worked also they made rifle stocks at springfield armoury in Massachusetts by a similar method in the 1800s (not using CNC though, not even an early version).
I am sure that some smart person could do the maths.
Is it also not the same sort of control you get when cutting threads?
Clive
PS. I am not being contentious just interested.
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In one revolution of the material your x axis will have to move to the min and max dia of your eccentric so unless you had a fairly slow RPM I would think the X would need to be rather rapid, especially on acceleration. But maybe I am just thinking about this the wrong way.
Hood
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Granted that the revs would be slower than normal but the acceleration would be gradual and the changeover point would be at the point with the slowest movement.
Just thought of the downside, backlash or would the compensation take it out
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If this is for cutting metal especially if using carbide then I would think you would need to keep the revs up so that you get the surface speed required for a good cut.
For comp to work I think you would have to look at it another way, ie have the spindle set as an axis and for that your spindle would need to be a servo or stepper.
Hood
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have a look at this vid.
slow going, needs accurate control
http://www.youtube.com/watch?v=CVpeChtENEY&feature=related
JB
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Even if you work out the X axis speed issue, producing the gcode to cut the eccentric would be something far not obvious.
Daniel
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Sounds like its back to 4 jaw chucks and dial gauges then.
Thanks for the inputs.
Clive
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You would need a lathe with a Y axis for a start so you could maintain the tool centre height.
Graham
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Excellent point there Graham, I completely overlooked that aspect.
Thanks
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Very Good point I will definately stick to 4 jaw chuck
Clive
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Looks like nobody watched the video posted by wantcnc ???
Phil
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I did Phil. It is so very impressive! I have no idea what it takes to make the gcode for this part... ??? Are there CAM packages that can handle such things?
Daniel
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I did too.
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Looks to me like the Mazak has a Y axis unless its just an optical illusion.
Hood
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Clive,
if its a repeat job bore a offset hole in a round billet and split it through the thick side then you can hold it in the three jaw.
Graham
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Thats a very good idea Graham, but I was only being lazy.
I seem to speed ages setting up 4 jaw chucks
Clive
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Having thought about it for a bit, that ony gives you an offset arc not an eccentric circle!!
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Looks to me like the Mazak has a Y axis unless its just an optical illusion.
Hood
It certainly has a Y axis, doesn't look like an illusion because the tool remains in contact (centre line) of the work. Any ideas how the gcode was made?
Daniel
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Any ideas how the gcode was made?
Daniel
Guy says he wrote a home made macro.
Hood
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The code is the easy bit the hard bit is getting a machine that can follow the code instructions, you need the X or Y axis to be in sync with the spindle. Then the code is generated using Sin and Cos of a selected arc length on a offset centre point, the Z movement is then divided into the number of cords.
If you make the conforming machine I will write you the code.
Graham
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The code is the easy bit the hard bit is getting a machine that can follow the code instructions, you need the X or Y axis to be in sync with the spindle.
Don't they both need to be in sync... but then from the nature of how Mach works, if you get one in sync, the other would be automatically in sync.
Then the code is generated using Sin and Cos of a selected arc length on a offset centre point, the Z movement is then divided into the number of cords.
If I see right, the part cut in the video is a square. I think using the method you suggest would cut a circle...?
If you make the conforming machine I will write you the code.
Ha..ha... thanks Graham. As you say it's the machine that is the hardest part, but I will remember your offer if I ever build/buy one ;)
Daniel
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I'm not sure yuo do need an Y axis, in that video the indeed use it, however in this video it is not used
http://www.youtube.com/watch?v=gX75gaAcWWA&feature=related
also it mentiones gibscam as the cam generator...
Still the machine axis sync seems to me the hardest thing to solve, stepper drive will be so slow that cutting speeds will be to low
, unless you have fitted servos
I do like the of center clamp insert though...
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This is why you need a Y axis
Graham
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Daniel,
If I was cutting a square on and eccentric peg then I would use the chuck as a rotary indexer and mill the flats, why make life hard :D
But the square code is doable too.
Graham
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Agree with you, Graham.
Just curious how would look the code for a square? Looks like it's Sin and Cos minus some product of them with some relative parameter...?
Daniel