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Author Topic: CNC'ing both quill and knee  (Read 15860 times)

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Re: CNC'ing both quill and knee
« Reply #20 on: February 11, 2009, 11:37:00 PM »
Thanks, I'll play with it this weekend.  If it looks like it will work, then I guess I will have to get started mounting my servo to the knee.

Vince

Well, it's not quite there yet.  It doesn't work properly if you move the Z axis while doing the tool change.  I'll fix that and re-post.

Regards,
Ray L.
Regards,
Ray L.
Re: CNC'ing both quill and knee
« Reply #21 on: February 12, 2009, 12:01:03 AM »
OK, I think this fixes it.  Put this in M6End.m1s:

REM Get the length of the previous tool, stored in UserDRO 1200 by M6Start macro
OldToolLength = GetUserDRO(1200)

REM Get the length of the current tool
NewToolLength = ToolLengthOffset()

REM Figure out how much tool length changed, and in which direction
OffsetChange = NewToolLength - OldToolLength

REM Get the Z DRO value before the new tool length was applied, stored in UserDRO 1201 by M6Start macro
OldZPos = GetUserDRO(1201)
REM Correct for any moves the user made while changing the tool
CurrentZPos = GetOEMDRO(802)
ZMove = CurrentZPos - OldZPos + OffsetChange
NewZPos = OldZPos + ZMove
SetOEMDRO(802, NewZPos)

REM Get the cuurent A axis (knee) position, and apply the new tool length
OldAPos = GetOEMDRO(803)
NewAPos = OldAPos - OffsetChange
REM Move the knee to the new position
Code "G00 A" & NewAPos

REM Return the the position we were in before the toolchange

x = GetToolChangeStart( 0 )
y = GetToolChangeStart( 1 )
z = GetToolChangeStart( 2 )
a = GetToolChangeStart( 3 )
b = GetToolChangeStart( 4 )
c = GetToolChangeStart( 5 )

if(IsSafeZ() = 1) Then
   SafeZ = GetSafeZ
   if  SafeZ  > z then
     GotoSafeZ()
   end if
   Code "G00 X" & x & " Y" & y
   Code "G00 Z" & z
else
  Code "G00 X" & x & " Y" & y
end if


 
Regards,
Ray L.
Regards,
Ray L.
Re: CNC'ing both quill and knee
« Reply #22 on: February 19, 2009, 07:55:30 AM »
Yes, I used a leadscrew. I replaced it with a new higher precision one but stuck with the screw so I wouldn't have to use a brake to keep the knee from drifting. I did add oilers to the gears and nut but it still works on it pretty good. I'm using 1850 oz in steppers and the final gearing is 6-1. I added gas springs and that helped my rapids some but 30 IPM is about all I can get out of it with this set up.

Brett

I am in the process of considering what stepper size, belt drive ratio etc.   Can you elaborate on your setup and how the 6:1 final ratio is reached?   I am thinking of the stock screws with a 1810inoz stepper and 3:1 belt drive.   Speed isn't terribly important as it will only be active during tool changes but more is better of course. 
Re: CNC'ing both quill and knee
« Reply #23 on: February 19, 2009, 10:28:11 AM »
Yes, I used a leadscrew. I replaced it with a new higher precision one but stuck with the screw so I wouldn't have to use a brake to keep the knee from drifting. I did add oilers to the gears and nut but it still works on it pretty good. I'm using 1850 oz in steppers and the final gearing is 6-1. I added gas springs and that helped my rapids some but 30 IPM is about all I can get out of it with this set up.

Brett

I am in the process of considering what stepper size, belt drive ratio etc.   Can you elaborate on your setup and how the 6:1 final ratio is reached?   I am thinking of the stock screws with a 1810inoz stepper and 3:1 belt drive.   Speed isn't terribly important as it will only be active during tool changes but more is better of course. 

I'm driving my knee through the stock leadscrew, using a 4.8:1 XL belt reducer, and the HomeShopCNC.com 850 oz-in servo.  I get 75IPM.

Regards,
Ray L.
Regards,
Ray L.
Re: CNC'ing both quill and knee
« Reply #24 on: February 19, 2009, 11:09:12 AM »
Yes, I used a leadscrew. I replaced it with a new higher precision one but stuck with the screw so I wouldn't have to use a brake to keep the knee from drifting. I did add oilers to the gears and nut but it still works on it pretty good. I'm using 1850 oz in steppers and the final gearing is 6-1. I added gas springs and that helped my rapids some but 30 IPM is about all I can get out of it with this set up.

Brett

I am in the process of considering what stepper size, belt drive ratio etc.   Can you elaborate on your setup and how the 6:1 final ratio is reached?   I am thinking of the stock screws with a 1810inoz stepper and 3:1 belt drive.   Speed isn't terribly important as it will only be active during tool changes but more is better of course. 

I'm driving my knee through the stock leadscrew, using a 4.8:1 XL belt reducer, and the HomeShopCNC.com 850 oz-in servo.  I get 75IPM.

Regards,
Ray L.

I seen your posts and that sounds like great performance.   Unfortunately, you are using servos and mine is a stepper system.    I am not sure how servo vs stepper rated torque would correspond.   Servos like more rpm's so that would explain your 4.8:1 drive ratio.    Right now, I am leaning towards 1810ozin stepper and a 3:1 belt drive.   I'd like 4:1 but using a online calculator the smaller pulley would not have enough teeth engaged at any reasonable center distance.   I could use idler pulleys to increase the belt wrap on the small pulley but I want to keep it simple so 3:1 at about 12-14 inches center distance between the pulleys is about as good as I can get.   Its looking like air springs are going to be necessary to get any reasonable speed.   

As I mentioned, the knee is only going to move during tool offsets at tool change time so speed isn't terribly important.
However.... going from a 1" long endmill to something like a 6" long drill and chuck would mean a 5" move which at 15ipm would take 20 seconds....... pretty slow and that would no doubt get aggrivating fast!   30-40ipm would be quite satisfactory.

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Re: CNC'ing both quill and knee
« Reply #25 on: February 19, 2009, 11:18:09 AM »
On my Bridgeport I used the stock leadscrew driven through a 3 to 1 reduction with a servo.  You can read about it here:

http://www.cnczone.com/forums/showthread.php?t=18178

Vince
Re: CNC'ing both quill and knee
« Reply #26 on: February 19, 2009, 11:20:56 AM »
What kind of tooling are you guys using to get repeatable tool lenghts with a semi automatic toolchange?
Are your drawbars powered too?

Regards
Fernando

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Re: CNC'ing both quill and knee
« Reply #27 on: February 19, 2009, 11:28:39 AM »
On my Bridgeport I have to set the tool length every time I use a tool.  I did add a powered draw bar to it.

Vince
Re: CNC'ing both quill and knee
« Reply #28 on: February 19, 2009, 11:29:44 AM »
What kind of tooling are you guys using to get repeatable tool lenghts with a semi automatic toolchange?
Are your drawbars powered too?

Regards
Fernando

My bp has a kwik switch 200 spindle. (not a adapter, its a entire spindle assy).   Its sort of like a cat30 but with the drive ears on the toolholder rather than in the spindle.   They repeat very well.

I like that term!   "semi automatic toolchange"      That pretty well sums it up.

Oh yea, for those surfing for build info.... My quill is driven by a 425ozin stepper,gecko 201,  3:1 belt drive to a rotron 5/8 ballscrew driving the quill using the mounting hole for the depth stop ring.   I have been running at 70ipm with extreme reliability.  I have about 3 thou backlash but believe probably about half of that is the cheapo bearings I used.   Down the road I plan on redoing it with a ground ballscrew, probably a ebay cheapie because of its short length.
« Last Edit: February 19, 2009, 11:35:10 AM by Sparky_NY »
Re: CNC'ing both quill and knee
« Reply #29 on: February 19, 2009, 11:39:10 AM »
I seen your posts and that sounds like great performance.   Unfortunately, you are using servos and mine is a stepper system.    I am not sure how servo vs stepper rated torque would correspond.   Servos like more rpm's so that would explain your 4.8:1 drive ratio.    Right now, I am leaning towards 1810ozin stepper and a 3:1 belt drive.   I'd like 4:1 but using a online calculator the smaller pulley would not have enough teeth engaged at any reasonable center distance.   I could use idler pulleys to increase the belt wrap on the small pulley but I want to keep it simple so 3:1 at about 12-14 inches center distance between the pulleys is about as good as I can get.   Its looking like air springs are going to be necessary to get any reasonable speed.   

As I mentioned, the knee is only going to move during tool offsets at tool change time so speed isn't terribly important.
However.... going from a 1" long endmill to something like a 6" long drill and chuck would mean a 5" move which at 15ipm would take 20 seconds....... pretty slow and that would no doubt get aggrivating fast!   30-40ipm would be quite satisfactory.

You're not going to get high speed from a stepper pushing that kind of load, no matter how you gear it.  The high-RPM torque fall-off will kill you.  So, either live with low top speed, or go to a servo (which is about the same cost as a large stepper anyway).  First step in any case should be to measure how much torque is required to move your knee, pad that a bit, and you can calculate how well any motor will work, and what speed you should be able to get.  Mine was about 40-45 in-lbs.

There's something wrong with your calculations.  I have 4.8:1 reduction (48:1 overall, including the bevel gears and leadscrew) using XL belts - 72 tooth on the screw, 15 on the motor, with only about a 9" center distance.  This gives more than 6 teeth engaged on the motor, which is all that's required.  I also have two 200# gas springs.

Regards,
Ray L.
Regards,
Ray L.