Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: polaraligned on October 20, 2008, 07:12:06 AM
-
Hi, Have a Series II CNC machine that I am currently working on.
Not my first, but I want to make this my last mill. :)
Quill unfortunately is a QC30 with 5" of travel.
The knee has huge box ways and is air assisted.
In most instances the quill is the better way to approach the
Z axis as long as you can get away with the 5" travel. And yes,
I want to keep the quill as my Z axis. But I would like to open
up the possibility of having more than 5" of Z travel using the knee.
My idea is to put a servo and drive on the knee and run the knee
under Mach control. Technically it is the " W" axis- because it is parallel to
the Z axis.
I don't know if it is possible to run these axis in concert with each other.
I guess if a job required more than 5" travel I could swap axis and
use the knee as the Z. This swap could be done in the mach settings
I guess?
Any input on my idea would be appreciated.
Thanks,
Scott
Edit: I see looking at Mach's config screen that the only names for axis's are XYZ and ABC.
I guess I would have to use B or C as the W axis.
-
Brett is thinking about doing that on his Hurco and also I am thinking I may do it on the Beaver mill if I ever get it finished LOL
What we are both thinking of is using the Knee just for tool length offsets, how it will be done woukld probably have to be via a macropump but to be honest I havent put much thought into it yet.
As for A B C or whatever I dont think it would really matter as long as your CAM can put out the right letter for any code it will spit out and that should be easy enough to do in your CAMs Post Processor.
Hood
-
Brett is thinking about doing that on his Hurco and also I am thinking I may do it on the Beaver mill if I ever get it finished LOL
What we are both thinking of is using the Knee just for tool length offsets, how it will be done woukld probably have to be via a macropump but to be honest I havent put much thought into it yet.
As for A B C or whatever I dont think it would really matter as long as your CAM can put out the right letter for any code it will spit out and that should be easy enough to do in your CAMs Post Processor.
Hood
Ha! That's exactly what I've always planned to do as well! I've got the knee CNC'd right now, and honestly don't see any down-side to it - it was dead easy to do, only took one day - so I may not even bother doing the quill at all now...
Regards,
Ray L.
-
Yup, that is how I did my Bridgeport clone. Used the knee for Z and it was very simple to set up. I will be using the quill on the Hurco for the z and the knee for tool length offsets because I think it would stess the machine too much to throw the knee up and down at 800- 1200 IPM not to mention it would take a huge servo, drive, and most likely an air assist ball screw or counter weight for that. I think using both will give the best of both worlds. Fast rapids and feeds and full working height will allways be avaliable no matter how tall the work is or how long the tool is.
Brett
-
Yup, that is how I did my Bridgeport clone. Used the knee for Z and it was very simple to set up. I will be using the quill on the Hurco for the z and the knee for tool length offsets because I think it would stess the machine too much to throw the knee up and down at 800- 1200 IPM not to mention it would take a huge servo, drive, and most likely an air assist ball screw or counter weight for that. I think using both will give the best of both worlds. Fast rapids and feeds and full working height will allways be avaliable no matter how tall the work is or how long the tool is.
Brett
Brett,
Did you leave the leadscrew, or put a ballscrew on the knee on your BP? I just have the leadscrew for now, and it works fine. But, I figure in time it will wear, and I'll want a ballscrew eventually.
Regards,
Ray L.
-
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
-
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
Brett,
Interesting. I'm using an 850 oz-in servo with 4.8:1 XL belt reducer, and can do better than 50 IPM, with no air springs (yet... Just put the servo on about a week ago). How much more it'll do, I don't know. I know it would go 100IPM *most* of the time, but that is scary fast for me, so I just cut it in half. I'm very happy with the way it works, but I do need to do something to provide positive lubrication.
One thing that surprised me - As I said, I used an XL belt for the reducer. On the X and Y, I used GT2 belts. The XL is MUCH noisier!
Regards,
Ray L.
-
I am wanting to add a stepper to the knee on my bridgeport (Quill now used a Z) just for applying tool offsets.
Did anyone get this working? How did you get mach to handle the extra motor and apply the tool offsets?
Thanks much!
-
I am wanting to add a stepper to the knee on my bridgeport (Quill now used a Z) just for applying tool offsets.
Did anyone get this working? How did you get mach to handle the extra motor and apply the tool offsets?
Thanks much!
Mach supports up to six axes, so you'd just assign the knee to one of the "extras". I think you'd then modify the M6End macro, to take the tool offset, and move the knee by the appropraite amount. Should be pretty straight-forward. I'll find out soon, as I've already servo'd my knee, and am about to servo the quil as well.
Regards,
Ray L.
-
I am wanting to add a stepper to the knee on my bridgeport (Quill now used a Z) just for applying tool offsets.
Did anyone get this working? How did you get mach to handle the extra motor and apply the tool offsets?
Thanks much!
Mach supports up to six axes, so you'd just assign the knee to one of the "extras". I think you'd then modify the M6End macro, to take the tool offset, and move the knee by the appropraite amount. Should be pretty straight-forward. I'll find out soon, as I've already servo'd my knee, and am about to servo the quil as well.
Regards,
Ray L.
I am wanting to add a stepper to the knee on my bridgeport (Quill now used a Z) just for applying tool offsets.
Did anyone get this working? How did you get mach to handle the extra motor and apply the tool offsets?
Thanks much!
Mach supports up to six axes, so you'd just assign the knee to one of the "extras". I think you'd then modify the M6End macro, to take the tool offset, and move the knee by the appropraite amount. Should be pretty straight-forward. I'll find out soon, as I've already servo'd my knee, and am about to servo the quil as well.
Regards,
Ray L.
I am surprised this has not been hashed out in the past. Hooking up the other motor and setting it up is very easy, its "tweaking" mach to send the tool length offset to that new axis and not the Z that will be the trick. I want to be sure it can be done before I buy and hook up the extra motor/axis. The "normal" tool length offset has to be inhibited from acting on the z axis also, we don't want both axis applying the offset.
-
My big mill has only 5" of travel with the quill. I too would like to use the knee for tool length offset. The mechanics are simple. I would be interested in the Mach solution if someone comes up with one.
vince
-
As a suggestion... dunno if it is practical,
You could use an auto tool zero routine with a touchplate in which only the knee moves for this.
THe routine would be something like this:
-Home the quill
-home the knee (optional)
-move the knee up so that you can put a touchplate on top of the material and wait for the tool to touch it.
-zero the z axis dro (which it already should be at zero)
-zero the knee (optional too)
I guess that would be a work around if you dont have a way of putting the tools with the same lenght every time.
Best regards
Fernando
-
The idea is if you have several different tools set up in the tool table and you do a tool change (M6) then if the tool was long i.e. a drill chuck with a big drill, Mach would automatically move the knee down. When you changed back to a shorter tool, the knee would come back up at part of the M6 command.
Vince
-
Am I missing something? Seems to me, my suggestion of modifying the M6End macro is quite simple. You have access to the tool offset through the tool length DRO. So, even if Mach does apply that somewhere, it's a simple matter for the macro to un-apply it by adding/subtracting the offset to the Z DRO, re-setting the DRO, then moving the knee by the appropriate amount.
Regards,
Ray L.
-
Hey Ray,
Well yes, your suggestion i simple... i was just proposing an alternate solution to whoever wants this and does not use the tool table.
Regards
Fenando
-
Am I missing something? Seems to me, my suggestion of modifying the M6End macro is quite simple. You have access to the tool offset through the tool length DRO. So, even if Mach does apply that somewhere, it's a simple matter for the macro to un-apply it by adding/subtracting the offset to the Z DRO, re-setting the DRO, then moving the knee by the appropriate amount.
Regards,
Ray L.
I guess it would be a simple matter for someone who does VB for a living and knows the ins and outs of Mach. For me, it would be easier to ask me to levitate. I'm sure there are many who would love to see a post of all the code required to make this happen, feel free to be our hero. If you ever need a Piller 400 HZ parallel cabinet installed and wired up or autopilot aileron servo replaced or even an Atos hang glider rib adjustment for racing, I'm your man.
Vince
-
Am I missing something? Seems to me, my suggestion of modifying the M6End macro is quite simple. You have access to the tool offset through the tool length DRO. So, even if Mach does apply that somewhere, it's a simple matter for the macro to un-apply it by adding/subtracting the offset to the Z DRO, re-setting the DRO, then moving the knee by the appropriate amount.
Regards,
Ray L.
I guess it would be a simple matter for someone who does VB for a living and knows the ins and outs of Mach. For me, it would be easier to ask me to levitate. I'm sure there are many who would love to see a post of all the code required to make this happen, feel free to be our hero. If you ever need a Piller 400 HZ parallel cabinet installed and wired up or autopilot aileron servo replaced or even an Atos hang glider rib adjustment for racing, I'm your man.
Vince
Well, I ain't no VB whiz, but I can learn enough to do what I need to do. Fact is, I consider VB to be one of the most abominable programming languages ever created. It's a God-awful mish-mash of about a dozen different paradigms, with more excpetions than rules.
In any case, I think we're talking about all of *maybe* a dozen lines of code:
1) Get the tool offset
2) Add/subtract tool offset to Z DRO, and reset Z DRO to this value
3) If necessary, do Z move to undo automatic tool length compensation, if there is one
4) Issue move command on knee axis, to do the tool length compensation
I'm guessing someone who's familiar with how Mach does toolchanges, and up on VB and all the Mach OEM codes, could do this in about 10 minutes. If I had a machine to work with, I'd guess I could get it done within an hour.
Tell you what, even though I don't have a machine, I'll try to play with it over the next few days, and see if I can do it in simulation. Should be pretty straight-forward, I think.
Regards,
Ray L.
-
I worked on an M6 tool change macro for my lathe for about a week and never got it working properly. Jason did it in about 5 minutes. The problem I have with programming is all the hidden syntax that no one ever seems to tell you or all the calls that are undocumented (especially in Mach). One extra space here, a missing comma there and it doesn't work and and you never know why. Then someone who knows what they are doing comes along and says, oh yeah, you obviously forgot to capitalize that word. It can be very frustrating to self teach.
It reminds me of a friend who installed his own sprinkler system. He told me how he meticulously square off every pipe, use the proper primer and glue, everything was perfect. When I asked him if he beveled the pipe before gluing his jaw dropped (he didn't). It an obvious thing to do if you know how to do it.
Vince
-
OK, I'm sure this isn't the most efficient way of doing this, but I believe it works as intended. Running it in simulation, it appears to work correctly. I'm assuming here the quill is the Z axis, and the knee is the A axis. When you change tools, it over-rides the change in the Z DRO due to the change in tool length, and instead moves the A axis by the difference in length between the old and new tools. So, the effect is Z does not move, or is returned to its previous position if you moved it during the tool change, and the tool length is compensated for entirely by moving the knee. The knee is moved minus for a longer tool, and plus for a shorter tool.
Put the following in M6Start.m1s:
REM Get the current tool length, and store it in User DRO 1200 for M6End macro
OldToolLength = ToolLengthOffset()
SetUserDRO(1200, OldToolLength)
REM Get the current Z axis position, and store it in USer DRO 1201 for M6End macro
OldZPos = GetOEMDRO(802)
SetUserDRO(1201, OldZPos)
REM Activate the new tool
tool = GetSelectedTool()
SetCurrentTool( tool )
Put the folliowing in M6End.m1s:
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)
SetOEMDRO(802, OldZPos)
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.
-
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
-
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.
-
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.
-
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.
-
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.
-
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.
-
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
-
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
-
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
-
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.
-
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.
-
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.
I have stepper drives for the 4 axis I now have so will stick with steppers for that reason.
I was using a online calculator from Stock Drive Products (SDP) website. They have a nice calculator for drive ratios, center distances, etc. When the tooth engagement gets too small the number turn red. Anything much over 3:1 shows a problem with engagement on the small pulley. I believe the engagement at 4:1 was indeed 6 teeth at 12 inch center distance but that came up in red which is supposed to mean it is not recomended.
Oh yea, I know what may be making the difference...... I am using 3/8 pitch L series belts in 3/4 width. A smaller pitch may be different. I used 3/8 pitch for my x and y because of the stepper power and the loads driven.
-
Yes, belt pitch makes a big difference. As I said, I used XL, which is 5-pitch. Again, with a stepper, you'll be hard-pressed to get better than *maybe* 25 IPM. A large stepper is NOT going to go fast (maybe 1000RPM at the very best), and torque falls off rapidly with speed, so you'll likely become torque-limited long before you reach that max speed. With a 3:1 reduction, 750 RPM would give you 25IPM. If you have to go to 2:1, you'll likely be looking at 15-20 IPM max.
Regards,
Ray L.
-
Yes, belt pitch makes a big difference. As I said, I used XL, which is 5-pitch. Again, with a stepper, you'll be hard-pressed to get better than *maybe* 25 IPM. A large stepper is NOT going to go fast (maybe 1000RPM at the very best), and torque falls off rapidly with speed, so you'll likely become torque-limited long before you reach that max speed. With a 3:1 reduction, 750 RPM would give you 25IPM. If you have to go to 2:1, you'll likely be looking at 15-20 IPM max.
Regards,
Ray L.
Its not a pretty picture, that I agree. I see you used a pair of 200lb gas springs which seems to be common. I was looking at them tonight at McMaster and see they also make them 225lb and 250lb fairly cheap.
I searched around and found this weight info over on the BP yahoo forum:
> for a standard J-head the weights are:
>
> Head 200#
> Ram Adapter 90#
> Ram 218#
> Turret 214#
> Column 715#
> Knee 257#
> Saddle 142#
> 48" Table 365#
> Total 2101#
Taking a wild guess that a 42 inch table is 200lbs, that makes 599 lbs the motor is moving, lets add another 100 for a kurt vise, the one shot oiler etc and we have 700 lbs jumping up and down! I think I am going to go with the 250lb gas springs after finding this information. Any wonder some people find the knee speeds slow!!!
I don't think I want to use a belt as small as a XL for moving such weight. Granted there is the screw and gears but its still a awful lot of force on such a tiny belt especially considering the accelleration.
-
Yes, belt pitch makes a big difference. As I said, I used XL, which is 5-pitch. Again, with a stepper, you'll be hard-pressed to get better than *maybe* 25 IPM. A large stepper is NOT going to go fast (maybe 1000RPM at the very best), and torque falls off rapidly with speed, so you'll likely become torque-limited long before you reach that max speed. With a 3:1 reduction, 750 RPM would give you 25IPM. If you have to go to 2:1, you'll likely be looking at 15-20 IPM max.
Regards,
Ray L.
Its not a pretty picture, that I agree. I see you used a pair of 200lb gas springs which seems to be common. I was looking at them tonight at McMaster and see they also make them 225lb and 250lb fairly cheap. Do the 200lb ones fully counterbalance the knee? What do you think of using stronger ones? Who knows what a 42 inch BP table, saddle and knee weigh other than a guess?
If anything, I have a bit too much. It now requires less torque to move the knee up than down.
Regards,
Ray L.
-
Yes, belt pitch makes a big difference. As I said, I used XL, which is 5-pitch. Again, with a stepper, you'll be hard-pressed to get better than *maybe* 25 IPM. A large stepper is NOT going to go fast (maybe 1000RPM at the very best), and torque falls off rapidly with speed, so you'll likely become torque-limited long before you reach that max speed. With a 3:1 reduction, 750 RPM would give you 25IPM. If you have to go to 2:1, you'll likely be looking at 15-20 IPM max.
Regards,
Ray L.
Its not a pretty picture, that I agree. I see you used a pair of 200lb gas springs which seems to be common. I was looking at them tonight at McMaster and see they also make them 225lb and 250lb fairly cheap. Do the 200lb ones fully counterbalance the knee? What do you think of using stronger ones? Who knows what a 42 inch BP table, saddle and knee weigh other than a guess?
If anything, I have a bit too much. It now requires less torque to move the knee up than down.
Regards,
Ray L.
Huh, now that is a bit strange. Those weights seem to be reasonable, as well as the total machine weight. In theory if the weight is totally "absorbed" by the gas springs the knee should move with almost no effort except the friction of the ways / screw and gears. I am thinking of those gas springs on the big hatch back cars, the hatch weighs 200lbs or so and lifts/closes with one finger.
I also in my ventures seen a power drive kit for the knee, it was spec'd at 152 inlbs which comes out to about 2500oz-in, right around the numbers that have been being thrown around considering the belt reductions.
-
I don't think I want to use a belt as small as a XL for moving such weight. Granted there is the screw and gears but its still a awful lot of force on such a tiny belt especially considering the accelleration.
You would be very surprised what these belts can handle, I know I was. Granted I am using a GT3 belt from gates rather than the standard timing belt but I was surprised when Gates told me that for the 17Hp servo I have on my spindle that the 20mm wide 8mm pitch belt would actually be a 60% over engineered solution with the pulleys I was using.This belt has replaced 6 x B section V belts that the lathe used with the induction motor that was originally on it.
Best thing to do is go to Gates website and register and then download their sizing software.
Hood
-
I don't think I want to use a belt as small as a XL for moving such weight. Granted there is the screw and gears but its still a awful lot of force on such a tiny belt especially considering the accelleration.
You would be very surprised what these belts can handle, I know I was. Granted I am using a GT3 belt from gates rather than the standard timing belt but I was surprised when Gates told me that for the 17Hp servo I have on my spindle that the 20mm wide 8mm pitch belt would actually be a 60% over engineered solution with the pulleys I was using.This belt has replaced 6 x B section V belts that the lathe used with the induction motor that was originally on it.
Best thing to do is go to Gates website and register and then download their sizing software.
Hood
And the "weight" being moved is totally irrelevent. All that matters is the torque at the motor. If the belt is going to fail, it's going to fail at the motor. If an XL belt is sufficient to move X & Y, then it's quite capable of moving Z, using the same motor. Don't design by "feel". Read the manufacturers recommendations, and the actual ratings for the belts. It's all in the specs.
Regards,
Ray L.
-
I don't think I want to use a belt as small as a XL for moving such weight. Granted there is the screw and gears but its still a awful lot of force on such a tiny belt especially considering the accelleration.
You would be very surprised what these belts can handle, I know I was. Granted I am using a GT3 belt from gates rather than the standard timing belt but I was surprised when Gates told me that for the 17Hp servo I have on my spindle that the 20mm wide 8mm pitch belt would actually be a 60% over engineered solution with the pulleys I was using.This belt has replaced 6 x B section V belts that the lathe used with the induction motor that was originally on it.
Best thing to do is go to Gates website and register and then download their sizing software.
Hood
And the "weight" being moved is totally irrelevent. All that matters is the torque at the motor. If the belt is going to fail, it's going to fail at the motor. If an XL belt is sufficient to move X & Y, then it's quite capable of moving Z, using the same motor. Don't design by "feel". Read the manufacturers recommendations, and the actual ratings for the belts. It's all in the specs.
Regards,
Ray L.
When doing my bridgeport conversion last winter I looked at every commercial conversion out there (and homebrew).
All the pics of the commercial ones appeared to use 3/8 pitch belt drives for the x and y. The knee stepper will be double the torque of the x or y so you are correct the torque transmitted is much higher due to the motor.
I wonder what size drive belts bridgeport used on the boss mills? I'd be shocked to find they are as small as XL's.
-
did you need to use a backlash in mach because of the gears on the knee or do you have a digital readout
-
did you need to use a backlash in mach because of the gears on the knee or do you have a digital readout
Now that I have a quill drive, the knee gets used only for applying tool length compensation, so backlash is not an issue. All knee moves are upward, even if that means first moving below the target position, then coming back up. This ensures the (considerably) backlash is always taken up, so no Mach3 backlash compensation is required. Even before I had the quill drive, the knee backlash was not a problem, since I do only 2.5D milling, so moves to cutting depth were always upwards moves. I got perfectly good accuracy despite the considerable backlash.
Regards,
Ray L.
-
I wonder what size drive belts bridgeport used on the boss mills? I'd be shocked to find they are as small as XL's.
On my BTC-1 which is basically a series 1 servo machine, Bridgeport used L sized belts on the X,Y, and Z. Now the Z on this machine is the quill. An L sized belt is massive overkill on the quill. I am doing a conversion on the knee to use Rays method of tool compensation and I will use an L sized belt just because I already have the belts and pulleys.
I do believe that an XL belt would work fine because of the limited speed of the belt when driving the knee. Power of the motor and the load is only one of the factors involved in belt selection. Speed of the belt drive is a major one and the slower you go the lighter the belt can be. Speed contributes to heating of the belt which degrades the rubber. The other item to consider is the amount of time running at speed. Unless you are build a super high speed machine that will always move at 300 ipm all day long, the belt will spend a fair amount of time just sitting while the other axis move. Hope this helps.
Mike
-
The belt on my knee drive is an XL, and it works fine, shows no sign of wear, even after using the knee as the Z axis for the last year.
Regards,
Ray L.