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16mm or 20mm , DIY CNC 60cmx50cm
Plan to build cnc for > 5mm-20mm plastic/acrylic, 5-20mm wood, maybe aluminum but not require.
Working surface is 60cm x 50cm , I've space limit.
I like design of https://www.youtube.com/watch?v=NKv3I7Zclhk will do just like that. Only I will do single-drive x-axis only not dual like in those vdo-clip.
So here is my plan.
-nema23 5A x3
-linear rod rail 16mm all x, y ,z axis
-router makita 3709
Question: > Ball screw should be 16mm or 20mm , pitch 5mm or 10mm?
Since it my 1st cnc so I don't need very fast speed only good and reasonable one.
Please suggest. Or any comment about those spec is welcome. This is for diy hobby project.
Thank
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
Since you only have a fairly small cut area I would be inclined to go with a 5mm pitch. On my X axis (1200mm cut area, about 1700mm long) I have two 3210 ball screws (32mm / 10mm), on my Y axis (800mm cut area, about 1100mm long) I have a 2510 ball screw (25mm / 10mm) and on my Z axis (200mm cut area, about 500mm long) I have 2005 (20mm / 5mm).
So I would be inclined to go with 20mm, but you could get away with 16mm.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
Looking at that video I see something common and bad... They have gone to the trouble of building it out of some decent sized alloy to give it strength only to let it down by the poor bearing placement. The bearings on the Y axis are way too close together. Think of it like this if you stand with your feet together and someone was to push you sideways at shoulder height you would flex and fall over (bearings close together) If you stood with your feet apart and pushed with the same force in the same place all of a sudden you wouldn't get pushed over (bearings wide apart).
Precision comes down to how much you control flex, not just the size of the material. I would also go steel over aluminum frame for the same reason. The other major issue with that design is where the spindle is relative to the bearings. You ideally want the cutting tip between the bearings to give the cutter maximum support, when the cutter is in front of the bearings like that design it is like holding a weight out in front of you with your arms straight only in reverse compared to holding the same weight close to your body.
It's all about removing mechanical leverage...
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
I would always use 10mm pitch screws on a router. And I'd go with 20mm diameter.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
From your guys answers I tend to use 20mm diameter with 5mm pitch then. From I understand speed will lower than 10mm pitch by half but I will gain more resolution right?
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The bearings on the Y axis are way too close together. Think of it like this if you stand with your feet together and someone was to push you sideways at shoulder height you would flex and fall over (bearings close together) If you stood with your feet apart and pushed with the same force in the same place all of a sudden you wouldn't get pushed over (bearings wide apart).
I can see your pint now. Then extend length base of y-axis is better. So that I sketch some in 1st picture. Which if them good?
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Precision comes down to how much you control flex, not just the size of the material. I would also go steel over aluminum frame for the same reason. The other major issue with that design is where the spindle is relative to the bearings. You ideally want the cutting tip between the bearings to give the cutter maximum support, when the cutter is in front of the bearings like that design it is like holding a weight out in front of you with your arms straight only in reverse compared to holding the same weight close to your body.
From what I understand is center of gravity should be middle of those fix-point in example 2nd pic, those in vdo-clip spindle is toward make it tend to fall result in wobble/vibrate while use. So I should adjust spindle a little bit backward like what I've sketch then. Right? Suggestion?
I know weight of spindle, but total weight of y,z axis not easy know until finish assembly. So to design to get center of gravity in middle of fix point not easy possible without complicate calculation. So I just guess/estimate then?
Attachment 398390 Attachment 398392
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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Originally Posted by
nquantum
From your guys answers I tend to use 20mm diameter with 5mm pitch then. From I understand speed will lower than 10mm pitch by half but I will gain more resolution right?
Correct, speed will be half, but the precision will be double. If you were planning on a meter by a meter table I would say go with the 10mm, because it would take longer to get to the other end of the table, but you are only going to have half the distance to cover compared to me so it doesn't matter if it only go half speed, you will get from one end to the other in the same time it takes me to do the same.
I am currently using NEMA 23 motors and I have gone as fast as 2500mm / min (2.5 meters a minutes) so you could expect to do 1.25 meters a minute with a 5mm pitch.
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Originally Posted by
nquantum
I can see your pint now. Then extend length base of y-axis is better. So that I sketch some in 1st picture. Which if them good?
The ones with the bend design seem good because they put the cutting tip equal distance between the bearings.
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Originally Posted by
nquantum
From what I understand is center of gravity should be middle of those fix-point in example 2nd pic, those in vdo-clip spindle is toward make it tend to fall result in wobble/vibrate while use. So I should adjust spindle a little bit backward like what I've sketch then. Right? Suggestion?
I know weight of spindle, but total weight of y,z axis not easy know until finish assembly. So to design to get center of gravity in middle of fix point not easy possible without complicate calculation. So I just guess/estimate then?
Yes you understand right. The closer you can get the cutting tip in the middle of the bearings on all axis the better. I was trying to get that point across with the weights. When you are cutting you are trying to push the cutting tip into the material. As Newton said "every action has an equal opposite reaction" which means while the cutter is trying to push down into the material an equal amount of force is also trying to push back up.
So getting back to the example I used before, if you are standing with your feet together with your arms out (bearing close together and cutter out in front of bearings) and you lock your arms rigid and someone comes along and pushes up on your hands that is like the cutter pushing up. Because the cutter is out in front it acts like a lever like someone pushing up on your hands. If you have your legs apart and your hands right in near your body. Pushing up with the same force will have less effect because there isn't the additional lever effect happening.
https://www.cnczone.com/forums/attac...d=398390&stc=1 https://www.cnczone.com/forums/attac...d=398392&stc=1
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
The wider you can get the bearings apart the more stable it will be. I am trying to get around 400mm between my X axis bearings. So you need to add 400mm to the 600mm (60cm cut you want).
I just finished cutting these on mine, build it right and you should be able to do similar.
https://www.cnczone.com/forums/attac...d=398394&stc=1
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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The wider you can get the bearings apart the more stable it will be. I am trying to get around 400mm between my X axis bearings. So you need to add 400mm to the 600mm (60cm cut you want).
Noted. For rail rod will use 16mm, ball-screw is 20mm
Once have decision on these spec will start sketch, and design.
How about "supported-supported", "fixed-support" ? Actually I plan to use "fixed-support" is it worth difference on this size of machine?
What difference between MOTOR >> Fixed --- [ball screw] --- Support and MOTOR >> Support --- [ball screw] --- Fixed. ?
Attachment 398398
Attachment 398396
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my laptop literally died right in the middle of posting so here comes the iPhone version!
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Originally Posted by
nquantum
From your guys answers I tend to use 20mm diameter with 5mm pitch then. From I understand speed will lower than 10mm pitch by half but I will gain more resolution right?
Don't dismiss the importance of feed rate, especially if targeting wood and plastics! If you expect to use steppers you need to at least consider higher lead leadscrews.
There are all sorts of things to consider from the torque curves of the steppers, too the spindle speed, too the types of cutters being used and the materials to cut. Id look up some info for optimal feed rates, spindle speeds & etc for the materials you expect to machine. Then see where achieving those feed rates (with various leadscrews) put you on the steppers torque graphs. You will want some head room.
The flip side is how much resolution do you need. Inna stepper based system this can drive you backwards on leadscrew lead. So you need to find the happy place where these competing issues are both good enough for you. On top of this realize that Micro Stepping can only be taken so far in achieving resolution.
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I can see your pint now. Then extend length base of y-axis is better. So that I sketch some in 1st picture. Which if them good?
.
The cutting actions apply a torque on your gantry which can vary dramatically. Your gantry support bearings have to resist this torque. In round rail systems especially you want a good distance between the bearings to resist this. This actually applies to the other axis also. Ultimately it comes down to how much mechanical displacement you can tolerate.
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From what I understand is center of gravity should be middle of those fix-point in example 2nd pic, those in vdo-clip spindle is toward make it tend to fall result in wobble/vibrate while use. So I should adjust spindle a little bit backward like what I've sketch then. Right? Suggestion?
Realistically you can put the spindle / Z axis anywhere you want as long as you can maintain stiffness. Keeping the spindle centered over the bearings only helps with static deflection. Unless of course the extension is so much that a significant increase in the lever arm happens.
The only good reason for a large Z over hang of the gantry support bearings is to enable working off the end of the machine for vertically mounted work pieces. Some users value that capability! That capability is only something you can verify. Otherwise think simple and stiff.
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I know weight of spindle, but total weight of y,z axis not easy know until finish assembly. So to design to get center of gravity in middle of fix point not easy possible without complicate calculation. So I just guess/estimate then?
Honestly i would not worry too much about it. Like you said the calculations would be complicated. I tend to prefer simple and rigid.
In any event in the stickies there is an excellent read that goes into gantry bean design. I highly suggest taking a look because in a nut shell a big square beam is the least complicated approach.
If you have ever used a hand held router you should have an appreciation for how different cutters apply torque to the motor unit. Depending upon the materials, depth of cut and so forth you might have control with one hand or struggle with two hands. A CNC machine sees the same array of forces, often significantly more. The reason of course is that tge human might back off if control becomes an issue. A CNC machine on the other hand tries to match commanded feed rates.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
nquantum check out the video I uploaded yesterday. Have a look at the way I mounted the bearings. Not sure if I would necessarily do it the same way again. In hindsight I would probably allow for more adjustment, but it does work well.
https://www.youtube.com/watch?v=xstnyLtNbjE
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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Don't dismiss the importance of feed rate, especially if targeting wood and plastics! If you expect to use steppers you need to at least consider higher lead leadscrews.
There are all sorts of things to consider from the torque curves of the steppers, too the spindle speed, too the types of cutters being used and the materials to cut. Id look up some info for optimal feed rates, spindle speeds & etc for the materials you expect to machine. Then see where achieving those feed rates (with various leadscrews) put you on the steppers torque graphs. You will want some head room.
The flip side is how much resolution do you need. Inna stepper based system this can drive you backwards on leadscrew lead. So you need to find the happy place where these competing issues are both good enough for you. On top of this realize that Micro Stepping can only be taken so far in achieving resolution.
Thank for remind me that. I never been cut thing with cnc before only hand saw for wood and plastic. What do you mean by "you need to at least consider higher lead leadscrews." can you tell more detail please? Higher lead?
I plan to use micro-step and speed control for router. Coz 35,000RPM , I think plastic will melt.
For the resolution I don't need much. Since this I build for next diy project, robot, uav, pc-case etc.
Well this meaning I can use 10mm pitch with micro-step. Can do thing of 5mm pitch can do with normal step right?
So I may need a way to calculate , the resolution I can get from feed rate / pitch / motor-step / maybe other factor then?
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The only good reason for a large Z over hang of the gantry support bearings is to enable working off the end of the machine for vertically mounted work pieces. Some users value that capability! That capability is only something you can verify. Otherwise think simple and stiff.
I see! I think most of my work will do on not big piece of cut. Not off the end of machine. So I keep little back spindle behind like I drawing then.
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Honestly i would not worry too much about it. Like you said the calculations would be complicated. I tend to prefer simple and rigid.
In any event in the stickies there is an excellent read that goes into gantry bean design. I highly suggest taking a look because in a nut shell a big square beam is the least complicated approach.
Simple and rigid, me too. "gantry beam design" OK I'll look at it for idea improvement.
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If you have ever used a hand held router you should have an appreciation for how different cutters apply torque to the motor unit. Depending upon the materials, depth of cut and so forth you might have control with one hand or struggle with two hands. A CNC machine sees the same array of forces, often significantly more. The reason of course is that tge human might back off if control becomes an issue. A CNC machine on the other hand tries to match commanded feed rates.
I never use router before, only hand saw for wood, plastic. That why I ask for idea here about general good pitch of ball screw for material I cut , wood, plastic, acrylic, maybe aluminum I hope if can.
Since router speed can adjust, also speed of step motor from curve. I think 5mm or 10mm should be good then.
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nquantum check out the video I uploaded yesterday. Have a look at the way I mounted the bearings. Not sure if I would necessarily do it the same way again. In hindsight I would probably allow for more adjustment, but it does work well.
Now sure I understand what you try to tell me. Here is what I saw:
- You machine 'gantry beam design' just like @wizard told me, metal and I guess very rigid.
- from x axis in those rail quite far apart and use 2-motor drive make it even rigid.
- you try to cut something don't know what it for
- notice spindle-holder have free 1 for what? another spindle?
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
nquantum if you plan to stick with the Makita router you won't need to go super fast because the router won't be able to cut fast enough to use the additional speed.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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Thank for remind me that. I never been cut thing with cnc before only hand saw for wood and plastic. What do you mean by "you need to at least consider higher lead leadscrews." can you tell more detail please? Higher lead?
I plan to use micro-step and speed control for router. Coz 35,000RPM , I think plastic will melt.
For the resolution I don't need much. Since this I build for next diy project, robot, uav, pc-case etc.
Well this meaning I can use 10mm pitch with micro-step. Can do thing of 5mm pitch can do with normal step right?
So I may need a way to calculate , the resolution I can get from feed rate / pitch / motor-step / maybe other factor then?
Microstepping is used to achieve smoother running mtors. It does not increase resolution.
10mm pitch will give you more than enough resolution, and much better speed than 5mm pitch.
You need to slow your spindle down from 35,000. Even at high feedrates, 15,000-20,000 rpm is all you want.
And plastic can easily melt at 15,000 rpm, if you aren't moving fast enough.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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nquantum if you plan to stick with the Makita router you won't need to go super fast because the router won't be able to cut fast enough to use the additional speed.
Haha right!
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Microstepping is used to achieve smoother running mtors. It does not increase resolution.
10mm pitch will give you more than enough resolution, and much better speed than 5mm pitch.
You need to slow your spindle down from 35,000. Even at high feedrates, 15,000-20,000 rpm is all you want.
And plastic can easily melt at 15,000 rpm, if you aren't moving fast enough.
I see, will add speed control to that.
I've some pencil drawing finish, will use computer to draw the plan then let you guys see/comment by next post.
Thank you.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
nquantum I was about to say that hand held routers don't have the same kind of power as dedicated spindles, but I just checked the specs on my almost new Makita RP2301FC, that thing is 3.25HP! (2100w) that the same as my CNC spindle. Here I was thinking it was going to be something like .75HP
Perhaps you might want to consider the 10mm pitch after all.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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but I just checked the specs on my almost new Makita RP2301FC, that thing is 3.25HP! (2100w) that the same as my CNC spindle.
The advertised power of a handheld router is not what it actually has. A 2.2Kw spindle should be quite a bit more powerful.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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Originally Posted by
Bad Wolf
nquantum I was about to say that hand held routers don't have the same kind of power as dedicated spindles, but I just checked the specs on my almost new Makita RP2301FC, that thing is 3.25HP! (2100w) that the same as my CNC spindle. Here I was thinking it was going to be something like .75HP
I'm not sure where you are located but in the USA a 15 amp, 120 VAC circuit will allow for 1800 watts. You won't get that for very long either, at best you de-rate to 80% if you want high reliability. Even on a 20 amp circuit you are cutting it close once you de-rate. In a CNC machine this doesn't include other power being drawn.
Then you have to consider those power values are sometimes marketing wishful thinking. Maybe not so wishful but rather the realization that hand held tools don't operate like production tools and thus have plenty of time to cool down. I have one of the big routers sitting in a router table a built years ago. I don't doubt that it puts out a lot of power and even more noise, but I'm pretty sure I wouldn't want to put it in a CNC expected to work 8 - 12 hours a day.
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Perhaps you might want to consider the 10mm pitch after all.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
Quote:
Originally Posted by
nquantum
Thank for remind me that. I never been cut thing with cnc before only hand saw for wood and plastic. What do you mean by "you need to at least consider higher lead leadscrews." can you tell more detail please? Higher lead?
a 10mm pitch vs a 5mm pitch would have the higher or faster lead. That is the linear distance moved per revolution is "higher". probably not the best idea here for me to be loose with terminology.
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I plan to use micro-step and speed control for router. Coz 35,000RPM , I think plastic will melt.
For the resolution I don't need much. Since this I build for next diy project, robot, uav, pc-case etc.
Well this meaning I can use 10mm pitch with micro-step. Can do thing of 5mm pitch can do with normal step right?
So I may need a way to calculate , the resolution I can get from feed rate / pitch / motor-step / maybe other factor then?
Yes you need to control that spindle speed else you will melt and burn things. Be careful though because you will have to cut the speed by more than half greatly impacting the power you might expect out of the spindle.
As for micro stepping do not assume that the stepper will be able to resolve accurately beyond about 10 micro steps. The higher values of micro stepping are there to deliver a smoother motion. In a sense micro stepping of say 64 or 128 steps are applying a sine like wave to the stepper coils.
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I see! I think most of my work will do on not big piece of cut. Not off the end of machine. So I keep little back spindle behind like I drawing then.
Simple and rigid, me too. "gantry beam design" OK I'll look at it for idea improvement.
Some place in the stickies there is an excellent thread on gantry beam design. Also if you search the internet for an author with the last name of Bamberg you should be able to find a paper he wrote on rapid machine design. I don't have the details at the moment to get you closer on that paper but he goes into great depth on the use of steel in machine design. Sometimes he goes a little too deep but it is very enlightening.
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I never use router before, only hand saw for wood, plastic. That why I ask for idea here about general good pitch of ball screw for material I cut , wood, plastic, acrylic, maybe aluminum I hope if can.
Since router speed can adjust, also speed of step motor from curve. I think 5mm or 10mm should be good then.
For most people 10 mm will be better. Especially if this is your first home built machine and you don't have access to machinery to build to high precision.
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Now sure I understand what you try to tell me. Here is what I saw:
- You machine 'gantry beam design' just like @wizard told me, metal and I guess very rigid.
In a way the gantry beam is key to getting very good performance out of a machine. That includes how it connects to the table. Sadly many DIY designs come up short in this respect.
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- from x axis in those rail quite far apart and use 2-motor drive make it even rigid.
The leadscrews and steppers will not make a machine rigid. This is very important to realize
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- you try to cut something don't know what it for
- notice spindle-holder have free 1 for what? another spindle?
Spindles can be of any class you can afford to get started. You will quickly learn though that an underpowered or flimsy spindle will limit your machines performance and drastically impact the quality of your work.
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Re: 16mm or 20mm , DIY CNC 60cmx50cm
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Originally Posted by
wizard
I'm not sure where you are located but in the USA a 15 amp, 120 VAC circuit will allow for 1800 watts. You won't get that for very long either, at best you de-rate to 80% if you want high reliability. Even on a 20 amp circuit you are cutting it close once you de-rate. In a CNC machine this doesn't include other power being drawn.
Then you have to consider those power values are sometimes marketing wishful thinking. Maybe not so wishful but rather the realization that hand held tools don't operate like production tools and thus have plenty of time to cool down. I have one of the big routers sitting in a router table a built years ago. I don't doubt that it puts out a lot of power and even more noise, but I'm pretty sure I wouldn't want to put it in a CNC expected to work 8 - 12 hours a day.
wizard I come from a land down under where power is 240VAC and the lowest available is 10A so that makes for 2400w. You can also get 15A and 20A here and 3 phase but it's not the norm, you need an electrician to do specialty wiring for it.
We supposedly "officially" went 230VAC decades ago, but it was never really implemented.Typical voltage here is more like 250VAC.
