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Re: Was about to get a toy- then I did some research...
Moving on to the mechanical side of things (at least for now) and essentially the gantry arm design. Am I right in assuming that it is the centre of gravity of the entire gantry assembly (incl. gantry arms, beam, z-axis, spindle etc.) that preferably should be half way between the X-axis (long axis) rail carriages?
My thinking is that any force applied to the spindle in the X direction affects the balance of the entire gantry assembly. Now, the reason I'm double checking this is that when drawing the gantry assembly (as in the attached, albeit, unfinished drawing) I find that the COG is quite far back (the left side mark) if the beam is also included in the calculations. I know some parts are still missing from the drawing, but even when included, the end result will not change much (in fact, what's missing is mostly parts on the left hand side of the mark). Bottom line is, in this scenario my gantry arms would raise straight up from the X-axis carriages (hence, neither would the inclusion of the arms affect the cog) and, essentially, leaving the spindle quite far in front of the front carriage.
Problem is that nearly all gantry arm designs I've looked at will have the spindle closer to the halfway point between the carriages or at least somewhere between the carriages. Now, when I calculate for the Z-axis assembly only (the mark to the right) the COG is naturally much closer to the spindle, and should I use this as my reference point my gantry arm design and more importantly the spindle position (relative to the X carriages) would end up looking much more like what I see others using. My intuition still says I should go with the COG of the entire gantry assembly as my reference point, but seeing that this would end up looking much different to the norm, it makes me wonder if I've overlooked something or simply using the wrong logic?
Attachment 27318
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
I still cannot bring myself to do something without having built an understanding of my own of the matter. Hence, the occasional silly questions :)
The only silly question is the one you don't ask...Keep firing away we understand.!
What's I'm trying to say more than anything is don't let it slow you down from building because you'll still end up back at or around what's been suggested.
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Re: Was about to get a toy- then I did some research...
Best would be if Spindle centre /the bit/ does not go further than than carriage, machine looked from side . But If not possible its not a problem . If square linear rail is used. Though for metal work i say better not, for a perfect finish i mean.
Red line shows the ideal, blue line the normal. I would say 250-260mm span for me is the minimum of the gantry legs/ bearings
Attachment 27319
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Moving on to the mechanical side of things (at least for now) and essentially the gantry arm design. Am I right in assuming that it is the centre of gravity of the entire gantry assembly (incl. gantry arms, beam, z-axis, spindle etc.) that preferably should be half way between the X-axis (long axis) rail carriages?
Yes Ideally but again without wanting to sound like a broken record don't let these kinds of details bog you down from the building phase. The COG being off a little like what your showing isn't going to make one jot of difference to how the machine performs or how it affects component life in a DIY environment.
Anyone who's built a machine and worried about these kinds of things will tell you that it was a pointless exercise and it's the smaller details that make a bigger difference to how the machine performs. Details like sturdy ball-nut brackets and adjustability, motor mounts, wire routing, Limit SW placement, access to grease nipples and lubing, etc, etc.
If you build a Sturdy structure and pay attention to key areas like Z-axis then you won't go wrong or notice if COG is off a little, but you will notice if the little details are missed.
My advice is to look around at other builds and pay more attention to the little details and pay less attention to if COG looks a little offset.!
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Boyan Silyavski
Best would be if Spindle centre /the bit/ does not go further than than carriage, machine looked from side . But If not possible its not a problem . If square linear rail is used. Though for metal work i say better not, for a perfect finish i mean.
Red line shows the ideal, blue line the normal. I would say 250-260mm span for me is the minimum of the gantry legs/ bearings
Attachment 27319
I've planned on using a 250mm span between the outer ends of the square linear rail carriages and as it stands right now the arms would look like the blue lines in your sketch (though if cog is centered with centre of carriages the bit would fall outside or just on the outer edge of the front carriage). For reference the alu extrusions are 45x90.
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
I've planned on using a 250mm span between the outer ends of the square linear rail carriages and as it stands right now the arms would look like the blue lines in your sketch (though if cog is centered with centre of carriages the bit would fall outside or just on the outer edge of the front carriage). For reference the alu extrusions are 45x90.
It does not matter as far as you use Hiwin 20 size or comparable rails. You could offset al gantry rail to the back, to compensate a bit for this. As Dean says look at other build for inspiration and to figure the details.
I will not tire to say that machine is as strong as its weakest point, so do not overbuild / did i just say that :cat:/ just take care not to have weak details
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
I've planned on using a 250mm span between the outer ends of the square linear rail carriages and as it stands right now the arms would look like the blue lines in your sketch (though if cog is centered with centre of carriages the bit would fall outside or just on the outer edge of the front carriage). For reference the alu extrusions are 45x90.
If it helps I use 300mm wide plates with this design.! Anywhere between 250 and 300 will work ok.
However, keep in mind how you are going to fasten the profile to the plates and fasten the plates to the bearings if going with gantry on rails setup.! It's easy to forget things like access to bolts or one blocking another.!
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Boyan Silyavski
I will not tire to say that machine is as strong as its weakest point, so do not overbuild / did i just say that :cat:/ just take care not to have weak details
I DO NOT BELIEVE WHAT I'M READING...:toot::toot: . . . FINALLY......:toot::toot:...We agree on something...:joker:
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Anyone who's built a machine and worried about these kinds of things will tell you that it was a pointless exercise and it's the smaller details that make a bigger difference to how the machine performs. Details like sturdy ball-nut brackets and adjustability, motor mounts, wire routing, Limit SW placement, access to grease nipples and lubing, etc, etc.
If you build a Sturdy structure and pay attention to key areas like Z-axis then you won't go wrong or notice if COG is off a little, but you will notice if the little details are missed.
That's the paradox I guess! I keep reading all the theory but as I haven't done this sort of a project before it's hard to tell what's essential and what's not. And as you rightly point out, doing the details/assembly properly will matter quite a bit for the end result (as it would for any project really), maybe even more than getting all the theory right ;)
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Boyan Silyavski
It does not matter as far as you use Hiwin 20 size or comparable rails.
20mm is the plan, but not sure yet about going full hiwin or not...
Quote:
Originally Posted by
JAZZCNC
If it helps I use 300mm wide plates with this design.! Anywhere between 250 and 300 will work ok.
The idea crossed my mind. Would help bring the cog slightly forward + more stability.
I could also get creative and hang a 5kg weight from the spindle :D that should balance it up!
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
That's the paradox I guess! I keep reading all the theory but as I haven't done this sort of a project before it's hard to tell what's essential and what's not. And as you rightly point out, doing the details/assembly properly will matter quite a bit for the end result (as it would for any project really), maybe even more than getting all the theory right ;)
Yes, Theory is great. However at the DIY level theory and reality often part company early on in the build process at which point reality often comes back and smacks you fully in the face.
I find if you have patience use Common sense along with doing the Duediligence like what you are doing now. Then provided you choose the right design for your needs and take care when building it that you will always end up with a machine to be proud of that won't disappoint.
Keep asking the questions like what you are doing and it will eventually make more sense, it won't make complete sense until you started the build, which at some point you will say "Aghh I get what Boyan was saying now." .!!
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
20mm is the plan, but not sure yet about going full hiwin or not...
If you want the best machine then you must bite the bullet and go with Profiled linear rails. If not then you are wasting your time worrying about things like COG or plate thickness because Boyan is 100% correct that the machine is only as good as the weakest link and round rails will by far be the weakest link no matter which axis you put them on.!
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
If you want the best machine then you must bite the bullet and go with Profiled linear rails. If not then you are wasting your time worrying about things like COG or plate thickness because Boyan is 100% correct that the machine is only as good as the weakest link and round rails will by far be the weakest link no matter which axis you put them on.!
Sorry for being a bit unclear, with "full hiwin" I meant as opposed to the "economy" type profiled rails. I've already been convinced to go profiled, although I expect to swear a few times more than had I gone with round rails...
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
I could also get creative and hang a 5kg weight from the spindle :D that should balance it up!
Someone hasn't yet gotten into the theory of their motor calcs yet! More mass on the Z axis means everything has more to accelerate! NIGHTMARE!!
Personally I think we should all just make them out of bamboo and some twine, powered by hamsters, and tamagotchis as control interfaces to just be done with it :)
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
AndyUK
Someone hasn't yet gotten into the theory of their motor calcs yet! More mass on the Z axis means everything has more to accelerate! NIGHTMARE!!
Personally I think we should all just make them out of bamboo and some twine, powered by hamsters, and tamagotchis as control interfaces to just be done with it :)
Interesting point! But you still have to considered the torque drop when hamsters get hungry and be sure to size the running wheel according to your choice of hamster, too small and your hamster will simply get stuck and start doing loops...Other than that you should be sweet :beer:
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Interesting point! But you still have to considered the torque drop when hamsters get hungry and be sure to size the running wheel according to your choice of hamster, too small and your hamster will simply get stuck and start doing loops...Other than that you should be sweet :beer:
Arghh but you'll always struggle if you use hamsters, what you need with a heavy Z-axis is Guinea Pigs...:yahoo:
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
AndyUK
Welcome to the forum :)
Yeah... this is quite a time-sink (and potentially money-sink) of a hobby.... ;)
Based on your post title, I'm guessing you were thinking of grabbing one of those pre-made Chinese jobbies off ebay?
They get an awful lot of flack (from me too!) but I think they do actually have a place; as long as you're prepared for how pathetic their capabilities are, they're a reasonably inexpensive way of experiencing the CNC process and way of thinking, allowing you to start exploring what you might want out of a machine.
The Shapeokos of the world give the same lessons, but are more expensive to begin with, although probably allow a greater amount of time before you outgrow it.
My first CNC was a simple conversion of a 3D plotting tank (think 40x40x40 work area, but about as stiff as jelly). It taught me lots about GCode, CAD CAM and what I needed from a machine.
I built my CNC after building a Rep Rap it really helped get my head around how it all works.
Hiwin's and ballscrews but the core principles remain the same.
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Sorry for being a bit unclear, with "full hiwin" I meant as opposed to the "economy" type profiled rails. I've already been convinced to go profiled, although I expect to swear a few times more than had I gone with round rails...
For a first time hobby builder I think clone rail is fine, BST automation on Alixpress are a good place to start.
If I was sinking thousands into a frame, decent spindle, etc I'd buy original and I already have original Hiwin on most my machine just one axis is clone.
I can tell you Hiwin's are definitely smoother than cheap clone rail before I fitted them but in practice on the router working you can't tell the difference. With 1610 ballscrews one step in 0.05mm so that's really what limits your resolution. Never consider microstepping actual resolution it's something very different. On a Mill clone rail probably makes a lot less sense.
If I was working it for cash 10 hours day I would definitely go original Hiwin.
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
If you want the best machine then you must bite the bullet and go with Profiled linear rails. If not then you are wasting your time worrying about things like COG or plate thickness because Boyan is 100% correct that the machine is only as good as the weakest link and round rails will by far be the weakest link no matter which axis you put them on.!
It was because of you and Boyan I never used the SBR 25 rail I have and bought Hiwin's and clone hiwin's.
One day I might use them for a plasma cutter, I did buy new bearings for them they do feel "nice" but very glad I went with rail instead.
One really annoying thing about them the mounts are 46mm apart.
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Desertboy
For a first time hobby builder I think clone rail is fine, BST automation on Alixpress are a good place to start.
No that's wrong way to look at it. When buying from China most of the cost is the shipping, the difference between Hi-win and the clone isn't massive so it's not worth wasting shipping. Don't spoil a machine for just a few $$ more.