Analyzing Which Z Axis Design Is Best
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- Опубликовано: 8 янв 2021
- In this video, I will compare two different z-axis designs. The difference is in how the linear rails and carriages are mounted. In the first design, the spindle holder has the linear rails mounted, and in the second design, the carriages are mounted to the spindle holder.
It turns out that each design has its advantages for different purposes, and that the deflection and rigidity of the entire z-axis are greatly improved if the correct design is chosen.
Enjoy!
Download Files From Video Here:
a360.co/3deHnVm
I think the point of "type 1" design is that the z-carriages will be placed much lower down, like right in front of where the horizontal rails are, to have a more direct force transfer to the gantry itself. You certainly wouldn't want those carriages way up high like you've shown. The deflection of "type 1" may change with z-position, but it will always be the strongest possible, which seems like a good thing to me. The main downside is that the bottom of the z-plate will end up closer to the toolbit, so it's not as good for making deep cuts. Another downside is that the moving weight of the z-assembly is heavier because the rails have to move as well.
Would be great if you made a full course on this for precision CNC machine builds using granite or epoxy granite.
Wow that was a lot of work to put together, thank you for that !
thanks a lot for the assembly
Great video. Glad to see you applying engineering principles for better design. Thanks.
Great modelling!
Hej William, fantastisk indhold!
Thanks a ton:). I am in the research phase of making a stiff router, too so finding your channel is great. I will either cast mine in Epoxy Granite or make it out of granite surface plate a la Fox - just cuz I like how he managed to make a very precise frame with basic tools.
Tak, er glad for du kan lide det!
Yes, that's the big question, should one use slabs of precision ground granite or cast the whole thing?
Maybe I can make it easier for you.
Granite slabs:
Is for high precision, and doesn't take much effort to design and build compared to casting.
Composite machine (cast):
Is for high performance and requires lots of advanced design-time and loads of experience to build successfully.
If I didn't have big plans for the machine in the future, then I would have gone ahead and build a granite CNC router.
Every Machinist is somehow a THIS OLD TONY fan 🤷
great video on the subject :)
Subbed for more ^^
why confine ourselves to just 2 X rails? The major problem I had with pcb making with my 3018 are the vibrations induced by the spindle motor. Anything with a fulcrum in the design greatly amplified those vibrations, increasing the the deflections at the tip of the router bit - breaking it, even with just pcb making.
Well that's eye opening, as usual !
Side note, you may have forgot to add the link of the project in the description 🙃
Thanks !
Hi Geekoid I'm glad that this was of some use to you.
I have always thought that design 1 with the rails mounted to the spindle holder would be the strongest, but once I had a CAD-model with the correct proportions I realized I was wrong, and had to make a video about it.
I have added the link now, thank you for reminding me ;-)
Hi all, small mistake cathed by @hüseyin güngör. I had accidentally switched the deflection values for when both z-axes were raised. The upper deflection of design 1 is therefore 0.0085 mm (not 0.0117 mm) and design 2 has a deflection of 0.0117 mm (not 0.0085 mm). The conclusion for this case remains somewhat the same, design 2 will still offer the most rigidity almost 80% of the time, except for when it's fully raised, then design 1 will be more rigid.
Hi Williams Garage Engineering ! Great Work & Excellent Video ! Very Impressive, with a great amount of details being provided ! However ! Where can I download the Files from this Video, as the current download link doesn't work ? With kindest regards GCG CNC Group.
Thank you for your kind words. Here is the link a360.co/3deHnVm
Will separating the xaxis linear rails make it more stable.
Hello, on video 12:23 probably you mixed the parameters by mistake did you ? It looks like designs1's parameters written under design2.
No they are correct. Design 2 has the least deflection in this case. As can be seen, the deflection values are smaller than those of design 2. - I'm still glad you asked and spoke up about it.
@@williamsgarageengineering6543 Can you check the 11:39 upper deflection looks changed.
@@huseyingungortasarmprojeleri Thank you, I know what's going on now. I have switched the deflection values for when both z-axied are raised. Luckily it's a minor mistake is their deflection is "relatively" close.... So, Design 1should have stated a deflection of 0.0117 mm when raised (not 0.0085 mm), and design 2 then has a deflection of 0.0117 mm instead of 0.0085 mm. Great catch, thank you for paying attention.
@@williamsgarageengineering6543 So we can say design 2 is better than design1 when lowered. When they are rised design 1 is better right ?
@@huseyingungortasarmprojeleri Yes, that is correct, but design 2 is also the stiffest when it's in the middle position between lowered and raised. Another thing to consider is that if someone wants to have a lot of top clearance for long end mills, then for design 1 the whole assembly will be less rigid, whereas in design two it will still have the same stiffness, except for when the spindle if fully raised of course.
What a totally unfair comparison! The design on the left makes no sense, the carriages should be mounted lower and the spindle upper. The design on the right has limited travel possibilities that's why the design on the left is used. You started with a good project: compare the 2 designs. But then you should compare both at best this is not the case, then try to compare both with a 300mm travel
someone who understands, confining the deflection and suported rails
1:58 the left one could potentially have the rails extended more down to have the carriages mounted equally much down.
Hi @Jonas A , I'm not sure what you mean, maybe you could elaborate a bit?
@@williamsgarageengineering6543 Don't trust me I am no mechanical guy. I am just trying different designs while trying to design a 600x600 mm foot print fixed gantry mill. But looking at the left picture at 1:58 I think the rails could be made longer to go further down and also extend the metal holding the rails. The rails (and metal holding rails) could probably be extended almost down to the collet since they will not be in the way? If they are extended for example 50 mm then the Z-carriages can be moved down 50 mm to maintain the same Z height. And therefor get 50 mm less leverage.
Maybe even the rails do not have to be longer, just moved. I guess it can be seen as moving the spindle up in the spindle mount and then to get back to same Z height move Z-carriages down.
@@Jonas_Aa Ahh alright, I know what you mean now. Yes, that is correct, what I refer to as the spindle holder could be lowered so that it also surrounds the spindle further down. But then it would be an unfair comparison if the design on the left didn't have that extra material too.
So we could definitely compare the two designs with the spindle holder extended further down, but I have just chosen not to. - You see, the spindle also has some stiffness, so it doesn't always make sense to support it the whole way down. Also, most of the deflection happens where the initial overhang is located (from the bottom z-axis carriage). So from my experience adding more support around the lower spindle almost has no effect on the rigidity of the system. Don't just take my word for it, feel free to test it if you want to know for sure ;-)
However, more material around the spindle can reduce vibrations as it absorbs the vibration induced into the spindle bearings by the end mill. I have a theory that more material around the lower part of the spindle potentially could increase its lifetime. Please note that the microstructure of aluminum doesn't make for great absorption of vibrations (in other words, aluminum is not very damp) therefore this is more relevant for cast iron and composite materials.
@@williamsgarageengineering6543
The problem is that design #1 isn't properly designed but instead has the flaws (or rather features of design #2 that aren't necessary with #1 and become flaws there) of design #2 unnecessarily incorporated. That's not a comparison of both designs respective potential.
You should design both the best you can and then compare. To generalize anything from this is just nonsense.
Design 1 is superior and if done right will be stiffer, that's why you usually don't see #2 on properly designed professional machines.
It's sometimes used for light machines with rather short z-travel as it's inherent drawbacks are less of a concern in such a case and if it's compared to a bad designed #1 axis it might even have an advantage.
@@heinzhaupthaar5590 does it matter if the rails are moving or the carriages are moving to be a good design?
Was this really approved by TOT? 🤷♀️
Sponsored by This Old Tony?!!!
Yes, in the timeline I'm from.
@@williamsgarageengineering6543 Nice, you rock Williams and well informed.
@@holypizza1 Thank you for the support!