I’m confused.
If the geometry on the z-axis supports 100mm of travel, why not just always build with a “drop table” to have the option to use the full travel? Could be easily accomplished by stacking material for the rails to raise the height of the YZ plates relative to the spoilboard surface.
Also seems like the gantry would be more stable the lower it sits on the YZ plates.
What am I missing?
Thanks!
I thought like you did, so I used elevator plates on my first table build.. it was a waste of time, I may never need that cutting depth lol. It also complicates things because you need to use longer bits (or risk it sticking a regular one out a lil bit), or else you’ll bottom out Z before you can cut thru the material! And it’s such a pain in the ass when that happens, again for a benefit I’m not using and therefore does not exist.
Plus logically, since they’re easy to install, just install em if ya need em! But I say don’t do it until you need to, it’s just one more thing to go wrong 99% of the time.
Yea, common endmills might cut through an inch/25mm, many less. You can get longer ones but if you’re cutting wood or harder, deflection can be an issue. If you’re cutting something soft like foam, then maybe.
Where the extra depth is more likely to be useful is with thick stock, not that you’re cutting all the way through it.
Having more Z sounds like a good idea on paper, but reality contradicts it.
Simply put, it is additional complication that few people actually need.
Cutting sheet goods, a drop table is only a chance to have a misalignment between the machine and and the spoilboard.
You guys almost have me convinced to stop asking questions. Almost…
I see the point about the challenges of working with thick stock and long bits, and most of my projects will involve thin stock, but why not just build in a manner that CAN take advantage of the full Z travel, but then just operate with the router at the lower range of travel the majority of the time?
Thanks!
I should add that my current table plan involves unistrut for the Y-rails, and the height I set them relative to spoilboard is easily modified (before I build).
Thanks!
Keep asking questions if you have them. Doing this is probably fine and isn’t breaking any hard rules. Just don’t want to go too far so you can’t reach the bottom. It’s just very common that people try and cover every possible situation and then incorporate things they’ll never use. I myself certainly fell into the trap of overcomplicating things. Typically, a drop table would add some cost.
You need to home the Z access which means it will have to travel further. And then you have to probe further, although you can jog part of that to make it faster. So there is a bit of a manageable time factor.
I’m not sure what effect that can have on rigidity.
You need to home the Z access which means it will have to travel further. And then you have to probe further, although you can jog part of that to make it faster. So there is a bit of a manageable time factor.
Does the typical workflow require hitting the z-stop at the top of the travel during startup, or can you use the touchplate and avoid the extra time to travel to the top of Z?
Also, is there a generally understood measurement of the “bottom of collet” position for one of the typically recommended routers relative to the “bottom of roller bearing” on the bottom of the YZ plate at both the uppermost and lowermost extent of Z-travel? That measurement would really help me visualize these relationships.
Thanks!
Yes. This is how you home the machine and ensure the beam is level. It only takes a few seconds and it very much worth the time spent
I did build with a drop table, but I don’t use it much with the spindle (actually can’t remember the last time.) I do use it with laser projects and a 4th axis.
I agree with the sentiments here. If you’re building full size, then just make sure it can handle the sheet goods you’re going to cut. If you think you’re going to do the occasional flattening of a live-edge slab or something then you might need the drop section.
I just cover my drop section with spoilboard most of the time. I remove the top spoilboard when I want to access the increased depth.
Hmm. It still feels like the default build arrangement essentially buries half of the available z travel into the bed. The arguments I’ve latched onto is that there would be extra time required to home z at startup, the table is a little more complicated, and that I probably won’t need that much z travel anyway.
I can see that these are compelling arguments, but I’m struggling. I have my materials to start building my table and probably just need to get off the keyboard and start making sawdust
Thanks for all of the feedback!
Don’t do that.
If you understand why, you better understand your own machine, and sometimes why the common solution won’t handle your specific use case. nobody is saying “that’s a dumb question”. Speaking for myself at least, I just try to answer the question.
The answer here lies in the design of the LowRider. The machine is at its most stable and rigid when it is at its lowest cut height. Traditional gantry machines, or machines like the Primo are most stable/rigid at their highest points. The lower you go the less stable it is, so the idea is to have as little Z as possible, and try to do the cutting as high as possible. The LowRider is stable at its lowest point. Therefore, you want to make sure that the load happens as low to the table as you can.
Drop tables allow you to cut thicker material, with the machine low. That’s their primary advantage with a LowRider. Using the full 100mm of Z isn’t very common. I don’t have cutting bits that tall. I have a couple of them that are in excess of 50mm, but only a few. For those, the 100mm of Z is plenty. For the LR3, it had somewhat less, about 75mm of Z in stock form. I realized that for some of my use case 75mm wasn’t enough. I knew this because I’d run into that limitation om my Primo. For that reason, I modified mine (During the Beta stage) to have an additional 50mm of Z. the modifications that I did for that proved to be quite popular. I did not need them for the LR4, as the 100mm of Z that this design offers was adequate to my needs. (See the 50mm cutting bits I referenced earlier.) I don’t have 60mm bits which need the 120+mm of Z to fully utilize.
I could use a drop table with those high bits, but I’ve figured a work-around for now. I probably will use a drop table at some point, but the table I have will do the job for now.
Based on the geometry of the design, this makes sense, but doesn’t it also mean that if we are operating at the lowest point in the stock layout (without a drop table), that we aren’t taking full advantage of this rigidity? Why not allow the gantry to settle in even lower on the linear rails to more tightly couple to the table?
I have 10cm cutting height on my new machine and never use it. Thickest stock I’ve dealt with was 45mm and I had problems with stiffness because of the 80mm endmill.
Sorry - my tone was intended to be more like: “you’re winning me over with your suggestions” rather than “I’m frustrated and won’t continue to seek advice”. Darn internet and its inability to convey nuance and tone. 
The active and collaborative forum here is one of the reasons I chose this path to start my CNC journey…
A longer endmill, especially at 1/8” or 3mm diameter in itself will get more flexible, deflect more at the same twist in the core/beam due to the longer lever AND exert more torsion on the spindle, core and beam.
So basically you’d want the table dropped enough to cut a few mm into the spoil board with the shortest endmill you’ll normally use for profiling.
Which is basically “not a all”
Addendum: my table is getting raised rails, but that’s more due to the fact that my tables also has a raised spoilboard.
This was also my thinking when I built my table, but the “why not” is that it requires a longer endmill. Longer endmill means more deflection and longer lever arm against the core, so you don’t really get an advantage.
Also in stock form, it cuts low enough that it doesn’t really matter in practice. Using rough numbers to make the example easier to see: in stock form, you’re cutting at like 85% of the lowest possible Z value. With elevator plates, you’ll cut at like 95% of the lowest possible Z value.
So yes the machine is more rigid the lower it is, but does that extra 10% of the lowest possible Z really matter IRL? Not really 
even less so when you have a longer endmill to allow the machine to be lower, it may actually be a disadvantage.
Again I had all the same thoughts you did, tried it myself, and found this stuff out experimentally. while I don’t recommend elevator plates in general, I absolutely do recommend experimenting yourself and seeing what works for you! That’s (at least) half the fun of this whole thing anyways 
To help me visualize this, can anyone say what the typical height from bottom of collet to top of spoilboard would be with the core at zmax position assuming the top of spoilboard is even with the top of the rails that the YZ plates ride on?
Thanks!
Roughly 100-110mm.
Alright. I’m moving on. No full-time drop table.
But one last question… I currently have my table designed to level the top of the uni-strut with the top of 0.75” MDF spoilboard. That detail requires a secondary notch cut in my cross-rails to level things up.
The notch is 10mm deep in Z. Can I skip this notch and just build with the top of rails ~10mm above the spoilboard? I’m assuming “yes”, but just wanted a confirmation before I start cutting…
Thanks!
Notched version :
Un-notched version
