LR 4: Too Small for Strut Plates

LowRider CNC Advice
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Long story short, I built a MPCNC Primo about 2 years ago. For some good and bad reason, I decided to convert it to LR4 since it was released.

Unfortunately, my space doesn’t allow me to make a huge surface. The cutting area is around 42" x 24". And even worse, for it to be pleasant to use, the X-axis needs to be for 42". So, the Strut Plates would be about 48-49". Therefore, it is impossible to produce them on my setup using simple techniques.

So, I started looking for solutions. I began by making a “temporary” version on the floor of my workshop, large enough to produce the Strut Plates. It works… but it’s really ugly to do. You have to set up a temporary rig, laying on the ground. Drill holes in your floor. Etc. And in the end, if you have to redo them, you have to dismantle your permanent setup to make a new temporary one. It’s a really bad idea.

I saw some video posts showing how to do it in 2 cuts by inserting a dowel as a reference point. Ok. That probably works. But, we’re starting to use more advanced techniques. A beginner who wants to build the machine with this constraint might not manage. This makes the machine less accessible, which I think is a shame.

So I wondered why the machine isn’t capable of producing its Strut Plates, regardless of the dimensions, by design.

I thought of 2 options. The first: separate the Strut Plates into 2 parts and make a joint in the middle. By merging two braces together, like this:

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We could fix the two pieces and end up with a comparable structure. But would making the Strut Plates in two parts weaken the machine?

The other option I considered is making mega Min and Max braces that would start within the cutting area. Something like this:

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So by design, the Strut Plates would always be shorter than the X-axis. I really like this solution! It seems simple and would make the machine even more versatile… However, would this affect the structure or rigidity intended in the design?

But above all, I wonder why Ryan didn’t plan for this? Is it a choice because it would interfere with the machine’s structure, or was it an oversight?

What do you think? Am I off-track with my solutions? Do you have any other suggestions to offer? Depending on your feedback and suggestions, I will decide how to proceed with the build.

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Why dont you just make it the 24" side and the Y axis the longer side: edit your cam software size/orientation accordingly.

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The machine will be much, much more rigid and capable with the X being 24", rather than Y.

Maybe some detail as to why you think it will be unpleasant this way?

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It’s a matter of space. If I set the X-axis to 24", the front of the machine will not be accessible, or at least it will be difficult to reach.

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Yes, it’s the video I was mentioning (without having the URL). I think it’s a more advanced technique. In fact, I haven’t figured out how to generate the G-codes to achieve that.

So, if the machine could be autonomous in cutting the Strut Plates, no matter the dimensions, that would be great. You print everything, use the tool to generate the G-code, and bingo, everything works.

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I don’t quite understand these comments.

The machine is designed for the short axis to be the X axis. This is the design of almost every CNC machine I’ve seen.

It’s that way for stability and rigidity.

If the machine is built as designed, it is certainly capable of producing it’s own strut plates, as nearly everyone here has done.

If you decide to build it differently, then of course you can’t blame the design.

There are still options to get it cut, however, you just will have to use more advanced techniques.

In that case, if those techniques are too advanced, then I would contend that this is a good reason not to change the intended design.

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A beginner should stick with the recommended configuration of X being the shorter axis.

Making it the way Ryan has designed it braces are used initially and the machine can cut its own strut plates.

To be honest the strut plates can be cut and drilled without the use of a cnc at all using a track saw, table saw, bandsaw or the panel saw at your local DIY store.

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Okay. To be honest, I didn’t expect to question the design of the machine this much. My initial reasoning was that the machine is designed to easily handle 48" x 96". 42" is below 48", so it should work just fine.

Unfortunately, due to space constraints (as I mentioned earlier), if I want the machine to be pleasant to use, I need to stick to that direction. So for now, settling for 24" in the Y axis seemed like a good idea. That said, I’m not ruling out that one day, I might find space to expand the Y if it becomes a necessity.

If we look at the question from another angle, what’s the problem with having a larger X than Y as long as we stay within reasonable machine dimensions? If it allows us to rotate it so that it’s easier to use in our environment?

That being said, if it’s indeed Ryan’s choice to impose a smaller X than Y in our builds, I fully accept that. I’ll do my best to improve my knowledge and live with the fact that I didn’t stick to the machine’s original design.

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I just want to mention here, my machine is currently 30" x 60". I did originally create the struts on a temporary setup on two sawhorses. You mentioned drilling the floor, but I can’t really imagine a situation where you’d need to drill the floor to get decent struts cut (but then again, my imagination isn’t that good.)

I set two sawhorses up, and 3 2x4 boards that I had trimmed to be straighter and the same size. Across that I laid a 1/2" piece of MDF (note here - I would use 3/4 if I did it again.) From there it’s attaching the rail and belts and squaring. Even that rickety setup produced good results for this purpose. (I did cut slow. And this was sacrificial, I just cut into that MDF, no spoil board.)

I considered keeping that piece of MDF for future use, but then I snapped out of it and saw material for another project instead.

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Well here’s the thing, and dont take this as I’m trying to be mean.

Whenever anything is designed, its designed to work in is stock form. As soon as you change a parameter, it’s not the designs responsibility to work, its yours to find a way to make it work.

I started with an oversized primo, and then moved to an undersized lr3 with an oversized Z and now an undersized lr4. It’s a better design and i don’t have a need for full sheets, so my cut size is 28x34 iirc. That required mod to the plate and it’s not a big deal to do it.

To keep things working easy for you, you can take some extra steps. Build full size temporarily, cut the plate, break down and rebuild to the final size.

See if anyone here is local and can cut it for you, nothing says you can’t get help in your build.

Google “makerspace” near you. See if they have cnc or laser big enough to do the job.

Or just cut it in 2 pieces and then glue it together, you’ll be nice and solid.

There’s options to make it work.

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Sawhorses with 2x4 and mdf sheet is a good idea.

I have used my floor has a base/table for the machine and add a spoil board a little bit bigger than the Strut Plate to cut it. I have used the full EMT pipe lenght (10’) for that. So I didn’t need to cut the pipe for that particular step. I have a lot of spare belt to do that. That was my temporary settup to cut it.

My initial question was to see if there is a relatively simple way to make the strut plates on an ‘inverted’ construction.

From what I can see, I’m not the only one with this kind of setup. I’m wondering why this wasn’t planned from the beginning. If there’s a good reason, it would be good to know and understand what we’re getting into if we go off on our own! :smiley:

That said, Ryan designed an incredible machine!!! It’s excellent work!

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I still don’t understand the confusion.

The easiest and most normal way, is when the Y is longer than the X. Cutting struts are easy.

If you choose to make your X longer than the Y, your options are

  • Cut the strut plates diagonal within the area, if they fit. This wastes more material though, and the machine is not as rigid in the middle with only temp strut plates on
  • Tile it with the dowel method as mentioned above.
  • temporarily bootstrap a longer Y on the ground, etc. to cut the plates.
  • Use a different machine to get them cut

I’m not sure what better options there can be?

The X gantry is longer than the X cut area. There’s no way around that. You can’t get your bit all the way to the extremes of X where the ends of the strut plate are.

You are asking your machine to cut something that is longer than the max of any of your working area dimensions.

You have to do extra work for that

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The simple answer is: because that’s not how it was designed to be used.

It states clearly in the docs:

“Width (X axis or “Beam”) should always be the shorter axis.”

So you are intending to use it against how it was designed to be used.

You are, of course, welcome to do that, but you must deal with the consequences of that. The first such consequence, is that it is harder to make your own strut plates.

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OK. I understand. Once the first consequence is over, what are the other problems we might encounter? My lack of experience with CNCs probably doesn’t allow me to foresee what comes next and fully understand the impacts of my choice…

In fact, what I don’t understand is the importance of having a shorter X than Y if we are within the machine’s limits. Once the Strut Plates are done… I don’t see what difference that would make.

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I have a wider X than Y as well, I made the video of flipping the plates. I did that because it is easier for me as well and I have the ability to make Y longer if I wanted to. But: I know how to flip a cut. It took a few tries with other projects, but once you have it figured out it’s pretty easy to do.
The wider X is obviously also not as rigid as a shorter X. The longer a beam, the less rigid it is. One might not notice it, but it is definitely there, not only on X but in Y as well because a longer beam twists more easily. You have to know your way around the limits of your machine to not mess it up too much.

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A big one will be that the assumptions of most CAD and CAM software will be different than your machine layout, so you’ll have to always be working around that.

Not the worst of problems, but one you’ll need to deal with.

You’ll also have to modify the default config for whatever controller you use. Again, not a big problem but it does mean you’ll forever be correcting this if/when you update control software or controllers.

None of this is the end of the world, and perhaps for your particular setup it makes sense to do.

Pictures and descriptions of your work space and work flow would help us understand and help you better.

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OH!..

you can also have some delivered :slight_smile:

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Somepne always has to do things the hard way…

Have you checked if the strut will fit along a diagonal? The diagonal should be a bit over 48" from 42×24.

And as mentioned, a tablesaw or tracksaw and a drill is capable of making struts. Maybe you don’t get the fancy wings on the plates, but that is not a neccessity. It is a cosmetic “nice-to-have”.

We are trying to help you get up and running.

I will say that the X gantry being the shorter axis makes the machine much stiffer, and more capable. Even if you have to unhook the front belt to load and unload the machine, it is likely that you will be happier making the short axis the X in the long term.

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I do understand your reasoning. If the machine is designed for 4’ X, and I’m only changing Y (which doesn’t seem to impact rigidity), then are there concerns?

  • As MakerJim points out, there will be a few small config things that will be nagging friction when updating software. Potentially on both the firmware, and the CAM side.
  • You’ll also only get the rigidity that the guys cutting full sheet, 3/4" ply are getting (well, close anyway). If you’re doing smaller, more detailed work, you may want more rigidity. But this is highly dependent on the projects you are planning.
  • Speed - one of the things I’ve learned over the years on this forum is that rigidity can also mean faster completion of the project. I’m using speed here to refer to your own throughput of cool things made. A more rigid machine can move faster, more consistently, with greater depth of cut, and more material removal.

It’s tough when you are new to CNC. I didn’t ever think speed was important. But when I was working in my garage, a cabinet guy drove by and asked me if I wanted to start cutting doors for him. He’s been bugging me by text for several months now. He sees it as an opportunity for some really custom work for his customers. Unfortunately I’ve declined that work for now. My machine isn’t optimized, and I’d spend all my free time watching the slow cuts eat away my weekends.

Since you don’t know where your CNC journey will take you, it’s hard to help with the modifications you’re making. But just to help with interpretation of some of the things you might read on the forums:

If you never try your machine with the shorter X, you’d never know how fast or deep you could cut, so you’d never really have all the data on the tradeoff. (This may not matter if you simply can’t run it in that configuration, so it may not be relevant at all.)

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