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Learning how to build Lotus Seven replicas...together!
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PostPosted: May 8, 2019, 12:49 pm 
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I am finally breaking down and going to build a CNC Plasma Table. I have had to build and design far too many times with more complexity that could have been accomplished easily with a sheet metal part. I have most of the mechanical design done in SolidWorks for the table. But I am also mostly lost on the electronics side. Which is putting a heavy slow down on the project due to electronic component mounting locations and what’s needed to finish the project.

So, I thought I would throw this out there. If anyone, or a group of people, here are interested in a joint design that we would share EVERYTHING with the community, we could make this happen. I would put together a full 3d model with a bill of materials, drawings for modified/machined parts, and a top-level mechanical assembly drawing package.

I would share my model to personal willing to add electronic components needed. I could (if needed) create the brackets and mounting points if they were positioned in the correct locations in model space.

Someone could then workout a plug and play type control system with all that would be needed. Or break up the work as needed to willing individuals.

When completed. I would like it to be free and accessible to everyone and be able to be built and assembled by a true novice (Maybe loaded to Grab CAD). I have learned so much from this site as well as many others. I would like to be able to give back with this extremely helpful machine.

If you are interested in joining in this project with me, please let me know!

I took my inspiration from this:

https://www.instructables.com/id/CNC-Plasma-Table/

But I want to take it further with (hopefully) a better design where one does not need to have a company cut and form the parts (Which can be VERY costly). But rather use mostly extruded aluminum. All bolt together with no welding. And a dummy proof (or as close to possible) wiring set up that anyone can handle. Also much more detailed build instructions. Especially on the electronic side. And ideally build cost around $1000.

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PostPosted: May 8, 2019, 1:09 pm 
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I had some stainless panels cut via CNC plasma and wasn't impressed. The cut edges were very hard and crusty, and had to be ground off before welding, which made the parts undersized. Not saying that it won't do what you want, but it's something to be aware of. Maybe mild steel isn't as bad.

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PostPosted: May 8, 2019, 3:06 pm 
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KB58 wrote:
I had some stainless panels cut via CNC plasma and wasn't impressed. The cut edges were very hard and crusty, and had to be ground off before welding, which made the parts undersized. Not saying that it won't do what you want, but it's something to be aware of. Maybe mild steel isn't as bad.


That's all operator based like most issues are. I work as an Engineer for a company that manufactures sheetmetal parts. If A part is undersized and the DXF or flat pattern is correct. The programming of the machine wasn't calibrated correctly.

Either way, a CNC plasma cutter is an extremely valuable machine compared to the actual cost to purchase or build one. I just had a thought that a joint design/build would be pretty fun experiment. If no one wants to join in, I am still working on this whenever I have a few moments to do so. I will still load it to GrabCAD with all the information for anyone to download and build.

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PostPosted: May 8, 2019, 6:37 pm 
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Sen2two, great concept and offer. Wish I had the electronics background to team up with you. Hopefully folks on the forum can provide those skills. Please keep posting your progress. I'll be following.

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PostPosted: May 9, 2019, 11:27 am 
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I'm following as well!

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PostPosted: May 9, 2019, 11:31 am 
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Take a look at Mach3 to control the motion with stepper motors. I have this software on several custom machines and its super easy to implement. You do need a parallel port or USB converter as it needs a P-Port interface to your motor controller. I used a Gecko G540 to drive 4 axes. It has 4 inputs for limit switches. Lots of options here. I do lots of electronics for work, but you dont need anything beyond the very basics (can you change a light switch?...maybe solder a few wires) to set this up.

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PostPosted: May 15, 2019, 8:48 pm 
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Few pics of how it sits right now. Mostly designed with 2040 Aluminum extrusion and off the shelf pulleys, guides, and belts. There are a few parts that would need to be machined or cut out on a plasma, water jet, or laser. But for those parts, I plan to make full mechanical drawings for those that have the ability to machine them. Or take the parts to a machine shop to be made.

Not the best images. And it is far from complete. But the main design is there. What is holding me currently is not knowing where (or if) and electrical components need to be mounted. Such as the limit switches which currently have modeled and sitting there. But not really mounted just yet.

You do not need to ability to use SolidWorks to help out and join the project. With a list of CNC control parts and other electrical parts needed, I would be able to model those parts and place them as needed into the model. even mock up wire placement.

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PostPosted: May 16, 2019, 8:24 am 
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What are your plans for a Z axis?

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PostPosted: May 16, 2019, 9:10 am 
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Do you know what kind of speeds you plan to run? I see you have stepper motors in your model. At 200 steps/revolution, you can figure out the linear resolution. Microstepping is also a possibility...all depends on your drive controller. It would also make some sense to work out how much torque you need so that you can size the motor current and drive. I am guessing you will have some sort of gantry to support the air hose and cable. Anyway, you want enough torque to insure you don't skip steps as there is no position encoder.

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PostPosted: May 16, 2019, 9:26 am 
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My experience with 2040 rail is that it's difficult to keep the moving rails from binding. My last project (long long ago) was for a rotating and sliding multi position welding frame. I had to end up adding pillow block roller bearings to keep everything moving /not binding.

You might be fine just making the bearing carriage longer to prevent this. I didn't have packing space for a high distance between the rollers.

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PostPosted: May 16, 2019, 4:28 pm 
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I'd go for servos instead of steppers. More expensive, but cleaner motion profile, less noise, and no missed step shenanigans.

You can get a used 4 axis setup with Samsung drives off ebay for ~$1K from South Korea, and that gives you the option to do pipe end notching with the 4th axis.

I'm doing a large format 3D printer build with the 200W kit, and I'm kicking myself for not getting the 400W one.


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