[FERNYER]

Hello everyone,

I'm in the very beginning of a custom build and was looking for opinions on the basic design I have started with. This machine will need to cut large rectangles out of thin film. (window tint) The rectangles can be small (10x15 inches), and large (40x70 inches), and everything in between. Because of the large sizes I will need it to cut as square as possible. Tolerances of height and width are around +- 1/32 inch (.031).

My background... I'm a software guy and have never worked on a "tangible" project like this, certainly not an engineer. Going to use Arduino for control and have spent time working on controlling steppers and other various motors with an Arduino.

So far we've decided to build the frame and gantry out of 80/20 t slot and linear bearings. The bed of the table will be 8 x 4 foot sheets of HDPE plastic (plastic cutting board material) made into a box with a shop vac hooked up underneath, small holes drilled into top of bed to hold the film into place when the shop vac is on. We will use a round cutting blade wheel and haven't figured out the best way to hold the blade. We might just look into retrofitting a hand held Fiskars rotary cutter but are certainly open to suggestions. The cutter will be connected to a 90 degree servo when changing from height and width cuts.

My main concerns I am looking for help on... the steppers and lead screws. Do you think a Nema 34 stepper will be strong enough to turn an 8 foot lead screw? I was going to use 2 Nema 34 steppers for the x and 1 Nema 34 for the y. The x has 8 foot screws and the y has a 4 foot. The z would just be a 2 foot screw and I was thinking a Nema 23 for that one to save some $. There won't be a lot of travel on the z, just up and down enough to pick up the blade.

Also, I've never worked with lead screws before. Will an 8 foot long lead screw be able to span that distance without drooping? It will be held on both ends and we can park the gantry in the center to help support the length when not in use. I know I can choose different diameters of the lead screws to address this issue but my main concern is the 8 foot span possible with this design? Thoughts?

I uploaded a REALLY ROUGH drawing of what I have in mind. Obviously not to scale... just so you can see the basic design. Notice the 2 motors on the x axis... ok to do or bad idea? I've spent a lot of time online at different diy designs and could not find a CNC with two motors on one axis like this. My thoughts are that I can use two different screws to tweak the gantry it if it's cutting out of square. Plus two motors might help with any power issues moving the 4 foot wide gantry the 8 foot span. However I could see it possibly getting into a bind if not careful.

Those are my main concerns for now. We want to get the steppers and lead screws on the way soon but wanted some opinions before doing so. Do you guys see anything in our basic design that we should change before moving forward?

Thanks in advance!

[ger21]

Spend a month or two here doing research. Just about every machine here uses two screws to move the gantry.

If all you'll be cutting is film, then I'd use a belt drive. Nema 23 steppers should be more than enough.
And reduce the Z axis to about 3".
Your bearings on your gantry need to be spread out at least 12" apart. It'll bind with them that close together.

[FERNYER]

Ok, I'll spend some time looking into the belt drives and see how they work compared to lead screws. That might be much easier to build as well and keep from binding. Thanks!

[RicknBeachcrest]

As Gerry said take some time and do your homework on this forum. Try not to reinvent the wheel on your first build. If you don't see a build like you are planning, there probably is a good reason.

Take a look at this system. It uses belts and seems like a good fit for a low stress machine like your looking at.

OpenBuilds Part Store

[dmalicky]

Unless you really *want* to design, build, test, redesign, rebuild, etc, your own machine, I'd suggest just getting a kit, like from CNC Router Parts.

A classic CNC beginner mistake is to start ordering parts to "get the project going". This almost always results in the wrong parts. Only order parts after a lot of research (months) is done and your design is complete and sound (6+ months). Or get a complete machine kit, but do enough research (weeks or months) to be certain it will be the right kit for your needs.

For Arduino control, grbl is a good solution: https://github.com/grbl/grbl

[Bl@ckrat]

http://www.cnczone.com/forums/diy-cn...6-x-5-5-a.html

personally , id follow this thread for idea's and have a chat to the builder