New Large Table Build in Houston, TX (Build Log)

[anitel]

OK. Here's my cnc table build. I've been watching this forum for years and lusting after a table like you guys have! Now it's my turn to try my hand at CNC.

Table will have an 84" x 102" cutting area as I need to cut out items that are large. Most cutting will be 1/4" and 3/8" material. I've studied all the plans but won't be following them... prefer to do things my own way and pick and choose features that fit my goals.

I've got some time over the holidays so I'm hoping to really push through this build.

I'm thinking about using hobbycnc.com stepper motors and driver kit. Anybody want to comment on the hobbycnc products?

I'm still not sure whether I'll be setting it up for plasma or torch.... maybe I'll just make room for both. I've got a Thermal Dynamics 38xl but it's on my **** list as it is just too small for my needs.

I want to thank all of you for going before me and sharing your builds. I never would have dreamed I could build something like this without your example.

Thomas

[lamicron]

Hi Anitel, Ithink you'll have to go higher in motors and drivers for that size of machine, because of the weigth of the gantry anbd the innercia forces. My table is a 4' x 8' , used 495 oz motors (nema 23) many people in the forum said that power is not enough, then i'll get 1.200 oz or higher steppers.
Good look on your project,

[anitel]

Ok. Here are some pics of the table. I'm going to try to build the gantry as light as possible so that normal size motors will work. If necessary I can fab the gantry in aluminum. Thanks for the comments Iamicron....

Gantry, bearings, etc work begins today.





Thomas

[millman52]

I really would agree with lamicron in the fact that 305 oz in motors will most likely not be adequate for your gantry especially for the speeds needed for thin gauge plasma cutting. The rating on stepper motors is holding torque at rest. The faster the motors turn the less torque they have. The Steppers also use this torque as the brake. Once the gantry of at least a couple hunderd # by the time you add all wireing, Z axis cable carriers etc. is moving & your program asks for a rapid movement change such as a 90 degree corner. I think the inertia of the gantry moving @ say 30-40 IPM will "push" the small steppers beyond their ability to stop it instantly for a 90 degree corner.

I would think you will need 700-800 oz/in motors for your gantry configured in a master/slave arrangement.

If you can calculate the apx total weight of your gantry, allow enough to overcome friction of your X axis guide rails, & the speeds you want to achieve for rapid movement between cut processes or parts. there are people on this board that would be willing to help you calculate just how much motor/driver you really need.

I have a 5' wide cutting capacity table (little over 6' actual width) gantry. It's built from steel but as light as I thought was still rigid enough to do the job. I used 740 oz motors master/slave arrangement on it. It might be a bit more than I really need but I didn't want a "do over" because trying to save $300-$400 dollars on initial cost. On a table that will make me thousands of $ in the first year of operation.

[DSL PWR]

That table looks stout. Just make sure you mount the slats on an angle. Putting them on an angle will greatly reduce the chance of welding the part to a slat as you are cutting. Ah.. very little chance of that happening you say, well let me tell you the odds are better than one would think...

Now this is just a question, but why do most people make the cut surface so high off the ground? My cut surface is about 12" off the ground, with an air bladder water table. This makes life so much easier when loading plate, and removing parts.

[lamicron]

That is a good observation, I made mine 30 inches high, and now i can see that is not easy to upload the plates at that heigth, also about using less material for the legs,

[anitel]

I know what you mean on height :-) I kept thinking don't make it too high, don't make it too high... it's about 40" high to the cutting surface ... oh well. it's no big deal for me as I will always be using a forklift to load the table. Also I kind of like to be able to use the table for a work surface when not cutting.

[anitel]

I've made some progress on the build but not nearly what I had hoped... isn't that how it goes? I got the x axis guides installed (3" x 1/4" flat bar) and the guide carrage with bearings built. Bearings came from skateboard wheels bought at Target (seen on other tables here at cnczone). Looks like it will work good but the moment of truth is welding the gantry together straight and true.
It's been an educational project so far. I'm pretty good with a welder and chop saw but I'm not used to thinking about blade thickness, heat soak, all the details for higher precision work.
Also bought the hobbycnc.com stepper kit with 305 oz motors.... I appreciate all the comments on motor size but I'm hopefull they will work as I only need about 10 IPM. If they are too small I'll use them on my bridgeport kneemill or liquidate on ebay.

Thanks for the comments.... more progress to come this week (I hope).

Thomas

[mxtras]

Looks good so far! (I think.....)

What's up with the light down there in Texas? Is it green like that all the time or are you shooting in Night Vision? Your pics are a bit difficult to see.

Scott

[anitel]

Sorry about the light and pics. The lighting in my shop is those High Pressure Sodium lamps or something like that... cameras don't like them but it looks normal in person. Also using my iPhone camera which is marginal at best but I am lazy. :-) More pics coming soon....

thomas

[anitel]

I've got the frame for the gantry built and installed. It slides easy with just the slightest push of a finger. Does want to rack a little so I'm glad that I will be driving it with a stepper motor on each side. The track will need to be kept clean otherwise it doesn't roll well. Next time I may turn the "track on it's side so that it doesn't have the large surface area to collect dust and debris.

I was very concerned about my table being straight (parallel down both main rails). Be it luck or skill I ended up with only 3/16" variance in the width of the table from one end to the other. The bearings don't seem to mind this at all. Table is also flat within about 1/16". Very important to me as I won't have THC at least for now.

I've ordered timing belt and gears from ebay to use as my drive. I was going to go with chain and maybe I should have but I decided timing belt would be easier to work with. Turned out to be kind of pricey ($300) as I need so much for this large table. Over 60ft of belt and 6 pulley/gears just for x and y axis' :-)

[millman52]

Thomas,

Where's the progress report. Have you became stalled on your project?