Plasma in Florida

[Jimmystractor]

1st- Great site. I've spent about 40 hours reading over the last 2 weeks. Although the information is very useful, I thinking this may be overkill for a plasma cutter. I've seen the UNCSA table on Youtube, so I know a few have made them. I thought about using lighter gauge metal on the gantry, Y car and Z with mid 200oz/in range NEMA 23 steppers and maybe a 17 to move the very light torch on the Z. I know if I try to change 1 or 2 things it effects other things and before I know it I'm making 20 little changes here and there. As far as I know, there is not a site like this for a plasma CNC table. I think time would be about the same, but it looks like cost could almost be cut in half. My other thought was to just ignore my(and others) better judgment, dive in and start making changes and see where it gets me. I'd love it if there were a set of DXFs specific for plasma with smaller steppers, BUT I understand that this site is made for those wanting a DIY router table. I don't mind being a guinea pig and taking the risk. I know someone did a chain drive, but I think this might be a little more to deal with as far as changes go. Of course, I could always just spend the extra $600 or so on the gantry and leave everything as it is. I was only thinking of future builders of plasma tables and multiplying the savings- That is the only way I can justify taking the extra time to figure things out. Any thoughts?

[smreish]

Jimmy.
SInce I was part of the UNCSA build we pondered fabricating the lighter, less powered table. In the end, the addition of the DUAL z-slide made the table useful for both CNC operations (plasma and routing), thus getting a better value.

The cost difference is truly insignificant if you go with ungeared NEMA 34 steppers and the GECKO 540 module (those together can save you about (600 to 800 dollars) and use mechanical tube for the frame instead of structural shapes.
Keep researching you use - you may find that a variant of the true MM is really what you want.

The biggest expensive cost in the PLASMA table was the THC unit. If you want, you can go ultra cheap and use a standard GECKO/pmdx style setup with a contact tip for torch control. If you want all the features of a great torch (height control, arc control, etc...) you will pay a pretty penny for that controller.

Good luck with your choices.

Sean

[Jimmystractor]

Thanks so much for the quick response. I really like the idea of sending ~$500 to get all the cut parts I need for the main structure, That alone would save a good deal of time. I just can't imagine ever using it for routing. I guesstimated around $500 on the high side for THC, but figured on adding that last. I'm not trying to get laughed off the forum, but I have to ask about this- http://cgi.ebay.com/270681060017 I'm starting off slow and it might be awhile before I would be using the table more than a few hours a week. If I could get 100hrs out of the electronics and my cheap plasma cutter I would be happy. If I got 100 hrs of cutting in, I'd have more than enough to get the geckos and vextas.

[danilom]

Look at the data of the motors, they have a low current rating and so usable with this driver but the critical matter is Voltage to use, motors have Phase Inductance (mH) 15mH and its too much, to use them at any reasonable speeds you would need more than 40V that is maximum for TB6560.

It would be usable maybe but there are no guarantees.

[Jimmystractor]

Are you familiar with the TB6560? I guess that is the mosfet model number? I know when I got my cheap plasma cutter, I felt ok knowing that it had toshiba mosfets. I was thinking in the same line as what you mentioned, but in a different way. I figured a max of 80 watts for each motor- 160 watts for both. Going with 80% that left me with about 1/6 HP to move a rather heavy gantry. 878 oz/in does not seem possible coming out a $72(shipped from Hong Kong) board that is supposed to control 4 878oz/in NEMA 34 motors. Aside from that, My thoughts were to get me up and running as quickly as possible with the smallest investment possible. If things go as planned, I would be able to upgrade the drive system, power source and add height control in a short time. I figured direct drive would give me more than enough speed if I used 20 tooth pinions on a 20 pitch rack, Since inertia of the gantry is all I need to overcome. I figured a resolution of .005" from what I've read- That would work for my needs. I'm still foggy on what micro stepping is, but it seems I might pick up some resolution there even though .005 would be OK. My main concern with the low priced generic drive system was if it would match the specs they claim and if it would last a reasonable amount of time. I've searched eBay, longs, cheap and other words and can't find any info here- I'm guessing that everyone else builds their mechmate to higher standards from the start. My biggest hurdle with building a mechmate is the actual drive system. The first thing I want to do is get the drives set up on my kitchen table(as suggested here) and get things moving with EMC2. From what I've read here, it is starting to seem like I have a good chance at accomplishing that. I'm going to try and educate myself on mH and micro steps now(gotta love the internet). Thanks for the input.

[Richards]

May I suggest that for your first design that you choose stepper drivers and stepper motors that others are using? Playing with electronics will get expensive. Trust me. I've got thousands of dollars tied up in my test benches.

You mentioned that you're 'foggy' on the concept of micro-stepping. Don't worry about that, we've all been there and we've all scratched our heads wondering what it was all about. Geckodrive's microstepping works. the Geckodrives use 10:1 microstepping, meaning that instead of requiring 200 steps to turn the shaft one revolution, you'll need to send 2,000 steps. That gives much finer resolution, but it requires a faster pulse generator. Fortunately, at the speeds that are required for a CNC machine, software that can generate 25,000 to 45,000 steps per second works just fine.

Also realize that even though a stepper motor can easily give you 5 thousandths resolution, the 'slop' in the system may give you less. The math shows that you could use a 1.25" pitch diameter pinion gear and Geckodrive 10:1 stepper drivers and get 0.00196" movement per step.

((1.25" X PI) / 2000 steps per revolution) = 0.00196"

That's what the math says; however, getting that kind of resolution mechanically would require total mechanical perfection. No slop. No backlash. No deviation in the rack or the gears. Perfect tension between the pinion and the rack at all times. In other words, you'd better start with a full head of hair, because you'll be tearing out large patches as you try to solve each problem.

Good luck. Keep us informed.

[Jimmystractor]

I was lucky enough to get a good look at Nils very nice MechMate on Tuesday and I thank him for taking the time with me.

http://i195.photobucket.com/albums/z5/jwilson4940/steeldeal.jpg

Look what I missed out on. Based on dimensions, I figured about 140lbs. I'm getting $.12 for scrap, so he was just about giving it away. It turns out that I'll be getting the ~500lbs for my table for the equivalent of $50. Last year on Craigslist I got 12 racks of republic shelving along with a bucket of clips for $100 I'm trading half of that(about 250lbs) for the structural steel I need to make my table- That does not include the gantry that will be made later on.

I've decided to make the table to MM specs all the way up to the rails and take my chances on the gantry with my own design- worse case I'm out $50 in steel and no more than $ 50 in electrical. I'm getting one of those cheap $270 shipped NEMA 23 CNC kits on eBay to drive my less than 40lb gantry.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180635010677
They usually go without a bid. If it doesn't work out for me I can resell for a quick $225 on eBay.

Once I have the extra $2500 pr so, I'll get the laser parts and propper electronics to have aMM spec table.

[Jimmystractor]

http://i195.photobucket.com/albums/z5/jwilson4940/nicerack.jpg
I got this at the space store in Orlando. I thought it was .8 module, but when I got home and measured it it was 32P. I expect it will work well for my plasma needs.

[sailfl]

Ahhh! Skycraft the store everyone wishes was in there town.

[Regnar]

Jim, I hope you picked up your wire while your where there. If not plan on making another trip back. I love that store. Next time Im looking for a T-shirt.

[Jimmystractor]

I think the rack will work well for my needs. The 7 pieces of 32P were $10 each. I figured 28 feet would be enough for an 8x4 table. I thought the rack and pinions would put me over $500. After picking up the rack for $74 and change, I think I have a good chance at staying under $500. I sold my lathe last week- http://cgi.ebay.com/230591356479 If I want to keep the guide bearings under $15 I'll need to find a new one soon. There are tons of 32P pinions on eBay since they are a popular size with the RC cars. I'm pretty excited.

I've got the wire I'll be using. If I decide to get fancy:
http://cgi.ebay.com/170397129061
http://cgi.ebay.com/120687346657
The only thing that I'm not sure about is the cable chain- I may be looking at $65 there.
They also had 2 axis cnc kits for $64.95. Came with an allego dual driver alot like this one:
http://www.allegromicro.com/en/Products/Part_Numbers/3977/index.asp
And 2 Vexta PK266-02A steppers. wouldn't work for me but I thought it was notable.

[sailfl]

Jimmy

Most of us are using shielded cable, the stuff you posted is not shielded. I hope you have good results with it.

[Jimmystractor]

Probably everyone is using shielded. I'm sure I'll need to do that too. Thanks for pointing that out. Do you think $62 is a good price for 100'? BTW, You are an early riser.

[sailfl]

Jimmy,

I think any thing under a $1 a foot is a good price.

Early bird.....

[MetalHead]

I have shielded 4 core if you need wire. I also have 8 Core. Let me know how many feet you need. I also have a bunch of other stuff.

[PEU]

Ahhh! Skycraft the store everyone wishes was in there town.

Thanks to Nils I visited that store too :)

[Jimmystractor]

I got another piece of the puzzle today:
http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSu7zK1fslxtUmx_v5Yt9ev7qe 17zHvTSevTSeSSSSSS--&fn=VHB%20Design%20Guide%20Low%20Res.pdf
I ordered some 3M 4941 tape. I'll be using it to attach the rack gear and maybe a few other things.