How Big Should I Build My Table


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Thread: How Big Should I Build My Table

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    Default How Big Should I Build My Table

    Hello Everyone,

    I'm in the all too slow process of building a CNC Plasma table. Cash restraints, baby and toddler, and running my existing business don't make things happen fast. I've got a Hypertherm 1250 with hand torch, and a MP3000 torch height control system from CandCNC.
    I've just about completed the floating Z-axis. I'm using hard anodized aluminium rails with plastic composite linear bearings. I'm hoping as well as being corrosion proof the plasma dust won't clog them up because there's no oil or grease on them. I also made the leadscrew from stainless and made the leadscrew nut from a self lubricating plastic composite called Vesconite. My only concern with the alum. rails is that if any plasma spatter hits them will it stuff them up due to the much lower melting point. That will hurt if it does because they weren't cheap. I will be taking some precautions to try and prevent this happening.
    So now I'm getting close to starting the table build and I'm a bit undecided as to what size table to make. I'm in Melbourne, Australia. I've been told that standard size sheets of steel here are 2.4 x 1.2 metres then the next size up is 3.0 x 2.0 metres. It also crossed my mind that I could consider building a table which can take the full 2.4 x 1.2 as well as half of a 3x2, i.e. 1.5 x 2.0 So in effect a max. cutting area of 2.4 x 1.5
    Is it wise to take the attitude of something small can be cut on a big table but something big can't be cut on a small table. Then what about steel prices. Is it more economical to buy big sheets as opposed to smaller ones.
    I have a few of my own things I would like to cut out, none of them requiring a large table (at this point in time). However I would like to try and make a back yard dollar here and there too from being a cutting service. I'm not exactly expecting to quit my present work with what I'd make from doing plasma cutting. I realise there's a lot of high class plasma and laser setups out there operating professionally whereas at this point in time I'm just a back yarder with a basic plasma setup using just air. I imagine the only advantage I may have is lead time and maybe price. Someone I know had to wait 3 weeks to get some small brackets laser cut. He said that plasma would have been perfectly OK though. Would I significantly increase my chances of picking up some pocket money if I had the capabilities of the bigger table. Would businesses shy away from me due to me being a back yarder or would they be more interested in lead time and / or price providing the cut quality and accuracy were acceptable to them. I wouldn't dream of looking for any work before I'd confirmed the accuracy and cut quality were consistent.
    Regarding handling 3x2 sheets, I could set something up to take care of this, perhaps a small gantry crane on wheels or something to transfer the sheet straight off my trailer and onto the table.
    Any feedback is welcome guys. Am I making a mistake or being sensible thinking big.
    Also something I think a lot of people with this hobby would be wondering is where would they start looking for work (just pocket money remember at this point). I also have a 1.5m between centre lathe, Bridgeport style mill, 330 amp mig, decent size press, horizontal bandsaw, pedestal drill and a general assortment of tools. I'm an industrial sparky by trade but for the last ten years I've been into excavation and it hasn't been nice to me at all. So I'm trying to get out of it and do something where my heart is. At least in engineering you shouldn't have someone standing there watching you telling you how to operate your machinery.

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    There are a couple of considerations here. While it's true it's harder to cut big pieces with a smaller footprint CNC cutter, you have to consider that almost all the work you will have the opportunity to work with will be to cut parts/objects less than 1 meter square. There is just not a lot of projects out there were they need the accuracy and speed of a CNC cutter to cut out big shapes from full sheets. If you were a production shop and did lots of multipart cut jobs (lots of quantity of smaller parts) working with full sheets from a time perspective does make sense. A good portion of the cut time on a job is loading/unloading and setup. The small shop/ backyard guy seldom is faced with having to do those type jobs (and wring every penny out of each part to make a profit). In fact I would avoid those type of jobs. You will make a lot more money cutting one-off or small quantity jobs and a LOT more if you can offer quick turn on custom cuts or to do personalized decorative cuts. Doing production cutting and working for low wages takes the fun out of the CNC experience!

    Usually custom jobs fall into one of two categories: Moderate sized cut pieces of 750mm sqr or less or large jobs of several meters long. Good examples are the decorative cuts for gates and fences that can stretch over 5 meters wide. There it's done in smaller sections and welded to a supporting structure.

    There is a market (depending on where you are) for brackets and panels for off-road builders or motorcycle guys. Even then you find a lot of your opportunities are decorative in nature and smaller than 1 meter in size.

    You can usually get steel suppliers to cut sheets down. My metal supplier will make one cut for free so I simply have everything cut in half. A 5 X 10 becomes a 5 X 5 ft piece and fits my table. More common sized 4 X 8 sheets become 4 X 4. My need to cut bigger than that over the last 6 years and thousands of cuts can be counted on the fingers of my left hand and leave enough unused to pick my nose (:-).

    If you have the room for a big table the incremental expense is not a lot after the gantry weight gets above about 50 KG. Smaller than that allows you to use smaller motors, smaller drivers, smaller power supplies and lower cost electronics.

    On the other hand if you never use it the oversize is not of much value.

    It's hard to advise when your market is undefined and it's hard to define until you start cutting. I can tell you that I made a lot of money with a table that only cuts a little over 4 ft X 4ft The amount of money you would save in raw material by buying bigger sheets only makes a difference if you can get 100% usage out of the sheet when you put it on the table. It did not take me long to realize I did not want try and compete with production shops and do shift work to make money.

    There are some interesting nitch markets that you can explore. It's way better to have a line of products that you can fabricate and make them custom to the buyer. Examples : Decorative firescreens, large wallclocks, personalized outside markers, etc.

    You might pop over to our commercial cutting site at www.FourhilllsDesigns.com. You will find decorative cutting is seasonal but it's profitable.

    There are some samples of decorative patterns on our support CD with the MP3000 in CDR (CorelDraw) format. One is an "Old Motorcycle". Cut some out, clean and paint them and hang them up....you will get some interest. Drop me a line and ask me for the Decorative Clock master art. You can use it with CorelDraw to quickly create personalized wall clocks that use a simple $5 quartz movement and large hands and yields a product that sells well for $125.00 USD(18" size).

    One last bit of experience: The custom bracket guys (needing a few parts to build their rock-crawler machine) will not see the value in paying you what you will need to get to draw, setup and cut a few pieces. You will get lots of "opportunities" to cut small jobs (especially for Free).

    We do not live close to a major city so my cutting business needed to adapt to the market. While we sell all over via the web, most business is local and based on finding nitch things that people will spend money on.


    TOM caudle
    www.CandCNC.com



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    Each market is different as Tom has pretty well outlined above. There are pros & cons to everything.

    My shop is a small operaton by most standards I usually employ 3-5 men & myself. I don't do any art work. & rarely cut anything under 1/4". Most of my cutting is 3/8" up to 1" thich & is done with Ox/Acet.

    I built a 5' X 10' table & 2 months after offering my services for hire, needed a 12' table. & still struggling with the idea of building a larger one. I was lucky in that I don't need to cut 12' parts. I just need to buy 4' X 12' sheets of 1" to make one of my best moneymaker jobs more profitable. With only a 10' table I have to load a 12' sheet, cut a series of parts then move the remainder of the sheet onto the cutting surface.

    This translates to lost time & $$$ having to spend the 15-20 min it takes to clear the table, move & realign the remainder of the sheet.

    Handling larger sheets even sheets of 1/8" steel is hard to do by hand.

    Steel suppliers, at least in my area will cut sheets just about any size you want. It just usually costs more. Some suppliers will shear standard 4' X 8' sheets in 1/2 for you at no or very little cost if you purchase the entire sheet(s).

    Sometimes there is seemingly no reason for steel cost to be different. I cut 1 specific part that I can get (4) from a 4 X 8 sheet of 3/8" & have quite a bit of scrap remaining. I can get (6) of the same part from a 4 X 10 sheet without much scrap remaining. However the 4X10 sheet is more expensive per #. Enough so that the parts I am after are cheaper per part cut from the 4 X 8 sheets. Go figure.

    You'll just have to decide what's best for you. A larger table takes up more floor space that might be better used for something else. There are so many varables than no one else can really help you decide "WHAT SIZE" to build. Especially when you have no idea what you might cut next.

    My personal opinion is if you have the room for a larger table, you can move larger material onto it & your electronics are robust enough to handle it then bigger is better.

    Happy cutting.

    If it works.....Don't fix it!


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    Default Thanks for the info Tom

    Tom,

    thankyou for the very detailed reply. To be honest I don't know how you do it. You supply great products at a price that brings sofistication to our CNC projects, then you have great support (I was the one who unknowingly had a stuffed motherboard in my newly purchased computer, and it crashed the one MP3000 software my unit used, but none of the other MP3000 softwares).
    I think I felt my stress levels instantly reduced after reading your reply. I already have a lot on my plate with a toddler and new baby and running my excavation business with its associated maintenance issues outside of income producing time. Not having the higher costs and longer build time of a larger table plus the need to build a little gantry crane is a bit of a relief.
    I wholeheartedly agree about having your own products to make in volume. To me this is the only way to simplify business and make more money. As the saying goes, "Make something once and sell it many times". The world is full of people who want you to make them something unique yet don't want to pay for the time and effort it takes from initial design to finished product. They can only relate to going into a shop and buying an existing mass produced product off the shelf. Of course if you try and educate them they don't want to know. Perhaps they wish to stay ignorant of certain facts so they feel more justified in wanting a do-it-for-nothing price.
    You've now gave me a much clearer picture of which direction I'll start with my plasma table. I do have some of my own product ideas but you've gave me a little bit extra too.

    Thanks again Tom.



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    Default Thanks millman52

    Hi Millman52,

    I just got your post after sending a reply to Tom. You must have been typing as I was typing to Tom. Thank you for the info. I think perhaps I've been thinking a bit too ambitiously considering my backyard space constraints as well as time and money. I have went the bigger is better direction with my lathe and milling machine and I certainly would like to go that way with my plasma table. I think for the sake of my stress levels I'll start a bit smaller and look at renting a small commercial space when the time is right. Then I can go and build something bigger and not have to just about walk over it to get to another place in the workshop.
    I think I will however look into setting up an oxy head too for any jobs needing thicker material cut.

    Thanks for your help.



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    Hello Millman52,
    How about cutting quality if u use gas cutting torch oxy/acet? Do you use any torch height controller on this machine and what type? I actually follow your thread on making this machine, but I did not ask you about torch height.



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    Quote Originally Posted by asuratman View Post
    Hello Millman52,
    How about cutting quality if u use gas cutting torch oxy/acet? Do you use any torch height controller on this machine and what type? I actually follow your thread on making this machine, but I did not ask you about torch height.
    The cut quality I receieve with O/A is excellent on materials over 1/4"
    I have a MP 1000 (CandCNC) in the system but it does nothing with torch height on O/A

    With O/A You simply set how high above the plate you wan to preheat. Then how high you want the torch to lift to pierce. In Sheetcam you can also choose between lowering torch back to cut height as your torch moves along the lead in, or you can lower straight down after pierce then along the lead in.

    I also have a hand wheel on the torch body In case material is warped enough the original preheat height becomes to close or to far from the plate.

    Then have a pair of keys on the keyboard emulated so I can jog the torch up/down while under cut.

    If it works.....Don't fix it!


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    Anybody here know, what cut quality of propane (LPG) gas compare to OA? I mean, which one better LPG or OA? Thanks.



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    Quote Originally Posted by asuratman View Post
    Anybody here know, what cut quality of propane (LPG) gas compare to OA? I mean, which one better LPG or OA? Thanks.
    LPG takes longer for preheats simply because it doesn't burn as hot as Acet.

    The cut quality should be pretty much equal.

    Because LPG isn't as hot I'm not sure how thick of material you can preheat to pierce. I'm sure it's well in excess of 1" though.

    If it works.....Don't fix it!


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    I am going to agree with millman52 that cutting with LPG will have near identical performance to Acetylene because it's the oxygen that does the cutting. Preheating is another animal entirely, though. It can take upwards of three times as long, depending on tip geometry. Bear in mind that my experience with the preheat is with hand cutting only so your results may vary.



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    Quote Originally Posted by Fegenbush View Post
    I am going to agree with millman52 that cutting with LPG will have near identical performance to Acetylene because it's the oxygen that does the cutting. Preheating is another animal entirely, though. It can take upwards of three times as long, depending on tip geometry. Bear in mind that my experience with the preheat is with hand cutting only so your results may vary.
    I don't use LPG just because of the preheat time. Also the tips are more expensive for my torch in LPG Than Acet.

    On 1" steel preheat with Ox/Acet is in the just over 1 min range. Bump that to 3 min I have just lost an hour on a sheet with 32 preheats which I often do

    That hour of lost time will more than buy me A 200 Cu ft bottle of Acetylene. Which will run nearly all day on 1" material.

    There may be other reasons to use LPG. If you don't cut a lot of material with oxy, or most of it is on thinner material, maybe up through 1/2". & it keeps you from leasing & maintaining Acet. tank.

    Another shop local to me here that keeps 1 & sometimes 2 tables running every day has tried Mapp, Porpolene, LPG etc. They always end up back on Acetylene.

    If it works.....Don't fix it!


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    Hey...
    I am "currently" using LPG and have to say the preheat time with MTHN (machine tips) is 150 seconds on 1". With a BTN or an HPN tip it goes down to 90 seconds but with slower cut speeds (from 20ipm to 16ipm). LPg is cheaper, especially if you have a tank on site to fill from. Dross removes slightly easier, often no dross at all. Your leads have to be bigger also due to the larger crater, so you cannot nest as close or do as small of holes. However you can chain cut if no holes are required. That eliminates the long pre-heat cycles.

    All that being said, I will still try acet and MAPP soon. Both gases have the same type of tips that are available for the LPG set-up, so even more speed can be picked up with less pre-heat time.

    WSS



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