May I be Nosey?

[William Adams]

Just as a side note on software, I don't believe Shopbot equipment uses G-code. They use an enhanced proprietary command structure and control system.

Interestingly, Shopbot opensourced their command language a while back:

http://www.opensbp.com/

[Rich Fennessey]

If you think you might eventually sell your machine in order to upgrade, then buying a supported brand will certainly have a better resell value. On the other hand, if you learn how to put one together, you can build yourself a bigger/better system later. Depends on how much time you have and how interested/talented you are at electro-mechanical assembly. Personally, if I was looking at approximately 25% more for a fully assembled, supported machine that I could work with immediately, I'd do that. But then again, I'm usually very short on free time and have a decent budget.

I'm personally very interested in the control/motion systems (I have BS Engineering) but was more interested getting started making things. I've actually done a couple of repairs on my system and have learned a lot about how they work. I had never looked at them real closely till I got mine through the door.

Either way you go, the experience should be enjoyable, educational, and productive. Best of luck.

[Art Mann]

Rich, I am a retired EE and manufacturing engineering manager at a very high volume automotive electronics plant. I am very familiar with 80/20 extrusion construction techniques, gantry style robots, stepper and servo motors and computer controls. My concern has been whether a kit is properly engineered to provide the same accuracy as a good commercial unit. I am becoming convinced that CNC Router Parts sells such kits. My threshold for a make/buy decision is ~20%. Being retired, I have more time and less money than you probably do. Your point about resale value is a good one.

If I can set it up, I plan to visit Camaster next week and see a machine in operation and get a more accurate picture of the cost of a Stinger I with options and accessories. I think that will help me a lot.

[bobby milam]

Resale could be an issue if that were ever an option. I see home made kits for sale all the time cheap and they nevvet seem to sell around here. Look at one of the manufacturer's that you mentioned with complete machines, you can't seemto find a user one that lasts very long after being listed.

I've about decided with mine that if it doesn't make enough money to buy a stinger then ill keep what I have as then it would be a waste of money. I have a goal and a plan that I am pretty sure will be able to use my existing cnc to pay for the stinger

[Jerome Stanek]

It is sounding like some of these people are buying a machine to fail and resell it. With a lower cost machine that is in the $3000 price range and you get back 50% that would cost $1500 but with a machine like a stinger $8000 and you get back 75% that cost you $2000. But if you parted out the cheaper unit you would most likely get more than the $3000

[Roy Nielsen]

Art,

A nice thing with the CNCRP is that if you later need a larger machine, you could upgrade quite easily to a 4x4 or 4x8 machine by simply replacing the side extrusions and a few more cross pieces (and of course base), longer gear rack, etc.

Ahren @ CNCRP has provided great customer service to me, from helping answer specific questions when I was designing and building mine (that was before he had his own full lines...he has been expanding his offerings quite steadily) to same or next day shipping on orders.

Roy

[Keith Outten]

The wonderful properties that aluminum provides has a place. The same can be said for other types of metal and of course I should include wood in the mix as well because all of these materials have been used to fabricate machines in one fashion or another.

CNC Routers are best built on a rock solid frame and in this case steel or cast iron are the best materials. Even the slow CNC machines are fast compared to a hand held router and the forces involved increase quickly as speeds increase. The fact that a CNC machine not only moves fast but it has to change directions quickly as well, this is where you will see with your own eyes what you have under the hood so to speak. Day to day machining won't place an abnormal amount of stress on a particular frame but certain operations will and that is when you realize whether you have selected the best material for your machine.

I ran two almost identical ShopBot PRT Alpha routers for several years. My ShopBot at home had a PC Router motor with steel channel rails, it was about two years older than the one in the sign shop at CNU which had a spindle and the newer aluminum rails. There was a considerable difference in the two machines even though the frames were nearly identical in every other aspect. The spindle in the ShopBot at CNU was much heavier than the PC Router in my machine at home and the aluminum rails were a far cry from being as rigid as the steel channel rails.

I can put down my PC 3.25 HP hand geld router and pick up my much smaller 1 HP Colt trim router in the blink of an eye. But I can't upgrade the PC router in my Stinger II to a five HP spindle and expect the machine to be able to handle the increase in weight. The gantry really isn't designed to move and change direction as quickly as I expect it to with the smaller and lighter router motor.

My point is that although upgrades are possible there is a limit based on the design of the machine and part of the equation is based on mass. Heavier frames provide not only an increase in strength but mass as well. Take a very heavy 5 HP spindle and send it to the opposite end of your table at high speeds and put the brakes on real quick just to see if your frame can handle the sudden change in momentum. A manufactured machine takes these and a whole lot of other issues into consideration, a home built machine might as well but it really depends on how much experience the designer has under his belt and how many machines he has designed that have been built and are in service.

Nothing I have said is news to anyone here however a decision to purchase one CNC machine over another is a complex one that is too often influenced by the cost over machine performance. This is not such a bad mistake when you buy a band saw that fails to meet your expectations but it can be a disastrous mistake when the costs involved are much much higher.

Every CNC manufacturer wants to develop and sell a low cost CNC machine and every one of them has found the bottom price point that they cannot go below and provide a machine that an owner won't curse they day they wrote them a check.

So, here is my advice! Spend the time to find out what specifications you need in a machine that will do the job you need to do. Then and only then start shopping and if you can't afford the right machine keep saving your money until you can.
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[Jeff Monson]

CNC Routers are best built on a rock solid frame and in this case steel or cast iron are the best materials. Even the slow CNC machines are fast compared to a hand held router and the forces involved increase quickly as speeds increase. The fact that a CNC machine not only moves fast but it has to change directions quickly as well, this is where you will see with your own eyes what you have under the hood so to speak. Day to day machining won't place an abnormal amount of stress on a particular frame but certain operations will and that is when you realize whether you have selected the best material for your machine.

So Keith, maybe a stupid queston, but can a CNC be put on casters? As long as the base is solid, can it be portable?

[Rich Fennessey]

I have my 4x8 Cobra X3 on heavy duty casters. I'm not sure if it has impacted the quality of my cuts. I have noticed swirls when pocketing corian when the head makes sudden acceleration (ie around corners and such). I'm thinking that casters might be ok if frame is solid since gantry and frame would move together. I should try my corian pocket cuts after taking the castors off some time. Casters were an additional option and I was never warned not to keep them on by anybody.

[Keith Outten]

Jeff,

I would not hesitate to put my Stinger II on casters. The welded frame is strong enough to handle any variation in the height of the wheels without flexing the frame. I slide my machine across the floor whenever I need to move it using a garage jack to lift the front end, I would never have moved my ShopBot for fear of losing the level and having to spend a days work getting it setup again. Cast iron frames would be a different story but welded steel square tubing makes a rock solid frame.
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[Keith Outten]

Interestingly, Shopbot opensourced their command language a while back:

http://www.opensbp.com/

I am surprised that ShopBot has released the code for their Control software. I used it for many years and it continued to improve as did their machines.
These days I am using WinCNC which has a card that has to be installed in the computer that sends the data to the CNC Control box. One thing I really like about WinCNC is that once a file is sent to the router the computer is free to use for design work or other tasks. I can run both my CNC Router and my Laser Engraver from the same machine and at the same time.
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[Jerome Stanek]

It has been posted here about the benefits of a welded frame and how that a frame bolted together is not sturdy enough for a cnc. I just watched a show how they make Peterbilt trucks and they are not welded but they travel the highways and stay together.

[Keith Outten]

Jerome,

Your right where trucks are concerned and for many high rise buildings as well. There are times when you need a connection to flex but a CNC machine is not in that category. A truck frame will also be made from a different type of steel than a machine frame.

I can't say that aluminum is never appropriate for CNC frames, it might be just the ticket if it is designed properly. Even so the welding process is a big part of a steel frame and even though you can weld aluminum I haven't seen a CNC frame made from aluminum that was welded. The process of welding aluminum is also more difficult and more expensive than steel.
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[bobby milam]

By portable, do you mean able to relocate to a different area of the shop or taken to a job site? For moving in the shop, you could always put on a retractable type of caster so it could roll when needed and be stiffer when not needed. If you mean more portable than that, I would be afraid not of the casters but of something else getting a little out of whack with a lot of moving. I have a small shark and the table on it flexes too much for me to want to make it "portable". Moving the table that it is mounted on around the shop has no effect on it.

[bobby milam]

It has been posted here about the benefits of a welded frame and how that a frame bolted together is not sturdy enough for a cnc. I just watched a show how they make Peterbilt trucks and they are not welded but they travel the highways and stay together.

You are trying to compare apples and basketballs. I have taken the posts here to say that there are benefits in having a welded frame for more precision and speed. I don't think anyone has said that aluminum cnc doesn't have it's place. My current machine isn't even aluminum, it is made with high-density polyethylene and bolted together. Is it sturdy enough for a CNC? Yes, as long as I remember it's limitations. It can't support a full sized router, it can't cut at the speeds of an aluminum cnc and isn't as accurate cutting if the material is too hard.


The frame on a truck is designed to have some flex in it. Yes they will stay together and yes they will be capable of driving in a 12 foot lane...well most of the time. You aren't trying to get .001 accuracy out of a truck driving down the road with a full load. There is also a reason that they don't make their frames out of bolted together aluminum.
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