View Full Version : Rectangular tube instead of C Channel

Sun 20 December 2009, 22:34
Hi Guys, I'm looking at building a MM. I have a CNC Bridgeport and a manual Bridgeport, buy I'm looking at expanding into a new venture and I think a MM will work well. One thing that I would want to change is the main C Channel. I saw that one build used an I beam, I would like to use a rectangular tube. I don't really care about the extra cost vs. the channel, my main reason I would like to do this is I want the stiffest and most ridgid frame possible. Secondly what I would like to do is add an epoxy granite mixture to the inside of the tube to add ridgidity and mass. I believe that this will help dampen any vibration caused by the router. I know that this will add costs, but again I accept this. I know that this machine is designed to cut sheet goods, but I don't see why the extra stiffness and ridgidity won't help when cutting sheet goods and would definately be an asset if cutting aluminum or when engraving. I look forward to any suggestions, criticism or input, Ron

Mon 21 December 2009, 02:32

I thought if I would ever build another machine, I would use rectangular tubing, two stacked on top of each other. I tend to feel this way because I have had problems with the straightness of my C Channel. I don't think you need to fill the tube with epoxy granite.

I will be interested in your progress and design.

Robert M
Mon 21 December 2009, 04:22
Gerald, Allow me if I may !! ]( or discard it, I’m ok with that too)[/[/SIZE]I]

Ron, See, you say a MM will work well !?!
I’m confused ( to be sarcastic) where you tend to come forward to make a MechMate compete with a SUPER heavy duty machine, while the original concept is to allow a simple, very economical diy solution at a very robust cost effective ratio effectiveness !
No complex structure, no completed filling and so on….nothing more than crud structural C-channel affordable steel, yet so many time buy so many has proven to be more than enough.

“[I]but I don't see why the extra stiffness and rigidity won't help when cutting sheet goods”

It may have a positive effect to think to improve it, but again, why devote energy on something that already make cuts more than perfect for what it is intend to ?
Kinda like seeking to buy a tank to go local grocery !
Not a good metaphor, but you and other get the point !
As it is design, it already does better than what it is needed for, cutting sheet goods and even other materials not indented to be cutting at, but did / does a dam good job at it.
As other has shown in this forum, it may even cut other fancy material better than some very fancy machining process machinery…. So no logical pragmatic reason for this tube filed design !?!

Not saying you have a bad idea, or you totally wrong…Sure redesigning a CNC with tubes, mass filled and so on may be ( and I should say more than “maybe”, but “will be” ) better, but again, the objective is to allow a simple design with simple access with as low & affordable materials as possible to do a simple, effective, hi-quality result….and it does it better !

( Funny or ironic to explain this as I'm one who did some design changes to have it do more than it is originally design to !!?? :o )

Anicalement, Robert ;)

J.R. Hatcher
Mon 21 December 2009, 06:25
I'm kinda with Robert on his thoughts, I also think the design of the MechMate is well tuned, I can't see a single weak link in my machine, I don't see any over or under design in any of the parts or components. I think if you beef up the base then you need to beef up the gantry ...... and if you beef up the gantry then you need to beef up the Y car ...... and then the Z slide ...... and then a router surly wouldn't work. Gerald started with a shopbot and saw the need for improvements, after several he realized its not a shopbot anymore. After several major changes to the MechMate would it still be a MechMate? :confused:

Gerald D
Mon 21 December 2009, 06:50
I see no harm in trying super-heavy x-rails. Once before I mentioned the possibility of a concrete table. The heavier, the better. But, is it worth the trouble? I think not.

Mon 21 December 2009, 07:35
The beauty of Gerald's design is that you can modify it to your heart's content, so give it a try and see what happens.

Mon 21 December 2009, 08:34
I can appreciate all of your opinions and I in NO way meant to demean or belittle Gerald's hard work. I like options. I know that these machines are highly capable and well thought out, but there is always room for improvement, or an easier way to do something (it may not always cost less money). I like the idea of a boxed frame. I would not want to beef up the Y axis because I do not want to add any extra weight to the moving parts of the machine.

I plan on buying the v rail, I don't have alot of time to build this machine. I need to start using it, also I hate grinding and I don't want to deal with the mess. Although something I may do to limit the grinding is machine the v on the channel, this way I will be truing the v to the table instead of removing a bunch of stock. Just some thoughts.

Gerald D
Mon 21 December 2009, 09:13
Our first table was boxed tube. I avoided putting boxed tube on the drawings because:
- it is not easy to get around the world in a convenient size for the height needed
- very unlikely to get a cheap used piece at a scrap merchant
- it is expensive purchased new
- limited lengths available (more scrap)
- the C section used for the second table performed as well

Mon 21 December 2009, 10:34
Thanks for the input Gerald. I'm sure I'll have more questions once I start building.