help me to design steel frame for my 10' X 5' CNC router

[palyoK]

hello there,
i am building 10' X 5' router i need help to design frame for my router i want to use steel, but in my region i don't have access to square tubes ,,,i am thinking about using sheet metal , a 14 gauge iron sheet , by bending it in 3.5" X 7" rectangle shape, or i can use "U" shaped channel and "I" beam, shown in picture below,
i guess by bending iron sheet i can get pretty equal surface for rails... and by using u shape channel and "I" beam surface can be a problem , and by using "I" beam it will be difficult to mount rack, ...i need your suggestion on this please
i will use nut with Allen bolts to fasten rails on sheet metal beams,

i am new here sorry for any mistake ,
thanks

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[wizard]

This is an interesting problem because rectangular tubing makes the job easy.

The first question to ask is how thick can you go with the sheet metal bending? The general approach is to opt be linear rails to taped holes in the gantry beam. This requires thicker material in the beam than simply looking at from the standpoint of mechanical engineering. In other words the beam has to be thick Engine ugh to hold the threads for the rail mounting screws.

You do have options here and in that you can buy linear rails with the paper holes instead of through holes. Then you beam can have clearance holes. Ultimately what you do for a beam depends to a extent upon what you intend to do with the machine. If you intend to machine aluminum it needs to be phisically stiffer. If you want very high Z clearance the beam needs to be more resistant to twisting.

As for I Beams and C channel you will almost certainly need a machine shop to machine them flat Enough to be usable. If you weld anything’s ng you are even more likely to need a machine shop. It can be and has been done though so If you have to go this way just understand that it is far more difficult. Over on YouTube “This Old Tony” builds a gantry from a structural C channel beam. That is only one approach to using structural C channel. One thing to note is that his beam required significant machining to flatten.

You have other possibilities if a large machine shop isn’t available. Hand scraping is always a possibility. Then there is epoxy leveling. In the end don’t get hung up on the idea that there is only one approach to the flatness problem on a gantry beam. There are many ways to solve this problem.

Given the materials you have available to you I’d probably try welding two C channels together. Ideally find somebody that can stress relieve the weldment and then flatten a face, Oh realize that your beam needs to be longer than the work area. Depending upon themachines design that could mean a beam 6 - 8 feet in length to cover the 5 ft working area, this is important when trying to find somebody to machine the beam.

The lack of square or rectangular tubing will make the base frame construction more difficult. Again your design comes into play but this might be an even better place to bend up sheet metal.

[palyoK]

thanks Wizard..!!
here 2 mm metal sheet can be bent , and i am thinking to bend a 2 mm metal sheet in g section because i believe bending sheet will give very good surface . i am posting some images here please have a look.

here i don't have any facility to surface the c channel , so i need advise on sheet metal frame ...

i am thinking to use 3X8 inch sheet metal beams..

please check images

thanks

[wizard]

thanks Wizard..!!
here 2 mm metal sheet can be bent , and i am thinking to bend a 2 mm metal sheet in g section because i believe bending sheet will give very good surface . i am posting some images here please have a look.

I have not problem with sheet metal for the base frame as long as you address the screw holding problem. If your linear rials use 6 mm mounting screws, 2mm sheet simply will not be thick enough to drill and tap. There are plenty of ways to address that of course. It is the use of 2mm sheet metal in the gantry beam that would worry me, remember that is a 5 plus feet span with not additional support.

Your pictures indicate the use of angle iron for a good part of the frame. You need to be careful because angle iron does twist rather easily over long distance. So something to keep in mind in your design.

This brings up a question though; if you have the machinery to cut and bend sheet metal, why not build the whole frame out of sheet metal bent too for legs and rungs of the frame? With a little design effort you can have a frame made of fewer parts yet more rigid.

here i don't have any facility to surface the c channel , so i need advise on sheet metal frame ...

You could always do epoxy leveling.

i am thinking to use 3X8 inch sheet metal beams..

You need to ask yourself how you will fasten parts (rails and racks for starters) to that beam. Further light sheet metal needs internal bracing to prevent the beam from going parallelogram. This can make internal access very difficult. Like all machine designs there are alternatives to internal bracing.

For one example alternative you could use longer "rungs" that bolt under the main beams and extend far enough to add gussets. The problem is this gets in the way of the rack drive.

Another option that helps with the thin beam material is to bolt the rails and the rack to backer beams. That is long flat stock that has been drilled and taped with a matching pattern for the rail mounting holes. Done right these bars can be installed without any of the difficulties of not being able to reach to the center of the beam.

Your 3 x 8 beams by themselves probably will not be a problem on the machines base. The problem rather is putting it all together in such a way that the frame is as stiff as is reasonable for the budget.

please check images

thanks

You are off to a nice start!!!! When contemplating your design, especially the cad images imagine if you can how you would actually assemble these nicely designed parts. If the electronic drawings don't do it for you full size mock ups in cardboard can be a help.

One of the stickies has an excellent series that goes deeply into gantry beam design. There si some great info there.

[pippin88]

Where in the world are you?

I'm very surprised that a place exists where you get can large sheet metal and bend / form it but you can't get some simple rectangular hollow section.

[palyoK]

Where in the world are you?

I'm very surprised that a place exists where you get can large sheet metal and bend / form it but you can't get some simple rectangular hollow section.

I am living in a town in Pakistan. ..
Well I can get shipped these channels from other cities. .but what I believe sheet metal will give good surface to mount rails. And sheet metal will decrease cost.
I will use Allen bolts with nuts to hold rails on thin sheet. ..please have a look at images

[wizard]

I am living in a town in Pakistan. ..

That is along ways away.

Well I can get shipped these channels from other cities. .but what I believe sheet metal will give good surface to mount rails. And sheet metal will decrease cost.

I would imagine that how well the parts come out of the brake depends a bit upon the operator. I do have this fear that metal might be just a bit too thin without plenty of bracing to prevent that parallelogram movement. I do not think that the picture you have shows enough bracing.

The basic layout of your machine is good though.

I always worry about gantry beams as this is a common weak area in DIY machine builds. A gantry beam would force you to use internal racing on the beam as there is no provision for external bracing. In either case I suspect that using a backer bar, drilled and tapped for the linear rails, would provide better support for the linear rails This would also allow for closing your “C” profile with a single sheet. Think of a sandwich of linear rail, closing plate, C channel flange, lateral brace and backing bar. That is a lot to lineup all at once and frankly is just one possible approach.

I will use Allen bolts with nuts to hold rails on thin sheet. ..please have a look at images

The nuts create an access problem which you apparently address in your design with access panels. That will work but but I’m thinking a solid panel would maximize what you can get out of the thin sheet metal.