1010322S Main Long. Beams - table edge carrying x-rails
 

Drawing sheet number 1010322S refers:

The main beams, or girders, of the stationary table are made of channel iron, or C-section steel.

- Length of the channel is X plus 600mm

- Depth (height) of channel, in the range 150 to 200mm. This height affects the clearance under the gantry. The MechMate beam is 180mm high.

The most important criteria when selecting the beams at the steel supplier are not the dimensions, but the STRAIGHTNESS. Don't worry about twist, the beams are very flexible for twist and that will be corrected during the build.

- Width (breadth) of channel, in the range 50 to 100mm. Very little affect on overall dimensions. Mechmate beam is 70mm wide.

The 60 degree angles at the ends are purely for aesthetics.

Gerald,

On you original table for your SB you used square tubing, why did you go to the C-section steel for the MechMate?

I don't know why he changed, but the instructions he gave me for making my table used C-section, and it is incredibly solid.
He says the 60º angles are for aesthetics, but you can get two side pieces from one 6m length if building a 10 foot table, which you can not with square cuts.
Gerald also told me this!

...............Mike

C-channel is a "lazier" option for the DIY bloke http://www.mechmate.com/Forum/clipart/happy.gif

Seriously though, C-channel is more widely available around the world, and bolting through it is easier. Strength-wise, it doesn't make a huge difference.

C-channels are available with either tapered or parallel flanges. Chose parallel flange if you want to use bolts and nuts through the flanges - otherwise you'll need tapered washers. The MechMate plans are for welded joints - there are no nuts inside the beams - the threads for the rails are tapped into the beams.

If the standard beam length in your country is *just* too short, then Mike John will explain a trick to you. Also, the x-rails may hang over the main beams by up to 100mm on each end, but it won't look too pretty.

Thanks,
I like the parallel flanges. And aesthetics are important, and as you've pointed out it can prove economical as well.

Gerald, I just purchased a C channel (74 x 150 mm). For Main longitudnal beams. If I use this will I be restricted to only 6" of Z axis travel. If I need to extend this further in the future(Maybe to 12").Could I just mount (Bolt) another C channel having same dimensions into the existing one.

The z-travel depends on a lot of things, the beam size, the table top thickness, that 1" of rail height you are making, the diameter of the V-roller under the gantry, the length of the router's collet and cutter, etc. A 6" beam is fine for cutting thick boards - if you want to get into thick 3D stuff later, you can add a spacer beam as you suggest.

X and Y stop question:
How much extra length is given for the x and y distances over the size of the cutting material? For instance, will the router bit center hang 12, 25, or 50 mm past the edges of the material when at the end of the x and y rails?
Thanks much..

Center of bit can go 50mm [2"] over on all 4 sides of the material. (100mm [4"] added in total per axis)

I'm not planning on going into hard 3D with this machine, my plans is to build another machine later on with a cuttin are of 3*3 feet for typical 3D cuts.
But, will a 120mm c-beam be good enough for the main beams..??? Cause this I can get cheap from work... The other size 180mm is a little more expensive. Actually alot even...

What is your total X dimension? What is the width of that 120mm C-section and how thick is it?

You realise the issue of the reduced z-height, but the beam must also still be strong enough to carry the mass of the machine.

The Complete length of my machine will be 3100mm
The beam is. this one here...
Height=120mm
Width=55mm
thikness of wall=7mm
thickness of ends=9mm

Those 9mm ends - are they tapered or parallel?

This beam doesn't sound too bad if you can get it cheap (free?). But, before I make a final answer, can you you get 4 lengths of this steel? (to make a "sandwich"). Can you get other slightly smaller sizes to make sandwiches?

the 9mm is tapered....
What do you mean with sandwich..???

Do you mean stacking them on top of eachother, or..????

Some guys do stack the beams on top of each other, but I was thinking something like this:

http://www.mechmate.com/Forum/messages/8/3346.gif

Left is the recommended channel, middle is your channel, right is a sandwich of your channels (20mm long welds, 300mm apart).

Single channels will be strong enough for light board cutting.

So you mean that the channel won't be strong enough as a single channel.. you think it would be better to go with the 180mm channel instead..??? I can get a 6meter lengthe for around $200

Or is it just to get the hight in order.???

I repeat "Single channels will be strong enough for light board cutting." (as in the middle picture)

Yes. but light cutting, I'm hoping to get it to do single pass when cutting, instead of doing multiple passes for each iten.

If the table is too light it:
- vibrates (cut quality suffers)
- flexes with temperature and humidity changes because the wood surface then starts to bend the steel.

$200 for a pair of beams is a good price (you can cut 2x3.1m from 1x6m)

I can't get 2*3.1meter from one beam. I can get 3.09 if I cut the ends in 45 degrees instead of 60...

It is no problem if the x-rails are a little longer (say up to 100mm) than the beams.

But offcourse if the tool is already going to go 50mm over the ends then maybe it kan be possible to make it long enough to reach from one end to the other... So maybe 6 meters cut in 60 degrees should be good enough I will stille have a few centimeters on each end of the X axis...

Look at drawing 1010246D and realise the beam needs only to go to the last screw hole. (Also see that extra length shown on the points of the rails - I cut those points after everything is assembled and I have looked how far I need to run the gantry). The design of the MechMate is very "forgiving" http://www.mechmate.com/Forum/clipart/happy.gif

I thiink I will be going for the 180mm beam... But with tapered ends instead of parralell.... this is what I have gotten a price for... But it should be ever as straight as the ones that arent tapered...

If have come across some used free C-channel for my main long beams, but the problem is the upper and lower surface are not running parallel to one and other. One side is about 1mm out of square with the outside long edge of the c section and the other side is 3.5mm out of square.

Looking at the construction of the Mechmate it seems critical that these surfaces run parallel. I include pictures because I am sure the above explanation is not all that helpful. Any thoughts?

Thanks for your time.

Good pictures! :) Bad problem :(

Channels seldom have perfectly square flanges, and the 1mm case looks typical. You should be able to use that without problems - the flatness is not super-critical for the MechMate. Bad spots can always be shimmed up. (Your rack & pinion will show uneven wear for a while, but the cutting quality and accuracy will not suffer)

But the 3.5mm situation looks rather bad. Avoid that channel. Unless you want to weld the whole channel at an angle so that the top face comes flat. Those 60 degree ends on the channel points will make it hard to see whether the channel has been welded at an angle :)

Thanks for info!! Great site.

Gerald,

I'm using C7x14.75 channels for the main beams. At 10 foot in length, just one beam weighs 147.5 lbs. I would like to reduce the weight of the table by drilling 4 inch diameter holes along the beam. This will reduce the weight considerably.

The table legs support the beams, so I don't think bending (along the X axis)is a concern (correct me if I'm wrong). What are your thoughts/design for this beam. If I reduce the weight by 30%, am I sacrificing structural integerity.

I want to reduce weight, because I'm a one man show and fabricating this table is getting more than I can bear.

Greg

Each 4" hole will weigh about -1.5 lbs. About 1% of the total weight. To save 30% in weight you will have to drill about 30 holes. You can't put 30 holes of 4" diameter side-by-side along a 10 ft beam because then holes will have to touch each other.

Sorry Greg, it will severely mess up the structural integrity. All I can suggest is getting some lifting equipment or people. Realise also that a typical production board laid on the table for cutting will also be in this weight class - an investment in lifting equipment is probably going to be needed in any case.