Forget about grinding the channels, because the volume of metal to be removed is far too much for our DIY methods.

1/8" off square can easily be fixed with long strip shims in the right places.

Is it a good idea to add an extra inch or two to the x and y dimension for clearance? Or does the x + 600mm[23.6"] allow for enough clearance? Im building a 3d model of what I want and it just doesnt look like it will clear. Maybe its just a problem with my model.

Does the spindle face the 0,0 corner or does it face away? im thinking about adding an inch to all sides just to be sure. I see guys with tables that are 50" x 100". Why? For the same reason? if I want to be able to cut up 48" x 96" sheets,... should my x = 96" and y = 48"?

What do you think?

The x + 600mm[23.6"] allows the center of the spindle to go 50mm[2"] clear of the table top. Spindle faces 0,0

Have a good read through the whole of The starting points for building your own MechMate - selecting table size, etc.

Thank you sir. Another question,... Im not saying you should but it would be very cool if there was a gallery of nothing but pics of the machines. I am still a bit clueless as to a few things. But if there was a gallery of machine pics with short comments of what we are looking at,... it would be a great help. A pic is worth a 1000 words. I know there are pic all off this forum but having to scrolling through all the threads hoping to find what you are looking for is kind of time consuming. If there was one place to go that would be awesome. Multiple pics of every square inch of the machines. I bet it cut cut down on the number of questions asked. Thanks gerald. just a thought.

Charles, That is the whole idea ;)

Having the Mechmate plan & build advise for free are already a gift handed to you on a diamond studded gold platter, what else do you want? Who said learning is easy??? :eek:

Read, read & read.... Then search, search, search, then read over again & again & again...

You are right.

C-channel vs Steel-Tube vs $$$$
 

I have a question more about design strength and not looks or "making a better mouse trap". My question is to the X-rail. I am able to purchased TS5x2x.25 steel tube for $94/20 ft. length as apposed to a C6x13 C-Channel for $150/20 ft length. My desision to use the steel tube is purely based on money.

I know Gerald has mentioned before that there is no difference in using either other than availabilty and easier to bolt and work with the c-channel. I have two options below using the steel tube and would like the opinion of anyone who could help me decide which is the better design.

The steel tube will be tapped and both will bolt the v-rail to the steel tube using 1/4"x3/4" hex bolts with washers, unless someone thinks 5/16" bolt would be better. However I am concerned about the surface area between the tube and v-rail. Option A only has 1" of mating area. Option B, if I weld an 1/8" thick by 2" wide steel to the top of the tube would have 2" of mating surface. I would like to know, if considering the current weight of the Gantry, movement, deep 3D cutting and any possible additonal weight for upgrades (bells & whistles), would Option A cause too much stess on the v-rails and cause them to twist outward and bend? Or would welding an 1/8" (or 1/4") steel on top of the tube be a better to minimize or prevent any twist or bending of the v-rail.

Any opinions would greatly be appreciated. Thanks all.

http://i585.photobucket.com/albums/s...AILOPTIONS.jpg

Sorry, some of the dim lines and 1/8" steel callout may not be visible in photo.

C-channel vs Steel-Tube vs $$$$
 

One other factor I forgot to mention. Option B would have a minimum of 3/8" material for the tapped hex bolt, unlike Option A would only have the 1/4" thickness of the steel tube, thus more holding power for the threads. Thanks for any help.-David

Wouldn't option B have a very large risk of distortion from welding, potentially resulting in even less surface area (in spots)?

Brad-Thanks for the reply. I thought of that and was only thinking of stitch welding 1" long beads every 4-6" down the length of the v-rail on bothe sides. Or in addition to the stitch welding add plug welds through the top of the 1/8" or 1/4" steel plate to prevent any distortion of the plate.-David.

Instead of stitch welding every 4-6" as stated before, I can place 1" beads at every bolt location every 6-8" down the length of the x-beam. Possibly setting up the components for welding in the manner below would keep the 1/8 or 1/4 inch plates true and flat, like using cauls to glue up long lenghts of wood when using multiple clamps.-David

http://i585.photobucket.com/albums/s...LOPTIONS02.jpg

Disclaimer: I should just shut up now, I'm NOT a metalworking pro, it's perhaps my weakest area. However:

What about an Option C: using a clamping strip inside the tube, similar to the gantry rail mounts?

I note that the gantry rail uses that strip because the specified tube is definitely too thin to rely on for threads, however the strip is only 1/4", and thus threading into just 1/4" is well proven for at least the weight of the Y-Car assembly.

So it seems to me that option A is sufficient, and has less manufacturing risk. If you want more insurance, than option C involves a well documented procedure.

Hopefully one of the real metal pros will decloak and set us both straight.

Yes true, I'm familiar with that detail. However I wasn't too concern with the thickness of the tubing member for tapping. With what I can purchase the 1/4" think tubing will probably be sufficient for the hex bolts. My issue is with the 1" matting surface on the top of the tube to the v-rails. The tube is 2" wide but with the two 1/2" radius corners, it will only leave 1" of bearing for the v-rail.

If using c-channels with square corners currently leaves a rough 1/2"-3/4" over hang for the v-rail. With the steel tube you can easily add another 1/2" to the above overhang. This is where my concern is. I'm thinking by welding on an 1/8"-1/4" steel plate, I would be back to the original overhang of 1/2-3/4" for the v-rail. I feel that the larger overhang would be too much of a cantilever, thus possibly twisting or bending down the v-rails over time enough to cause problems. Thanks-David

Dave,
Your concern is irrelevant. The rails requires 0.25mm (0.01") tolerance. Without machining/surfacing/milling, steel fabrication achieving tolerance to 1mm is consider very good. So you must shim to get to the desired tolerances. When you shim your rail, the contact/mating area will be as big as the shim you put in. One thing about shimming, it will take forever to shim the whole mating surface.
I cut out shim washer & insert them in the bolt, max contact of my 25mm sq shim are about 25mm sq (1" sq) or less at each shim location.
I will stick to option A
About your concern over cantilever effect, will that little flat plate give meaningful improvement? IT would be more meaningful to scrutinize the height of the tube to increase torsional resistance. Also, will the load ever cause this cantiliver effect to give detectable/measuarable problem? Have a finite element analysis modal & see how much the improvement will be, then you decide.

The gantry tubes are thinner wall and the outer radius at the corners is much smaller, leaving a nice wide contact area.

KenC- True, I did forget to consider any shims under the bolt contacts. The reason for my inquiry regarding the mating contact is because I read earlier in another thread someone mentioning the radius versus 90° corner in regards to contact area for the x-rail.

Gerald- I'm not sure if we're on the same page. I am familiar with the gantry tube assembly, but I'll be using tube for the x beam where the x v-rails and x-car will ride on. My current tubing will only leave 1" of contact and I'm worried if after shimming the x v-rail that the weight of the gantry will twist the v-rail downward and cancell any shimming done. However with the weight distributed over four v-wheels, will the small 1" contact matter anyway?

Dave, For 56 dollars (less than a tank of gas for most) I know I wouldnt be the ginnea pig for this. Time is money as well. Tapping holes, welding on strips and worrying if the outcome will work...........doesnt seem cheap anymore.

True that. Even though the plans call for the machine to be welded together,... doesnt mean we can go nuts with it. The more you weld the more out of shape everything could possibly end up. Why do you think the Y Car is welded together with small welds all in strategic spots?

What you plan on doing will end up being very crooked and twisted and flat out messy. You need to try and figure out another way to do it if you cant go according to plan.

Or,... you can ignore us and learn it the hard way:) Up to you:) You life. Your money. Your time.

This idea was abandon. I did not want to create more work for myself, I just wanted to see if it would be an issue later on, but after forgetting that shims are required, the addition of a plate cancels out the shimming. Between using 1" wide shims at the bolt locations and the large 1/4" thick cross-section of the L-steel v-rail, I believe any twisting due to the canteliver will be removed from the equation.

Also this part of the project is much larger and bulkier than the gantry, requiring longer, thicker and stronger cross-section steel members, which should have very little movement if welded together or other components added on. The gantry on the other hand are all large area steel plates (minus the 2 tubes in the Y diretion), which can be more prone to warping if too many welds are applied without the proper jigging. If proper precautions are taken for the table/base during the welding process such as squaring, jigs, clamps, etc., any distortion should be minimal. Whether there are any distortions or not, shims will always be required to fine tune the entire machine after the build.

Also the $54 savings is only "so far" on these two steel members. When you start to add additional savings throughout the entire project it may add to several hundred dollars if not more. For some it's a big factor, for many it's irrelevant. Also, the only additonal work required is tapping all the whole on the top of the beam. Holes would have still have to be drilled if using the additonal nuts underneath.

Thanks-David

Square Tube Beams
 

We are just starting our build. We have left over material that we want to use as much as possible to save on cost. We have some 3" x 8" square tube that I want to use for the main beams. Anyone see a problem with that? They are pretty hefty with 1/4" wall.

Those would be great.

Sounds perfect size for the main beams. Make sure you put the mechanical seam on the bottom of the tube so you don't hit it with your drill and tap.

Hello all,
I need help determining my X length. The Y will carry 2 cutters, cutting points are about 14" apart. Do I just add the 14" along with the 600mm to the X length or am I missing something?

Thanks,
Bilal

Are you widening the Y car and space between the gantry beams?

No I am not, I might have to trim just a bit from the inside of Y car for clearance of drill.

How will you address dust collection?
It seems your logic of adding 14" to the length is sound. I can think of nothing off the top of my headthat you might be missing...

I know it's a bit of a silly question, I just want to make sure I'm not missing anything.

I wasn't really worried about dust collection for the time being, 95% of what I plan to cut is acrylic and aluminum plate.eventually I'll bring it out along the corner of the Y car from the spindle side of the gantry.

Could you check out the last two comments herehttp://www.mechmate.com/forums/showt...2116#post72116
and give me your recommendations?

Thanks,
Bilal

Should be rock solid...I think the x bracing is overkill , but I have no formal training in designing steel structures.

ok Darren, thank you.