[jerseyguy1996]

Just for craps and giggles I shrunk the width by 12 inches so that it has a 24X48 inch cutting area. I could live with this. It shaves about 40 lbs off of the weight. I could also get by with smaller base cross tubes. 2X2 may be excessive. 1.5X1.5 is probably enough. That would shave a total of about 70 lbs from the original design. This is what it looks like 12 inches narrower.


Bolt Together CNC Router - Small by jg1996business, on Flickr

[LeeWay]

It was a good suggestion previously to design your gantry length wise. Then later if you move, you can design a base to fit that gantry a lot cheaper than redesigning the entire machine and loosing all the structural parts because they are too short.
Since it may be this small too, I would give serious thought to a CNC router parts kit. I think even the lesser quality skate bearing carriages would rival or equal the ones you are planning on using. This is just to confuse you a little further.

[pippin88]

How thick are your tube walls? Strength / stiffness is determined much more by section rather than wall thickness.

[jerseyguy1996]

It was a good suggestion previously to design your gantry length wise. Then later if you move, you can design a base to fit that gantry a lot cheaper than redesigning the entire machine and loosing all the structural parts because they are too short.
Since it may be this small too, I would give serious thought to a CNC router parts kit. I think even the lesser quality skate bearing carriages would rival or equal the ones you are planning on using. This is just to confuse you a little further.

I'm using the CNCRouterparts skate bearing assemblies on the Y and Z axes. I could design it into the X axis as well with a slight bit of work.

[jerseyguy1996]

How thick are your tube walls? Strength / stiffness is determined much more by section rather than wall thickness.

Any of the tubes that will be tapped will be 1/4 inch thick walls. That would be the base cross tubes, the 2 tubes that make up the gantry, and the tubes that make up the gantry risers. Most everything else is 1/8 inch thick walls.

[handlewanker]

Hi, 6mm thick walls just to tap into means you have to have all that weight just for the tapping area.

I saw somewhere on the forum a link that showed a carbide drill without flutes or cutting edges that punched a hole through steel plate purely by the softening/plasticising effect of localised friction......probably need to do that with a drill press.

The end result is that you get a hole that is conical in cross section and has a depth roughly twice the thickness of the parent material and that means if you use one on 3mm thick tube you get a 6mm thick localised tapping area to tap into.

it's similar to drilling a small hole and punching it through with a tapered punch like they do with thin sheet metal to get more metal to put threads into..

You'd have to do some sums to see how much thinner you can go before too much flexing creeps in, but if it did flex you could screw it down to the floor instead of just letting it stand there.

If I was in your position and had to use thinner tube I'd drill and countersink the tube out bigger and weld bungs in the places I wanted to tap into, grinding them off flush with the top face etc.

Last resort is to buy up an old not fit for the road motor home, park it in your front drive, if it's big enough, and gut the interior........something like they did in Breaking Bad, but permanently parked out front.

Neighbours can't complain if they think it's a motor home per se.
Ian.

[jerseyguy1996]

Attics can be a problem if they aren't load rated.

One approach would be to build a 24 x 48 machine with the gantry the long ways. You could then reuse or extend the machine when more space is available.

So as far as building the gantry long ways, are you referring to something like this? I didn't put in all of the screws and the spacing of the cross tubes is off but I just wanted to get an idea of what it would look like.

Bolt Together CNC Router - Short by jg1996business, on Flickr

[wizard]

So as far as building the gantry long ways, are you referring to something like this? I didn't put in all of the screws and the spacing of the cross tubes is off but I just wanted to get an idea of what it would look like.

Yes something like that. The main reason is that you would be able to recycle the gantry when space becomes available. Obviously there are negatives as there are with any design but the positives are as follows:
1. You can reuse the gantry on a longer machine when space becomes available. Since this is a stated desire it makes such a design worth considering.
2. You can still work with full sheets on a machine like this as long as the parts you are cutting out are no longer that the 2 feet or so of X travel you build into the machine.
3. Since the goal is to reuse the gantry down the road it is far easier to justify a more robust design for the gantry. That would mean a big box beam with profile rails and the like.

The negatives are that you would need dual lead screw drives for the X. Also you will likely need to have a bit more X travel that 24". Finally a machine that is only 24" wide might not be ideal stability wise, you will need to assure yourself that it won't tip over easily.

[handlewanker]

Hi, provided you only wanted to cut wood and not too aggressively at that, I think this might work......not the ideal layout as the beam would need to be overly strong to resist twisting.

Any time you extend the width of a router instead of the length you increase the slewing tendency by a factor of ?.......wide is bad.....longer is good......double ball screws for the Y axis would need to be fitted in any case......no option there.

In any design you like to think of, the width is always less than the length.

Increasing the width is a path you don't really want to tread unless you have no other option.

The main issue here is the weight factor, and increasing the beam proportions is a no gain as the length you shave off the Y axis is only a small amount of tubing, whereas the beam needs to have a much stronger design to be stable and that equals more steel and weight or just the same.

As weight is the main problem component in this design, I would think that aluminium sections bolted together would probably work better.

For the present problem of the attic loading, aluminium is an 80/20 factor for feasibility and preference......80 against for cost, strength of materials and amount to offset the lack of rigidity and 20 for as a solution to the load bearing attribute of the attic floor.

Steel rates high on the preference but low on the weight factor.

This would mean a trip back to Go, and a complete re-design with a whole ally build, staying with the original design layout proportions.......at least it would be easier to cut and drill.....tapping into the sections is another issue to ,overcome.

With this re-thinking, I would consider a moving table design, even though it increases the length, as you gain on the pure strength of the fixed bridge and short side supports.....bridge design can stay the same almost as you'd need steel flat strip rails to run the bearings on.

Going to the extreme of weight shedding, I'd look at having the X and Y axis rails in aluminium too, double width and running nylon rollers on them.......my pallet truck runs on nylon rollers and that's rated at 2 tons capacity.

You might be able to cut aluminium if the build is strong enough, but I wouldn't hold my breath on that one.
Ian.

[jerseyguy1996]

Yes something like that. The main reason is that you would be able to recycle the gantry when space becomes available. Obviously there are negatives as there are with any design but the positives are as follows:
1. You can reuse the gantry on a longer machine when space becomes available. Since this is a stated desire it makes such a design worth considering.
2. You can still work with full sheets on a machine like this as long as the parts you are cutting out are no longer that the 2 feet or so of X travel you build into the machine.
3. Since the goal is to reuse the gantry down the road it is far easier to justify a more robust design for the gantry. That would mean a big box beam with profile rails and the like.

The negatives are that you would need dual lead screw drives for the X. Also you will likely need to have a bit more X travel that 24". Finally a machine that is only 24" wide might not be ideal stability wise, you will need to assure yourself that it won't tip over easily.

I actually really like this idea. If I move into a bigger place it would be a relatively easy task to convert it to being able to handle full 4X8 sheet material. The gantry is already 9 inches wide. In this configuration it would need to span 60 inches. I don't imagine the width would need to be much more than that if any.

[the4thseal]

things are looking good. i don't know if this was mentioned but if you wish to be able to process a 4x8 sheet the trave has to be significantly more than 48x96". just a thought.

[jerseyguy1996]

things are looking good. i don't know if this was mentioned but if you wish to be able to process a 4x8 sheet the trave has to be significantly more than 48x96". just a thought.

Originally I was looking at 36X48 but given space constraints I will probably end up settling on 24X48. I've designed the size of the entire structure to insure that the spindle can reach each corner of the 24X48 inch work area.