Welding up free T-slot extrusion instead of bolting together a frame?


Results 1 to 5 of 5

Thread: Welding up free T-slot extrusion instead of bolting together a frame?

  1. #1
    Member
    Join Date
    Mar 2006
    Location
    US
    Posts
    42
    Downloads
    0
    Uploads
    0

    Default Welding up free T-slot extrusion instead of bolting together a frame?

    So one of the industrial plants I work in has scrapped a HUGE amount of aluminum T-slot extrusion and I have free reign over picking through it, the only rule is that it has to hit the dumpster first before I can load it into my truck. Some of it is bent, some of it has been crushed, but there is a LOT of it that is in perfectly fine condition, just odd lengths and sizes and not all of it matches.

    Some of it is 50mm x 50mm, and some of it is 100mm x 100mm, it's all some generic version of 80/20's stuff but I have no idea what brand. First thought was finally I'll build that CNC plasma table...but I don't have enough power in my workshop to run a 50A plasma, and while the plasma would be great for cutting 3/8" steel exhaust flanges and bracketry, it would do me little good for aluminum plate that I'd need to cut, most of which is 3/8" thick or thicker.

    Now I'm looking at building a 24" x 36" CNC gantry mill, thus I'd be capable of a lot more flexible work than the plasma, but ultimately at a much slower cut rate and higher per-cut cost. The advantage is less outright power required, as I could get away with a MUCH less powerful air compressor to run the mist coolant. Currently the entire shop has 240V 30A service...when I run the TIG welder on a heavy aluminum casting the lights used to dim a bit before I converted to all LED lighting.

    The new shop won't be built for 5 years-at which time I'll have 200A service to the shop and dedicated shop air. Until then, I'm stuck with what I have.

    Given that I have absolutely no issues with welding together my frame instead of bolting, and have been doing plate fabrications (brackets, flanges, etc) for over a decade with reciprocating saws and files, what kind of advantages can I get from using this free material vs buying steel channel and tubing? What kind of disadvantages? I do plan to mass-load the base with sand or machinery grout to help dampen vibration and the gantry will ride across the narrow axis to help improve rigidity.

    Since there is a crap-ton more of the 50mm stuff, I plan to stack two of them side by side and stitch weld them together into a 100mm x 50mm section for the short spans in the base, if I run out of 100mm section. I've done custom auto frames from scratch, so I'm familiar with how to build frames and frame-like structures and the techniques needed to keep things square and true.

    Next round of questions is what size of 4-way linear rails and steppers (I'm thinking nema 23 425oz steppers would be OK) should I be planning around.

    Similar Threads:


  2. #2
    Member
    Join Date
    May 2013
    Location
    washington
    Posts
    480
    Downloads
    0
    Uploads
    0

    Default Re: Welding up free T-slot extrusion instead of bolting together a frame?

    I would not weld much of anything except to the extent of welding up custom angle brackets that you will need to bolt the aluminum together.

    the reason is simply for future re-design and re-use, flexibility. also if you intend to bolt the linear rails directly to the aluminum, then making a mistake and welding the joint 1 degree off will be a real pain to correct.

    welding the aluminum will not add any rigidity to the system if the bolts are sufficient to prevent the bolted joint from slipping under load. a grade 3 1/4-20 bolt can put 2000 pounds of clamping force, and if you have 4 of them per corner joint, that's 8000 pounds of force, which means 2000 pounds at least would be required to make the joint slip. if the joint slips you'll have to deal with the bolts loosening over time.


    depending on which alloy of aluminum you have, it has almost no intrinsic dampening. so i would recommend not mass loading the system.. but rather build your aluminum structure and glue the base of it with silicon or butyl rubber to granite counter top remnants. the silicon or rubber will provide the compliance needed to prevent temperature changes from warping it, and both are a fairly good dampening, with the granite providing the global stability and mass dampening

    Granite has about 2/3rds the modulous of elasticity as does aluminum and the same density, but it has a dampening coefficient that is hard to get elsewhere.

    you can glue the aluminum together rather than weld to turn your 50mm extrusions into 100 mm extrusions. no warpage.. you could even shim and clamp them to get them globally flat to .001 while the epoxy cures.



  3. #3
    Member
    Join Date
    Aug 2009
    Location
    USA
    Posts
    291
    Downloads
    0
    Uploads
    0

    Default Re: Welding up free T-slot extrusion instead of bolting together a frame?

    Quote Originally Posted by Eldon_Joh View Post
    Granite has about 2/3rds the modulous of elasticity as does aluminum and the same density, but it has a dampening coefficient that is hard to get elsewhere.
    I see what you did there...



  4. #4
    Member
    Join Date
    Mar 2006
    Location
    US
    Posts
    42
    Downloads
    0
    Uploads
    0

    Default Re: Welding up free T-slot extrusion instead of bolting together a frame?

    If I mass-load the base, it'll likely be embedded in polymer concrete. Not suggesting filling tubes or anything of that sort.

    Right now, things are looking better as far as material usage if I were to build a double-column mill, instead of a gantry mill. Far less material used, and a more rigid machine, and fewer cuts to make to my free material.

    Looking at it from the perspective of a double-column mill, the total length of the base would be 48", the width of the base 30", and the height of the columns is roughly 17", which yields:

    An X axis table travel of 24 inches.
    A Y axis machine head travel of 20 inches.
    A Z axis machine head travel of 10 inches.

    Since almost all of the motion control parts are metric, that means I'm looking at ballscrews that are roughly 650mm, 500mm, and 250mm lengths, and slightly longer rails. Since this machine will be expected to do aluminum and hopefully will be capable of cutting mild steel, I am looking at 20mm wide, 4-way linear rails. Overkill for most machines, but still inexpensive, comparatively.

    Having built both the lathe and metal shaper from the Gingery Metalworking series, I am very familiar with how machines can be constructed in such a way as to machine themselves, and that has been part of the driving force in the sizing. The cutting area will actually be slightly larger than the table size, so that the machine can true its own table and if I can achieve sufficient rigidity and damping, should be able to machine its own T-slots into the table. Hand-scraping is not out the question, I scraped a LOT of castings to get the ways straight and true on the shaper and lathe. It wasn't hard to learn or do, when you're working aluminum or cast iron.

    Might get some time to throw a few drawings together this evening, but a more thorough inventory of the plate scrap bin is in order first. I think I have a slab of 1" thick cast iron that's 30"x48", but it's not machined on any face or edge other than the saw cuts and it may be cracked. It's been outside leaned up against the barn for probably 20 years now. If it's still there and not cracked, it will definitely become the machine's base.



  5. #5
    Member
    Join Date
    May 2013
    Location
    washington
    Posts
    480
    Downloads
    0
    Uploads
    0

    Default Re: Welding up free T-slot extrusion instead of bolting together a frame?

    I would use that cast iron for the table. band saw cut strips of it, machine them into a T, bolt them (and locktite) to the table to make your T slot table. since you are dealing with a rough surface you might consider using a filled epoxy such as jb weld to fill up the gaps between the T and the table.

    if it is cracked in a place that won't let you make a table from it, don't worry about the crack if you're using it as the base of a machine. bolt a strip of metal across the crack.

    for the size of the machine you're building 20mm rails are not overkill at all. performance also depends on if the bearings are preloaded or not.



Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Welding up free T-slot extrusion instead of bolting together a frame?

Welding up free T-slot extrusion instead of bolting together a frame?