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DICKEYBIRD
08-16-2009, 08:48 AM
I say semi-noob since I spent quite a bit of time welding (oxy/acet & SMAW) various auto related projects 30 yrs. ago when I was still a hands-on mechanic for a living. Back then, I had no brains whatsoever and just welded the heck out of everything with no forethought and it worked fine as far as I could tell. Nothing ever fell off anyway.:)

I've practiced a bit lately with the SMAW and feel confident that I can stick 2 pieces of metal together and they won't fall apart under the force of gravity.;) (Man, I wish they'd made auto-darkening helmets 30 yrs. ago....what a treat to use one!)

Anyhoo, I'm fabbing up a surface plate/buffer stand and want to weld it up in an order that induces the least amount of warping. The mount for the plate is just a rectangle of 1.5" x 1/8" angle iron with a couple of straps to line up with the granite plate's airy points. (Jargon, gotta luv it, eh?)

Anyone want to share their tricks for welding said rectangle up so that it's closer to a rectangle than a parallelogram when I finish? I think I can cut the miters close enough on my 4x6 bandsaw. I'm thinking I should clamp the 4 pieces down on my "welding" table (pretty bold statement but it IS made of metal anyway) with a little gap and spot each of the 4 corners in a diagonally opposite sequence in 3 places on each corner, checking and adjusting for square after each spot: 1) Do all of the bottom-inside joints. 2) Do all of the top joints 3) Do all the bottom-outside joints,

Also, I'm thinking I should assemble the whole stand with spot welds and not weld everything solid until all the parts are in place and aligned as best as possible. Make sense?

Oh, in case you're wondering why the heck would I have a buffer with it's abrasive residue anywhere near a surface plate, imagine a wood "cap" that fits over and completely covers up the plate with the buffer mounted on top of that. The cap will mount to the perimeter of the frame to prevent fretting wear between it and the plate and will be easily removable with thumbscrews to access the plate when it's needed.

Rustybolt
08-16-2009, 08:59 AM
Also, I'm thinking I should assemble the whole stand with spot welds and not weld everything solid until all the parts are in place and aligned as best as possible. Make sense?


When there isn't a jig to hold everything together that's the smart way to do it. That way you can tweek the setup to insure everything is straight.

The way I weld up a frame to keep it from warping is to weld a little at a time in each area and let it cool. That way your not sinking so much heat into one area at a time. Others might do it differently.

wierdscience
08-16-2009, 09:05 AM
I usually tack the four inside corners first,then the four outside corners after checking for square.

DICKEYBIRD
08-16-2009, 10:22 AM
Thanks! You're probably right Mr. wierd, (dunno yer 1st name sir) it should end up flatter that way.

Now on to figger'n out how to jig up the 4 legs "splayed" out 7.5 degrees and have them end up somewhere near correctly aligned. Yeah, right.

torker
08-16-2009, 10:38 AM
We have a welding section here now....
The things you're talking about welding...including the legs...
I always tack them up then tack (heavy tacks) solid baces wherever I need them to hold the works in square or whatever til all welding is finished.
Then simply remove the bracing and grind the tacks off.
A far simpler way of doing it that trying to control distorsion with (hopefully) proper weld placement or sequences.
Russ

wierdscience
08-16-2009, 10:41 AM
Thanks! You're probably right Mr. wierd, (dunno yer 1st name sir) it should end up flatter that way.

Now on to figger'n out how to jig up the 4 legs "splayed" out 7.5 degrees and have them end up somewhere near correctly aligned. Yeah, right.

Just do it one leg at a time,tack the corner and tweak it out checking with a bevel gauge set to 7.5*.I'm assuming your going to use a base frame somewhere near the floor for stability right?This is where you tack everything up and adjust to suit before and during welding.

Course it has four legs and there is absolutely no chance of it ever sitting flat on any floor,so don't sweat that detail.:)

Darin

DICKEYBIRD
08-16-2009, 11:05 AM
Course it has four legs and there is absolutely no chance of it ever sitting flat on any floor,so don't sweat that detail.:) Hey now there's a good point! I should change the CAD drawing to have 3 legs and start a contentious thread on computing the appropriate leg angles so that the airy points of the s/plate are properly transferred through the load-bearing elements of the structure, through the ABEC 9 caster swivel bearings onto the correct points of contact with the floor.

Of course there's all the right-wing/left wing economic ramifications; my gawd, the HEALTH CARE issues that go along with the cutting & welding of steel...is it US made steel or Chinese steel? Should I use modified genny, stock genny power or grid power? Should I use carbide inserts, jig ground or hand ground HSS tools? Cutting oil, motor oil or chainsaw bar oil? Micrometers, USA or Chinese calipers? Piston or wedge?

Ahh, I'm getting light-headed with all the possibilities!:)

wierdscience
08-16-2009, 11:09 AM
Nah,no need to do all that,the 1-1/2 x1/8" angle should be enough to get things started:D

DICKEYBIRD
08-16-2009, 11:14 AM
Nah,no need to do all that,the 1-1/2 x1/8" angle should be enough to get things started:DNow THAT'S funny, I don't care who you are!

DICKEYBIRD
08-16-2009, 08:58 PM
OK, back to serious stuff. I cut & welded up the rectangle like Darin suggested this afternoon and had some trouble with the welding. I clamped it up and hit the inside corners with 3/32" 6013 at about 75 amps, I think. My old Century AC/DC box is a little vague in the amp adjustment area.

Anyway, the spots went well, they filled the gaps in well and were burned in nicely. After checking for square, I spotted the outer inside corners, raising the heat a bit due to the increased mass. Results were not as good, too cold. I ground out welds, raised the heat some more, then switched polarity to electrode positive and still was having trouble getting the bead to lie down where it should be.

I finally switched to 1/16" 6013 and was able to get the beads down where I like them and finished the rest of it. That seems crazy on 1/8" angle iron. I guess my eyesight & technique has gotten old & fuzzy.:(

(And no, I ain't EVEN gonna post pictures for you guys' entertainment.;))

Evan
08-17-2009, 06:08 AM
Part of the solution to distortion is understanding how it works. When the metal is heated initially it expands producing stress that results in strain in the form of bending of a member. When the metal becomes liquid that stress is removed and the metal responds by assuming the original position. Then when the metal in the weld freezes the original position is locked into place again except now the temperature is near the melting point. As the weld cools the material shrinks producing stress the pulls the metal into a new shape.

The result is that if you place a weld on one side of a section the section will be pulled in the direction of that weld as it cools. The answer to dealing with this is tack welds as mentioned already but the placement of such tack welds goes a long way to minimizing the distortion.

If tacking a box section to a plate such as might be done for a table leg the tacks should be at the corners of the tube and should be placed on alternate corners in sequence instead of working around the tube in order. If tacking the end of a round tube then 4 opposing tacks should be place as alternate pairs.

The general principle is to place small tacks on opposite sides in pairs. This puts the warping forces in balance and the bending cause by the first tack will be compensated by the opposing second tack weld.



The specific principle is to place tack welds at points where the material is strongest such as the corners of a square section. This results in the least distortion for a given amount of induced stress.

The warpage can also be controlled by clamping parts so that they are able to resist the bending forces caused by the tack welds and later full welds. Braces may be used including clamping a stronger piece of material along the entire length of a part that has intermediate welds such as for leg braces.

As for your specific welding problem a little preheat goes a very long way to making good welds in difficult places.

DICKEYBIRD
08-17-2009, 08:40 AM
Thanks Evan, good explanation of the forces at work.

Duhh, I didn't even think about pre-heat. In this part of the project, the welds just need to stick the pieces together reliably and the beads will be hidden. I think my welds accomplished that fine. However, as in all my cobbled up projects using what I happen have on hand, I consider it training for a later project where I may be doing it for money and appearance and speed may be more important.

I don't have oxy-acet. equip at home yet; would a hardware store type propane torch put out sufficient heat to pre-heat 1/8" to 3/16" stock enough to help?

What I really need is throttle pedal hooked up to the amp adjustment. Now there's a project.;)

Evan
08-17-2009, 01:03 PM
Propane produces plenty high enough temperature to heat steel red hot even with just air. The problem is getting enough heat. I use a acetylene-air Prestolite torch rigged for propane with a large tip that produces a flame about 2 inches across and 6 inches long. It will heat a piece of shed 40 1" pipe enough for hand bending. The prolem with the bottle torches is not just the small flame but the 1 lb bottle. It rapidly cools from the expansion of the liquid propane which then reduces the pressure and flame size. This can be somewhat alleviated by having a pan of warm water to put the torch bottle in. You don't need to heat the work red hot for pre heat. Even just a few hundred degrees hotter makes a really big difference.