Alum or steel plate: which is flatter

[audiisaac]

I need to build some semi-dedicated welding jigs to assemble 1X1 box tubing frames. I need to be able to change the setups once or twice a month so I will be drilling and taping the plate for 1/2-13 fasteners on a grid. Originally I was going to buy a 3/4+" 5'X8' hot rolled plate, but have recently been thinking about aluminum. Any thoughts as to what would be flatter?

THanks!
Isaac

[walker]

I think the aluminum would be flatter, as it gets treated a lot better than the steel, mostly due to its cost and its use in appearance products. CRS is flatter than HRS. 3/4" plate is awful thick plate for a jig to hold 1" tubing.

[raferguson]

Adjust it flat

Even 3/4 inch thick plate will have some "sag" over 8 feet of distance, assuming that you support it at the ends. If I did my calculations right, the expected sag would be about 1/4 inch over 8 feet. If I was super-concerned about flatness I would probably go with somewhat thinner plate, maybe 1/4 inch thick, and make a support frame with adjustability to adjust out any lack of flatness in the plate. That would require a very good straightedge; one would need to research in order to figure out where to obtain such a high quality straightedge. Or perhaps a high quality level might work well. Anyway, it would be a lot more practical to shim out any lack of levelness if the plate was only 1/4 inch thick.

Another concern would be any distortion from cutting the plate.

I would be interested in hearing from anyone who has made a fixture of this type, what they did, and how level they were able to get it.

Richard

[FusionKing]

It only needs to be as flat as you can make a welded 1" tubing assembly.
That isn't really anything super critical. Flat but not dead nuts flat without machining.
I'm sure others will chime in with better advice.

[cncmachinist]

I build a lot of fixtures for my CNC mills and such and a few for welding purposes but I have lots of 3/4 through 6in thick AL plate all over the shop for welding I would use AL because if the shear thickness i can get and machine and precision grind flat for specially parts I make but AL plate isnt cheap.

If your jig needs to be portable make it on a roll around cart with a thick plate that can be angled i have a few made with 4in cast iron tops with T-slots in them for clamping and such also you can get a acorn table from most scrap yards at scrap rate but they need some clean up and they will take your 1/4 steel plate bolt it to that when welding and it will stay flat.

heres a pic in case my explanation isnt clear

since I cant find the pic of the angled iron table ill try to get some pics tomorrow but is basically a smaller section of acorn plate that I milled T-slots into.

probably overkill for 1in tubing but once you use these tables the old 1/2 steel plate tables look like wimps

[tommy2069]

i rather steel plate for welding jigs on one little slipup and up got a gouge hole in the aluminum but if you scatch arc on metal just sand it down .not saying not to use aluminum but in all the shops i worked in we allways had 3/4"plate tables to work on .sure they was heavy but we could lay out a crane boom and not wory about it warping.

[shorerider16]

I personally prefer steel tables if I am working with steel because it gives the option of tacking fixtures to the table if the need arises. Grind any scabs off neatly when your done and nobody will ever know they were there.

[tommy2069]

we had 6 fab tables in out shop made from 3/4 plate and they was 8'wide by 44' long. we had to use the overhead crane to move them. we also had some 2"bolts with plates welded on the bottom to level them out when needed and yes it's really nice to be able to weld a padeye to them to pull off of then just grind them off.we could wash welds off without having to worry about warping anything.

[HAWK]

audiisaac,

I think steel will serve your purpose fine. As mentioned any weld tacks are easily removed. When laying out square and flat frames I like to use spacer tabs. I usually choose 1/4" x 4" flat bar and use one tab in each corner as well as periodically spaced over the length of your frame. The tabs help alleviate any jig surface sag keeping the frame flatter.

HAWK

[nocheepgas]

Super Flat

Not sure how it would work for your purpose but if you need a really flat surface, try granite. I wouldn't use it to fab up all your stuff, but if flat was critical you could certainly weld on it, drill holes and put inserts in it for hold downs. It would probably be cheaper than aluminum.

Just throwing an alternate idea out there.

[Country Metals]

If your material isn't that big, you can always have your top blanched (sp?). Basically they will put a mill on your table top and get it smoothed to within .003. I build a lot of 1 1/2" tables and I had one done. I like it better then my granite table since I can weld to it. It is well worth the money in the long run.

My table is only 30 x 60 but I think my guy could do 5x10 sheets. Of course they would need to be 1/2" or greater since anything less would sag pretty easy.

[con_fuse9]

Not sure how it would work for your purpose but if you need a really flat surface, try granite. I wouldn't use it to fab up all your stuff, but if flat was critical you could certainly weld on it, drill holes and put inserts in it for hold downs. It would probably be cheaper than aluminum.

Just throwing an alternate idea out there.

Granit is an interesting idea. Might be worth a talk to a counter top shop. Most of those places are hurting anyway because of the lack of custom houses being built.

You could talk to them about strategically locating bolt holes as well. Maybe get a discount if you pick uglier colors. Around here is $100 linear foot installed.

[Doughboyracer]

I have...

...Nevr thought of that thanks. I have a good size chunk of that in the shed from a demo project.

[audiisaac]

If your material isn't that big, you can always have your top blanched (sp?). Basically they will put a mill on your table top and get it smoothed to within .003. I build a lot of 1 1/2" tables and I had one done. I like it better then my granite table since I can weld to it. It is well worth the money in the long run.

My table is only 30 x 60 but I think my guy could do 5x10 sheets. Of course they would need to be 1/2" or greater since anything less would sag pretty easy.

Could I get the contact info for the company that did the grinding? I have a 72" X 72" X 1.5" table that would benefit from being reground. I am also in the market fro a new table in the next 6mo-1 year. it will be in the 5'-10' range and 1"+ There is a grinding shop neer by but the largest that they can do is 48" round so i did not look into it.

[audiisaac]

Thanks for all the input. I have redesigned the jig and came up with a way to make a "space-frame" for each operation. Instead of each jig having its own sub-plate I am bolting each jig to my 1.5" welding table which holds every thing flat and straight.