Can anyone at dms help machine some aluminum flat stock to be flat within .001" per ft or two. I’ll need a couple of 2’ and 4’ pieces. I’ll provide the flat stock.
there are some difficulties in maintaining that tolerance over a 2 - 4’ workpiece.
- is the work HOLDING surface flat? The machine for this is the bridgeport mill or haas. The surface can be indicated in. In the case of the haas it can be faced in the case of the mill it has to be trammed which is not an easy thing.
- how will it be held? If in the vise you can just give up now because it will vibrate like crazy. If on the table you have the hold downs in the way.
- pressure is critical. Because this is aluminum squeezing it in any fashion will likely cause it to bow or flex. Things look good until you release it and it bows back.
you didn’t indicate the starting thickness, but things get worse as it gets thinner. there maybe some other issues. Example, just 2 days ago, I had a critical round part that had to be flat like this to .001. we achieved it by facing it to it’s zero height. Of course we did our due diligence and made sure the fixture was flat first. Made the first pass then Rotating it 120 degrees and running the same tool path (zero). rotate a final 120 degrees and run the same toolpath. the final flatness was to withing a 1/2 of a thousandths. the workpiece was under 2" so plenty of room to rotate. Not going to be possible to rotate a 4’ piece on the mill. On the Haas it might be possible to run over the same length at different angles to achieve similar results.
So - the question is really about flatness and thickness. If the thickness is not critical, the manufactures are often to withing 0.005 of the published thickness and maintain that throughout (which means flat). So I’d start by measuring what you got. We’ve got a granite slab and height guide but neither are calibrated, so it’s impossible to say whether it would be accurate. A micrometer may serve just as well.
regards,
Nick
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This is for to check for flatness for tools and stuff in my future workshop. Let’s say to check my in feed and outfeed tabled for a jointer.
It won’t be to hold anything. Thickness…maybe 1/4 to 3/8"?
24" pieces can easily be done on Bridgeport since all you need is one edge cut flat and true, other edges won’t matter.
No sure, but 36" can be done on Hass.
Repositioning the stock for a second cut can get very close but .001" might be a challenge. You can check flatness on surface plate and a feeler gauge.
I would like to do something similar to the OP.
Small model rockets use a 1/8" or 3/16" steel rod as a guide until they accelerate to a speed at which the fins start working. Unfortunately, the rods tend to flex and whip when the model is heavy and/or when there is more than a light wind.
We use aluminum extrusions as guide rails for large rockets, but they are overkill for the small ones.
In the early days of the hobby, a C-rail was commercially available to address this problem:
http://www.ninfinger.org/rockets/nostalgia/68estp56.html
But they are no longer being sold for that purpose.
What I think will work is to buy the small square aluminum tube in 36" lengths from the orange or blue big box store and mill a 1/8" wide slot along the entire length of one side. The slot does not have to be ruler straight, but it should not wander from the centerline too much or too quickly. I am thinking it can be clamped between two long pieces of steel during the milling process. Thoughts? Can the Bridgeport cut the entire 36" length without having to manually reposition the piece?
It would require an adjustment on table. However, the tolerance you would need for this application would be well within well with the error of machine miss match. I’d guess ±.005". However do at the 24"/12" mark and when mounting, put the shift at 12" when it is still slower with the last 24" all one cut and that would minimize the shift. I think it can be held to ±.002 realistically both as to straightness and width of cut.
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I’m just asking for academic knowledge. Is grinding a better process for flatness than milling?
Surface Grinders can do much better. But it is for the finishing passes, typically when only a few thousandths remain and you need a very smooth and flat surface. Grinders typical can hold .0001" but ones that can do 36" are very expensive.
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Yep, what David said