First post!

Ok, I've been lurking for a while, but now i should have my shop up in another month or two, so a metal cutting cnc machine is in the planning stages!:rainfro:
What I'm thinking is 12" (maybe a little less) Y travel, 18" (maybe a little more) X travel, and 10 - 12" Z. My question is, when using the #3060 80/20 extrusions similar to LeeWay's layout, ( http://www.cnczone.com/forums/showthread.php?t=32609 ) could lead be poured into the open ares of the extrusions to fill the cavities and add some rigidity/vibration damping? I was thinking heat the extrusion in an oven to about 200*F, then pour in the molten lead. Since the aluminum would be expanded much farther than it ever would in daily use, shouldn't this lock the lead into place when the part cools? The part would have any major bows caused by heat corrected in a hydraulic press and then milled or scraped flat prior to attaching the slides. The base and column are the only two pieces that would receive this treatment. Would it work, and would it be worth it? The machine would be used for aluminum/steel milling, feeds and depth of cut could be kept light, I've got more time than cash obviously :violin:

Lead may help with vibration damping but it will do nothing for rigidity.

Also you should check into the price of lead, it is not cheap.

well, i can increase rigidity with some mic6 tooling plate, which isn't too expensive. and i have a few hundred pounds of lead laying around somewhere around here, so that isn't a problem. Would anchoring cement (the kind that expands as it cures) be a better option? The only worry i have about the cement is drilling through the extrusion after its set. Maybe a masonry bit? :confused:
Nice reply time, btw thanks!

... i have a few hundred pounds of lead laying around somewhere around here, so that isn't a problem....

A few hundred pounds of lead???? Maybe you should look at the price of lead, sell your lead and by a machine from Widgitmaster. :D

I really cannot comment on whether it is worth trying to make the extrusion more rigid; I just wanted to point out that lead would not add to rigidity.

lol, well the price of lead has dropped, my source is old batteries. i.e.- neutralize acid and then melt. batteries are only going for about $3 scrap price down here now, so not much there in cash, but about 20-30 pounds of lead in each. i had another idea of building box section with 1/2'' 1018 cold rolled and then filling with anchoring cement, I'll probably look more into this option, thanks for the replies

You should look into the epoxy concrete, or epoxy granite as a filling product. It is stronger than concrete or steel, dampens vabration much better, and it does not expand so it want change the shape of the tube its being poored in. It also adhears/clues very good so holding it in place is not problem, add a few cross screws if you want to help it have something to hold on, but it really doesnt need that.


The truth is with the this 80/20 many people have built machines and found there was no need to fill them because it performed so good the way it was. But filling it will help and make it that much better. You can even run a threaded rod through the epoxy and put a load on it to make it even stronger. They use this type technic in bridge building to add strenth and control flex. If I understand right the rod runs all the way through the concrete, then it has plates or just nuts to clamp down on it after its cured. You can do some research and find the exact methodes.


Jess

The trick in "prestressing" is to add the load BEFORE you let the epoxy cure. Then when it is cured you can cut off the extra all thread, you would want to do say 6 all threads in a big tube to equalize the tension. This puts the mass under tension and yes it makes it a lot stronger. Neat trick indeed.

Evan