Low cost idea for machine ways. Thoughts?

I was just brainstorming (very dangerous, and painful) about a router table. I am trying to come up with a low cost alternative to store bought ways. How about 1 1/2" gas pipe, polished in a lathe and running in 2, 1” long Delrin or Nylon bushings spaced about 6” or more apart. Then filling the pipe with a rigid material, maybe fiberglass reinforced concrete or another material. Any suggestions? Epoxy or other plastic? Also, running a 5/8” dia. piece of rebar through the middle, centering it with caps on each end, maybe even pre-stressing it a little before it sets up. Would the pre-stressing add to ridgity without the added weight of filling the pipe? I realize the accuracy would depend on the job of polishing. But would this setup be rigid enough?

Make the bushings open on one side like a C.
That will allow the tube to be supported by a rib or even an edge emerging from the frame. It will look like this "O--". I will not take credit for the idea. I've seen this in use on a high precision low load application: a laser photosetting machine. It used a recirculating ball bushing with a slice missing.

"Make the bushings open on one side like a C.
That will allow the tube to be supported by a rib or even an edge emerging from the frame. It will look like this "O--". "
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This could lend itself to designing an adjustment in the bearing to take up any play or wear in the bushing. Maybe a set screw on each bushing carrier to tighten the bushing.

Been having the same thoughts, but with 1" pipe and using supports over the length.

You would be much better off just going to a larger diameter pipe. A 1 3/4" pipe will be almost as rigid as a 1 1/2" solid steel bar. A 2" pipe will be more rigid than a 1 1/2" solid bar. Adding concrete or rebar down the middle will not change the rigidity of the pipe much at all.

The suggestions about the open bearings with supported rods is probably the best idea.

Jeff

Would filling the pipe not reduce resonance and vebration?

Pipe is neither round, straight, nor consistent in diameter. Therefore, it's not suited to use with sleeve type bushing. This is why guys using pipe typically have skate bearings riding on it. Hard chromed hydraulic cylinder rod material is within .0005 of the stated accuracy of Thompson round way shafting, and costs about 15% as much. It's plenty accurate for use with polymer bushings in DIY projects.

"Hard chromed hydraulic cylinder rod material is within .0005 of the stated accuracy of Thompson round way shafting, and costs about 15% as much."
Do you have a source?

http://www.baileynet.com is a ready source for cut lengths at about 1/3 the cost of Thomson shaft, and a bit of searching will turn up cylinder rod at prices far less than Bailey's prices.

Another alternative is to use ground and polished shafting. The diametral accuracy of DGP or TGP shafting is very good. The spec for sizes up thru 1.5" is +0/-.001". Because it's not chromed like cylinder rod, its cost is substantially less. It should be available thru any local steel warehouse. With standard CRS shapes bumping 70 cents a pound currently, I'd imagine ground shafting will be in the $1.50 range in full lengths, but this still puts the cost of 1" stock at only $4/foot. If you insist on having cut lengths, prepare to pay more for the cutting than you pay for the stock.

Quote:

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Originally Posted by metlmunchr

Hard chromed hydraulic cylinder rod material is within .0005 of the stated accuracy of Thompson round way shafting, and costs about 15% as much.

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I have a printer bar which is also chromed as far as i know.
It used to be very smooth.
Now there are bubbles in the chrome.
It does not run smooth anymore.
Could this also happen to the metal you suggest ?
http://home.wanadoo.nl/vroemm/cnc/pr...ar-bubbely.png

Probably not (as in peel/blister). Unless chrome is properly applied and baked afterward, problems like what you illustrate in your photo can occur.

From the adjacent pitting, it would appear that the surface was not properly prepped prior to plating. Oil, wax or rust pits would prevent chrome from adhering properly. Over time, it will tend to blister/peel, especially if it was NOT copper plated and/or properly etched before chrome plating.

The Q&D (quick and dirty) method of plating involves NOT putting a bonding plate (flash plate or "strike" of copper or nickel) between the base steel and the chrome.

Ground and UNPLATED steel shafting should not encounter such distress - as in plating peeling. However, it could be prone to rust or corrode due to handling unless it is protected somehow. Black oxide and oil (Dexron ATF or WD40) is one way to inexpensively protect unplated steel. There are others but oxide and oil is about the cheapest we've found.

I'm not sure what you are looking for in precision as far as your ways go, but if you pick up the latesst copy of ShopNotes they have a panel saw build article in there. Yeah I know you are not building a panel saw but they did approach the linear movement problem slightly differently.

It might ba adaptable to lower cost routers. In any event I posted this news in another thread so won't waste anymore space here.

Dave