Long linear rods

Hi, where can i find a long linear chrome rods? On aliexpress i can find only max 300mm 8mm, but i need at least 1000mm 8mm. It's a possible solution to put near 2 o 3 rods? or the leap between them will create vibrations?

And if i use regular calibrated steel rods from and ironware? and maybe i polish it with a 600 - 800 - 1000 sand paper?

I don't know what you're building but a thousand millimeter long 8mm rod is ridiculous 8mm diameter rod is not even really good at 300 mm long. Even with nothing on it it will sag by its own weight in the middle a little less than a millimeter way too much for anything accurate to guide

How much diameter need to be to have a lenght of 1000mm? To avoid is weight, it's possible to use a linear chrome tube?

I'm actually considering upgrading the X rods on my printer to 10mm, even though I have a standard 200x200 print bed. It doesn't take very much pressure to cause the 8mm rods to deflect when I am changing filament. I can only imagine that it moves while printing too.

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Yaro
How much diameter need to be to have a lenght of 1000mm? To avoid is weight, it's possible to use a linear chrome tube?

everything that large usually uses something that supported all the way rectangular linear rails and bearings are the rule but they're very expensive. Cheaper alternatives not so accurate would be maker slide or continuously supported round rods from the VXB or similar. And mount them to a structural member such as an extrusion here is a picture of a large router I made about eight years ago I don't know if you could make out the supported rails on the gantry

Edited 2 time(s). Last edit at 06/29/2014 07:39AM by cnc dick.

It's bit heavy to build. If i use from 300 to 400mm bars, which diameter do you advice me? more diameter on X axis that have also a Y axis on it, or X and Y same diameter?

Thank you.

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Yaro
It's bit heavy to build. If i use from 300 to 400mm bars, which diameter do you advice me? more diameter on X axis that have also a Y axis on it, or X and Y same diameter?

Thank you.

the point is you can't do anything that large with a round unsupported rod there is a point where bigger diameter rod doesn't make it any better because of its own weight unsupported one thousand millimeter long is out of the question for anything accurate. What are you trying to build I think somebody mentioned hollow rod which is better but trying to buy a good hard hollow round Rod 25 mm diameter would be very expensive and hard to get. And still that would not be the best solution still would not carry hardly any weight. For 400 mm long 10 mm diameter is probably okay for a printer but I would use 12 mm diameter

Edited 1 time(s). Last edit at 06/30/2014 08:46AM by cnc dick.

If you do want long, smooth hollow tubes, check out a motorcycle breakers yard (or eBay/craigslist etc). Look for forks for small off-road style bikes which haven't been crashed. The fork legs are tough and chromed on the outside. As an added bonus, the industry already sells bronze bushings ready-made to slide on them

The issue you'd have, going that route would be finding enough of them, and dealing with the mess of freeing the stanchions (the chromed tubes) from the fork legs.

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ybanrab
If you do want long, smooth hollow tubes, check out a motorcycle breakers yard (or eBay/craigslist etc). Look for forks for small off-road style bikes which haven't been crashed. The fork legs are tough and chromed on the outside. As an added bonus, the industry already sells bronze bushings ready-made to slide on them

The issue you'd have, going that route would be finding enough of them, and dealing with the mess of freeing the stanchions (the chromed tubes) from the fork legs.

that's a good idea I been around motorcycles all my life and I've built machinery and I never thought of it that's is definitely a good idea

I'm just going to throw OpenBuild's V-Slot out there as an option. It's the route I'm going for extended length linear motion.
Problem is that they are all too often out of stock on half of their products, but I'm a patient person and finding them the best option for my needs I am willing to wait for each purchase as things jump in and out of stock.
I'm at 800mm lengths at the furthest, and I quickly found even 12mm rods was not enough. 20X60mm ali extrusion along both lengths is more sturdy, but oriented along the wider, 60mm length and there is no visible drooping in my unprofessional, livingroom testing. Absolutely no question that it's more stable.

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IF you stretch the rods at the ends it will reduce, not eliminate the sag. How much tolerance is required? I use 8 8mm rods on my delta. They are 36inches long.... Roughly 914mm, the do move a small amount, however they are not bad. You have to stretch them a bit if you want them to stay put.

As others have mentioned. Tubing would be better. Steel wire conduit could also serve as a cheap alternative. Although if you have access to a lathe I would try machining them round and true. However getting bearings that ride on them may prove difficult.

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Would a 3 axis bearing like a roller coaster wheel work in this situation? You could use thiner rods/tubes with support welded to the back. If you used tubes you could make the supports do double duty as connectors allowing you to create a linear run as long as you want.

Thanks Mike

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Miertam
Would a 3 axis bearing like a roller coaster wheel work in this situation? You could use thiner rods/tubes with support welded to the back. If you used tubes you could make the supports do double duty as connectors allowing you to create a linear run as long as you want.

Thanks Mike

That's how the original mendel was set up. No linear bearings.

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