Re: [CAD_CAM_EDM_DRO] Re: Guides

On Wed, 14 May 2003 17:02:18 -0000, you wrote:

>Alex...
>
>Like I said earlier, I'm having good luck with chain driven leadscrews. The reason I went with leadscrews over a chain loop drive was for machine resolution. I forget the exact numberes, but a roughly 1" pitch diameter sprocket driving the gantry directly in a loop would have only delivered .002 or so per step. I wanted more than that, which meant some sort of reduction drive...and lead screws were the simplest way.
>
>Someone mentioned chain stretch. The chains will stretch, but only to a certain point. It's like a motorcycle chain. You constantly adjust the cahin in the first 1000 miles. After that, you might adjust once a year.
>
>I adjusted the chains on my machine 3 times in the first week of steady operation. In the past 3 weeks, I have not noticed any excessive play in the chains. The thing I noticed about roller chain is that they do not have to be guitar string tight. I found that the machine runs better with a little play in the chains and when measured with a dial indicator, has no more backlash than with a tight chain.
>
>All that said....If I had been able to find timing belts in the right lengths, I would have gone that way instead.
>
>I would stay away from HD casters for rollers unless you're building a plasma or flame cutting table where accuracy is just not important. The problem with those casters is that the wheel can be quite a bit out of round. In some cases so far out that you can see it by eye. That will cause your Z height to vary all over the place as the gantry moves.
>
>You can buy sealed roller bearings from MSC Industrial for $2 or so each. They make great roller guides. MSC also sells cold rolled flat stock which would work great for the rails.

You can get ABEC 3, 5 or 7 bearings for about 13 dollars up to 20
dollars or so. These will fit on an 8 mm shaft and are roughly 22mm
in diameter. Your local mega-sports store will sell them as roller
blade bearing replacements in tubes of 8.

Harvey

>
>Ross
>
>
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