Re: [CAD_CAM_EDM_DRO] Re: Guides

Thank you,
Ross, Dave for your enlightening comments.
The bottom line is that small guy can fight back.
Will try to incorporate your suggestions into design,
Regards, Alex

----- Original Message -----
From: Ross <rrcarl@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, May 14, 2003 1:02 PM
Subject: [CAD_CAM_EDM_DRO] Re: Guides


> 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.
>
> Ross
>
>
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