Re: [CAD_CAM_EDM_DRO] Linear Slide Components

Scott, et. al,

You make the point that rollerskate and/or roller blade bearings aren't up
to the challenge but my experience is exactly the opposite. Do you honestly
think that your commercial linear component bearings would hold up to your
12mile/30% grade challenge? A 12mile/30% grade works out to about a 20,000
ft vertical drop btw? And to the contrary, I know several people that have
roller-bladed an entire marathon - and lived to tell about it. I suspect
several of you have rollerbladed several miles at a time and you would have
to attest that the bearings held up just fine. Most bearings of these type
have significantly higher speed and life-expectancy requirements than
anything in the cnc world would require. So these bearings seem to me to be
designed for exactly what you stated was desirable for CNC - heavy work-load
and designed for non-stop use. I know you can buy a can(12 bearings) of
abec-7 roller-blade bearings for $10. Isn't that more than sufficient for
the needs I am talking about?

Quite honestly, I don't see where all of the inaccuracy is coming from in a
home-made (read non-comercial linear components) solution. As an example, I
would refer to something like thk slides which must be screwed/bolted to a
substrate surface every 6-8 inches. It seems to me that the stiffness of
the substrate and the accuracy of the placement of those bolts will have an
enormous effect on the accuracy of this system. Having never actually used
thk or similar slides - am I wrong? Obviously a hand made solution has the
same issues; however, my point is that the implementation of a given part
looks to me to be at least as important as the part itself.

As for the alternatives to having components made at commercial machine
shops, I was hoping that there existed things like mail-order job shops that
were more cost effective and people might have names numbers etc.

----- Original Message -----
From: "Steve" <robo_man@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, March 31, 2002 4:01 PM
Subject: Re: [CAD_CAM_EDM_DRO] Linear Slide Components


> From: "Lee Wenger" <wenger2k@...>
> > One of the major elements is obviously the linear slide components and
to
> be
> > perfectly honest I don't understand why the need (in other words, the
> > quantifiable difference) to use commercial quality components that
> increase
> > the cost so dramatically. People regularly bash any use of anything
other
> > than commercial grade linear slide components? Why, why is it that a
> > V-wheel on angle iron or skateboard wheels against a hard flat edge is
> such
> > a horrible idea?
>
> We have a 30% grade road that runs for about 12 miles where I use to
> live. A friend thought it would be fun to skateboard down it. He made it
> about 1/3 of the way down before the wheels got soft and the bearings came
> loose, landing him in the hospital. Other then the fact that they aren't
> built to handle heavy loads,and non-stop use, there is no reason not to,
> unless accuracy matters. If you aren't going to place heavy loads on it,
not
> going to use it for more then a little while non-stop and don't need to
hold
> a tolerance then there is no reason to spend the extra money.
>
> > From what I've seen, as soon as you use any commercially
> > available linear components the cost of those components alone is well
in
> > excess of $1000 for a 4x8
>
> It's not a cheep hobby.
>
> > I'm not being defensive but rather truly trying to determine the
> difference
> > between these approaches.
>
> It all depends on what you want to make.
>
> > Another question I have is how does one go about squaring a large table.
> I
> > certainly know how to do traditional construction type of squaring and
> what
> > a 3-4-5 triangle is and all that but how on earth do you measure these
> > things to sufficient accuracy on such a large scale. I'm assuming my
> > framing square will be completely useless as it would only be suitable
for
> > initial setting but I would need a far more accurate way to finalize my
> > squaring.
>
> It totally depends on how accurate you need to be. A framing square
might
> well be as good as you need. An option for large home built machines is to
> build it with some adjustment in it. Put something large on the table with
> the back edge as square as you can. You then cut the back, front, right
and
> left. Check size to make sure you cut the front/back, left/right even.
Then
> flip the object on the table over and line up the back edge. When you
check
> the right or left side it'll be off twice as much as the table is out of
> square. Adjust the table until you've taken out half the distance and
start
> over to make sure it's right.
>
> > Last question, I don't own a mill and will need to make some parts for
my
> > machine. Do you all have suggestions as to lower cost ways to produce
> some
> > of the machined parts I need made outside of the traditional commercial
> > machine shop?
>
> A hammer, a chisel, a file and a micrometer. There isn't a huge amount
> you can do with a machine that you can't do by hand. The difference is
that
> the machine might take 20 min and doing it by hand might take hours, days
or
> even months. What you are paying for at a shop is mostly their time, but
> it's also what they know and the machines they have to do things faster.
IE
> I have no interest in hand scraping in ways, it's worth the price to send
> them out to some one with a big grinder. If it's not worth it to you, then
> use what ever tools you do have and do it your self.
>
>
>
> Addresses:
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>
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