Re: [CAD_CAM_EDM_DRO] Re: Linear slides

John,

A profiled ball linear rail is prob overkill for such a light load.
Try thompson shafts (easy web search). I can check MSC
prices for you... let's see .. (oh this book is heavy)...

1" x 36" casehardened linear shaft (not drilled) $39.91
1" unmounted super ball bushing linear bearings $33.02 ea

For linear rail
thompson 20 mm x 1 meter rail $309.82

Bearings $126.55 ea

48" redi-rail $87.81

The dynamic load capacity of the linear shaft bearing is about 1000 lb.
Shaft bending would be too high at that load but you don't need that much
anyway.

Static load only is given for the 20 mm rail bearing- 4720 lb.

336 lb radial load given for the redi-rail.


Dash,

What you said is certainly true. I would have reps and sales
engineers for linear motion components visit often at a large
corporation I worked for even though I rarely bought more
than a couple units at a time. As a small business now,
I still have reps come by.

I can certainly get some price breaks for larger quantities
and have considered holding a small inventory for retail
sales. I build industrial units for in house use only.

The problem is the cost of the units. Ballscrews, rails,
servos, etc are priced out of sight for most
hobby markets. Or at least I think so.

Take a look at distributors like MSC. They have linear rails
and ballscrews listed in unit quantities with prices. But look
at the prices!

That leaves surplus. Plenty of that around but it cannot pass
through too many hands. And it isn't exactly free.

About the best I can do for new or new in the box surplus
for let's say a one meter by one meter by half meter XYZ
machine is as follows:

Profiled linear ball rails:
three sets $1,000 or so

three servos $750

three encoders $120

Three ballscrews $600

bearing blocks/ballscrew
end machining $1200 (a BIG problem)

So the best I could do for a kit for an accurate, rigid,
zero backlash xyz machine would be $3670. I could not
do those types of prices for a one time deal. And my accountant would
quickly advise me to go in to another
more profitable line of business...like ditch digging or
asking if you want fries with that order. :^)

I toyed around with the idea but concluded the market isn't
there. I would have to invest in considerable inventory to
do this. Please somebody prove me wrong.

You could drop that to $2600 or so if you can machine
bearings and ballscrews... but that involves machining
hardened materials to tenths. If you can do it and have the
machinery great.

I guess the better news is that such a kit would be industrial
quality and accuracy. A hobby tool does not need to survive
8 hours a day or be repeatabe to sub thousands. So use
thompson rails, acme screws, steppers, timing belts, and
pillow blocks. Consider used parts. Note the price difference above. Others
kit up such packages and many look great.

Note that very small machines could be much less with
a little luck on ebay and surplus dealers. Lots of short
pieces and cutoffs around. Small low voltage servos
seem plentiful.

Or rebuild an old machine. That is the cheapest way I know
of getting a good cnc platform. It's fun too. Hobbyists can
do this and have a great time. Of course many on the list have gone this
route so there is a good knowledge base. Labor costs usually preclude
doing this in industry so old machines are dirt cheap. You have to know
where to find them (usually not machinery dealers).

What are yout thoughts ?

Les


Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html

----- Original Message -----
From: "the_dutros" <the_dutros@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, February 15, 2002 8:05 AM
Subject: [CAD_CAM_EDM_DRO] Re: Linear slides


> The problem is that this market has not embraced the internet yet,
> insted preferring to use the hideously inefficient "distributor"
> model. As it is with ball screws and step motors, you can fing the
> manufacturer, who will be glad to point you to a distributor, who
> will be glad to give you a "quote."
>
> The biggest falacy is that even places that manufacturer products
> that use these items don't buy in quantities much larger than
> a "hobbiest" would.
>
> I have been watching this sort of discussion for some time, and am
> about to propose a "solution."
>
> -DASH
>
> --- In CAD_CAM_EDM_DRO@y..., "John H." <johnhe-uk@s...> wrote:
> > Oky Doky, I'm now giving up my search on the Holey Grail of sites
> that lists
> > prices and not just model numbers.
> > I'm looking for a very, very, rough idea of how much a 1000 -
> 1200mm linear
> > slide would be to carry anything over 5 - 15kilos. Infact, has
> anyone seen a
> > site selling linear rails, slides, bearings etc with prices on it?
> Or is
> > this a "If you've got to ask you can't afford it" thing. [John gets
> his
> > oxygen mask ready for the replies]
> >
> > John H.
>
>
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