Re: [CAD_CAM_EDM_DRO] Precision components and machining
Posted by
Marcus & Eva
on 2002-04-01 08:23:51 UTC
Hi Lee:
I've read your posts with interest, and I think you make some excellent
points.
The accuracy you can expect from a "cobbled together" solution such as you
describe will be determined by the care and quality with which you design it
and put it together.
Buying industrial grade components will make that task a bit easier, because
some of the critical bits are already done to a standard that you can rely
on, but yes, you still have to do your bit in ensuring that a precision
ground rail is mounted to a flat mount, or the quality of the rail will have
been wasted.
What you always trade off, is hours vs dollars, or dollars vs difficulty.
For a guy like me, who machines for a living, the trade off that I can live
with is very different from that of a hobbyist who cannot justify large
chunks of money to save a few hours.
However, you do have to consider that you WILL need to spend SOME money to
make this kind of project go, and you can get "penny wise and pound
foolish".
If you're looking at a project that will cost you a few thousand bucks
anyway, it's a foolish thing to put its success in jeopardy over another
fifty bucks.
With that in mind, getting your machining jobbed out is a realistic option
if you can minimise the machining that has to be done, and make the
machining that is needed, easy to do.
That requires good design, which means that you need to know something about
machining in order to make the machinists job easier.
That, in turn, means having experience, and if you don't already have some,
the very best way is to get the gear and have at it.
A very good alternative is to use somebody else's gear.
For many of us, that means signing up for a night school course and doing
our machining there.
Of course, there's also buddies who can be imposed upon.
What you need to do is rack up the expected cost of getting it all jobbed
out at 80 bucks an hour, and then go shopping for your own gear.
Your level of confidence, the numbers you come up with, and the extent of
your personal network, will quickly tell you which option is most viable.
Don't forget that you get to keep the gear if you buy your own, and the
machining knowledge you gain will help you a LOT when it comes time to run
the CNC. (Never mind the ability to fix and tinker)
My own take on roller skate wheels and angle iron??
Sure it'll work, as long as you stay within its limitations.
How to do that??? Give it a try. Crash and burn if need be.
You'll find out in a hurry, and you won't have busted the bank getting
there.
Cheers
Marcus
PS: I don't know of any mail order shops who could do what you are wishing
for.
Don't forget, you need to be able to communicate a lot of information that
takes time to absorb.
Time costs a lot for any business with high capital costs; that's why
machine shops have to charge what they do.
Rates are typically $1.33 CDN per MINUTE in my region!!!
MC
I've read your posts with interest, and I think you make some excellent
points.
The accuracy you can expect from a "cobbled together" solution such as you
describe will be determined by the care and quality with which you design it
and put it together.
Buying industrial grade components will make that task a bit easier, because
some of the critical bits are already done to a standard that you can rely
on, but yes, you still have to do your bit in ensuring that a precision
ground rail is mounted to a flat mount, or the quality of the rail will have
been wasted.
What you always trade off, is hours vs dollars, or dollars vs difficulty.
For a guy like me, who machines for a living, the trade off that I can live
with is very different from that of a hobbyist who cannot justify large
chunks of money to save a few hours.
However, you do have to consider that you WILL need to spend SOME money to
make this kind of project go, and you can get "penny wise and pound
foolish".
If you're looking at a project that will cost you a few thousand bucks
anyway, it's a foolish thing to put its success in jeopardy over another
fifty bucks.
With that in mind, getting your machining jobbed out is a realistic option
if you can minimise the machining that has to be done, and make the
machining that is needed, easy to do.
That requires good design, which means that you need to know something about
machining in order to make the machinists job easier.
That, in turn, means having experience, and if you don't already have some,
the very best way is to get the gear and have at it.
A very good alternative is to use somebody else's gear.
For many of us, that means signing up for a night school course and doing
our machining there.
Of course, there's also buddies who can be imposed upon.
What you need to do is rack up the expected cost of getting it all jobbed
out at 80 bucks an hour, and then go shopping for your own gear.
Your level of confidence, the numbers you come up with, and the extent of
your personal network, will quickly tell you which option is most viable.
Don't forget that you get to keep the gear if you buy your own, and the
machining knowledge you gain will help you a LOT when it comes time to run
the CNC. (Never mind the ability to fix and tinker)
My own take on roller skate wheels and angle iron??
Sure it'll work, as long as you stay within its limitations.
How to do that??? Give it a try. Crash and burn if need be.
You'll find out in a hurry, and you won't have busted the bank getting
there.
Cheers
Marcus
PS: I don't know of any mail order shops who could do what you are wishing
for.
Don't forget, you need to be able to communicate a lot of information that
takes time to absorb.
Time costs a lot for any business with high capital costs; that's why
machine shops have to charge what they do.
Rates are typically $1.33 CDN per MINUTE in my region!!!
MC
----- Original Message -----
From: "Lee Wenger" <wenger2k@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, March 31, 2002 6:38 PM
Subject: 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.
>