Re: [CAD_CAM_EDM_DRO] Re: machine design was: Re: Re: re:Re: Lead screws for ever...(plastic)

:-)...

Very cool.. You're obviously talking from experience as well, that's the
scary bit :-).

The closest I've got to what you're talking about is a machine I built last
month to test all of the "freeware" and shareware software out there...
I'll dig out a photo of it and put it in the files area... Words don't do
it justice... I'll also post some pics of my current "CNC" lathe for folks
to giggle at.

I've seen most of the plans on the net, I've got a list of links which runs
in to three "page downs" so to speak. I've been planning this machine for
about 18 months, and I've looked at pretty much everything I could find, and
I've been reading this list for a while which has been quite helpful, as
well as a couple of newsgroups.

For some more details on my machine, which might be useful to other list
readers...

I'm going to make the
base and bridge out of 1" MDF and then take them down to a local foundry.
They are going to cast them up in solid aluminium. They have given me
guidelines on what can and can't be cast, and the cost is by weight of alloy
used in the pour, plus a nominal charge for setup.

Then I truck the thing down to a machine shop and get the critical faces fly
cut (after passivating etc) and drilled for mounting rails etc. Total
cost is going to be in the order of $500-$700. To get enough 12mm plate ali
to do the same thing was going to cost $700 just for the material.

Guide rails are going to be 20mm ground steel, with split Glacier bearings
on the moving bits.
Bed is 10mm billet with spacers to support MDF sacrificial above the bed for
vacuum hold down if I decide on that.

Screws were going to be Kerk, but we've been there already.

The one trick is that I'll not be paying "real" charges for access to the
big CNC mill required to do the fly cutting, but it's a good way to get a
really solid machine base for little effort, MDF is so much easier to work
than metal.

In theory this whole process starts when I get my new lathe, so I can make
some of the motor mounts etc, and experiment with the nut problem. That's
next week.. Cross fingers.

re: our exchange rate.. Sucks. It was sitting about 50c US to our dollar
for ages, but it's slipped to 39.something..

Cheers, Chris.

* Design engineer, Assembly worker, Cleaner.
* Ohmark Electronics. PO Box 5302, Christchurch, New Zealand.
* http://www.ohmark.co.nz

----- Original Message -----
From: <ballendo@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Sunday, October 29, 2000 2:23 PM
Subject: [CAD_CAM_EDM_DRO] Re: machine design was: Re: Re: re:Re: Lead
screws for ever...(plastic)


> Chris,
>
> Thanks for mentioning what you will use the machine for.
>
> Have you seen Dave rigotti's hobby CNC plans?
> The luberth plotter site(s) I've mentioned?
> Neil Gillies Seagull site? (R/C sailplanes and home made CNC
> machines/SW)
>
> One of the things I like about this list is its diversity. We've got
> guys who hold "tenths" (while they're smilin' for the camera...)
> And guys who are wondering what "tenths" are...
>
> Which means we have a large VARIETY of machines to talk about.
>
> You can make a machine from the hardware store parts bins which can
> prob'ly do the sort of parts you may need. In models, it's RELATIVE
> DIMENSIONS which usually matter, NOT ACCURACY! (I'm using strict
> definitions here)
>
> As long as the airfoil is proportionally correct, it will work!
> As long as the WWII plastic model "tank" LOOKS right, it is.
> As long as the parts FIT together, it all works.
>
> There's NO WAY I'd pay anywhere NEAR $4K(don't know the exch. rate)
> for 3 screws/nuts for a "hobby" machine. UNLESS I was going into
> production; Then EVERYTHING changes!
>
> Let's look at a "worst case" scenario. You build a machine out of
> WOOD! Using 3/4 mild steel (cold rolled) rods for guides. And MAPLE
> blocks with holes in them (soaked in oil) for linear bearings. Other
> maple blocks to mount the leadscrews. And "hardware store" threaded
> rod for leadscrews. You try "coupling nuts" on the screws, but decide
> that there's too much "movement"(the word backlash is unknown to you
> at this point), so you (big spender that you are) splurge and buy a
> TAP!
> And some DELRIN (from a plastics store). And make your own nuts. They
> still bind, so you buy a DIE and "chase" the threads of
> your "leadscrews". Then visit the DUMP and tear stepper motors out of
> old IBM printers(and throw away those funny disks with the holes
> in 'em attached to the motors,'cause ya don't know what good THEY
> could be!).
> You figure out some 4 transistor drives from an electronics magazine
> article. And puzzle out some software that "spits bits" to
> your "drivers"(you're learnin' the lingo, now) and makes the thing
> go.
>
> And you know what you find after all this? That it WORKS!!! You
> make parts! And they work, TOO! and then...
>
> You start to notice that parts made on one part of the machine table
> don't ALWAYS fit parts made on another part of the table. So you
> start to make parts that need to fit other parts on certain "parts"
> of the table! And again, it WORKS!!
>
> I did this. NOW, I've done a LOT more. With MUCH better machines. But
> you know what? Machines don't hafta cost thousands and weigh hundreds
> of pounds to WORK. That's STILL true.
>
> The point of all this is to keep it in perspective. Most ANY cnc
> machine you can contemplate will do a good job, within its'
> boundaries. Good construction with poor parts beats poor construction
> with "best" parts nearly EVERY time.
>
> Ballendo
>
> P.S. Good luck on the "nut" design. We'll be watching for it.
>
> >Chris wrote:
> >I was suprised, as they were more expensive... I was setup for the
> >fall by a chap from the SKF dealership here telling me they were
> >significantly cheaper..
>
> >at the end of the day this machine is going to cut balsa and plastic
> >for models, probably not a big deal..
>
> >My problem is that I have a quote sitting on my desk for nearly
> >$4000.00 NZ for the three screws/nuts I want. Considering this is a
> >hobby machine after all
>
> >I'm sure I could still get the end product for well under $1000
> >for all three axis, time isn't really a problem,
>
> >The other up side of doing it myself it that if it works I'll be
> >able to pass on the nut design to the list.
>
> >Cheers, Chris.
>
>
>
>
>
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