I mentioned the 2" x 2" because that allows staying with Gingery's orginal specifications. Alternately people could profitably use a 2" x 3" or 2" x 4" profile extrusions to increase the bed depth and thus yield strength.
Otherwise I agree with you.
What I personally would use would be a 3" x 3" or 3" x 4.5" profile extrusion with a 3/8" x 4" CRS ways. In addition to the shallow bed Gingery's design suffers from narrow and thin ways relative to the spindle center height.
And I'd reinforce this with 5/8" diameter steel rebars running the length of the profile inside, and held in place with CNC Zone's best homebrew EPG mix.
The resulting bed structure will be multiples stronger than Gingery's original design.
However, one has to rescale and re-dimension all the major parts (headstock, tailstock, carriage) for the increased width of 4" ways. This in turn requires approximately doubling the foundry capacity from 1 to 2 quarts, or from 57 to 114 cubic inches. Call it 10 lbs of Al. This would a B10 or A16 size crucible. Or a 5" ID x 8" tall steel pipe crucible.
--- In gingery_machines@yahoogroups.com, "John Dammeyer" <johnd@...> wrote:
>
> If you search the archives for postings with my name you'll find a number
> of postings I made some years ago on the subject of the relative
> relationships of the Gingery dimensions.
>
> The small section lathe bed on the Gingery was designed to fit the casting
> capabilities of the 1 quart or #6 crucible. But it's totally wrong for a
> 7" lathe. It's one of the weak points of the design. Way too much flex.
> The 2" square 8020 wouldn't be much better.
>
> John Dammeyer
>
> Automation Artisans Inc.
> http://www.autoartisans.com/ELS/
> Ph. 1 250 544 4950
>
>
> > -----Original Message-----
> > From: gingery_machines@yahoogroups.com
> > [mailto:gingery_machines@yahoogroups.com] On Behalf Of Pierre Coueffin
> > Sent: Tuesday, October 19, 2010 9:44 AM
> > To: gingery_machines@yahoogroups.com
> > Subject: Re: [gingery_machines] Re: 8020 bed was: epoxy
> > granite was: outsourcing the bed scraping
> >
> >
> > I've yet to see a lathe, but a lot of DIY types seem to use 8020 to
> > build gantry type mills or CNC routers. The fact that it seem to hold
> > up with minimal flex in such a precarious setup is encouraging.
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
>
http://groups.yahoo.com/group/gingery_machines/app/peoplemap/view/map
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