Fwd: [OpenLathe] Re: Unimat & Metalmaster Small Bar Ways Lathes

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Sam Putman

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Mar 13, 2010, 12:53:49 PM3/13/10
to RepLab Discussion List, Open Manufacturing
Good to see some activity on this list of late

-Sam

---------- Forwarded message ----------
From: charcad2006 <charc...@yahoo.com>
Date: Fri, Mar 12, 2010 at 7:02 PM
Subject: [OpenLathe] Re: Unimat & Metalmaster Small Bar Ways Lathes
To: Open...@yahoogroups.com


 

Bruce,

Thanks. Those plans are helpful for study. I've seen that photo of the lathes themselves before someplace else. Maybe CNC Zone. I didn't know there was an entire project package.

Notice the lead screw center mounted between the bar ways? The Unimat adopts this also. I can't think of a better way to equalize the traversing force on the carriage. The old fashioned side mounting screw and carriage apron (ala my Atlas 10x24 or any Chinese machine) has to induce a constant twisting force. Plus there's a big elaboration of bearings and pillow blocks to support it all.

For the bar ways I have our favorite Alloy 4142 HT-TGP (heat treated, turned, ground & polished) in mind. 1" diameter is around $26 ea for 24" lengths.

One problem with that design is the ratio of the ways base to spindle height. For maximum stability the ways' width ideally should be 120% of spindle height, which is 1/2 of the swing. For a 4" swing that would be 2.4". This is Goldilock's just right for a small "bar ways" lathe with 3" x 3" bed based on a length of 8020 t-slot aluminum extrusion.

A CNC equipped Sherline with 3.5" swing runs about $2300 delivered, including a computer. Subtract computer and this is still about $1700. Sherline manages to use 135 oz/in stepper motors and free Linux EMC2. This size of stepper is cheap and can be run with recycled computer power supplies ganged in series. There are also several public domain driver board designs available for that class of stepper.

I want to develop a comparable CNC project lathe design that's buildable for about $250-$300 cash outlay. My concept is to use a small stiff CNC router - dozens to hundreds of plans available - to assist with the fabrication. Plus a 1/2" el cheapo drill press.

And small aluminum castings for those who want to avoid the cost of aluminum stock for the headstock, carriage and tailstock.



--- In Open...@yahoogroups.com, "Bruce" <bbellows@...> wrote:
>
>
> Mark
> Here is the link to the planes for the small lathe
> http://groups.yahoo.com/group/OpenLathe/files/small%20cnc%20lathe/
>
> Bruce
>
> --- In Open...@yahoogroups.com, "charcad2006" <charcad2006@> wrote:
> >
> > Bruce,
> >
> > While looking at these I thought of you.
> >
> > http://www.lathes.co.uk/unimat/
> > http://www.lathes.co.uk/metalmasterusa/
> >
> > I've been contemplating a small project lathe design. Something in the Sherline class. Cheap, easy to build, high local parts content, easily adaptable to CNC or ELS.
> >
> > This is a photo essay on building a home-made copy of a Unimat lathe.
> >
> > http://www.lathes.co.uk/unimat/page15.html
> >
>

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Sam Putman

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Mar 13, 2010, 12:54:34 PM3/13/10
to RepLab Discussion List, Open Manufacturing
---------- Forwarded message ----------
From: charcad2006 <charc...@yahoo.com>
Date: Sat, Mar 13, 2010 at 7:16 AM
Subject: [OpenLathe] Re: Unimat & Metalmaster Small Bar Ways Lathes
To: Open...@yahoogroups.com


 

Bruce,

The Unimats are worth some study in the small lathe class. Quite small actually. 3" swing by 5" between centers for the first ones.
Tony's history shows they changed quite a bit in design composition over time. Cast iron parts to zamac die castings to aluminum die castings...

Consider the reputation Unimats have to this day among model makers. There's a simple reason the mix 'n match materials don't matter in small machines. Relatively large parts are required before differing coefficients of thermal expansion will sum enough to matter.



>reaffirms my view of their simplicity and built in accuracy.<

Exactly. I think this class of design obtains this by separating the fabrication of the "ways" from the "bed". The "ways" - which are round bar in our case - require the precision. The chief requirement for "bed" is yield strength.

The traditional lathe design combines ways and bed into a single piece of cast iron. And therefore requires heavy foundry, milling, grinding and heat treating equipment. Gingery simulated these results by mounting CRS flat bar on top of a "bed". Cast aluminum and hand scraped in his case. The pros and cons of this CRS emulation have been argued out before.

What is not in dispute is that no commercial lathe manufacturer has ever deemed this approach suitable for professional results.

This product:

http://www.speedymetals.com/ps-59-68-42gr1.aspx http://www.speedymetals.com/information/material63.html

was not generally available in Gingery's time. Neither was 8020 t-slot extrusion.

Some rough costing:

1" 4142 HT-TGP round bar, 24": 2 x $23 = $46
3030 series 8020 t-slot extrusion, 24", approximately $30
Acme precision leadscrew 1/2" - 10 tpi $15.60 per 3' at McMaster Carr

So far we've spent about $92. For this we got a vastly superior lathe bed, ways and leadscrew than the old Gingery design. I have some 3" x 3" (3030 series) 8020 pieces here. Without compromising headstock design stability we can build a 5" swing lathe on this.

The machine that emerges is 5" x approximately 16" 'tween centers.

If we want closer to the original Unimat size then use 8020 2" x 2" (2020 series) and 3/4" 4142 HT-TGP shafting. This will produce a 3" x 8" or longer machine. All costs fall accordingly.

Here are two related designs in the small precision bench lathe class.

--- In Open...@yahoogroups.com, Bruce Bellows <bbellows@...> wrote:
>
> Thanks Mark
>
> Nice little lathe. Seeing so many examples of round bar lathes just
> reaffirms my view of their simplicity and built in accuracy. If you are
> looking for something like a Sherline I have the drawings to produce one
> that came from a school project, complete with a bill of materials. It
> also has a bed with round shafting. Come to think of it maybe I should
> build one, I've probably got most of the material on hand. The plans for
> it may already be in the files section on the group home page. I'll check.
>
> Bruce

>
> charcad2006 wrote:
> >
> >
> > Bruce,
> >
> > While looking at these I thought of you.
> >
> > <http://www.lathes.co.uk/metalmasterusa/>
> >
> > I've been contemplating a small project lathe design. Something in the
> > Sherline class. Cheap, easy to build, high local parts content, easily
> > adaptable to CNC or ELS.
> >
> > This is a photo essay on building a home-made copy of a Unimat lathe.
> >
> > http://www.lathes.co.uk/unimat/page15.html
> > <http://www.lathes.co.uk/unimat/page15.html>
> >
> >
>

__._,_.___
Recent Activity:
Please note: this is an open source project and all postings to this group become public domain by posting them.  Questions should be directed to the moderator at Open...@gmail.com
.

__,_._,___

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