Re: [CAD_CAM_EDM_DRO] Cast resin for a cnc mill design - good idea?

I beg to disagree a bit. The "small" DreamMachine I'm building has an
envelope equal to or greater than 18 x 12 x 8. The estimated weight for
this machine is in the neighborhood of 400 pounds...and that's includes
having both the lathe and the milling machine as a single unit.
This unit uses heavy ribs and will be made from cast iron. I've got all
the prototype parts made from weldments for the bases, columns and slides.
The total weight for those is less than 200 pounds.

Also, I have a 9 x 49 Bridgeport type milling machine installed in my shop.
It only weighs in at 2000 pounds.

Smoke

>Hi Tom:
> I think you have a good basic approach for this project, but I am
>concerned that you have underestimated the size of a milling machine with
>the work envelope you have described.
>A capacity of 18x12x8 implies a pretty large machine; all up weight is
>probably going to run several thousand pounds if you want to get decent
>rigidity.
>The problem works out like this:
>You can have either a small table running on long ways, or you can have a
>long table running on top of a short saddle.
>For an 18" stroke machine you need to have a minimum of 36" of guiding
>surface if you want to keep the table fully supported.
>This means either a 36" wide base or a 36" long table.
>A 36x12 table (if you choose the long table approach) will need to be at
>least 4" thick.
>If it's ribbed cast iron you are talking about a 500 lb lump and you

haven't

>even put a vise or a block on it yet!
>Imagine the size of the bearings, motors, and ballscrews you will need to
>drive this thing!
>Notice, I'm not saying it's impossible; what I am saying is that it's a BIG
>project in the most literal sense!!!
>Cheers
>
>Marcus
>-----Original Message-----
>From: Tom Murray <thomasm923@...>
>To: CAD_CAM_EDM_DRO@yahoogroups.com <CAD_CAM_EDM_DRO@yahoogroups.com>
>Date: Sunday, April 22, 2001 10:59 AM
>Subject: [CAD_CAM_EDM_DRO] Cast resin for a cnc mill design - good idea?
>
>
>>In the recent past there was a thread covering the topic of using
>>epoxy and polyester resins in the construction of mill frames. A few
>>weeks before that thread started, I was surprise to learn that at
>>least one commercial manufacturer (Light Machines) builds the frame
>>of their mills out of resin. I began to wonder if this would be a
>>good way to build a home-built system, for there are some obvious
>>advantages. First of all, casting resin is a lot easier than casting
>>substantial pieces of iron or aluminum. Second, although the
>>underlying structure should be solidly joined together, I don't think
>>there is any need for welding it. Third, from what I have read, it
>>seems that cast resin cuts resonance by a substantial amount.
>>
>>In the near future I plan to build a desktop cnc mill. This mill
>>won't be very large, but a bit larger than a Taig or a Sherline, with
>>a travel envelope of about 18"x12"x8" (x,y,z). I am only in the
>>planning stages, but I am ready to sketch my design out in my cad
>>program. As I stated earlier, I am considering using cast resin in my
>>design. Within the resin there would be an embedded substructure
>>built from iron pipe, with sand-cast aluminum parts to join the pipe
>>and to provide areas to attach linear ways and other necessary
>>components. This design solution is attractive to me because I don't
>>have access to many metal-working tools and I am not very adept at
>>welding. On the other hand, sand casting is something that I would
>>like to pursue, so building a small electric foundry to cast the
>>aluminum parts fits right into my plans.
>>
>>I would like to hear some thoughts from the group on this approach. I
>>have learned so much in the past months that I have spent lurking
>>(for the most part). I am looking forward to picking some of your
>>brains on this topic.
>>
>>Tom Murray
>>
>>
>>
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>
>Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the

discussion of shop built systems, for CAD, CAM, EDM, and DRO.

>
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