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

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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