Re: [CAD_CAM_EDM_DRO] re:Levelling large table

Hi Doug,

About 2 months ago, I received a Nasa TechBriefs. In it was a short, ~200
words, write-up on composite laminators switching from aluminum tool plate
to plate glass. Cost and inherent flatness were given as the reasons. I
received a quote from a local glass company of $288 for 72"x144"x1/4" sheet
delivered, $4/sqft. I will use polyethylene sheet edges and covers to
protect the glass when not actively laminating.

I am using surplus fabric cutting room tables for my cnc fabric cutter and
foam carver. They are not as stiff as I remember them when I worked in a
cutting room in high school. I am iterating a stiffening solution using
finite element program to get the natural frequencies higher. Additional
shear reinforcements and some additional legs are planned to be added.

My plan for leveling is to install more deep section support members under
the tabletop(hardboard faced MDF) and using, as yet undesigned, leveling
jacks attached to these supports, remove as much of the tabletop sag as
possible. Then construct dams around the perimeter, install plastic sheet
on top of tabletop, screw down sheets of 10ga expanded metal mesh and pour a
self leveling floor mix(Mastertop 112 $30/bag for 23 sqft @ 1/4" thick) into
the dammed area. The actual working surface will be either polyethylene
sheet or plate glass.

I have not yet designed the machines yet, nor the attachment details to the
tables. On both the cutting table (78"x240") and the foam router table
(72"x96") I have some regenerative blowers for vacuum holdown. This feature
complicates the design. Unfortunately I have more ideas than time and
money.


I like your idea about seeing Les Watt's setup.

Good luck.

Joe Fahy

----- Original Message -----
From: "Doug Harrison" <prototype@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Monday, January 15, 2001 1:20 PM
Subject: Re: [CAD_CAM_EDM_DRO] re:Levelling large table


>
> > Hi Doug,
> >
> > What did you decide to do on leveling the table?
> >
> > Thanks,
> > Joe Fahy
> >
> Perhaps it was you that gave me the idea of using an oil trough and
> micrometer head. This got me started on several new ideas. Here is my
> current thinking:
>
> The frame must first be stress relieved or it will change over time. I
can
> do this with a propane flame thrower - not perfect but better than
nothing.
> Fine thread jack screws on the legs will provide levelling adjustments.
>
> We will build a trough around the top rails and pour hot epoxy. This
epoxy
> is 100% solids and has very little shrinkage. The heat is to reduce
> viscosity. After curing the dams will be removed and the miniscus filed
> away (Smoke pointed this out).
>
> The table will be .625 cast aluminum tool plate bolted to the frame. A
> viscoelastic tape will be applied between the epoxy bed and toolplate to
> provide some damping and allowance for thermal movement.
>
> I originally planned to put the linear rails on the plate surface. The
> Hiwin rep says they work equally well upside down, so I am thinking of
> mounting them underneath the plate. Depends on the accuracy of the plate.
> This will allow me to use the entire top surface for machining. It will
> also serve as a work table and laminating bench. Z accuracy will be
> slightly comprimized with the rails on the bottom due to thickness
> variations in the plate (up to .005"). However, Z axis variations are not
> much concern for my application. I can alway improve it by flycutting the
> spoilboard.
>
> The Y axis rails will also be upside down to get them as close as possible
> to the bed. I need 24" Z travel and this will help rigidity. The gantry
to
> bed clearance will most likely be adjustable in three steps - 6" for flat
> sheets, 12" for bigger stuff and 24" for foam cored molds.
>
> I plan to use dual X axis screws and dual motors. Need to go up to north
> Georgia soon to see Les Watts' machine before I start building though. He
> has some brilliant ideas on accuracy mapping.
>
> The rails and screws will be ordered this week.
>
> Doug
>
>
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