Re: [CAD_CAM_EDM_DRO] Clamping Fixture

Tom,

What you describe is along the lines of what I have been thinking about building over the last several years, I've just have not done it yet. I always seem to do it the had way with mutiple setups and have not really taken the time to fiqure out a good repeatable fixture/jig clamping design for my application. That's what is driving my motivations right now. So thank you very much for the description, it seems straight forward to me. SOme pics would be great as well if you have time.

Thanks Again

Victor A.

----- Original Message -----
From: Tom Hubin
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: Thursday, March 08, 2007 12:31 AM
Subject: Re: [CAD_CAM_EDM_DRO] Clamping Fixture


Hello Victor,

I often make fixtures for arrays of parts on my Sherline 5410 CNC mill.
FYI, my Sherline 5410 has a center to center area just a bit over 8.0 x
4.0 inches.

I design 1/8 inch or 1/16 inch diameter dowel pin holes into my work.
Sometimes just for alignment on the fixture but often for accurate
location in a complex assembly. Dowel pin holes can be drilled slightly
undersize then reamed to perfection. Slightly less than the dowel pin
for a press fit or slightly larger than the dowel pin for a slip fit.

If you don't need quite this much accuracy then you can work with
countersunk screws.

In either case, their are usually 2 or 3 plates involved. The bottom
plate has holes for 10-32 screws to secure to the Sherline table with
T-nuts. Also, four 0.2505 inch diameter reamed holes near the corners of
my work area. That is, as far back and forward and right and left as
possible. These four reamed holes are used with quarter inch steel dowel
pins to locate the plate on the table.

The top plate is for the array of parts that I am making. There will be
several 1/8 inch dowel pin holes that match dowel pin holes in the
bottom plate. Convenient screw size clearance holes in the top plate and
matching tapped holes in the bottom plate. As much as possible I use
dowel pin and screw holes that will be in the finished parts. However, I
create dowel pin and screw holes anyplace that I find necessary.

Usually I do all the drilling in the top plate, including any alignment
holes. The plate is secured to the table in any number of ways.
Alignment need not be perfect since all work later will be referenced to
the dowel pin holes.

Then I secure the top plate to the bottom plate with dowel pins and
screws. Then do any milling and additional work. Then I flip the plate
over to machine the backside. Then cut out the parts with the mill. If
they are all screwed down then they won't fly off as you cut away the
last of the outline.

But suppose your part has tapped holes and not through holes. Then I use
a middle plate with dowel pins and screw clearance holes counterbored
from the bottom up. So the top plate (or array of parts) is secured to
the middle plate from the underside of the middle plate. Then the middle
plate is secured to the bottom plate from the top.

For reference, I make a square piece that can be secured to the bottom
plate using dowel pins and screws. I use an edgefinder to find the edges
of the reference part and define the X and Y coordinates. Then remove
the reference part and you are ready to go.

So, the bottom and middle plates and the reference part are made once
and used forever. The top plate is machined into an array of parts.

Tom Hubin
thubin@...

*********************

Victor A. Estes wrote:
> Rexarino,
> Yes this is worth building a fixture/jig for because I will be doing
> this setup quite a bit.
>
> I have been doing this in the past by clamping, milling, moving the
> clamps, and the milling again, a pain. So it's time to make this job a
> little easier and a little more accurate results on my part.
> Victor A.





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