Summary:
Completed fixture plate, clamping test blank.
This is a fixture plate for clamping flat pieces of 6in stock. It is designed specifically to accommodate pieces 19in and 11in long, but can be used for any length larger than 3in, so long as proper precautions are taken. You will likely see this fixture used in a number of other projects, primarily relating to ME72.
Purpose:
Our ME72 robot, has a number of very large components cut out of 1/4in plates. Rather than fixture them in a double-vise setup (too slow), use super-glue fixture (not allowed in the shop), or cut them on the water jet (not high enough accuracy), we decided to fabricate an aluminum fixture plate. Since all of our 1/4in parts are cut out of the same 1/4in by 6in stock, we only made provisions for clamping 6in pieces. However, the design could be easily expanded to hold other sizes, or even non-square stock if need be. Note, that although the X axis clamps are nice, they are not required for proper clamping.
Design:
The general design is fairly simple. The parts index off of two rows of 1/8in dowel pins pressed into the plate, and are held in place by a row of Mitee-Bite hexagonal fixture clamps. The plate has a machined reference surface along the left (x) most edge, and two machined reference slots along the rear (y) edge. Additionally, there are two 1/4in dowel pins sticking out of the bottom of the plate which index against the T-Slots on our Fadal (tram is checked using the reference slots).
Note: The tramming pins did not end up working out the way we would have liked. Either because of T-slot issues, or because we installed them poorly the default tram is off by 20 thou. This is unfortunate, but only ads about 10 minutes in tram time.
Design Files: [Click Me]
Fabrication:
Fixturing:
Our first step (after milling a reference flat onto the left edge) was to install two vises in the Fadal VMC15. This let us securely grip the stock with minimal vibration. The following process was used:
Wipe down table and apply protective layer of WD40
Install first vise and tram.
Install second vise using steel bar to rough-tram.
Tighten close side of second vise and tap vise into tram.
Setup:
Next, we dialed in the tool offsets, and set up the fixture coordinate system. For the Y axis this involved the standard Fadal process using an edge finder. For the X axis, where we were travel limited, we created a “virtual” 6.5in fixture setting tool, and measured off of a 1-2-3 block clamped against the reference edge of the part.
This was not an ideal setup, but it seems to repeat to within a thou or so.
Cuts:
The piece was then cut as follows:
The majority of the top was faced with a spiral tool path.
The edges were faced with custom tool paths designed to remain within allowable travels.
Reference flats were cut along the +Y side.
All holes were spotted and then drilled.
Each hole was then drilled or taped as required.
Pins:
Finally, we pressed the pins in place using locktite retaining compound to ensure the 1/8in dowel pins wouldn’t pull out. In order to ensure consistent heights, we pressed the pins through a 3/16 plate. This both ensured the pins would be below the top of our parts, and helped us guarantee the pins would go in straight.
The tramming pins were pressed in without the benefit of retaining compound on the theory that we might at some point want to remove them.
MISC Photos:
Copper shims help compensate for undersized stock.
The fixture plate after cutting our first few parts.
Using a 3/16 piece of stock to press each dowel pin to a consistent height. The hole used was drilled undersized and reamed to a slip-fit.
The spiral tool paths worked very well, and proved easier to contain within allowable travel.