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Mario Alvarez

aligning fixture to tables using 2 dowell pins

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I need to trim some composites for aerospace

I having problems aligning the fixture using 2 dowell pins to the machine's table

any suggestion of how to do it the easiest way

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49 minutes ago, Mario Alvarez said:

any suggestion of how to do it the easiest way

You will have to be more specific about your table.

Is it just a normal slotted table or does it have a sub plate?

If sub plate does it have holes.....what type....?

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1 hour ago, Mario Alvarez said:

I need to trim some composites for aerospace

I having problems aligning the fixture using 2 dowell pins to the machine's table

any suggestion of how to do it the easiest way

What problems are you having?

When I was trimming composite panels at the Interiors Responsibility Center for Boeing, we used Tool Hole, and Slot method for using the two dowel pins to align the fixture.

You will never get two perfect dowel pins in both the fixture and the table. However, if you use Pins in the Table, and a Tool Hole (as the location), and a Tool Slot (to provide orientation, to "clock" the part), you'll have the best of both worlds.

Our vacuum fixtures had Aluminum Base Plates, where we inserted a hardened Dowel Pin Bushing for the Tool hole, and a Hardened Slot Bushing for the Tool Slot. Both were pressed into the base plate.

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10 minutes ago, Colin Gilchrist said:

You will never get two perfect dowel pins in both the fixture and the table. However, if you use Pins in the Table, and a Tool Hole (as the location), and a Tool Slot (to provide orientation, to "clock" the part), you'll have the best of both worlds.

Colin is correct, you are not likely to get a perfect match using premade holes and fixtures, in the applications that I have seen the dowel holes were intentionally oversized, losing some of the precision, but allowing the same fixture to be quickly setup and removed.

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Depending on the capabilities of your machine, as long as your Pins are machined into the bed of your machine accurately, you can simply place two pins into the holes you want to use, and then use the crane to lower your fixture onto the Locating Pin and Slot Pin.

We would use a 3rd Pin, located at X-30.0 Inches from the Locating Pin. This was our "start point", and the operator would use MDI to drive the machine to this "-30 inch" position. The first tool in every program is a .375 Dowel Pin, held in a collet. When the Operator would MDI in the "start pin position", that point was always at -30., 0., 3.

That point is -30 in X, nothing in Y, and 3" above the height of the table. Our dowel pins stuck out about 2.75 inches from the top of our table. What this allowed the operator to do, was slide a "check bushing" up the Start Point Pin, to see if the spindle was aligned with the pin axis. If not, the Operator would jog the machine manually, until the pins were in alignment. Then, in our Programs, we had a G92 Start Point of -30, 0, 3. This "tells the machine to use its current location in space, as that coordinate".

2 minutes ago, Thee Byte™ said:

Colin is correct, you are not likely to get a perfect match using premade holes and fixtures, in the applications that I have seen the dowel holes were intentionally oversized, losing some of the precision, but allowing the same fixture to be quickly setup and removed.

Tool Hole, and Slot is the better method here. It allows both "Position" and "Orientation" to be established.

The type of work you are doing, is basically what I did for about 5 years. Even on a 'pressed panel', we would machine a 'foam border', that snaps together like a puzzle. The lower left corner of the 1st Foam Piece would have the Tool Hole machined. The puzzle piece that is at the farthest "right lower corner", would get the Tool Slot machined in it. The Tool Hole establishes position, the tool slot clocks the panel to the axis of the Pins. (Hopefully you machined the 'Dowel Pin Locations' into the machine table, with the same head that is going to cut the parts...)

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