How to clamp workpiece squarely onto mill table

[Maplehead]

Hi All

Every time I search the subject question I get answers on how to cut-to-square a piece.
I already have a piece that is square. It is an 8" square sheet of acrylic by a 1/4" thick.
I want to clamp it onto my 123 blocks and have it square to the table. My dilemma is that I can't first clamp down square the 123 blocks. So for me to do it now I would have to clamp down both items at the same time while trying to make square the 123 blocks with a machinist square and getting one edge of the acrylic sheet parallel to the 123 blocks, thus making the sheet square to the table.
The above method is awkward and difficult.
Any better ideas?
Realize the pic is not how I intend to have it clamped. I just threw in the pieces to get an idea of what I am asking.

 

[woodchucker]

so still confused by your question, but let me see if I can answer.
I would put a piece that just fits into your table slot, stone the slot if there are burrs. That will help get a reference point. Use that piece as a fence

 

[Tony Wells]

Make yourself some "feathers". That's what they are for.

http://hobby-machinist.com/threads/how-would-you-setup-this-part.20696/#post-178433

 

[Metal]

a few things
1. using toe clamps like that you want to have the screw closer to the work piece than the triangle that goes to the table, or else a majority of the clamping force doesn't get to the work piece
2. If you do this a lot, consider a sacrificial layer, basically you put something under the acrylic, flycut or mill it to be level, and then clamp the acrylic to the table with that inbetween, this makes sure the flexible material is supported all the way and you can cut into the sacrificial layer if you need to.
3. The farther you clamp from your table the more small inaccuracies in the table are going to pronounce themselves.
4. To make this easier you might want to also consider what woo suggested, make a "vice stop" that fits snugly into the T-slot and gives you a surface you can butt the edge of the part against to get real close to square, once it is clamped down you can remove the stop and away you go.

 

[francist]

Most 1-2-3 blocks have at least some of the holes threaded. You could very quickly make up a few small tabs out of just about anything flat and secure those to the threaded holes in the edges of your blocks and sticking up a little past the top. Basically a little stop fence on your blocks. This would at least allow you to keep the blocks aligned with the edge of the plastic sheet while you fussed with clamping. You could unbolt the tabs once you were clamped.

Overall I think a fence or sacrificial layer to the table as suggested above is probably better and anytime you can butt something up against a fence it helps with stability. But I'm not sure what the ultimate purpose of the setup is for. Milling the sheet?, mounting something else for milling onto the sheet?, something else? Making that known might garner some more refined responses.

-frank

 

[Wreck™Wreck]

Simple really, clamp part and mill.

What is the problem?

 

[DaveD]

I wouldn't worry about the placement of the 123 blocks as long as they are under the clamp area and won't get hit by the cutter. That way all you have to do is align the work piece.

If it was me I'd just get some scrap pieces of ⅛ or ¼ aluminum or whatever you have laying around. It could even be another piece of scrap plastic.

 

[RJSakowski]

If I want to clamp a previously squared workpiece to my table so any subsequent milling will be parallel/perpendicular to the previously squared edges. I will roughly align the workpiece to either the edge or ways on the table. Then I will sweep one edge with a test indicator and adjust the workpiece accordingly.