How to Hold and Make This?

[Phil3]

In a previous post, I asked about a larger vise to make a project, but some responses suggested holding the piece down on the table. That solves the problem of a limited vise jaw opening, but I don't know how to make a part like the one below to do that.

The part below is 5" long and 3" wide. I need to make the exact same thing except dimensions will be 5" long and 4" wide, and will be made out of black Delrin. My vise will not open wide enough to hold the raw material (4.5" x 12"). Please forgive my naive questions, but am not that experienced. I am thinking this process would work, but I am confident there is a better way.

1) Cut raw material to a 6" x 4.5" work piece.
2) Clamp work piece to table, but raised up with parallels.
3) Machine one 6" x 4.5" surface flat. Flip over.
4) Machine other 6" x 4.5" side flat, machine features, drill holes, countersink.
5) Machine all four edges to dimensions, using side of end mill (this never gives a good finish...argh).
6) Position work piece in vise on edge. Use rounding endmill to make rounded corners.
- The bevels on edges are not mandatory and I can do these if need be.

It is critical that the two holes are parallel with the 5" long edges and that the 4.5" width be with a few thousandths.

Other approaches welcomed.

Thanks,

Phil

 

[RJSakowski]

I would cut the stock 2" over the length of the finished part to provide a clamping area. I would clamp the stock to the table and mill one face. I would then flip the part over and rest on some sacrificial stock to clear the unmilled edges and machine the second side. While still clamped, I would side mill the long sides and drill the two holes. This will ensure that the holes are parallel to the sides. Then without removing the clamps, clamp the part from the long sides. When the second pair of clamps are secure the first two can be removed. This will ensure that the short sides will be perpendicular to the long sides. Finally, side mill the short sides. All your critical geometry will be done in a single setup.

 

[Boswell]

are you making one of these or hundreds?

 

[Phil3]

Thank you RJSakowski for your suggestions. They sound good to me.

Boswell, I will be making one for a friend, but possibly one more, and then a third one, but in 3" width (vs 4").

 

[Boswell]

For low volume like that, the I think what RJ suggested should be just fine. I have a number of milling projects with the parts clamped to the table. Sometimes on sacrificial support sometimes on parallels laid flat. If you use parallels just be VERY careful that the part is supported well and that you don't cut into the parallels. Please do not ask me about how I know to be careful about that

 

[pontiac428]

OP never said how thick the Delrin will be. If it is less than 1" or so, I'd ditch the parallels and vise, the Delrin will flex under the face of the cutter on the free span between the parallels. Edge clamps on the mill table would work a treat.

 

[JimDawson]

I might add to RJ's suggestions, put a sacrificial piece under the part and clamp down, rather than parallels. Could be plywood, MDF, particle board, plastic, aluminum, almost anything that is flat.

Here are a bunch of parts with MDF

 

[Phil3]

Thanks to all for the helpful replies. RJSakosski's method is thwarted at one point because it is not possible to simultaneously clamp the ends (short side) AND the long sides of the work piece. The photo shows why. The mill table is too shallow to allow clamps along the long side.

To complete facing of the piece, I can clamp the piece with a clamp at each end using the center slot, and then add two more clamps at each end in the first and third slot (then removing the center clamp). Since clamping the ends is the only apparent way to hold the piece, I do not see a way to mill those ends (short edge) without moving the work piece. Am I missing something?

To the question of Delrin thickness, it is 0.800" thick, but a substantial portion of it will be milled down to 0.270" thick. Deflection of Delrin is a concern.

I need a bigger mill!

Phil

 

[pontiac428]

Making machine rests?

Looks like you need to break it down into a few steps. Leaving the ends long as RJ recommended, clamp a piece down and face mill the critical part of the field. Then drill your two center holes. Then remove the part, flip over and repeat. Then mount the part on a sacrificial backing using the two bolt holes. Mill your edges to dimension. Voila? Maybe.

 

[MikeInOr]

I have never worked with Delrin... but I would consider drilling then countersinking the two holes. Then put the two bolts in the piece and screw it to a couple shop made T nuts with the correct threads to secure it to the table. (Or just drill and tap a couple existing T nuts with the correct size/thread... just do it off center to the side of the existing T nut hole.) You could use what ever you want as a shim between the table and the stock to raise the stock up off the table for milling the exterior dimensions... you would just need to drill two corresponding hole in your shim stock. If you hit the bolt heads while you are machining out the center of the part.... you went too deep! You wouldn't need any sacrificial clamping surface so no wasted material.

Maybe Derlin isn't rigid enough to be secured with only the two bolts?... it was just an idea.