Machining the "flip" side of a panel

[johnm]

Folks -

Okay, I did a test run of a set of Picket Fence tips that will insert into a rectangular hollow plastic fence tube - at least that's the idea.

I need to machine a .080 shoulder around all four sides of the picket head so that the sides of the picket head are flush with the hollow post. I think I can figure out how to cut an .080 relief into the "tenon" area of the picket on the sides of the head, and one face - but how do I accurately lay out the orientation of the parts on the sheet so that I could flip the whole panel over and machine the reverse face of the "tenon" down .080?

I did a search on nesting of parts, and it doesn't look like there's an easy (read: don't want to buy $3k software) method. I can lay the parts out from the center of the panel, but that's not going to be close enough, because those shoulders have to be machined to within about .010 of each other or the picket heads aren't going to seat squarely in the tubes. I can get parts laid out and nested manually, but not with the absolute symetry (sp?) that I think I need to keep things properly registered.

Any ideas or remarks on how to accuratly layout components so that the flip side can be machined while preserving some method of registration?

I'd appreciate your remarks. I need to figure out a way to make about 2800 of these picket heads quickly and accurately if I'm going to get the work.

Thanks!

John
Lakeport, CA

[mikejohn]

John
Keeping well away from the rhetoric in another post
, if you email me, I think I can help you.
.....................Mike

[edcoleman]

John:

A technique I've used to register a sheet for two sided carving is

-layout 4 1/4" dowels around the perimeter of your sheet.

-Drill these dowel holes through your sheet and into your spoil board.

-Machine side one, remove the sheet (leaving the dowels in the spoilboard).

-Flip the sheet over and drop onto the pins.

-Machine the second side.

If your machine is square, everything should line up.

-Ed

[johnm]

Ed -

Yes, that's a good idea, however the issue for me is having the parts laid out symetrically on the panel so that when I flip it over, I can accurately machine the tenon area of each picket head base. If I'm off by .010, it'll show and without having some better way of nesting the components so that they are symetric, I don't think I'll be able to make those cuts accurately.

The other thought I had was that I could nest the parts so that all of the tenons were in line, then flip the panel, and assign zero to a physical point on the first picket, rather than run from an absolute zero.

What do you think?

John

[johnm]

Folks -

Here's the file with the fence picket finial. The file of the nested pickets for cutting was too large to upload. I need to machine a relief for a tenon on all 4 sides of the base, about 1.5" high.

Hope this gives you a better idea...

John
picket finial

4867 (19.6 k)

[srwtlc]

John,

Your .dxf doesn't open right for me (just opens another window with a bunch of stuff), but along with what Ed is saying above about using dowels, you will need to take your original drawing and mirror it around the axis that you're going to flip your sheet over to and then make a pocket toolpath at each needed location. If you're using PW you may have to make a new drawing from the mirrored one so that you get the axis in the same location as the other side or mirror it in your cad program and relocate it to 0,0. As Ed also stated, if your machine is square and if the zero point remains constant it should work just fine. If you need some help getting a flipped drawing drop me a line.

Scott

[cnc_works]

Hope this comes out. I don't have much to add to the solution, but here's the dxf file.
picket

4868 (21.4 k)

[cnc_works]

OK, egg on my face. I dunno why this is being saved as a .lnk file. I renamed the original file from .lnk to .dxf, opened it in rhino, changed the line color from white to black and saved it as a dxf file, then attached to post.

Maybe someone can tell us what we are doing wrong.

Donn

[gerald_d]

Hi John

The most important thing for perfect registration after flipping something over, is to be sure that your y-axis is perfectly square to your x-axis.

Here is a quick proposal for your pickets:


4869

Lay a board on the table, clamp/screw down lightly.

Pick any 0,0 position, and after doing this, don't ever fiddle with it again until the whole job is done!

Drill the blue holes right through the board and some distance into the table top. (Imagine telling a Thermwood owner to do this
)

Knock in some dowels and remove the screws/clamps if you wish. But you may need some hold-down if you are going to use a spiral-up cutter.

Clear out all the tenons on one side of the board.

Flip board over, and dowel it back to the same dowel holes. At this point the squareness of your x to y axis, and the straightness of your rails is critical - otherwise the dowels won't fit. You may have to work with smallish boards to solve inaccuracy problems.

Pocket out the tenons and cut the outer profiles.

It goes without saying that your dowels/pickets must be symmetrically laid out on your board for the flip-over.

[srwtlc]

If you based your toolpath off a mirrored drawing of the first side, you wouldn't have to worry about having the pickets layed out symmetrically, just the dowels. That would allow nesting them in any manner if that is desired.

[mikejohn]

John
The steps as I see them, very similar to those above.
Draw your picket shape by drawing one side and mirroring down the centre line to ensure it is symetrical.
Decide on a centre line for your drawing.
Indicate a position for a dowel hole towards the top and bottom of this line.
Lay a number of pickets with the centre line of the picket along the main centre line.
Now place pickets anywhere to the left side of the centre line.
Delete the half pickets to the right of the centre line
Mirror the whole drawing about the centre line.
Now ,like Gerald says, clamp the board, drill the holes, dowel, dont move 0,0, cut the tenons one side almost completely through, flip sheet, cut rest of tenon and picket shape (right through).
Take note of the need to be square (don't listen to the latest pop music
)
.............Mike