Edge jig for flipping material

[EricSchimel]

I've been doing a bunch of cutting lately that requires me to mill both sides of a full sheet of plywood (4x8). I've got a pretty good system down where I drill holes through the piece and my table and I use metal dowel pins to register the sheet in place.

My problem currently is that my holes are starting to wear out. I've moved them around, but it's a losing battle. As my spoilboard gets thinner, and I cut more complicated sheets my options for registering with firmly planted holes are shrinking. (Literally)

I've always thought that squaring the whole sheet with the machine first, and then registering it against an "L" shaped jig would be the best way, but my table is 97x49 which doesn't leave me a whole lot of room for a fence/jig along the sides.

I've done the trick where I mill a channel around the edge so I can see 0,0, but I feel like a physical stop is the way to go.

Has anyone come up with something sturdy that can go around the edge of a table that I can easily remove and replace when needed?

[gundog]

I use a different strategy I have a product that requires me to machine both sides. The material is never square and I don't want dowels in my table because I use the table for so many other things. What I do is in the drawing I make sure the parts are centered in X & Y and I use the mirror option and flip horizontal with the drawing make sure you physically flip the same as you did in your drawing. I drill 2 - .125" holes in a corner opposite of each other in the material in a portion of the waist material. I use those holes to locate the sheet after the flip. I have a couple pins that I turned on my lathe that come to a point with a .125" side I insert in the drilled holes. I insert a shaft I machined to a point and chuck it in the spindle. I send the machine to the location of the pins and move the sheet to line up in the 2 points. Depending on the level of accuracy needed this works pretty good and I have been doing this for years and made thousands of parts this way. I hope my description makes sense.

I also watched a video once of a hinged jig that flipped the part so it was always the same but would not work for a full sheet then an offset was used.

Mike

[barrowj]

Like "gundog" I do alot of smaller hardwood designs and also centers by hold down holes with both X and Y axis of my piece. What I do different is to drill 3/8" holes in the spoilboard with the shopbot using toolpaths from the drawing, then install a 1/4" insert. I try to space them evenly so that even over time I can reuse them for other projects. This way I can flip them either way and not loose registration. I have also done with for full sheets of plywood, I try to design it using a template with the inset holes.

Hope that helps.

Joe

[bleeth]

I have my spoilboard and all under it trimmed so it's edges are zero.
It's easy to rig up an end stop along y. Carefully mark the center of the end of the board you are cutting and the end of your spoilboard at y24.
Put your board to the stops with the center points aligned. Mill. Flip, repeat. Using the center mark and only one alignment fence eliminates worrying about the inevitable minor size and squareness deviations in typical sheetgoods.

[bobmoore]

when the holes start to elongate in your spoilboard one trick is to get a tube of plumbers epoxy putty. You break off a small piece and knead it between your fingers to activate it then fill the hole and scrape flat. It cures in about 5 minutes then you can remachine the hole in the epoxy. Do it as many times as you wish as the epoxy sticks to itself on subsequent applications. For the most accuracy machine 4 locations rather than just 2 as it is surprising how far off you can be with 2 locater holes.

[coryatjohn]

I use the "hole-in-the-table" method but when I'm doing something that doesn't work with my standard holes, I do the "bit in the spindle" method. Another words, the hole is in the piece and it's at a certain coordinate, then I move the spindle to that coordinate, slightly above the material and align the material to the bit. Then, to be sure I have it right, slowly lower the bit into the hole while shifting the material ever so slightly. It works quite well but not as easily as a metal dowel in the table. The bit method never wallows though and it's extremely easy to have it anywhere on the table.

[dlcw]

Here's my method

.http://www.talkshopbot.com/forum/attachment.php?attachmentid=27260&stc=1 http://www.talkshopbot.com/forum/attachment.php?attachmentid=27261&stc=1 http://www.talkshopbot.com/forum/attachment.php?attachmentid=27262&stc=1

These blocks fit as tight today as they did when I first drilled them. I use them all the time with SBLink for plywood processing with flip operations.

[Keith Larrett]

This is my method. Not sure if it would provide the accuracy some people might need, but it is accurate enough for my needs. Both the X-axis and Y-Axis fence slide out the way once the plywood is on the table. I don't lose any cutting area on the table. Occasionally I have to replace the fence, normally because I forget to move it out the way before starting to cut :rolleyes:

I make the fence oversize, install it and then run the router down the x and y axis at zero to cut the fence to size.

I'd love to have a pneumatic pop up pin system, but have no idea how to do that :confused:

[myxpykalix]

Keith.....very cool. I'm surprised at how clever some of these systems are. Good old AMERICAN INGENUITY...

[EricSchimel]

Thanks everyone for the suggestions!

I'm surprised that the "bit in the hole" method works so well. I can totally see that working for smaller parts, I worry about doing full sheets... If I align the top corner and I go to the other corner and shift the sheet to line up there, I'd be afraid I'd lose the spacing on the first corner and then I'd end up chasing it around alignment endlessly.

I think I'll try that plumbers epoxy. I've found that the metal dowels in the table do work well, it's just the worn out holes that really mess that up. If I can fill and re-drill the holes I think I'll be in business.

I also really like those fences and end stops, I really want to build something like that. Maybe something that has Y and X 0 that I can drop in and use to line up the sheet, and easily pull it off before I start cutting.

[gundog]

Yes I do run back and forth several times before it is right.

Mike

[MogulTx]

Like many others, I use a registration pin to locate parts. I do a LOT of different designs. The way I deal with multiple holes, is to fill them. My trick is to use "bondo" ( a polyester resin that hardens quickly)... I use a spatula to ensure that I don't get much deviation in the surface of the table and it is removed when I run a flattening pass over the area affected. This extends the life of my spoilboard quite a long time. It also allows you to redrill for new positioning pin locations with zero expectation of a degradation of the location. - Plus you can usually be ready to machine things again in as little 10-15 minutes.....

[EricSchimel]

As someone who formerly worked in autobody, I had a thought about Bondo too. That should help me fill some of the other little pin holes in my table.

[bleeth]

I've been using bondo for spot repairs to an otherwise good spoilboard for years. It works fine.
If I were planning on drilling a hole in it for a threaded stud I would probably mix up some epoxy with wood flour or cotton fiber so the plug had internal strength.

[EricSchimel]

Just did the Bondo trick, works great. Filled the holes and re-surfaced my table. All good!

[donek]

I put some masking tape down and then hot glue a piece of 1/8in masonite to the tape. I then cut the masonite to form a stop that the edge of the material aligns to. It only takes 3 points or stops to register a corner in exactly the same position every time. If you are flipping the part, you simply make stops for the opposite edge.

When doing two sided cuts on parts that are smaller than an entire sheet I will set up so that I have two stations. One cuts the back side and the other cuts the front side. I place two blanks on the table and cut both back and front. Flip the back side cut over and put it in the front side station and place a fresh blank on the back side station. Then run the exact same program again. There's no program changes and you can have anyone perform the change over with minimal training.

[ADAPT_Shop-Brady]

I did some searching, but this was the closest thread I could find on the topic. I remember seeing someone post their process when doing 2-sided milling on a plywood part where they were able to design the part so that when flipped over, the waste material border held the flipped stock in place for machining the second side. Anyone recall this or have any pointers?

[ADAPT_Shop-Brady]

I did some searching, but this was the closest thread I could find on the topic. I remember seeing someone post their process when doing 2-sided milling on a plywood part where they were able to design the part so that when flipped over, the waste material border held the flipped stock in place for machining the second side. Anyone recall this or have any pointers?

Found it: https://www.youtube.com/watch?v=BLD4dFoXC7o&app=desktop