Hello,
When it comes to tiling or double sided projects, I always see people using dowels exclusively. Is using dowels a must? Why can’t you just flip the stock upside down and reprobe X and Y? In theory it should work exactly the same, no?
Thank You,
Alex
It could work if you could guarantee that the material is in exactly the same spot after you flip it. The pins, dowels and jigs ensure that the reference point is always the same.
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Hey Borgorl,
rebrobing X,Y gives you only one point. It would not prevent the workpiece being rotated after flipping over. Two dowels ensure that.
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Here’s what I do/did. When I installed my waste board I left it a bit long on the front edge. When surfacing the board it left a small lip. I have several pieces of 3/4" mdf that I cut to different widths on my table saw. I push tight to the lip and then I push the wood I’m going to tight to the MDF. After securing the other 3 sides I remove the mdf and finish securing the project wood. Now the wood is parallel to the X axis.
Next I use the 1f to cut the wood to size. If it has a good square edge I’ll secure the wood with it on the left side. I’ll create a simple tool path that cuts the wood in both width and length removing the top and right side. If the wood doesn’t have a good edge I’ll remove both the left and right sides. The CNC router will be able to size the wood much more accurately than I can do on a table saw. It makes for flipping then probing easy. When you flip the board you have to use the 3/4" mdf setup board again before probing it.
Works every time for me. But you can’t cut the lower right corner off when cutting the first side. If you do you’ll have nothing to use for probing after flipping.
Dowels work well as long as you’re pieces are about the same size. If the holes are too close or too far apart you’ll need to make several holes. I already have lots of holes in my waste board and didn’t want more.
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Alex,
I rarely use dowels, and lots of times I cut multiples of 2 sided things with numerous bit changes
I make sure that my stock is exactly the size of my drawing blank and I use a center point on my drawing and an exact center point on my stock as my 0:0:0.
I set up stops to hold my stock in 2 directions with adjustable clamps the other 2 ways. This way if I’m using multiple bits on multiple pieces, I can cut all the pieces with one bit, change the part or the bit, re-zero Z and cut them again.
Cutting both sides is no problem since zero is in the center, when I flip the piece and put it against the stops, it’s centered again.
I also put a marker dot in the upper right corner of my stock so that I never accidently turn a piece the wrong way (guess how I figured that one out!)
Most things you don’t have to be 100% dead accurate, but if I have to be, I cut the blank on the CNC first along with a center point.
If I’m doing multiple pieces, I plane and sand all of them to the same thickness first.
The pictures show a run I did last year of some 2 sided coasters using multiple bits.
Hope this helps,
Pony
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I have used dowels. But if you need a double sided carve on an existing piece, you can’t put dowel holes in it. You could make a jig that has the dowel holes - or you could just make it so you can flip the piece over within the jig. As long as you’re using down cut bits, you only need to secure in the X-Y.
Another good approach for some pieces, is design so that you do NOT need exact alignment. If you make the backside (meaning not visible side) oversized by 1mm, then probing will be more than accurate enough. You just need a fence to ensure the piece is perfectly straight along X or Y. This is good for pocketing out a recess for T-Nuts, to make them flush.
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Anything can work as long as you constrain all the degrees of freedom you are not changing. Dowels constrain, along with table surface, all motion after a flip. Other ways have been described. I’ll add one
I change the zero point in Fusion so that it is the same corner however I rotate it. I have a Y fence I align to. I have milled six sided pieces this way.
I wish I had a picture to show, but I’ll try to explain. Imagine a 1 unit cube. Lower left bottom corner is a xyz 000. I rotate the cube so the face on the table (XY z=0 plane) is on the left. The corner that was in the bottom left is now the top lower left xyz 001. I zero off that corner for the second cut on the new face.
Ok, maybe words don’t make it better. Here’s a turner’s cube I cut all six sides by zeroing off the same corner, as it moved around during rotations.
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My friend, words don’t necessarily make it better, but those of yours sow confusion.
See Adam’s video, https://www.youtube.com/watch?v=za2QyLGTBBI, it’s about precision touch blocks but addresses what you’re asking about.
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LoL yeah, I can see that.
Here are a couple of pix showing what I described poorly
Blue highlighted is the corner I zero for each face as the stock is rotated for each side.
First cut on first face
Second face
Third face
Rinse and repeat for all six faces.
In CAM, the coordinate zero also stays attached to this corner, not staying on front left as it rotates.
Stock needs to be bigger so it frames all edges. It also has to have tabs to connect from frame to final object. In the case of the turner’s cube, the outside cube provides that work holding.
Using a fence for the front face, it does not rotate around z axis rotation. The table surface ensures it does not rotate around x or y.
Since CAM is always relative to that corner, any errors are related to how accurate and repeatable you can do a full xyz probe after every rotation.
Hopefully that is a little less muddled.
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Here is another example where I used the base as a reference for a 5 sided cut.
The base is 2” long. This was 3 of the 5 sides cut.
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The following workflow has worked well for me, achieving an acceptable variance between both sides of a project:
-
Configure X-Y Zero in CAD
Set the X-Y zero point in your CAD software to the center of the workpiece. -
Determine the Number of Dowel Holes
I typically create 4 dowel holes, though for smaller projects with less waste material, I sometimes use just 3. -
Place Dowel Holes Strategically
Instead of randomly placing dowel holes, as I’ve seen others do, I place them equidistant from the center X-Y zero point. This ensures:
- No need to create mirrored copies of the holes (if using 4 of them).
- If using 4 dowel holes, I can skip using the double-sided feature in Vectric because the orientation doesn’t matter when flipping the piece.
- Example: For a 10x12-inch square workpiece (with the final product being 8 inches square), I placed the dowel holes 5 inches left and right of center on the X-axis and 4.5 inches top and bottom on the Y-axis.
- If using 3 dowel holes, I place the third hole on the Y-axis centerline, equidistant from the X zero point, and will then have to of course mirror this placement on the spoilboard.
- Cut Dowel Holes in the Spoilboard
Before cutting the second side, I carve the dowel holes into the spoilboard. Here’s how:
- Choose a clear area on the machine bed, avoiding dog holes, T-tracks, or other obstructions.
- For the above example, I jogged the machine to X10" Y15", set this as my center point, and cut the dowel holes at this location.
- Key Point: Using Gcode for Accurate Jogging: When jogging the machine, I use a Gcode (MDI) command “G90 G0 G53 X10 Y15” noting the G53 machine coordinate system. This ensures that I can always reference a fixed, unchanging point, even after restarting the machine because the G53 coordinate system is what the machine sets after performing its homing operation and never changes no matter how many times you probe or set a new X-Y-Z location for your workpiece
Command breakdown:
G90: Absolute coordinates.
G0: Rapid move.
G53: Use machine coordinates, ignoring the workpiece zero point.
X10 Y15: Workpiece center on the spoilboard.
-
Place the Workpiece on the spoilboard for the First Side
Position the workpiece anywhere on the bed. I often use dog holes and PVC dogs for quick alignment. -
Mark and Drill Dowel Holes in the Workpiece
Mark the center point of the workpiece using a ruler or other method. Then, using the same dowel hole toolpath as Step 4, cut the dowel holes into the workpiece. -
Flip and Align the Workpiece
After carving the first side I flip the workpiece in any direction I prefer and align it using the dowels on the spoilboard. -
Cut the Second Side
Use the same Gcode move command from Step 4 to jog the machine. Then, set my working (G54) X-Y zero points to this location, like I would normally or when using a probe, then just perform a Z-probe and start carving the second side.
This method ensures consistent alignment with minimal setup adjustments and makes flipping the workpiece straightforward.
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the only way to do flip is to have fence that is cut by machine. i do that a lot. throw down loose ply and cut back to known xy. 6,8 on my machine.
to use flip, you need to square up the backside of the material. so i use 20.5 inch wide material, but it calls for 20. if flipping side to side, i cut that back to 20 in and then flip. works well, if you don’t square, or are undersized, it will be an issue.
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I cut a BUNCH of 2 pc, double sided ornaments over the last 2 days. In the 1st pic, you can see how I simply set up a bolt in the waste board and 2 sets of stops to hold the blanks which were cut the same size.
In my case, I find this to be the easiest way and allows for quick changes.
I engraved all on one side, then flipped sideways and engraved the other side. Once that was done, I cut them all out.
Now to shellac & paint.
Pony
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You absolutely don’t need dowels. Dowels are just an easy way to explain the extremely complex two sided machining process. Check the image below. You can build a mini jig using your machine. The latter is important to make sure that bottom and right walls are lined up precisely with X and Y respectively. and then, as long as you can set your XY zero correctly - this thing will work great.
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