Two sided machining

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Two sided machining

Postby ken whiklo » Mon Apr 01, 2019 11:27 pm

I tried to figure this out by myself, obviously not smart enough. Attached is a project I am working on. Now all of the measurements and the simulation tells me that this should be right on, but it is not. Top and bottom are not centered over one another. I am at a lose to figure out why. I have tried various methods to get the center of the work piece. Still get inconsistent result.
trivet star.crv
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Re: Two sided machining

Postby jimwill2 » Tue Apr 02, 2019 12:25 am

There was a good post about the same issue on the Aspire side of the forum yesterday. Most likely you are not getting an exact placement when you flip it over.
I think the beauty of two-sided design is the ability to put positioning dowels for an exact flip. Good luck!


http://forum.vectric.com/viewtopic.php?f=27&t=31845&p=230413&hilit=two+side#p230413
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Re: Two sided machining

Postby gkas » Tue Apr 02, 2019 12:30 am

Your double-sided project looks OK. Your most likely problem is that when you flip to the second side, you are not getting it centered. A little bit off will make a big difference. Also your blank had better be EXACTLY 7"x7", or it will not center when flipped.
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Re: Two sided machining

Postby Rcnewcomb » Tue Apr 02, 2019 12:34 am

Have you looked at using the asymmetrical dowel hole process? It is described beginning at 3:50 in this video: 2-Sided Machining Guide
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Re: Two sided machining

Postby highpockets » Tue Apr 02, 2019 2:01 am

Is 7"x7" the finished dimensions of your project?
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Re: Two sided machining

Postby SteveNelson46 » Tue Apr 02, 2019 2:15 am

You also have an overlap and two intersections. I found them with the vector validator. You will have to zoom in real close to see them.

I just used the asymmetrical dowel method on this pen and pencil box for my grandson. It works really good.
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DJ Pen Box1.jpg
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DJ Pen Box3.jpg
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Re: Two sided machining

Postby ken whiklo » Tue Apr 02, 2019 4:29 am

highpockets wrote:Is 7"x7" the finished dimensions of your project?

Yes
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Re: Two sided machining

Postby ken whiklo » Tue Apr 02, 2019 4:39 am

SteveNelson46 wrote:You also have an overlap and two intersections. I found them with the vector validator. You will have to zoom in real close to see them.

I just used the asymmetrical dowel method on this pen and pencil box for my grandson. It works really good.


Did you plug the holes after machining?
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Re: Two sided machining

Postby highpockets » Tue Apr 02, 2019 5:16 am

ken whiklo wrote:
highpockets wrote:Is 7"x7" the finished dimensions of your project?

Yes


The problem with trying to use a finished dimension piece of material for a two sided project is it's very hard (as you've found out) to find exact center and then depend on the material to be cut exactly square.

My suggestion would be to make your material 8"x8", add a 7"x7" vector to represent the finished project size. Next put a 1/8" circle vector in the scrap material on the horizontal center line. Use the Mirror Select Object to copy the circle to the opposite side of the material. Make sure to check Flip about job center and Create a mirror copy.

For the two registration circles I'd use the Drill toolpath and a 1/8" EM, set the depth to material thickness plus 1/8". Create another Profile toolpath using the 7"x7" vector to cut out the material to final dimension.

Change Flip direction to horizontal.

Cut the two registration circles first then the rest of Top side. Flip the material and use 1/8" pins in the registration holes to align the material, run the toolpaths for the bottom side with the "cutout" profile toolpath last. Depending on how you're holding down your material you may want to use tabs for the "cutout" profile.

How this makes since....

Image 395.png

Image 394.png
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Re: Two sided machining

Postby ezurick » Tue Apr 02, 2019 11:49 am

I am glad I am not alone in fighting with the 2 sided dilemma. 7x7 should not matter if it is centered. You could set down a 12 x 12 and use 7 x 7... should not matter. Not sure why a few other are asking that. I may not be the brightest bulb... but someone would have some real explaining to do on that one.

I was fighting with a vector file I found on instructibles.com (I think) that was a cross with amazing grace in the cross. I wanted to do double sided and for the life of me, I could not get it centered when flipping it, regardless if I flipped it side-ways or top-to-bottom. I had tried other crosses and it worked perfect. The problem had to do with the centering of the actual vector on the first one. Something was amiss in the vector and I could not figure it out. I could see the vector drawing of the cross was kinda crooked... but when I copied to the other side, it looked perfect. When I cut it out, it was off by quite a few thousands of an inch... I finally gave up on it and admitted I couldn't fix it. Wasted quite a bit of wood trying too.

Looking at your .crv file.. theoretically, it should be fine when flipped... I haven't tried to cut it, but it must be like that darn cross I was fighting with. 2-sided is not that easy and tutorials are just too limited. I've seen youtubes of folks doing it in vcarve and stopping there and saying, easy. No, show me HOW you done it on the actually CNC machine too. vectric tutorials do the same... either just the vcarve or just the machining. Not both and they always do easy or simple ones. I hope you figure it out. It looks perfectly square and centered.. but?
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Re: Two sided machining

Postby Wayne Locke » Tue Apr 02, 2019 1:55 pm

Double sided in Aspire is “perfect” ie it absolutely positions things relative to the center or another reference point. A 7 X 7 block is a perfect 7” X 7” and exactly 90 deg. How’s your block?. I have been a professional furniture maker for 40 years and 1/32” accuracy is usually fine on a tablesaw but not CNC. Only serendipity can make a perfect block like Aspire with woodworking tools, not to mention positioning errors. Just measure your block with two different tape measures and you are unlikely to get CNC level consistency. Plus every error is doubled when doing double (ha ha) sided machining. That is why dowels or other positional aids are absolutely essential when flipping material.

Aspire nonchalantly assumes a precision that mere mortal woodworkers are incapable of. In real life I don’t even know what a thousandth of an inch is but it has bitten me many times.
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Re: Two sided machining

Postby ken whiklo » Tue Apr 02, 2019 3:57 pm

Thanks to all that posted. I have only been at the CNCing for a few months but it appears I am not the only one having trouble with this two sided stuff. I am cutting these out of Maple and so to get a dimensional lumber 8" wide would require a 1" X 10" which would get very pricey. All of my results have been close but not close enough when CNCing. My last attempt I made a two sided jig square to 90 degrees. My material is square. So I centered the bit in the corner of the jig. What I forgot was the bit is 1/2" so I needed to be 1/4" further on x and y. In the tutorial they make mention of zeroing z on both sides of the material. So if the material is square, and the thickness is the thickness, once you have your set up why would it be necessary to reset any axis. The material is the same thickness from both sides? If, and I say if, your set up of the bit is correct, with the jig in place this should be repeatable. Now that's my thinking but I have been unable to produce it in the flesh.
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Re: Two sided machining

Postby SteveNelson46 » Tue Apr 02, 2019 5:32 pm

ken whiklo wrote:
SteveNelson46 wrote:You also have an overlap and two intersections. I found them with the vector validator. You will have to zoom in real close to see them.

I just used the asymmetrical dowel method on this pen and pencil box for my grandson. It works really good.


Did you plug the holes after machining?


Ken,

No, I didn't plug the holes. I didn't see any need to. If they need to be plugged on subsequent projects I'll do it then. After all, it is a spoilboard.

I have had my machine for only a couple of months and the pen and pencil box was my first two sided project. It took a couple of attempts to get the indexed lid and the base to fit properly but that had nothing to do with the two sided dowel method and I had no issues with it. The Vectric video was "spot on" and simple to follow. If you use this method be sure to make the dowel holes a snug fit. Pre-made factory dowels are rarely the diameter they say they are.

Andrew Pitts has a video on Youtube where he used a jig to make a two sided dish. I haven't tried this method but it seemed to work out good for him.

https://www.youtube.com/watch?v=i5ojCcb-7GA
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Re: Two sided machining

Postby gkas » Tue Apr 02, 2019 11:20 pm

SteveNelson46 wrote:
ken whiklo wrote:
SteveNelson46 wrote:You also have an overlap and two intersections. I found them with the vector validator. You will have to zoom in real close to see them.

I just used the asymmetrical dowel method on this pen and pencil box for my grandson. It works really good.


Did you plug the holes after machining?


Ken,

No, I didn't plug the holes. I didn't see any need to. If they need to be plugged on subsequent projects I'll do it then. After all, it is a spoilboard.



I only started plugging my leftover alignment holes to stop my confusion. When I get do a lot of double-sided machining, I lift the project to flip it..... and have to figure out which set of holes match.. :oops:
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Re: Two sided machining

Postby garylmast » Tue Apr 02, 2019 11:54 pm

After I surface my spoil board, so I get proper alignment for setting my material, I've take an engraver bit and scribe several lines, a couple thousandths deep, across my spoil board about 12" apart, parallel with both X and Y direction. I then run a pencil along each groove so each line is highlighted. When I set my material, a quick measurement from the alignment lines puts my material square to the machine.

I only started plugging my leftover alignment holes to stop my confusion. When I get do a lot of double-sided machining, I lift the project to flip it..... and have to figure out which set of holes match..


This is one of the reasons why I will set up a jig instead of using dowels for alignment. Shooting some scrap wood around my material using brads or screws is only takes a few seconds, simple, and don't have to screw around figuring where the dowels go. I also use a center zero position. I have done several dozen double-sided projects now, and I just don't have problem using this technique.

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