Double Sided Milling and Ver 10 VCP

[Wayne Locke]

The pins compensate for inaccurate material size for one. If you have several tape measures make 12" marks with them. The marks probably don't exactly match up. The pin method uses the mathematical precision of the software. 1/32" is decent accuracy on the table saw but is a !/16" error on a double sided cnc job. Should doesn't really matter just use the pins and be done with it.

[ezurick]

I just can't figure out where the 1/16" offset is coming from.

If I remember correctly, it's actually 1/32" error. The error gets doubled when you flip it. Save yourself some grief and follow John's advise and use pins. If you want a jig... make the jig with pins. A very good example is the folks trying to make the Next Wave chess pieces with a jig, and no pins. Everyone has terrible alignment problems.

I under stand the pinning process as I have watched many videos on it. My jig is pined to the spoilboard so it doesn't move. The board fits in the jig at the same place front and back every time.
I don't have to set X & Y zero since the boards are cut to the same measurement. Yes, I measure every board and use jigs on my table saw to make sure of that. Again from what I have been
reading, the software should make adjustments to compensate for flipping the material. I have contacted Vectric about this and see what they say.

Thank you all for your input.

John Frankforther

I don't think double-sided job will work with a stationary jig. I am not the brightest bulb in the chandelier when it comes to geometry, but if there isn't a proper reference to flip, I don't think anything will match. Don't beat me up, I am just trying to reason with this.

[johntech]

[/quote]

I don't think double-sided job will work with a stationary jig. I am not the brightest bulb in the chandelier when it comes to geometry, but if there isn't a proper reference to flip, I don't think anything will match. Don't beat me up, I am just trying to reason with this.[/quote]

The main reason I am using the jig is because all the other milling I do it works flawlessly.
Also in viewing the first 2 sided milling video from Vectric they did say that you could use a jig to do 2 sided milling.
That is the type I am using that is shown in the video.

So to put this post to rest, I will try using the pin method as suggested.

John Frankforther

[sharkcutup]

The problem here is the relationship between jig pin holes versus board placement within the jig. Sure the jig is pinned to the spoilboard but is the centerline of those pins in relationship to the centerline of the board placement the exact same.

In my own opinion using a jig for two-sided jobs you are taking on and maybe compounding errors into the equation whereas pinning material directly to your spoilboard with pins you are not possibly adding any possibility of error into the equation.

Hope that this makes sense!

Just my thoughts/opinion!

Besides I have done many two-sided jobs without a jig and have had no problems!!!

Now if you make a jig with pins then you have a repeating centerline!

Sharkcutup

[ezurick]

I am not positive, but what I have done in the past is create a new spoilboard (or jig) that is larger than my job and have a permanent XY on that, which would also have permanent reference holes for the pins on the new spoilboard. That works if you have a double sided job that needs duplicating. I think that is what Vectric is referring to, imo. Anyway, hope everything works out for you...

[Jim_in_PA]

Similar to ezurick, I regularly use a fixture to do two-sized chair seat cutting for a client. I happen to use x-y at the center of the workpiece for this and the fixture has inherent boundaries to hold the workpiece for both the top and bottom operations in exactly the same place. That said, most of my double sided cutting uses index pins on an axis and get flipped relative to that axis. Some are oriented to X and some are oriented to Y, depending on what they are.

[Bill_L]

Been doing double sided machining of 4 x 8 sheets of poly for years and have always used dowels. Every cut is dead on. The sheet in the photo has the dowels positioned at either end.

[linkreincarnate]

The problem is warp and twist. I was trying the pocketed spoilboard method and I kept getting misalignment too. I measured both ends and the middle of my stock for thickness and width and got 88mm. I thought that meant I was perfect. Good to go right? It wont fit? Hmmm looks like my stock bows in the middle a bit. This causes the ends of the stock to sit hard against the left side for the top operation. but when I flip it for the bottom op it will press hard against the opposite side. Now if I flip it to carve it without compensation of the zero it's not going to be aligned.

OK fair enough. Pins will give me perfect alignment relative to the model in the stock. But what about 4 sided machining? Vectric doesn't have a tutorial on how to do that with dowels.(Do they?) Would building some sort of center supporting manual indexing jig work? I assume the problem is that rotating in a jig doesn't mean perfect rotation about a center because and warp or twist in the stock changes the alignment of the piece when it's rotated. Dimentioning the stock first is an problem because cutting the wood itself can cause warping and humidity can cause warping quickly. The only way I can think of to do 4 sided machining then would be to use like a spiked end to hold either side being careful to get it in the middle of each end. Then you could rotate it and it would rotate without respect to the outsides of the stock only the center line of the spikes. Your model would be centered on this line even if the stock was not. Any warp in the stock wouldn't matter because it wouldn't affect your rotation about the center line. Seems like a complicated jig though. Am I reasoning through this correctly? Can someone explain how to use the pin method on a 4 sided part?

[highpockets]

This Vectric Tutorial should help

[linkreincarnate]

Yes I followed that. They don't mention how to properly align things with dowels though and the jig method really doesn't work with anything but milled dimentionally stable stock.

[TReischl]

If you are trying to do precise, good work then starting with warped, twisted, cupped wood is a HUGE mistake.

The only people who can build things with warped, cupped and twisted wood are carpenters building houses. And even they cull out some of the really lousy stuff. Of course we all know that there is no such thing as a flat wall, or square corner in our homes.

Seriously, you cannot expect good results when you have already rigged the process to fail. Folks who have been working with wood for a while will always talk about flattening and squaring before beginning a project.

Edit: I have done quite a few double sided projects using a fixture, I am not a fan of the pin method. The pin method works no doubt about it, as long as there is extra wood to drill holes in. Usually I cut my stuff to length and width on a TS and RAS. Both are equipped with digital readouts so accuracy and repeatability are never an issue. The work fits in the fixture snugly. It works because I have prepped the stock correctly, it is not twisted and warped.

Four sided fixtures are no different than two sided fixtures. In fact it gets easier as you go to sides 3 and 4 because you have precisely machined sides from the first two operations.

[Mark's Wood Chips]

This post is very timely for me because I'm attempting to make a double sided carved walking stick longer than my table. My first attempt was a failure because I indexed off the sides of my board and despite EXACT measurements my cutout and carvings were about 1/16" off. Impossible I said (plus a few other things). I then used the pin method and both sides were absolutely perfect! I'm now a firm believer in using pins for both tiled and double sided work.

Mark