Getting Familiar With Rotary Cutting

Topics related to wrapped rotary machining in Aspire or VCarve Pro

Getting Familiar With Rotary Cutting

Postby TReischl » Sun May 10, 2015 9:36 pm

Now that I have the rotary axis up and running I am learning some interesting things about it and using the "wrapping" software.

The wrapping feature is just that, a wrapper. Here is an example:

Lamination STL Model.JPG


This is an STL file from Hexagon. Notice that the cuts are straight into the material, no tapers. The screen shot was taken in Aspire while the model was being imported.

This is a file showing the part after it was "unwrapped" and in the flat. The wrapped job setup was used. The cuts are tapered.

Unwrapped STL File.JPG


Here is a shot after wrapping:

On Line with Cut.JPG


Note that the sides of the cuts are now being shown tapered.

So, creating a model in a modeling program will not yield the expected results. This is not to say the part cannot be cut. I created straight line vectors and used the profile tool on line to make the cuts. So the sides can be cut straight. However, the preview of those cuts does not show the sides being parallel.

On Line with Cut.JPG


In other words, in the case of wrapped rotary maching, the preview does not necessarily show what is actually being cut.

Is this all terrible and should we send a delegation to HQ to demand redress? Nah, because this feature is correctly listed as WRAPPED rotary machining.

However, we do need to be careful when using this feature and understand the parameters of its use.

I did quite a bit of research when I was working with this model. From what I have seen there are virtually no reasonably priced 4th axis plotters available. That does not surprise me at all. The only way to do a "real" 4th axis plot would be to create a model of the work being cut using something like voxels. That is no big deal. However, that model would have to be rotated in increments to produce the effect required. Rotating millions of voxels in space requires a lot of computer horse power and would be pretty slow on most of our computers.

I am wondering though if Vectric could forego the "live" simulation and possibly create a preview that shows what is really being cut? Let us low power computer users do the rotations after the cut model is generated?

One of the other issues that has always plagued 4th axis users has been the perceived market for 4th axis software. It is nowhere near the size of the 3 axis market. Which explains why companies that do have this ability charge an arm and leg for it.

As far as I am concerned it is going to get worse for me personally. After this initial research I have come to the conclusion that a lot of what I do would best be cut on a rotary. Here is an example:

Small rectangular workpiece. Let's say 3 X 7 X 3/4 thick. Needs work on more than one side. With a bit of simple fixturing mounted to the headstock and tailstock this party could be spun making all 4 sides machinable. Of course instead of using just a down and dirty rotary setup, a more sophisticated piece of gear would have to be contrived. Working off axis requires a brake without dependence on the motor to hold the work in place.

With the above gear it is possible to also machine "out of plane". A simple example would be to cut chamfers on the four edges.

The issue with doing more complex work with a rotary is having the software able to depict what is going to be cut. I am not worried about how to program it. But I would like some verification before firing up the machine. The chamfering edges is a good example. It is a straight line cut, the locations in y,z (I rotate about y) can easily be trigged out or found using CAD. Then it is just a matter of:

G0X-.125Y-.795Z1.6
G1Z1.23F50
G1X7.125F150

Why I want the verification is obvious. Just one lousy miserable typo can wreck a persons whole day when doing this stuff.

So, I am thrilled that I can wrap stuff around an axis. Now it is a matter of figuring out how to make even more use out of this ability.
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Re: Getting Familiar With Rotary Cutting

Postby rdean33422 » Sun May 10, 2015 11:43 pm

There are many things to take into account when doing rotary machine.
I have Cut 3D and make many of my models 4 sided so I use the rotary to hold and rotate the models to 4 positions.
I just manually index the rotary 90 degrees for the next cut. Sure beats trying to locate the part 4 times.

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Re: Getting Familiar With Rotary Cutting

Postby Rcnewcomb » Mon May 11, 2015 5:25 pm

In other words, in the case of wrapped rotary machining, the preview does not necessarily show what is actually being cut.
Is this all terrible and should we send a delegation to HQ to demand redress? Nah, because this feature is correctly listed as WRAPPED rotary machining.

I believe I can provide a bit of background on this as a whiny user who pushed Vectric into adding wrapping in the first place. I provide this by way of background.

When I purchased my first CNC machine back in 2005 I bought the indexer rather than getting a larger table, mostly because I thought items done on the indexer were cool and it took me back to my days in shop class where the turning lathe was my favorite tool. The problem was that there was no affordable (under $5K) CAD/CAM software for creating indexer files, so the indexer sat unused save for some experimentation with trying programs to do index swapping. There was no way to preview so you had to cut the item to see what it looked like. In retrospect I would have made more money with a larger table than I did with the indexer.

I admit to being a vocal, whiny user who cajoled Vectric into adding a wrapper. There initial support for wrapping in Aspire 2.0 still exceeded my expectations because it showed the toolpath in rotary. This was a huge step forward for indexer owners.
AspireWrap20.jpg

The developers at Vectric know that wrapping isn't a full solution for rotary machining, and that the preview breaks down in certain edge cases. The reason you have to switch to flat view to calculate toolpaths is to serve as a constant reminder that the software is doing wrapping, not true 4-axis CAM.
ToolpathFlat.JPG


There has been some discussion of Vectric doing indexer CAM the "right" way but it is a bit of a chicken-and-egg problem. There aren't that many indexers out there so there isn't much software. And there isn't much software because there aren't that many indexers. Vectric also wants to ensure the software is as easy to use as possible.

I've been experimenting with a 5-axis CAD/CAM package that sells for over $10K and I am amazed how incredibly difficult it is to use. But if I need to machine an impeller with undercuts that is the tool I would have to use. I wouldn't even try this with wrapping - wrong tool for the job, wrong job for the tool.
impeller.jpg


In the mean time I can create unique "artsy" profitable items on the indexer using wrapping features with ease.
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Re: Getting Familiar With Rotary Cutting

Postby TReischl » Mon May 11, 2015 6:06 pm

I hear ya, Randall.

Hopefully I did not come off as being "whiny" or "whinging" (english version of whining I think?). You have never struck me as being "whiney".

Anyhow, I have a long background in rotary machining. I wrote the rotary software for a very large Japanese laser company. It too was a "wrapping" package. Of course, on a laser about the only thing ever cut on a rotary is tubing and that has relatively thin walls. Even so, to do intersections I had to calculate the outer intersect as well as the inner and then transition from one to the other to produce a cut that would allow a tube to fit into the piece being cut for welding.

I agree with you 100% about the chicken and egg thing. Same thing I faced back in the day. Of course the economics were a bit different, the company was selling 500K+ lasers and needed to be able to say "yup, we can do rotary cutting". In the case of Vectric that dynamic does not exist. It is more like: "How many users will spring the bucks required to fund this endeavor?"

When you wrote about using a 10K package to program that really strikes a nerve with me. I had the experience of running a seat of Senator for a while. YIKES! I am not even sure if Senator is a viable package anymore. What I do know is that even with my background in software development and machining it was incredibly difficult to use.

I did not start this thread to throw rocks at Vectric by any means. What happens when wrapping is pretty obvious. The voxel model (I call it that, not sure what the Vectric Team calls it) has to collapse about the centerline. For those not understanding this, take a piece soft material with a thickness. Then try to make one end meet the other without leaving a hole in the middle. So the only way to do it is to send some voxels off into byte heaven.

I started another thread about backplotting. I believe it is important to have a true backplotter to allow someone to verify code AND be able to modify g code and still verify what the program will do. Frankly, the casual user making signs and the like will never have a need for a true backplotter because the existing on screen preview is very good and the posts seem to be bug free. The beginning user could take advantage of one to eliminate the tendency to blame the software for machine or operator errors. Maybe I am just "old school" since I started writing gcode before the advent of CNC on a Friden flexowriter. Yup, for those younger readers, before there was CNC, there existed NC. No computer on the control to edit, no software to write a program. Get out calculator and practice what you learned in trigonometry class. Then type it all in to produce an 8 track punched paper tape. Then go run it on the machine to find all your mistakes. (finger on cycle stop, block by block). Companies like Numeridex did very well by creating software that could read a paper tape and use a pen plotter to show what was going on. Ahhh, the so called "good ol' days". Uh huh.
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Re: Getting Familiar With Rotary Cutting

Postby Rcnewcomb » Mon May 11, 2015 6:46 pm

You have never struck me as being "whiney".

I'm sure Brian and Tony from Vectric would be to differ. :D

Then type it all in to produce an 8 track punched paper tape. Then go run it on the machine to find all your mistakes.

There's a blast from the past. My first job out of college was writing paper tape programs for wire wrap machines. I used to be able to read this:
PaperTape.jpg
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Re: Getting Familiar With Rotary Cutting

Postby scottp55 » Tue May 12, 2015 1:01 am

Randall,
Hoped never to see one of those again!
We just stuck those in the Pratt Whitney Tape o Matic :)
Never did understand why my brother got SOOOO Irate, if we spilled coffee or coolant on them(OR Go^ FORBID..step on them) :)
VERY part time "Monkey Machinist" back then.
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Re: Getting Familiar With Rotary Cutting

Postby IslaWW » Wed May 13, 2015 4:10 pm

Ted...
Thank you for posting such concise information. Hopefully this will help many users know the advantages and disadvantages to wrapped machining on a rotary axis. I think that the "value" (feature per dollar) is there for those who wish to cut objects that are more organic and artistic. For those that require true and pure geometric applications, like your example, more robust software and most likely hardware is required.

I have done some playing and testing of indexed multi sided (off axis centerline) machining and have some anecdotal info as it pertains to stepper torque, rotary reduction ratios and force that can be generated at a given distance off center. If I can be of help email me. (email in signature, lower left)

Here is a video testing fairly aggressive straight plunges and off center machining on one of my previous machines: https://www.youtube.com/watch?v=P-5_ZMINDEU
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Re: Getting Familiar With Rotary Cutting

Postby TReischl » Thu May 14, 2015 12:17 am

Thanks for the offer Gary! Right now I cannot cut off axis. I need to do some research on adding a drive to my setup with a G540. Do not even have a clue as to how that is done.

After my initial tests with the 4th axis I needed to get it cleaned up so it is easier to work with. There was no easy way to ensure alignment between head and tailstock. The last few days I have been redoing it and here is what I have:

1.jpg


It is now all on one board with a rail that provides for alignment of the tailstock. As it is now I can swing 8 inches, but that would not be real practical with the current Z clearance. I am planning on adding 2-4 inches of Z height, but then I will need to make torsion box for my regular cutting to get it up to height. I used to have one on the machine but removed it when I was doing thicker work.

3.jpg


I also made some clamp blocks to lock the Y axis in place while doing rotary. Even with the rotary on the machine I still have 48 X 24 lefover. Plenty of room for the vise and most projects. I am finding I do most of my work these days with the vises. I have two that I use so i can clamp a 10 wide board that is 48 inches long on the table. Most of the time I only use one though.

4.jpg



Tomorrow I am going to run some tests to make sure my headstock and tailstock are at the same height.

Doing this sort of thing is exactly why I built my own machine. I know exactly what to do. For instance, to increase the Z height all I have to do is order two pieces of extrusions from Automation that will cost $16 each, undo 16 bolts and put the new Z blocks in and rebolt them.

Weird, I just looked at the preview for this post. The thumbnails are right side up, but when I click them they are rotated over to the way they were taken. Strange. . . . .
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Re: Getting Familiar With Rotary Cutting

Postby TReischl » Fri May 15, 2015 1:18 am

I cut a sample part today, the system worked great! Everything is tuned in now. I told it to cut a 1.875 dia and it cut 1.878 over 28 inches of travel.

Put a more informative post on the main Aspire forum but here is a pic:

12.jpg
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Re: Getting Familiar With Rotary Cutting

Postby Rcnewcomb » Fri May 15, 2015 5:44 am

It's coming along nicely!
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Re: Getting Familiar With Rotary Cutting

Postby Greolt » Sat May 16, 2015 12:18 am

Good to see another member doing and sharing rotary axis work.

All helps to get more users to see the potential.

And to realise this is something they could have a go at.
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