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View Full Version : Flipping material - GUY!



Bob Savage
02-17-2010, 2:37 AM
There's something simple that I'm missing here, but I just cannot see it.

I have this part I'm cutting (see picture) which is two sided. I have two projects. The material is 10"x4.5" and the part is dead center in the material. The reverse side has the same part, dead center but flipped upside down. On my table I've got two reference edges with XY0 set to the very corner. I am stuffing the material into the corner and flipping the part end over end to cut the opposite side.

Problem is, I'm ending up with a difference of about .180" from end to end, which scraps the part.

There's something in the geometry of this part I'm missing, because to my eyes I should be able to simply flip the material and have a perfect cut.

So, what am I missing? Why is there such a big offset? Help! :eek:

Gene Crain
02-17-2010, 10:31 AM
Do you rezero your table before cutting each side?


GC
Plantas y Maderas SA de CV

Jim Beachler
02-17-2010, 10:55 AM
Bob, Is there excess material on the piece that will be removed?

When I do items that flip over, I drill a through hole at the start point.
Then when flipping it over, I use the same hole for the starting point for the back side. This is not 100% perfect but for the job that I do it is sufficient.

Another idea is that if it is off by the same amount, why not compensate for that when setting the starting position on the second side?

Eric Mims
02-17-2010, 10:55 AM
side to side it isn't aligned, or long wise? either way, you could try programming in a couple or 3 drilled holes that go through the part and into the spoilboard some ways. Then use a metal pin, wood dowel, drill bit shaft, etc to simply confirm or hold the part in the correct position when flipped.

Harry Hagan
02-17-2010, 12:23 PM
Any alignment error will be doubled when flipping it end-to-end.

Bob Savage
02-17-2010, 1:37 PM
Do you rezero your table before cutting each side?



I do not, because the 0 is in the same place for each side. The part is flipped and centered for side 2.



Bob, Is there excess material on the piece that will be removed?

When I do items that flip over, I drill a through hole at the start point.
Then when flipping it over, I use the same hole for the starting point for the back side. This is not 100% perfect but for the job that I do it is sufficient.

Another idea is that if it is off by the same amount, why not compensate for that when setting the starting position on the second side?

There's a little excess, however, I can add more if necessary. I've done the hole drilling thing, using those tapped inserts (forget the name) in my spoilboard and a template to drill the holes in the material. The two-stop method I'm using seems to be the same method with a different approach, except I have to ensure the part is exactly the correct length. I did have some luck with the drilled method, so perhaps I should go back to it since it's also a good hold down method.



side to side it isn't aligned, or long wise? either way, you could try programming in a couple or 3 drilled holes that go through the part and into the spoilboard some ways. Then use a metal pin, wood dowel, drill bit shaft, etc to simply confirm or hold the part in the correct position when flipped.

Long-wise. I've done something similar to this, and *thought* this method was just another way of doing the same thing, but it looks like I need to whip out some cheap wood and do more experimenting. Man, when I did Aerospace/Aircraft years ago, I was excellent at building jigs and templates... I must be getting senile. :)



Any alignment error will be doubled when flipping it end-to-end.

At first glance that made sense, but thinking about it, I'm not sure why. Wouldn't it double the error flipping it either way?

Harry Hagan
02-17-2010, 1:49 PM
Yes. Flipping it either way doubles alignment error. I just thought that would emphasize the necessity to be very precise on your setup and clue you in on why the error was so great.

Bob Savage
02-17-2010, 2:17 PM
Yes. Flipping it either way doubles alignment error. I just thought that would emphasize the necessity to be very precise on your setup and clue you in on why the error was so great.

I've got a small pile of scrap wood that's emphasized this. ;) I've done this before with better results, but was using the two screw method. I think I'll go back to this methodology, although it generates more wasted material per part. Then again, I should be aligned very closely with the method I'm using, as long as the length of the material is accurate and matches my setup in Aspire, so I'm at a loss for this one. But, what works, works, so I may change...

Guy Mathews
02-17-2010, 5:56 PM
Bob,

How are you measuring the length of the wood? Are you taking your tape measure and using that little hook and making a mark, or are you measuring starting at 1 inch and going out to 11 for a total of ten?

The little hooks are never reliable for accurate work.

Guy

Bob Savage
02-17-2010, 6:04 PM
Bob,

How are you measuring the length of the wood? Are you taking your tape measure and using that little hook and making a mark, or are you measuring starting at 1 inch and going out to 11 for a total of ten?

The little hooks are never reliable for accurate work.

Guy

I was initially going from 1" to 11" but then switched to using a square that has a scale on it. I cut one piece at 10.125" by accident, adjusted the material size in the project, recentered, retoolpathed, and same results.

Last night I thought my job xy0 may have been off but after moving my dust boot and taking another look, it was right on.

This should be working, right?

James Jaragosky
02-17-2010, 8:20 PM
I was initially going from 1" to 11" but then switched to using a square that has a scale on it. I cut one piece at 10.125" by accident, adjusted the material size in the project, recentered, retoolpathed, and same results.

Last night I thought my job xy0 may have been off but after moving my dust boot and taking another look, it was right on.

This should be working, right?
I work from the center when setting up a project. The center of a file is always the center, regardless of the shape or size of the of the material.
Jim J.

Bob Savage
02-17-2010, 8:33 PM
I work from the center when setting up a project. The center of a file is always the center, regardless of the shape or size of the of the material.
Jim J.

Hi Jim,

How do you maintain your point of reference when flipping the material, without moving the part off-center? I'm not understanding how using the center would maintain positioning over using the corner.

Guy Mathews
02-17-2010, 9:36 PM
Bob,

Since I do not know how you are setting up your projects and whether or not you are making a sacrificial spoilboard for this project I can only guess at what you are doing. I am going to step by step this the way I do it starting with CAD, then CAM then actual machine.

In CAD starting at X,Y,Z 0 in the positive quadrant draw a rectangle that is just a little bit bigger then the the piece of stock you are going to be working with. This rectangle is your Area Clear for your sacrificial spoil board. You will use this to create a surfacing program and establish the X,Y,Z home position.

Next, with in this rectangle, draw your stock rectangle or bounding box. This represents the material you will be cutting. The stock material you are cutting has to match this measurement for this to work. You must also start from the X,Y,Z, home position. Do not guess that you are there. Make sure it is there. Use grid snap to ensure that you are at X,Y,Z home.

At this point, you are ready to add your vector artwork of the project you want to run. This will be centered in the bounding box. You must ensure that you are centered both horizontally and vertically. No if, ands or buts about it.

You are now ready for CAM. Generate a tool pathfor the area clear rectangle. Make sure the bit size in the computer coincides with the actual bit you are using.

Generate your toolpaths for your vector art. Your tool path stock must be the same size as your bounding box. If your stock is not, when you create the flip in your CAM program, you can be off.

Lets move to the machine now.

Start your machine and reference return or G28 or C3 or do whatever it takes to make your particular machine orient itself to the manufacturers reference position.

With that being done, slap a piece of sacrificial board on the table anywhere you want. Yes ANYWHERE! Make sure the piece is bigger then the area clear rectangle that you drew in the beginning.

Move the machine to the plywood and set a new work position by using the G92 commands for X and Y or the G92 radio buttons (X,Y Zero) on your UI.

Now that this is done, move the spindle over to the approximate center of the board and lower the cutting bit that you are going to area clear with to the plywood. I find a piece of paper works best for setting Z height when working with wood. Sorry to all you CNC purist who read this, but I work with WOOD, not NASA. No I do not use those stupid aluminum plates that come with the machines for zeroing Z. They are a waste of my time.

G92 your Z. You are now ready to area clear your sacrificial spoilboard. The depth I prefer when doing this is .125 inches. This gives me a good level board, and it also gives me a clean right angle to position stock against.
What is very important here is that the bit size is correct with what is programmed. For example if you program for area clear using a half inch end mill and you actually use a sharpened end mill that is now .47 in diameter, you are screwed.

Anyhow, run your area clear program and when the program is done return the bit to the X,Y 0 and with the spindle running, drop the Z until it bores a hole in the corner. You have now cleared the radius and your stock will fit tight against the X and the Y. At this time, you can also lower your bit .125 and reset Z zero if you are going to use this bit. In my case I have an ATC so after I have measured all my tool offsets, I just have to re-zero Z and I am good to go on all five bits.

You are now ready to run your program.

Run side one, flip the piece over, run side two. Voilą. Works for me every time unless, the stock is screwed up, or area clear with the wrong bit, or I do not center my models in the bounding box.

I am sure there 500 other steps that I left out of this explanation but they are not important. The basic jist is up above.

Now the downside, unless you know how far you moved the machine from the G28 position to the sacrificial spoil board (write it down) you may not be able to go back to that location if the machine loses power or you reposition for another job. (Yes I am aware of WINCNC returning to last known job orientation on startup so please save the replies, that is why I made the statement may not)

I suspect, that this may be part of the issue with you. Are you absolutely certain that your work position is truly X,Y 0 from the first time you cut it?

This is the reason I use sacrificial boards. Plus, if I have to go into another project I can always setup a new spot somewhere else on the table and come back to the other one at a later date.

Well Bob, I hope that my long fingered (instead of long winded) ...response clears up the mystery for you.

If I get some time, I will blog this with photos and everything.

Guy

Gene Crain
02-17-2010, 9:40 PM
Hi Jim,

How do you maintain your point of reference when flipping the material, without moving the part off-center? I'm not understanding how using the center would maintain positioning over using the corner.

Maybe Joey or Jim can help here, have you posted this on Vectric as well?


GC

Gene Crain
02-17-2010, 11:09 PM
...this may be why...

GC

Bob Savage
02-17-2010, 11:40 PM
Guy,

It took a couple reads, and I'll probably read again, but I think I see your methodology. Very cool! A blog with pics would be killer! By the way, are you the guy that had a link to a video on your website with a girl/woman talking about getting directions from strangers? I thought it was but couldn't find it again.


Maybe Joey or Jim can help here, have you posted this on Vectric as well?


GC

I haven't, but figured Jim would have the answer because it's how he works.


...this may be why...

GC

Who is that ugly guy? Haven't seen him around, but if he gets anywhere near my machine, I'm thinking I'll have to just let him do whatever he wants. :D

Angie Orfanedes
02-18-2010, 12:20 AM
As part of your design put a hole all the way through on center at the top and the bottom of your design (spaced above and below it). This should be done by your machine as part of the first setup. Holes should go into your spoil board. Flip piece over - locate piece on pins (same size as holes) which themselves are located into spoil board. Clamp piece, remove pins, finish second side. Should be perfectly aligned. Hope this is clear.

You are getting measurement error to edge more than likely.

Bob Savage
02-18-2010, 12:25 AM
As part of your design put a hole all the way through on center at the top and the bottom of your design (spaced above and below it). This should be done by your machine as part of the first setup. Holes should go into your spoil board. Flip piece over - locate piece on pins (same size as holes) which themselves are located into spoil board. Clamp piece, remove pins, finish second side. Should be perfectly aligned. Hope this is clear.

You are getting measurement error to edge more than likely.

Now this is a simple, interesting idea! Thank you very much for the input.

Keith Outten
02-18-2010, 3:51 AM
Bob,

How are you measuring the length of the wood? Are you taking your tape measure and using that little hook and making a mark, or are you measuring starting at 1 inch and going out to 11 for a total of ten?

The little hooks are never reliable for accurate work.

Guy

I tested two measuring tapes today, they are both off.
Starting from one inch for the second test they were both off.
The error was 1/32" on one tape and 1/16" on the other over 30".
That's 1/16" to 1/8" error when you must flip a project.

I use a sheet of Corian for my test piece, it is exactly 30 inches wide.
I calibrated a 24" caliper based on my 6" dial caliper to verify the width of the Corian sheet. It wasn't the best method but it was the only technique I could come up with in the shop at CNU. Scribing a line 15" from each end proved that the caliper is calibrated or at least confirmed the first calibration using the 6" dial caliper and that the sheet is dead on 30" wide.

The moral of the story is that you must have an accurate means of measuring your material.
.

Jerome Stanek
02-18-2010, 7:45 AM
Why not just use your cnc to drill a hole above and below your piece in the center and use pins put them in your cut file

Guy Mathews
02-18-2010, 9:34 AM
Bob,

I am currently going in 23 different directions so the blog will come in due time. I have more info to add in regards to my CNC build. I am back logged in jobs, and am currently trying to get the company website going full bore and of course I have a wife and kids.

Some quick things for you to think about.

1 Reference holes will only work if they are properly positioned in the bounding box. They work great, however, they add in a tool change and while that may not be a factor for two beer taps, it adds lots of time when your production runs are in the hundreds. For me, reference holes are cost prohibitive.

2. Reference holes will only work if your X,Y, 0 position is established. If you willy-nilly your start point and guess its location the next time you cut, you are going to be off times 2 the next time you do a flip. This was pointed out earlier in this thread.

3. Reference holes the plus side! If the above criteria is met, they work great, however, everything in CNC is based on known factors. If you guess one of these factors or do not compensate for it, such as stock length, you will have the problems that you are trying to solve.

I will blog the vacuum jig. I have another in the works, so this blog will cover 2 things. Proper positioning and of course, making a vacuum jig.


Hope this helps you out.

Keith, I am not suprised at your results with the two tape measures. Most tapes are geared toward construction not CNC. Plus, when you let the tape snap back, they end up getting screwed up over time.

Perhaps someone will invent a 24 to 36 inch digital caliper for CNC guys like us! Oh wait, I have digital upcut saws!
Guy

Robert Alexander
02-18-2010, 1:26 PM
I tested two measuring tapes today, they are both off.
Starting from one inch for the second test they were both off.
The error was 1/32" on one tape and 1/16" on the other over 30".
That's 1/16" to 1/8" error when you must flip a project.
.

The moral of the story is that you must have an accurate means of measuring your material.
.

In my former career as a sheetmetal worker,the smart guys allways measured on the 1'' mark instead of using the end of the tape. Even if it meant getting two people to measure. It saved lots of money and time later on.

Keith Outten
02-18-2010, 2:59 PM
Robert,

Note my line number two:
Starting from one inch for the second test they were both off.

I checked both measuring tapes from the one inch mark to 30". Both of them were off over the 29".

I compared two different pieces of Corian this morninig, there is a decrepancy in the two widths so you can't assume that Corian sheets are exactly 30" wide anymore :(
.

Bob Savage
02-18-2010, 3:56 PM
Thanks for all the input!

I did some online research and there aren't many accurate options for a length over 18", and that's a stainless rule with 100ths.

It's almost as if you have to put the material on the CNC and profile it to get the exact size you want, and as Guy mentioned, your bit better be right on.

Lots of good ideas in this thread that will work though, thanks again.

James Jaragosky
02-18-2010, 9:43 PM
Hi Jim,

How do you maintain your point of reference when flipping the material, without moving the part off-center? I'm not understanding how using the center would maintain positioning over using the corner.

Bob, I am self-taught in all aspects of CNC. I may or may not be doing things the right or most efficient way.
After surfacing the spoil board, I apply a piece of 1x6 or 1x8 ww across the x-axis. I then use the cnc to cut the 1x6x.5 ww along the x-axis so it is perpendicular with the gantry/router bit. This gives me a perfect reference point to set my work against.
If I will need to cut something on two sides, I measure and mark the dead center of the material on both sides before starting the first cut. I set up my file to work off center and use a small bit (1/16) or laser pointer and target my center point.
By using the 1x6 ww as my reference point for perpendicular with the gantry/router bit and the center of the material along with a file based on center, I have been very successful whenever I need to flip something.
This may not be the most efficient method but I works for me.
Hope you find something that works for you.
Jim J.

Walter Plummer
02-18-2010, 9:48 PM
How about stating with your stock oversize and routing the design on the 1st side. Then while it is still on the router cut it to size around your design so when you flip you know it is to size and centered?

Bob Schlowsky
02-18-2010, 11:03 PM
Bob;
Try and flip off of the middle of the offending axis. I found it to be the most accurate. I put a scribe line top to bottom at the center of my material. After it is clamped in place I mark the guide to match it. When I need to machine the opposite side I align off of the same vertical scribe mark.
I have also used a V bit to mark the material via the Cad file, then I know I am exactly in the center - no ruler needed, transfer that to the guide as well as the opposite side. I align to my mark again after flipping it.

Bob Savage
02-19-2010, 3:32 PM
This is an excellent thread and I'm really enjoying the visibility to different approaches.

I think what I'll try tomorrow is to route a couple holes into a spoilboard to install threaded inserts. Then as a part of the project, I'll center on the project, and put the same holes in the material before flipping. Obviously, the holes will need to be drilled so the bolt is tight.

I'll report back with my results.

James Jaragosky
02-19-2010, 4:07 PM
This is an excellent thread and I'm really enjoying the visibility to different approaches.

I think what I'll try tomorrow is to route a couple holes into a spoilboard to install threaded inserts. Then as a part of the project, I'll center on the project, and put the same holes in the material before flipping. Obviously, the holes will need to be drilled so the bolt is tight.

I'll report back with my results.
be careful of anything mounted in the spoilboard that can destroy a bit.

Bob Savage
02-19-2010, 4:51 PM
be careful of anything mounted in the spoilboard that can destroy a bit.

Absolutely! I've been screwing down all my work so I've been careful, and in some cases creative so I don't hit a screw/bolt. The nice thing is that I can find the open/clear spots in my Aspire project and as long as my rapid clearance is not too low, no bits break on bolts.

Guy Mathews
02-19-2010, 5:30 PM
Bob,

You have come a long way in a short time. Keep going man!!!:cool:

Guy

Keith Outten
02-20-2010, 10:48 AM
I often have to flip large signs and full sheets of Corian, that's why I have been looking for a measuring standard for the shop at CNU lately. I have been using the project center line as my point of reference, its not a precision means of relocating the blank or sheet but it is accurate enough for most projects.

The picture below is one of three 28" by 46" back loading directories that I am making for an academic building. When I cut the outside perimeter of the sign I will cut into the spoil board just deep enough to leave an outline of the sign shape. When I flip the directories over to machine the window rabbits I will just align the blank to the outline and clamp it down.

The material is Tumbleweed Corian, the inserts will be a 1/4" thick beige colored Corian that are laser engraved and paint filled.
.

Gene Crain
02-22-2010, 9:55 PM
...maybe outsource it to James!!! :D:D:D


Gene Crain
plantasymaderas DOT com

Gary Hitchcock
02-26-2010, 10:57 PM
Don't flip end to end, roll it over.

When I twoside I drill a hole and align the centers,
I'm using a carvewright with their point & click software.
will alow me to remove the drill hole before I save the image
to memory