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Old 12-11-2011, 01:46 AM   #1 (permalink)

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Default CNC plasma tube notching w/ bendtech.

As i try to make my frame/buggy/whatever building more automated, cleaner, more exact and of course more repeatable- I determined I needed a way to notch tubes with a plasma (cnc controlled of course). This makes any angle of notch and the machine handles the clocking of notches.
The machine was simple because I already built a 2 x 4 table to cut my plates and tabs.

Just added another motor, sprockets, mounted bearings and a simple frame.
A rotating axis is similar to linear in at the diameter your cutting at (tube OD) is a certain distance around (circumference). A 1.5" tube is 4.711" around so you just need the tube to rotate 360deg when the machine moves 4.711". I made this cut with the free notching script available on the internet.

But I want a solution that will work with my 3d models without a ton of leg work per part. Bendtech really is one of the best solutions on the market for tube frames.
All of the features are extremely useful and does away with trial/error if used properly.
I purchased bendtech with a mind of using its wraps in this machine. Seeing as a lot of builders use bendtech I figured it would be a worth while endeavor. Bendtech will only let you print wraps (which is sad) but its not hard to get them into a raster (image, postscript namely) file.
So here it is - how to bring your notching wraps into a cad program directly (sort of).
One just needs to make a new printer that prints and check the print to file option, then select a generic-ms publisher driver (XP).
Now when you hit print, windows will ask you for a file name. My compture puts all the files in the main bendtech directory.
Once you have the post script files, then you can import them into various programs to convert them into vector files, I used coreldraw to save them as dxf files.
So now I can get from bendtech to my machine for notching and making bend ref. marks.
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Old 12-11-2011, 02:56 AM   #2 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Very cool!
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Old 12-11-2011, 12:11 PM   #3 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Cool idea, but I don't see how this can be very accurate.
Unless the torch is somehow tilting as well as moving linear.
Am I not seeing something here?
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Old 12-11-2011, 05:29 PM   #4 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Its not a "machined" notch so it does fit a bit differently. At the same time IMO its as good or better because the thin ears on the sides of the welds are lost. Welding on those thin side ears isn't good practice, it really makes the sides of your joint weaker.
I don't mind having a beveled edge, any good welder knows filling in a beveled joint is way stronger than welding 2 pieces butted together.

I know everybody likes the perfect machined notch but there are other ways.

As far as accurate, its generated by bendtech and its known for being a great solution so I'm going to trust it.
All I'm doing is automating what they've already proven.

Last edited by JGSturbo; 12-11-2011 at 05:37 PM..
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Old 12-11-2011, 06:37 PM   #5 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Its been a while since I've used bendtech for notching but IIRC they have two different methods built into the program for notching. If you are using a endmill/holesaw method it will match the OD of both tubes for the notch for a "machined" fit.

It will also compute what they call a "grinding" method which will match the ID of the notched tube to the OD of the fitted piece as if you were to simply go at it with a grinder and cut-off wheel. Like JGS said, this method leaves the entire wall thickness of the tube available for welding.

Its a pretty sweet set-up, can't wait to see more of it in action.
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Old 12-11-2011, 08:12 PM   #6 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Right and its the grinding method (AKA the wrap) that we are using for a plasma torch cut path.

Ultimately- I'm considering a machine designed just to notch and mark tubes. it would be a long gantry and A-axis with a torch holder and some sort of engraver. The torch is obvious and the engraver would enable adding reference marks for bending. For those of us that are modeling complete cars this and a small torch table would be our answer for reverse engineering our models without a lot of hand calculation/planning. Both machines could share the same drives/computer/software. Torchmate, plasma cam, etc. are releasing similar devices. I'd like to build a machine that would accept 20ft lengths of tubing. It would be pretty long but not very wide or tall. For anybody who likes building tube assemblies it would be more than worth the space. It would eliminate the need for a carriage/indexer on the bender (mostly, still nice to have).
I'm even discussing an output for the DXF files needed directly from bendtech, a plug-in if you will.
We shall see, all the tech exists and is readily available. Trying to cut down my "shop" time as kids and family stuff make it hard to come by. I have more "planning" time than ever
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Old 12-11-2011, 08:23 PM   #7 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Here is an illustration showing how tubing should be notched. If you know how to notch (with welding in mind) you should never leave a knife ecge for a crappy weld. There would be nothing wrong with the fit shown in this illustration. Any other beveling of the tubes would be a waste of time.

As I said, cool idea, But not practical IMO.
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Old 12-11-2011, 08:45 PM   #8 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Frankly people have been notching pipes this way for a long time, mostly laser and it works so whats not "practical" about it?
All the way around the tube it leaves a really nice bevel to lay the weld in, very practical. It fits a lot better than your assuming it does. And machine control means better accuracy/repeatability than hand notched parts.
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Old 12-11-2011, 09:46 PM   #9 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

Neat stuff.

Are you going to build a feeder "axis" to advance the tubing when doing the 20 footers?

I know on RDC most of the big builders are using laser notched and cnc bent tubes.
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Old 12-11-2011, 10:50 PM   #10 (permalink)

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Default Re: CNC plasma tube notching w/ bendtech.

I'd considered doing a bar feed but if the y axis can move 20ft its not needed. This would be the hobby version of the pro. Laser tube cutting.
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