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Old 09-15-2019, 08:09 AM
smkymtns's Avatar
smkymtns smkymtns is offline
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New to bending tube

I am hoping this is just a newb question and that I am doing something wrong. I bought a Probender Pro4 LE bender years ago and I am finally getting around to tinkering with it. I am working with 2" x .120 DOM and a 2" die with a 6" CLR. The outside radius of the bend is getting flattened and I don't know if I am doing something wrong or if this is normal. I have poked around the net a bit looking for an answer. I understand from reading that this is a high stress area in bending, but to my untrained eye this looks excessive. I cut a small ring of 2" PVC to help show the flattening. If this is not normal, are there any suggestions to correct this? Not that I want to spend more money, but would a 7" CLR die work better. According to the Pro-Tools website, I am within spec for the die with my tubing.

Thanks,

pat


IMG_4669 by Patrick Harris, on Flickr


IMG_4672 by Patrick Harris, on Flickr
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Old 09-15-2019, 11:00 AM
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mikes82GT mikes82GT is offline
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While you may not be able to get mandrel bend quality on any roll benders, it's still better than the muffler shop crush bends. That looks acceptable enough to me, but what do I know?
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Old 09-16-2019, 11:48 AM
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Maxx Levell Maxx Levell is offline
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It definitely looks worse in the first pic than in the second. I've never cut a ring like you have to check the flattening. But my 1 5/8" tube bends don't usually look that pronounced. Is the ID of the pvc 2"?

What are you using the bent pieces for, and is it something you can live with? You might give someone a call where you got the bender...they're generally pretty good about answering questions like this.

Sorry I'm not more help...and I'm interested in seeing any additional replies on this from some more experienced folks.
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Old 09-16-2019, 12:23 PM
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TS3g TS3g is offline
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6" CLR on 2"OD tube is pretty tight. Typically a CLR 3 times the OD is considered the bare minimum for acceptable bends for rotary draw machines without a mandrel, but may show significant deformation, which you are witnessing. You either need thicker material or better yet, a larger CLR (like the 7" mentioned) to reduce the deformation.
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Old 09-16-2019, 12:24 PM
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smkymtns smkymtns is offline
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Thanks, guys. A buddy stopped by my shop yesterday and he wasn't too surprised by the flattening. I do plan on calling the vendor one day soon when I can get home early enough. I will be building a cage and I want to make sure that I am getting the best possible result out of the bender.

The first time that I bent a piece I noticed the flattening and took a picture, but it was hard to really see the 'flatness' in the picture. I had the 2" ID PVC lying around, so I cut a small ring and it does help show it much better. The rest of the radius matches the PVC ring perfectly and the tube measures an 1/8" less on the flat dimension.
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Old 09-16-2019, 12:34 PM
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smkymtns smkymtns is offline
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Quote:
Originally Posted by TS3g View Post
6" CLR on 2"OD tube is pretty tight. Typically a CLR 3 times the OD is considered the bare minimum for acceptable bends for rotary draw machines without a mandrel, but may show significant deformation, which you are witnessing. You either need thicker material or better yet, a larger CLR (like the 7" mentioned) to reduce the deformation.
Thanks for the reply. Do you think the deformation will reduce structural integrity (much) or is it be more cosmetic? It looks like this project will require more spending just to get it off the ground. Already dumped a bunch into my trailer just so I can use it to pick up a load of tube!
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