# Di-Acro Model 2 Bender



## Clockwork Bikes (Jun 17, 2006)

I've fashioned a Kinda Quick Lok Clamp and am able to bend now.





































This is a piece of 3/5" x .035" 4130 and as you can see there are a few problems. The outside radius has flattened, the tube narrows during the bend, and there's distortion at the end of the bend. Has anybody worked through these problems?

Thanks, Joel


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## j-ro (Feb 21, 2009)

I wonder if it would change if you used a profiled roller rather than a push block.

It seems like the ones I bent for you had some flattening but not quite that much.


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## Clockwork Bikes (Jun 17, 2006)

I tried a profiled roller and it was way worse. I think the radius for this tube is just too tight.

-Joel


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## RCP FAB (Jun 15, 2011)

What's the clr on the die?


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## Clockwork Bikes (Jun 17, 2006)

2 inches.


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## TacoMan (Apr 18, 2007)

We send out all our tubes be be mandrel/draw bent and they turn out perfectly. These types of machines and tooling are very expensive but is the only way to get nice bends in thin tubing. 

If you are not familiar with these machines, they insert a precision mandrel inside the tube to match the ID. The mandrel is a series of linked together hardened oval balls. As the bend is made, they pull the long lubricated mandrel through the tubes.

The inexpensive die benders are really meant for thick wall tubing or where deformation is not an issue. You can get better results if you pack the tube with sand and cap the ends.


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## dbohemian (Mar 25, 2007)

Clockwork Bikes said:


> This is a piece of 3/5" x .035" 4130.
> Thanks, Joel


What size is the tubing? 3/5th??


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## TrailMaker (Sep 16, 2007)

Hey;

I'd say it is simply too tight a radius for that material. It is my understanding that 3.5 is about the limit for
a pure mechanical bend. Frankly, I think the results are very good - even surprising - given these 
circumstances. Perhaps not what you would want for bike aesthetics, but far better than I would have 
expected.


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## Damon777 (Jun 11, 2012)

Nice job on the "quick-lok". Looks to be quite effective.

2.5 x tubing OD is the minimum suggested CLR on these benders.

How tight is your tooling to the tube? The tubing/CLR is may not the issue here. It appears to me that the tooling is not properly supporting the tube in the "vertical" direction, allowing the tubing to distort and flatten on the OD. If you mic the OD of the tube in the bend area both parallel with the bend axis and perpendicular to it, what are the measurements? If the tubing was allowed to "swell" in the vertical direction, then your tooling is not quite tight enough. FWIW, I would not expect a grooved forming roller to do any better with this bend.


Hit me up via PM and we can discuss further. 

FYI: I realize this is my first post here, but I have lurked around for years and finally stumbled onto a thread I have some expertise in.


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## Clockwork Bikes (Jun 17, 2006)

dbohemian said:


> What size is the tubing? 3/5th??


Oops, that's 3/4"


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## TrailMaker (Sep 16, 2007)

Damon may be correct;

Frankly, I had assumed the dies were very well profiled and snug to the material. The fact
that it did not buckle at all, and "looks"to have simply flatted on the very outside of 
the radius without "growing" in the vertical led me to that assumption.

The material on the inside of the radius is being compressed. If the tube slips in the holder, 
it will buckle there. You've got that covered. This compression also explains the "lump" at 
the end of the bend, like the leading edge of a wave of deforming dough bunching up under 
a rolling pin. The outside of the radius is being stretched, and anything being stretched 
around a bend will want to pull inward. Metal is like anything, and when altered in shape 
will take the path of least resistance. If the dies are not completely snug to the OD pre 
bend, the tube will grow vertically and ovalize. If it is not allowed to grow, the outside 
stretch will continue until it rips, but at some point it will still flat to some extent. The only 
way to stop that is to support it internally with another mandrel. My apologies if this is all
redundant or obvious.

It "appears" as though the die is supporting the tube pretty well, especially since you've
been able to achieve a pretty decent bend in thin/stiff material at that tight a CLR, but there 
may indeed be room for improvement there.


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## Damon777 (Jun 11, 2012)

Cerrobend may also help without the need to weld on endcaps. My post count isn't high enough for links, but you can do a google search and find the wiki on wood's metal.



Trailmaker is spot on. I just happen to have some experience with the Di-Acro equipment and how to troubleshoot the tooling.


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## TrailMaker (Sep 16, 2007)

Superb Info +++++;

And not simply because you agreed with me! 

I want some of the Cerrobend stuff. Sounds far too fascinating to resist!

Now all we need is all the proper circumstances to allow you to share all the rest of your
bending knowledge. I'm betting that many readers will find it most useful, and that you'll be 
valuable resource here.


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## Damon777 (Jun 11, 2012)

As long as there are bending (and some other metalforming) problems, I'll try and help troubleshoot them. I am a mountain biker, which is why I have been lurking around for a while. I just wandered in here when I saw Di-Acro in a thread title from the main page.

Guess I am here to stay now.


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## Damon777 (Jun 11, 2012)

FWIW, I have seen some success with using polyurethane of a fairly hard durometer as a mandrel inside some thinner walled tubing. You just need a way to pull it out.


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## Clockwork Bikes (Jun 17, 2006)

Glad to have your here Damon777, and thanks to everybody else. I've got some more bending to do.

-Joel


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## RCP FAB (Jun 15, 2011)

I haven't had a chance to try it yet, but I have heard freezing soapy water in the tube (ends capped with push on rubber caps or electrical tape) works well.


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## bee (Apr 7, 2008)

I have heard of ferrocene and the sand in the tube method for bending tubes.

How thick OD tube can you bend in that thing?


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## Damon777 (Jun 11, 2012)

The benders are rated for 16ga, but that's not to say people haven't gone thicker. How hard can you pull?


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## edoz (Jan 16, 2004)

RCP FAB said:


> I haven't had a chance to try it yet, but I have heard freezing soapy water in the tube (ends capped with push on rubber caps or electrical tape) works well.


I've done it successfully, but it took some experimentation getting the soap to water mix right. Too much water and it wants to expend and pop out the ends of the tube, too much soap and it actually shrinks.


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## TacoMan (Apr 18, 2007)

Some of the finest handbuilt race car headers are sand bent, and they use larger dia, thinner walls, and tighter bends. I have never tried it, ~10 bucks for mandrel bending saves a lot of my time.


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## RCP FAB (Jun 15, 2011)

TacoMan said:


> ~10 bucks for mandrel bending saves a lot of my time.


I guess....

To me walking over to the bender and bending up a pair of chain stays, for a specific frame, that won't be quite the same as the last or the next is the time saver.

The other alternative is to draw them out, send them to get bent and hope they work like you planned. If not, repeat the process. If the stays don't work how I want them to, I put them aside, maybe for something else down the road and try again.


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## stuntnuts (Dec 7, 2010)

Nothing beats bending in-house. Getting your bends dialed in is the challenge, but once it's sorted out....it's glorious.


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## TacoMan (Apr 18, 2007)

RCP FAB said:


> I guess....
> 
> To me walking over to the bender and bending up a pair of chain stays, for a specific frame, that won't be quite the same as the last or the next is the time saver.
> 
> The other alternative is to draw them out, send them to get bent and hope they work like you planned. If not, repeat the process. If the stays don't work how I want them to, I put them aside, maybe for something else down the road and try again.


I agree, we have several tube benders that work fine -for our race car chassis building. But for thin-wall heat-treated tubes, not so much. We could bend them if we went through all the extra work to pack them with sand, but it is easier to just send them out since we normally run 10-20 at a time.

Another alternative is to miter/weld them. Not as pretty, but much stronger than a yielded piece of bent tube. Years ago we made our rigid forks like that. But I think because of tire/chainring clearance, a curved tube fits the space better on chain stays.


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## Clockwork Bikes (Jun 17, 2006)

Much better bends with this 6" CLR radius collar from Di-Acro. It's actually for a #3 bender, note the 3/16" lift under the roller to get it on-center with the radius collar.

I actually had a tour of the fabrication facility lined up but when I called to confirm I was shocked to hear the parent company just sold Di-Acro and that all their product would be distributed from a warehouse. No sense in seeing that. I hope this doesn't mean fabrication is going overseas.


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## TrailMaker (Sep 16, 2007)

Hey;

There ya go! You ought to be pretty pleased with that. Looks like slightly less deformation
than I was getting with my Pro Tools 105 on the 3.5CLR. Makes me think that I was right in 
wondering if a larger CLR would do the same for me. That should be plenty of arc for normal 
stays, and look clean too.

Now get busy and let's see some product!


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## Damon777 (Jun 11, 2012)

I suppose I can let the cat out of the bag now.

I worked for Di-Acro prior to the sale, and am no longer with them because of it. I have spoken with the new owners, and they have led me to believe that the machines will still be built stateside.

I was the engineer responsible for tooling design. I do not have access to the drawings, but can assist with setup, bend troubleshooting, and tooling design questions. When I originally posted in this thread, I was employed by them, and did not want to ruffle any feathers with anything that could be construed as advertising.

P.S. I was looking forward to your visit. The sale was a surprise to all of us.


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## Clockwork Bikes (Jun 17, 2006)

Damon, that's really good to hear. Can you shoot me an e-mail too? [email protected]

Thanks, Joel


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## Jamenstall (May 18, 2004)

Damon

Sorry to here you were let go. I hope your able to find something soon.

I just got something in the mail from them last week. There was nothing on there that led me to believe that they were under new management.


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## Damon777 (Jun 11, 2012)

No worries guys, I was working before my severance ran out. It actually turned out to be a blessing for me.


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## Damon777 (Jun 11, 2012)

SOFTBUTT said:


> Damon
> 
> Sorry to here you were let go. I hope your able to find something soon.
> 
> I just got something in the mail from them last week. There was nothing on there that led me to believe that they were under new management.


Acrotech is still the same company, they simply sold the Di-Acro product line. The majority of my job was dealing with the roll bending machines, and they kept that product line.


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## Chopshopchopper (Aug 18, 2009)

I'v wanted to try using a bender like the diarco and fashion my own mandrel to pull threw rite at the radius. A ball bearing welded to a steel cable held in place as you pull threw the bend. I think it could work.


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