Bender question

[Shawn Pedersen]

Looking for some feedback on my tube bender from those who have made them or attempted to make them. I'm on my 2nd mandrel setup that I switched to a follow pressure bar style and had good success but on my second tube I ended up with a little bit of wrinkling on the inside (mandrel radius side) of the stay radius. 4.250 CLR with the Nova .75 29er S-bend stay. .020" wall. They were filled with ice. Radius' were milled pretty much dead on...tight suction type fit. There is no wiggle room anywhere in the assembly that I can find. I suspect I didn't secure the tube well enough the second time and it slipped? Otherwise they look awesome..perfectly round all the way around, look nearly perfect. Any thoughts? Thanks!

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Here's my link to my flickr page on the build: https://www.flickr.com/photos/109733516@N07/sets

Shawn Pedersen
Seattle,WA

[edoz]

I'm gonna go with tube slippage, without checking out your setup in person. I think that's what causes most bending problems, especially if your tube was filled. Try a locking collar type deal on your tube, something like this: WP5141593 Shaft Collar - Grainger Industrial Supply

[Alistair]

Shawn,

number one culprit in my experience is tube slippage. That parallel clamp you're using there isn't going to get the job done (imo). What you want is something like a half of a tube block of the appropriate bore that bolts down to it's mating half, bolted to the end of the bending form there.

Also, you might want to forego the ice. It sounds like your set up is made accurately enough to do without it?


Alistair.

[fortyfour]

First thing is somewhere along the line, you did not maintain point of tangency.

Two possible causes (one, or the other OR both):

1. Tube slipped letting the follower get slightly ahead of or slightly behind the point of tangency. That causes an unsupported section and a chance for a ripple / bulge to form. Your method of fixing the tube is insufficient on the other end. Create a tube block type setup on that end and it will hold fast.

2. Improper back pressure: If I am seeing the image correctly, you are relying of your machining precision to create back pressure on the follower and tube combination. You need that roller to have adjustability so you can fine tune the amount of back pressure on the follower. My hunch is after that first pass on the first stay went AOK, but may have wallowed out that through hole (even a slight bit will have an effect). Instead of a hole/pin, create a slot + pin that can be adjusted to put downward pressure on that roller and (IMO) I think your problem will be solved.

That's just my .02 cents from bending A LOT of tubing.

Most likely the most important two points to bring away are to ALWAYS maintain point of tangency, and have the ability to create enough back pressure.

[MrkiMedo]

Here's my link to my flickr page on the build: https://www.flickr.com/photos/109733516@N07/sets

Shawn Pedersen
Seattle,WA

I see on your flicker page (tools album) that you have also experimented with wooden mandrel, how did that work out (or to what extent)?

[werksmini]

Ice cracking into smaller cylinders causing the bends to not be uniform? Shot in the dark...

[bencooper]

A 50/50 mix of water and washing up liquid is supposed to produce flexible ice.

At least according to something I saw on How It's Made.

[Shawn Pedersen]

Thank you everyone! I'll definitely make tube holding my number one priority along with getting consistent pressure down on the wiper die. Steve, I will also try some higher quality tubes at some point along the journey to see what results they provide. I really liked that the Nova tubes were larger diameter and tapered and thin wall all in that package so it was appealing but I'll see what I can find with other tubes.
In my first version (that you can see on the flickr pics) I had a half tube block and a v block holding the tube securely and no issues which is why tube slippage was my first guess. The only real variable was the wiper die instead of the roller and a slightly tighter CLR (4.25 over 4.6).
I just got in a hurry this time underestimating the need for full capture of the tube in both directions, not just up!
Kris, I was looking for ways to get an adjustable tension like you say but the fit was so tight that I thought I could get away with it, but you're totally right. I expected a threaded bolt under pressure in an aluminum hole to not budge :) I'm going to incorporate a threaded plate that holds the roller (like what the tube rollers have for the top roller). Ultimately, I'd like the side arms to be able to bolt into ANY bender die and have an adjustable top so to future proof it a bit.

Davorin, the wood one was just to practice the setup on my rotary table. However, I bent some 1/2" .035 tubing on it just for fun and it bent perfectly, no issues.

I did add some soap, as it was recommended from wherever I saw the ice trick...the question that I had that wasn't clear was how much soap to water ratio is effective. Some other recommendations I got were to cap the ends with a tiny hole in the plate, submerge the tube in a tank with water and allow it fill up, tape the end and freeze...that would keep the ice from wanting to blow out the ends (which it does if you handle the tube for more than just a few seconds and allow the ice to not be bonded to the tube). Using Resin WS8 or sand is another filler option.

[DeeDub76]

What about using Cerrobend?

I have never used it, but it sounds like a lot of work for making curvy tubes.

[VertigoCycles]

Shawn, measure the diameter of your bent tube twice, both "in-plane" and then 90* from that. I'm betting they won't be the same. You can get close to a very good bend with this type of bender, but you may never get it perfect with absolutely no bulge. It may sound counter-intuitive, but in my experience, sometimes adding more pressure to the forming die has the opposite effect of making the starting and ending bulge more pronounced.

The only real way of bending high ratio tubes to small CLRs is to use a proper mandrel (you do not have one) and a proper wiper. You might find you have the best luck with the softest material, one that's more likely to stretch along the outiside of the bend. Even then, it's still likely to flatten out a bit.

When you setup your die on the rotab, how did you ensure that the center hole of your lever arm pivot was concentric with the rotab?

Also, in my own experience, I have better luck milling the groove for the die and form about 0.002-.003" shallow to leave about a 0.005" gap so the forming die isn't bottoming out on the bending die when you pull it. ie: for a 3/4" tube, mill the grooves 0.373" deep instead of 0.375"

EDIT: FWIW I'm no expert machinist by any stretch of the imagination. This is just what's worked for me.

[Shawn Pedersen]

Thanks for the info Sean. To center the rotary table under the spindle and to center the die I used my coaxial indicator.

Endless hours of research on this project have come up with so much cool info. This page is in line with everyone's thought on the tube slipping.
When a good tube bends bad - Part II - TheFabricator.com

Cerrobend (CS Alloys Bend 158) was recommended by Alistair in a previous conversation. Looks promising. CS Alloys - Cerro Alloys Tube Bending Filler It's all over Ebay.

[VertigoCycles]

Thanks for the info Sean. To center the rotary table under the spindle and to center the die I used my coaxial indicator.

Endless hours of research on this project have come up with so much cool info. This page is in line with everyone's thought on the tube slipping.
When a good tube bends bad - Part II - TheFabricator.com

Cerrobend (CS Alloys Bend 158) was recommended by Alistair in a previous conversation. Looks promising. CS Alloys - Cerro Alloys Tube Bending Filler It's all over Ebay.

If you can avoid it at all, don't use cerro bend. It works, but it's pretty nasty to use and adds loads of time to the process. You'd be much better off buying a nicer bender.

[Shawn Pedersen]

That was mentioned in the conversation. I should clarify, that it was mentioned as something to look into,not "recommended". I agree...at some point you just need to have the right tooling to just do the job quickly.

[bambuko]

Have you heard about WS8?
Tube Bending and data sheet

[Shawn Pedersen]

Yeah I've heard of it just recently in my searching. I saw that someone I follow on Flickr was using and buys it out of the UK but his name is slipping me and couldn't find it in my recent activity. Looks promising though for a bender setup like mine. I really don't have the grand to drop on premade ones...I have way more time than money at the moment and this is just a hobby out of control :)

[Rich Beaudoin]

...I have way more time than money at the moment and this is just a hobby out of control :)

I would guess that statement is true for the majority of people on v-salon

[Alistair]

Yeah I've heard of it just recently in my searching. I saw that someone I follow on Flickr was using and buys it out of the UK but his name is slipping me and couldn't find it in my recent activity. Looks promising though for a bender setup like mine. I really don't have the grand to drop on premade ones...I have way more time than money at the moment and this is just a hobby out of control :)

Maybe it was Andy Walker's Flickr where you saw it Shawn? https://www.flickr.com/photos/afwalker50/14360504597/


Alistair.

[Shawn Pedersen]

Yes, it was Andy Walker. Thanks Alistair!

[mxboy349]

Anyone every use this type of bender? Made by Clark & Lewis. It's a manual not hydraulic. I looked at this one last week and it was really well tooled. Looks like it will do up to 1.500 diameter tube. Price seemed fair. Just wondering if anyone has used one of these for bicycle tubing. Can’t seem to find much info on web. Here are a couple of pics and you can see more on my flickr album.

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https://www.flickr.com/photos/175116...57656421505213

[Craddock]

A rotary draw tube bender is great for bends of up to about 6" radius. The segmented ball mandrels aren't compatible with butted tubes.
Good fit and setup of the tooling is crucial for good results.