Tube Benders

I'm looking to buy a tube bender for 6, 8 and 10 mm copper tube. An apparently identical item is available from Screwfix, Wickes, RS, etc. in a variety of colours and prices but nowhere can I find listed the bend radius of the bend former, something I need to know for my project.

If someone who has one of these devices could pass me this information, I would be very gratefull. TIA.

I have seen one that says 24.3mm radius, however this is not defined as inside, outside or centre line. My bet would be centre line radius as it is about 2.5 x diameter, 3 x diameter and 4 x diameter for the 3 sizes it bends. 2.5 diameter is about the tightest you can go with simple tooling that presses the pipe around a former without getting too much ovality or other issues with the bend.

Martin C

eBay... cheap as ... does 6-8-10mm

https://www.ebay.co.uk/itm/224834946061?hash=item345935040d:g:AdEAAOSwH71iBhs9.

George.

Buy from Screwfix, keep the receipt, measure the information you require, return for refund. Report findings here and earn the eternal gratitude of everyone.

The only small tube bender I could find that lists the radii is the Swagelok one and it is quite pricey.

If you want ot risk your cash, you can buy the 6mm, 8mm and 10mm one on Amazon for less than £11 (look for NBEADS, currently £8.99)

Thanks for your replies gents.

Martin, this makes sense and near enough to go ahead and buy one.

George, not quite sure of your drift. The web address brought up polishing spindles.

D31k, see above, bullet to be bitten at Screwfix tomorrow. (more money but easy returns)

These are cheap benders from eBay and they work OK on copper tube. Important to anneal the tube before bending or it will kink and not produce a smooth bend.

The large bender is for 1/4", 5/16" & 3/8" OD tube with a bend radius to the centre of the tube of approx 1". Bend angle = 180 deg because of the offset handles.

The smaller bender is for 1/8", 3/16" & 1/4" OD tube with a bend radius to the centre of the tube of approx 5/8". Bend angle = 90 deg.

Edited By Paul Lousick on 23/02/2022 01:28:01

Making boilers for a living means I sometimes have to bend a lot of copper tube. The small tool above does a very good job but the bigger tool can be a nightmare to get right as the copper wants to crease rather than bend, Buy extra tube and perfect the technique. I measured radius as 1inch to centreline.

As Fizzy said, practice first to perfect the technique and to determine how much the tube stretches. Bending is one of the least accurate engineering processes. Shown here bending 5/16" tube with the fixed handle mounted in a vice.

held i

Hello from America, I am looking for a article that was published in your magazine listed as being in volume 94 and 95 as the one used at R.R. motor company. What I am looking for is a print/drawing for a model pipe, tube and bar bender, I need to bend the piping on my 3/4" 3 1/2 scale 4-8-4 northern, so I am looking for a tool that is small and compact. Thank you for your time.

Ask the vendors, before purchasing? Avoid those that do not reply and retain a copy fromthe vendor you choose. Check the reply for truth, on arrival of the bender. Return, if they did not tell the truth.

Volume 94 appears to be 1946. When asking it helps to provide the year as most people can relate to that more easily. Nest you need to provide the title of the article.

Nothing shows up in the online index for tube bender in Vol 94 or 95. Need more detail.

If you can identify which issue and pages etc or author name, there are members with back issues who can often help out with copies etc.

It sounds like an interesting project others may be interested in too. The Rolls Royce connection is intriguing.

Edited By Hopper on 12/06/2023 10:30:57

When I was at school we went on a visit to Stewarts and Llloyds steelworks Corby.
I was chastised for talking about pipes. "These are tubes - pipes are what you smoke."

Nevertheless, there was an article in Eim December 2020 entitled "Bending Copper Pipe"

Just for you here

Will remove on 140623

Edited By Anthony Kendall on 12/06/2023 10:43:23

We had a manually operated Hilmor draw bending machine for very thin wall, small bore tubes in stainless steel. An example can be seen here (but may disappear at some point in the future as it is an auction site) Hilmor tube bending machine

Most people are likely to have heard of Hilmor as they make tube benders used for copper pipe in domestic and industrial settings.

Mandrel draw benders like this support the tube being bent with an internal mandrel that stays at the point where bending takes place as the tube is drawn past the mandrel and the bend progresses along the length of the tube. It can take some force to withdraw the mandrel after bending which is why there is a big lever at one end of the bed to do it. They rely on a bend die made to the required tube size and the required bend radius with a close fitting mandrel. They also have a follower die that matches the tube outside diameter. This means the tube is supported all around the circumference by the bend die and the follower and internally by the mandrel. I don't suggest anyone here wants to go as far as making a tube bender with a mandrel. If you are going to make a bending tool I would suggest that you have a bend die and follower that suits the outside diameter of the tube you want to build.

If you look at the copper pipe bending tools for Ø15mm and Ø22mm you will see that the bend die has a U shaped groove and that the follower fits into this groove to keep it correctly aligned. The follower is then used to push the tube around the bend by a roller on a lever. In order to avoid crushing the tube the pressure on the follower is usually some distance ahead of the point where the bend is taking place. Benders for copper pipes have this set as the material is a known factor. To get this correct the roller position on home made tooling means this may need to be adjustable. The Hilmor press benders we used at work had a leadscrew that was operated by turning the handle on the end of the lever (adjustable bending lever) , this also allowed the use of different bend dies for different radii and diameters. Set the roller too tight and you crushed the tube on the inside of the bend, too loose and the bend radius and ovality started to increase.

Paul said in 2022 that bending was one of the least accurate industrial processes. We used to bend anything from 1/4" tube up to 2" NB on one CNC bending machine to tolerances of ±0.1mm on lengths and ±0.1° on angles. Try and get something welded to that tolerance.

Martin C

Edited By Martin Connelly on 12/06/2023 13:03:37

I did quite a lot of searching when I wanted a bender for 8 & 10 mm pipe. I concluded the bend radius on the red ones in the above photos was way too tight for those pipe diameters. A view confirmed by reviews that suggested crinkly bends was the default result. Made my own set with 90 diameter former giving a 4:1 R:d value on 10mm pipe (or tube). Home manufacture with a welded assembly is not difficult.

Photo here on my Flickr albums

**LINK**

I subsequntly revised the arm to a single side design.

Martin

Wall thickness and hole diameter can make a large difference to the job. Thin-walled tubing is obviously more difficult to bend neatly.

NDIY beat me to it ! For good bending you need a wall thickness that will take the strech or commpression, thin wall will just kink. I made a hydraulic tube bender that will happily take 2"NB and 40mm solid. Noel

For what it's worth, I needed a small pipe bender to bend some small bore central heating tube, and purchased one exactly like the red one in the photo above. But I found when I got it home that it creased the tube on the bend.

I looked at it very carefully and noticed that the part with the straight grooves that you draw round to press the pipe into the curved grooves, was slightly - about 1/2 or 1/3 of a mm perhaps - offset sideways from the curved fixed part, meaning that the top grooves were not exactly in alignment over the bottom grooves, and this is what caused a crease in the side of the tube on the bend.

I went back to the shop and explained the problem, and they let me open the boxes of all the small benders they had in stock - about 8 of them, and check each one for this alignment. Most were also slightly off but I found one that looked pretty well spot on, and this one did not crease the pipes.

So I would suggest going to your local professional plumber's merchants rather than buying online, so you can make the same check before buying.

.

Edited By John Doe 2 on 12/06/2023 22:48:54

You've just sent traipsing back down the garden to the workshop to fetch my tube-bender formers, to establish their bend radii to tube diameter rule.

Mine is made by Rothenberg, a reputable manufacturer of plumbing (and other trade?) tools.

This bender uses a near-semicircular former pushing the tube between a pair of grooved, fixed posts on a Y-shaped yoke; each die and yoke being specific to tube size.

Quoting the die "diameter" across the groove centre (i.e the diameter of the block itself), and by tube sizes, their approximate diameters and ratios are:

- 6mm tube 46mm dia die: 7.6:1

- 8mm . 5/16" : 55mm : 6.9:1 [The 5/16" dimension is embossed on the former as well as the mm size.]

- 10mm : 66mm : 6.6:1

- 12mm : 68mm : 5.7:1

However, I use the words "semicircular" and "diameter" advisably because the dies are not full semicircles; so their actual diameters would be somewhat larger than the chord lengths I have measured.

As a rough guide then, this set uses bend radius of about [3.5 to nearly 4] X tube diameter.

'''''''

The Rothenberg set originally had a pistol-grip ratchet driver to push the former across the yoke, but on my set this was totally unserviceable and I was unable to repair the previous attempted repair. So I replaced it with a simple screw-action driver, a little like a small drilling-vice action, but gave it the neat locking-pin arrangement that held the former to the original, and now to the end of the screw.

The ratchet driver was of course to expedite use by professional tube-fitters making copper spaghetti every day; but the slightly slower action of a screw-in driver hardly matters in very occasional hobby use.

Though I cross-drilled the handle for a tommy-bar, I have not found that necessary. I did not knurl the handle, but cut shallow flutes in it instead.

I have now augmented this by buying a pull-round bender like the blue one in Paul Lousick's photo (thank you Blackgates) for the 1/4" and below tubes, and a quick test on some off-cuts gave very pleasing results. I have not measured the ratio but it looks about 3:1 bend radius to tube diameter, which I have seen published as a safe minimum.

I've put some 1945-46 tube bending stuff here

(The article by Mr Barker may be worth drawing up)

Edited By Ady1 on 13/06/2023 01:02:58