Best way to fold this ?

[Die HardenedbedwayParticipant @diehardenedbedway41166]

Hi folks

 

I need to make a lot of rectangular loops as shown here but am unsure of the best way to go about it.

 

Are there any small commercial bending machines that can accommodate this size of fold ? Ive had a search but cannot find anything suitable. The only things I have found are box folders that are way too big

Maybe I will need to make a jig specific for the job

 

Ta

 

Carl

 

Edited By Die Hardenedbedway on 31/08/2022 08:39:47

[Die HardenedbedwayParticipant @diehardenedbedway41166]

[Clive FosterParticipant @clivefoster55965]

I'd make a simple jig from a rectangular metal block with a fence to define the gap. Start at one end and work your way round clamping as appropriate to stop it moving. At that size the simple "caulk gun" style squeeze clamps should hold OK.

Radius the corners as apprpriate for the metal thickness. Zeus book has the sizes. Sharp bends in stainless is hard.

If the block is simple rectangle with parallel sides the shape ill be underbent. Either use a second jig with suitably angled sides or a piece of angle iron arranged with the upstand in the middle to form the final bend around. Could get fancy and hollow out the jig to overbend so it comes out straight. Nice when you get it right but may take some experimentation.

Making the bends would be a job for my small nylon faced Thor dead blow hammer I think. In stainless steel thats a classic "get someone else to do it" job!

Clive

Edited By Clive Foster on 31/08/2022 08:55:54

[HopperParticipant @hopper]

Have a look on YouTube at chain-making machines and wire bending machines. They way they bend the links out of straight bar could be adapted to your purposes, even if hand-operated for the home shop. Simples for a bloke who can make a time machine!

[Andy_GParticipant @andy_g]

Posted by Die Hardenedbedway on 31/08/2022 08:38:55:

Are there any small commercial bending machines that can accommodate this size of fold ? Ive had a search but cannot find anything suitable. The only things I have found are box folders that are way too big

There are bench top / vice mounted benders for metal strip (used for ornamental metalwork).

This sort of thing (not necessarily these specific machines though):

Micromark Universal Bender

Metalcraft RBR Tool

(Many examples of home made ones on Youtube too).

 

Edited By Andy_G on 31/08/2022 09:44:33

[JasonBModerator @jasonb]

Think I might go with a press tool, machine rectangular "U" shape in a piece of bar and then a second piece to fit inside the "U" but reduced in size to allow for the thickness of the 1mm stainless.

You could then press one into the other with the strip of stainless between which would bend it into a U shape, then fold the two ends over the top and no need for additional clamping

I've used the method several times to bend strip into a rounded U shape and other profiles so should also work for this rectangular shape.

[Clive FosterParticipant @clivefoster55965]

As Jason shows simple pressing works pretty well for curves and shallower bends in less stiff materials such as alloy, mild steel, copper and softer brasses. Hard brass tends to crack when you are least expecting it.

Not so easy with stainless steel which has serious spring back issues. Less of a problem with shallower bends and curves but you still need to allow for it. Found that out the hard way when I tested tooling somewhat similar to Jasons second picture with some ordinary steel rod before switching to (expensive) stainless for the real thing. Had to tighten up all the bends by hand afterwards.

Sharp bends can be a nightmare. Even the professionals often resort to experimentation. Even when you have got things sorted stainless also has a nasty habit of changing its mind on you half way through the job needing "some adjustment" for the last 50!

If pressing you are probably best off making each bend individually with a relatively thin forcing blade having a suitable radius tip working into an open ended Vee former. Nice radius on the sides of the opening too so the bent material can push through without marking so it over bends enough to cancel the spring back. Not the fastest way of working but once sorted with suitable end stops to define push distance its effective.

Ordinary hand lever bench press will do just fine in your size.

For obvious geometrical reasons the Vee former has to move rather than the blade so its all a bit inside out. Sort of thing that can seriously mess with your head if you don't think it through carefully. Who once made a bending tooling set up that worked just fine except for extracting the finished job! Yup. Moi. Ooopsi, red faced variety.

Hard bit is devising a set up that aligns the stock material correctly so the bends are in the right place and the thing doesn't come out twisted. Radius end on the pusher means you can't align on a scribed line as you do when using the magnetically held "Vee and sharp pusher" devices in a vice. Very effective on the right jobs. So glad I bought mine. Even with those it can be hard not to end up with a twist in the bend. Like what I've been known to do!

If you had enough to do to make serious tooling up be worth the effort it might make sense to refine a basic inside block former by adding lever operated rollers to form each corner from the outside to work quickly and accurately. Not as easy as it sounds because the lever and roller assembly has to be made so that it can be taken off to remove the finished part. Forked end and pull the spindle I guess.

Clive

PS I hate bending to accurate shapes, mostly 'cos its usually onsesy – twosey so job is done before the method gets sorted.

Edited By Clive Foster on 31/08/2022 16:12:50

[Die HardenedbedwayParticipant @diehardenedbedway41166]

Cheers chaps

Cheers Clive, I had something like this in mind.

So a simple block with radius around it set on a flat bit of something laying about and then a bar with a soft face that can be placed in each hole and worked around ?

The other snag is that these would initially be laser cut and then tumbled. The tumbling process seems to harden the skin a bit?

I shall have a play. Great info. thank you

Carl

[Howard LewisParticipant @howardlewis46836]

Such a basically U shaped can be made in a box and pan press brake, although it might be necessary to be remove the work sideways at the end, or depending up the size of the work and the folder, it might be possible to remove the work after the final bend, by removing the upper blade to allow the work to be withdrawn..

With a BIG press brake it could be done using a block to hold own the outer ends while the final bend is applled.

Failing that, make the two outer bends, and then the outer ones will have to be made around a former.

Howard

[Clive FosterParticipant @clivefoster55965]

System like your diagram will work fine once sorted. You will need to support the pivot for the bending par at each end, so it doesn't twist on you, and locate both the blank material and the former block both accurately and firmly. Basically a sharp U section carrier for material and former block. Weld up from decent plate and finish machine for accuracy or straight out machine from solid. Drop through pins to locate the block so it can be held with an external clamp and as pivots for the bending arms. Pull the pins so the former comes out with the bent strip ready to push out of the middle.

May be easier to arrange things with two separate tooling set-ups. One to do the basic U and another for the second set of bends to close the rectangle. Arranging room on the former for the over-bends on the basic U whilst still keeping the corner positions right for the closing bends may be tricky.

With separate tooling sets the formers are basically (very) truncated triangles with something like 85° in the corners rather than the theoretical 90°. Objectively it doesn't matter if there is too much room on the internal former for the over bend as it can be defined by stops setting the end point of the bending arm movement. It's much easier to arrange with two formers. Whether its better to have two separate set-ups or just swop formers in the basic U is a moot point. Inner former for the second set of bends cannot be clamped so the location pins have to work harder. I'd probably do two sets so I've only got one pair of bending mechanisms on each to sort.

For a production jobbie combining the sorted separately tooling into one would be sensible but trying for all in one straight out might be too tricky.

As a side note on the accuracy of tooling needed for a reliable bend about 3 weeks ago I got the job of sorting a very hefty commercially made, manually operated, single bend at a time device. It was producing twisted bends so the actual bend wasn't exactly at 90° to the long axis of bar being bent. Monster thing welded up from 1/2" and 3/4" plate with 1" diameter central pivot. 6 ft long pole to drive the bend. Probably heavy enough to produce a localised gravity field distortion! Taking out maybe 20 thou in total wear and play from the various parts fixed it. Biggest single error pair was probably around 10. I was expecting stuff flopping left, right centre and sideways needing a re-boring, bushing and refacing job rather than the simple fitting of slightly oversized parts and refacing it actually got.

Clive

[DC31kParticipant @dc31k]

A very small thing to add to the good advice above: stainless bends slightly differently depending on whether it is bent along the rolling direction of the sheet or across it.

If you are to have the blanks laser cut, it might save a lot of heartache to insist that all parts are oriented the same on the sheet (as the laser cutter's nesting software might try to rotate some parts).

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