TOOLS TO MAKE FORMERS FOR A SMALL PIPE BENDING MACHINE

Hi All,

I have to make formers for a pipe bending machine for copper tubes 3 mm to 6 mm but I do not know the cutting angles, rake etc to be grounde by hand. The kit is from Hemingway.

Who can help ?

Thanks and regards.

Pierre

I have made two Heningway kits - the Boring Bar set and Worden T&C Grinder, and their instructions did offer suggestions for some of the more awkward operations. Do they not, for this tube-bender?

Anyway, assuming this to cut the grooves in formers of the usual type with semi-circular section grooves, like cut-off rope pulleys, I would suggest investigating two alternatives:

1) A tangent tool.

That requires "only" grinding flat the end of a piece of HSS round, or silver-steel (which will need hardening and tempering). Give it a shallow rake but not too much, so the end stays closely circular. No more than 5º. The slight ellipse it will in fact have probably won't matter much, but you could make a "finishing tool" that is fully circular to just scrape the last few thou / bit of mm away.

You will need make a suitable holder from square- or rectangular- section bar, having regard to being able to put the nose of the cutting-edge on the axis. The tool-bit has to be inclined slightly forwards for better front clearance without losing too much top-rake. Usually tangent tool-holders are cranked so their clamp section is below the top-slide or QCTP edge, which also takes the clamp-screw further away from the work.

Depending on the formers' material you might find it worth digging out the bulk of the metal with a parting-tool first. As the tangent-tool does its stuff it will meet an increasing length of cut, as happens with screw-cutting, so might need modest speeds, gentle feed and plenty of cutting lubricant.

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2) A button tool - if you use insert-tooling, of appropriate radius for the smaller tube sizes. Those are made in metric sizes, though very accurately.

Cutting the entire groove in larger sizes with a carbide button might be asking a bit much, so rough it out first.

It would seem feasible to make a button-tool using silver-steel inserts, turned with a recess to give the cutting edge and front clearance; then hardened and tempered. You'd need make a suitable holder, from mild-steel bar. Use a slot-drill or counterbore to form the pocket for the tool itself. Short of having a suitable tool-grinder for it, the tool would be two-use only (turn it 180º )  as you would not be able to regrind it satisfactorily, but that may not matter much. A carbide tip is consumable too... but silver-steel is cheaper!

The advantage would be a perfectly circular-arc groove.

Oh, in both approaches, you are left with tools you can go on to use for other turning operations...

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Thankyou for asking, for this question is pertinent to my wanting to refurbish an old Rothenberger tube-bending kit, at the same time making extra formers to extend its range downwards to include 3mm /1/8" tube!

Notably, its formers are embossed with both the metric and nearest Imperial, tube size, suggesting a little distortion of the curved part of the tube, due to the slight diameter mis-match, is usually acceptable.

Edited By Nigel Graham 2 on 05/07/2022 15:27:03

I will be bending copper tube soon and am considering making a tool and formers.

The formers for the design I intend use are cut using a milling cutter. The bar for the former is held horizontally in a rotary table on a milling machine and the groove cut by an end mill or slot drill while rotating the former. After a number of passes you should get a good semicircular groove.

Take a look at https://modelengineeringwebsite.com/artisans_pipe_bender.html His bender is a copy of one that was written up in ME a few years ago. Like him, I cannot find my copy.

JA

The method is described in "A Review of Pipe Bending Options", MEW of January 2016, on the last page of the article.

Edited By JA on 05/07/2022 16:10:52

Would you be able to point out reasonable sources for sizes under 6mm dia. please. I can only find 5mm dia., made by Sandvik at profiessional prices. Smaller than that I cannot find.

Sorry - I drew a blank too. I have just spent some time searching my own stock and the likely suppliers, for this reply, sure that what we want are available!

I have a couple of 5mm dia inserts but they were from Greenwood Tools, who ceased trading I think even BC. I'd have suggested JB Cutting Tools but I am not sure if it is still trading - they were talking of being at the Midlands Show and Companies House suggests it is still extant.

Protool looks a useful bet but assumes you know the industry codes for these things... which I don't. Round carbides are not very expensive individually, but the cost soon stacks up when you want a reasonable stock of them.

'

I think you and I (with my Rothenberger set) will have to fall back on making tangent tooling or button tooling, using round tool-steel stock for the former and silver-steel for the latter.

For making buttons, produce the rake by plunge-cutting the face with a Vee-tool given exaggerated front and side clearance, or by countersinking until the drill cuts the outer face. The rake recess needs be no more than a mm deep. Give the side clearance by taper-turning, carefully avoiding reducing the rim diameter - or taper-turn from over-size until the rim is correct size. Obtain the best surface-finish you can. Harden and temper to perhaps straw colour.

For what it's worth, if the former is of aluminium or Nylon, even a mild-steel cutter might hold its edge just long enough for this one-off-per-size task, if the groove is first roughed out with a parting-tool or Vee-tool. (The pipe-benders plumbers use for domestic pipework seem to have aluminium-alloy dies; and those on my Rothenberger bender look like die-castings.)

Alternatively we can use the milling technique that JA cites. I have not tried it, but it is a perfectly valid method, advantageously using standard cutters the size wanted.

You could use MRMN type grooving tools with the round ends 2.3,4,5mm here from APT . I also have 1mm dia insert for my Mini-thin holder. Or just grind some HSS or even gauge plate

Also not too hard to turn a button from silver steel and mount it  onto your own holder with a small screw. Same type of thing that is used to make gear cutters

Edited By JasonB on 05/07/2022 19:14:49

Re. JA's posting (above), I went for "Artisan's" design of tube bender and have been well pleased with how it works. I also used same procedure as JA proposes to adopt tp make the various formers. Using the mill this way, it is easy to make many in a short time. I recollect making about 20 before giving up and have only ever using about 6 since then ! I think you can still get get a copy of Artisan's article on CD via David Carpenter's website.

I made the small pipe bender that was the subject of a forum topic on here not so long ago .

To make the formers , I made a tangential holder , simple vertical vee with a slight forward slope and a clamp , which held twist drills of varying sizes . By grinding the shank end to get the clearance angle , perfect grooves of varying sizes were produced to match the tube required to be bent (but they have to be decent quality drills ).

Of course no damage was done to the drill flutes , so cost saved on buying drill rod pieces to achieve the same , some may say I am Tight as a ***** **** , and I would have to agree ! .

The Hemmingway one was in MEW33, author used gauge plate as the turning tool shaped to suit, then moved tool slightly sideways so the form was 0.005 over size then finished with emery.

HSS toolbit ground to a radius to match a radius gauge would be the quickest easiest way. Google lathe form tool for videos etc.