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View Full Version : Shop made Diacro tube bending mandrels?



Bob Farr
02-23-2011, 03:05 PM
I recently acquired a nice ratcheting Diacro No.4 bender with a platform, quick clamp and a few limited pins and mandrels. I'm pretty excited about this find! I'm still checking around for a source of mandrels but I'll hazard to guess the factory made ones are NOT cheap.

http://i58.photobucket.com/albums/g272/frankenglide/Diacro41.jpg

I downloaded the manual from Diacro's site and it shows a couple styles of tube radius collars, forming rollers, and a long "following block" for forming a tighter radius in thin wall tube material. I highlighted them in these pictures:

http://i58.photobucket.com/albums/g272/frankenglide/Diacromandrel1.jpg

http://i58.photobucket.com/albums/g272/frankenglide/Diacromandrel2.jpg

I forsee using the bender for small diameter bar stock (1/4 - 1/2" OD) and 4130 tube (3/4 - 1-1/4" OD, 14-16ga max wall thickness). A concave forming roller for the bending nose doesn't look too complicated to make on the lathe, but the one-piece center mounted forming block (colored orange, teardrop shaped) and the long following block (colored yellow) seem a little more involved.

I have zero bending experience and not much more machine shop experience. I do, however, have at my disposal a Hendey universal 12-inch shaper, a Gorton O-16A universal vertical mill (2/3 scale Bridgeport), and a Sheldon 11x48 lathe. I'll also have a Van Norman No.6 horizontal/vertical mill ready for use soon.

How necessary is it for the inner forming block (orange) to have the teardrop shape? Could I make it in two parts: the round inner section turned on the lathe and the extended/clamping portion cut another way, then joined? What methods would be best for making the long groved following block? It the long forming block really necessary and an improvement over using a forming roller? Will shop made forming blocks need to be hardened?

Thanks in advance for any bending experience or advise you're willing to share.

Bob

ckalley
02-23-2011, 03:21 PM
I've made bender tooling like that before from plain old mild steel. If you plan to use it a lot, I'd suggest using something stronger, like pre-hardened 4140 or O1 tool steel. The machines you have should be more than up to the job.

Craig

Circlip
02-23-2011, 04:16 PM
Teardrop shape allows parallel clamping on left hand side of former and overbend on RHS. Not complicated to machine new formers, for tube work Aluminininium is good. Have seen formers made with a top and bottom plate of mild steel with a plywood or MDF core sandwich.

Depends on material and quantity of bent items required.

Regards Ian.

mc_n_g
02-24-2011, 12:14 AM
I think you will need dies for each size tube you will be bending. You will also need different dies for different radius bends. Luckily everything is straight radius dimension of what you need.
If they are standard outer dimensions get ball mills and have at it. The rollers should be the easiest on the lathe.
The teardrop shape is required to overbend to account for spring back in the material.

Toolguy
02-24-2011, 12:24 AM
You can easily make the orange die with a ball end mill the size of the tubing and a rotary table.

DR
02-24-2011, 07:35 AM
I have the same Di Acro machine.

The good news is industry standard bending dies can be adapted. Many have the same 1" canter hole. I was able to buy almost a whole pick up truck load of various size surplus dies for near scrap price. Many are hardened steel with ground surfaces (obviously very expensive), others are relatively crude plastic for non-marring of soft tube.

The bending method shown is compression bending. Draw bending is another method that can be done using easily made internal mandrels for thin wall bending.

Bob Farr
02-24-2011, 07:34 PM
*** I was able to buy almost a whole pick up truck load of various size surplus dies for near scrap price. ***

I'd love to stumble on a deal like that! Thanks for the tips and suggestions gentlemen.

Bob

Arthur.Marks
02-24-2011, 10:44 PM
They're actually real straightforward to make. If you have one, calculate the number of degree before it is a straight cut. It is the same amount on each die; you just need to scale up/down the overhang from a perfect circle OD. Here is one I made. You can see the layout lines if you look closely in the photo. It may give you a better idea on how to draft it. Yep, a rotary table and a ball endmill and you're good to go. Nothing else needed.
http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/Widgets/DSCN3196.jpg