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Using a Bridgeport Slotting Head as a nibbler ???

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awemawson:
Recently had to make some rectangular cut outs in 2 mm aluminium sheet with a hand held nibbler which is always a pain to get neat, so I was casting about for easier methods.

There are 'Throatless nibblers' where the die pokes out of a table and cuts on the down stroke - very handy, but not cheap and they take up floor space.

There are punch and die sets for Fly Presses, but the depth of sheet is very limited by the upright of the structure and again they take up much floor space for the arm to swing.

Then I cast eyes on my Richmond 3 foot radial arm drill. Very heavy construction, lots of room for biggish panels, perhaps I could make some sort of reciprocating punch holder, and rig the corresponding die on the table with guides for the sheet.

Then I thought - don't be daft - you've got precisely that hung on the back of the Bridgeport in the form of a slotting head.  :ddb: Crank woggles a cutter up and down at a rate set by change gearing, and again masses of room for a biggish sheet of metal. Only issue that I can see is arranging some form of 'stripper' to stop the sheet being pulled back up by the punch as it withdraws.

Anyone been there and done this? Or have any comments on the strength of 'push' of the standard Bridgeport slotting head. How much force does it take to ram (say) a 3 mm circular punch through 2 mm aluminium sheet or 1.6 mm galvanised sheet?

philf:
Andrew,

Depending on the grade of aluminium, the force required for punching a 3mm hole in 2mm thick material could be anywhere between 100 & 400 kgf (220 - 880 lbf) which isn't inconsiderable.

Phil

BillTodd:
Hmmm,  Looking at my roper whitney punch and thinking how much leverage has it got and how much force to punch 2mm ally? 

Well the punch moves not much more than the thickness of the piece, while the handle goes from a  hand-full to about an inch and half.  so say 20:1 . I recon I can easily lift 40kg with my fingers so say 400N max at the handles making a maximum force of about 8000N at the punch  (close on a ton)

That's gonna give that bridgeport a shaking ;-)

Bill

JHovel:
I would think that its wll within the capability of a Bridgeport head. That force is not created by a stationary weight, but by the 'decelration' of all the inertia in the ram and drive of the entire mill. I'll be very interested in your attempt! Looks like a great out pf the box use of a slotting head.
Cheers,
Joe

awemawson:
First results are very encouraging  :ddb:

Not having a suitable punch and die to hand, I reached for a 5 mm slotting tool that I already had for the slotting head - but what to use as a die  :scratch: For a rough and ready test, just really to see if there was enough ooomph in the system to slot 2 mm aluminium I hit on the idea of setting the vice jaws slightly over 5 mm and using them as the die. OK no shear action at the front and back, only on the sides. But this is just 'proof of concept' not full implementation  :lol:

How do we space the jaws - suspend a 5.2 mm drill on a parallel, screw the vice tight and see what happens. Turned out far better than I'd expected, and certainly worth developing as an idea. Only issue was the lack of a stripper plate to stop the victim aluminium sheet being lifted by the punch as it withdraws. But for a first attempt I'm very pleased.

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