Using a CNC machine as an automatic hammer

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Re: Using a CNC machine as an automatic hammer

Postby macona » Thu Jan 24, 2013 1:41 am

Extruded aluminum would not work for something like this. If you dont want this thing to ring like a bell it needs to be made from cast iron or possibly polymer concrete. This would be best with gibbed dovetail slides. I wouldnt even use linear rails, there is a pretty good chance of brinelling the rails and trucks from the impact.

Yes, if you have not experience building something like this it will be difficult and will cost a good chunk of money. I would start out with something like a worn out milling machine like a bridgeport. Replace the head with some sort of power hammer and install ball screws on the X and Y axes.

Programming a random tool path may not be too simple. Maybe if you can write something that will create a random point cloud and then turn the X-Y coordinates into code.
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Re: Using a CNC machine as an automatic hammer

Postby cvoinescu » Thu Jan 24, 2013 2:21 pm

Someone suggested applying pressure instead of hammering; that may work better and stress the machine less, and that was what I was thinking when I suggested the ShapeOko. It should be capable of applying a few kgf -- not sure whether that's enough, though. Another idea would be to make a contraption that raises the hammer, then lets it drop freely. That way, the machine does not suffer any impact stress; it'd all be between the hammer and the table, and you can pack more punch.
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Re: Using a CNC machine as an automatic hammer

Postby Fred » Thu Jan 24, 2013 3:56 pm

Brinelling - an excellent word. Thanks for teaching me something new today, macona.
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Re: Using a CNC machine as an automatic hammer

Postby wolvescaptain » Thu Jan 24, 2013 4:30 pm

macona wrote:Extruded aluminum would not work for something like this. If you dont want this thing to ring like a bell it needs to be made from cast iron or possibly polymer concrete. This would be best with gibbed dovetail slides. I wouldnt even use linear rails, there is a pretty good chance of brinelling the rails and trucks from the impact.

Yes, if you have not experience building something like this it will be difficult and will cost a good chunk of money. I would start out with something like a worn out milling machine like a bridgeport. Replace the head with some sort of power hammer and install ball screws on the X and Y axes.

Programming a random tool path may not be too simple. Maybe if you can write something that will create a random point cloud and then turn the X-Y coordinates into code.


Isn't that effectively the same as a CNC? Or does it work differently?

metalman wrote:For what you want to do you should first try a pneumatic planishing hammer. Harbor Freight sells a cheap one for about a hundred bucks. http://www.harborfreight.com/pneumatic- ... 94847.html They do about 1000 -2000 hits per minute and have several interchangeable hammer heads for different size impressions. I built one from a cheap air hammer with a modified hammer head and some 1-1/4 pipe for about $30. Then I graduated to a CP sytle hammer once I saw how much better they were. But I still have and use my original home built hammer and a HF plashing hammer plus a couple mechanical hammers too. A boy never has enough toys or hammers...

If that isn't fast enough for you then you can add a CNC X/Y table later. For sheet metal work, normally the metal is held by grippers on the X axis gantry and the hammer is stationary. My big mechanical hammer weighs between two and three thousand pounds and has a 48 inch throat. The X/Y table has to be fairly heavy too to stand up to the pounding that the sheet will receive.


That looks interesting, but I don't think it is delicate enough. The hits I need a really tiny and delicate. Read below to get an idea

cvoinescu wrote:Someone suggested applying pressure instead of hammering; that may work better and stress the machine less, and that was what I was thinking when I suggested the ShapeOko. It should be capable of applying a few kgf -- not sure whether that's enough, though. Another idea would be to make a contraption that raises the hammer, then lets it drop freely. That way, the machine does not suffer any impact stress; it'd all be between the hammer and the table, and you can pack more punch.


This would actually be pretty ideal, as this is what I am currently doing manually - raising the hammer with my hand and letting it free fall.

I am talking about a small round-ended hammer, and really delicate hits. Think of raising a little hammer an inch or two and letting it free fall, that's all I need.
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Re: Using a CNC machine as an automatic hammer

Postby cvoinescu » Thu Jan 24, 2013 5:53 pm

wolvescaptain wrote:Think of raising a little hammer an inch or two and letting it free fall, that's all I need.

I'm racking my brain thinking of how that could be done. So far, the only thing I came up with is a powerful solenoid. Engage it, it pulls the hammer up; disengage after a brief interval, while the hammer is still rising; the hammer keeps going up a little, then falls back down and hits your workpiece. The hammer could ride on a rail (e.g. MakerSlide with the wheels really loose) to keep it positioned approximately where it needs to be (sub-millimetre accuracy not required, I assume). The only problem is you need to solenoid energized to hold the hammer up to move the X and Y, or a mechanism (a fairly loose spring, rubber band or the like) to keep it a little above the surface when the solenoid is not energized.

Writing this, I realized that a belt-driven Z axis may be able to raise the hammer and let it fall. I can even see how it would work on a ShapeOko. Dispense with the Z screw and lead nut. Use a closed belt, mounted vertically on the X carriage, behind the Z rail; have the belt run loosely through a slot in a piece fixed to the back of the Z rail. A small block clamped to the belt can then raise the Z axis from below the slot. Raise the hammer to the desired height, then quickly drive the Z down, moving the clamped block out of the way and letting the hammer fall freely. With only the mass of the belt and little block to move, accelerating at 1 g should not be a problem. It's a bit like the anti-wobble mechanism Bart just adopted for the ORD bot, which lifts the Z but can not push it down, only with a belt instead of a screw.
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Re: Using a CNC machine as an automatic hammer

Postby Kellerkind » Thu Jan 24, 2013 6:07 pm

The first thing that comes to mind would be a http://en.wikipedia.org/wiki/Trip_hammer ... if we replace the Steam engine/Watermill by a Electric motor, mount a Tube instead of a spindle to the cnc and have a machined Iron cylinder with a custom shaped head dropping down inside the tube ( with the tube as a very low tech linear guide ) after being lifted by a cam, it might even work out...
but considering he has access to a big cnc, my first way would still be asking its operator if the force is acceptable for the machine if we just use it to push in the metal a bit on a soft surface
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Re: Using a CNC machine as an automatic hammer

Postby macona » Fri Jan 25, 2013 12:50 am

wolvescaptain wrote:
Isn't that effectively the same as a CNC? Or does it work differently?


That is cnc. Programming is going to be a pain though to get a random stippling pattern. Each point must be programmed in and they need to be close to each other otherwise it will take forever to complete a sheet.

Maybe something more random. something that drops a whole bunch of 1" steel balls from a distance, a small conveyor picks them up to be dropped again. Maybe put the platen the sheet is mounted to on a rotating stage to try and cover all the areas. The more I think about it the less CNC sounds like a good ideal.
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Re: Using a CNC machine as an automatic hammer

Postby cvoinescu » Fri Jan 25, 2013 1:20 am

macona wrote:Programming is going to be a pain though to get a random stippling pattern. Each point must be programmed in and they need to be close to each other otherwise it will take forever to complete a sheet.

That's the least problem. One way to fix that is to generate random impact points, then sort them -- for instance, divide them in a couple dozen bands by their Y coordinates, and sort the points within each band by X coordinate, alternating left-to-right and right-to-left between adjacent bands. That should give a nice economical movement. If that creates visible banding, the bands can be blended by swapping a fraction of points between adjacent bands, prior to sorting by X. Any number of similar tricks can be used (e.g. split the points in two sets, and do them in two passes, banding one set by X and the other by Y).
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Re: Using a CNC machine as an automatic hammer

Postby Kellerkind » Fri Jan 25, 2013 10:18 am

programming of the code is maybe a challenge, not a problem.
A Problem stands in the way of sucess.
- if Programming stands in the way it usually is just a matter of time till it can be solved...

Of cource there are different approaches how to generate a pattern, especially since the order of the points also changes the pattern.
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