[silyavski]

Hi,
I am currently designing a very sturdy CNC with a moving gantry.
Basically it will be all steel soldered construction, meter by meter table size, RG 30 size Hiwin Roller bearing slides on X Y, rack and pinion drives - possibly CNC Routerparts with 960 oz-in Nema 34 Motor.

Now the funny part. Instead of spindle i will mount a bench sand rammer /tamper/ with steel head and i will use it to form a wok like object from 1.2mm soft steel sheet 60 cm in diameter and 12-14cm in depth. Obviously any sturdy machine will cope with Incremental sheet forming using non vibrating tool with a small radius. But for reasons too complicated to explain, i need it hammered.

I design it not being cheap on bearings, bearing blocks foot distances, rail length and and metal i use for the table and the gantry.

So i am not worried about vibrations and sturdiness, nor i am worried about the roller bearings/ ok , may be a little, but not so much to change them in the design to plain Frelon open supported round shaft bearings/. The metal sheet is really soft and shallow passes or smaller radius head of the hammer can cure eventual problems

I am worried about how i make the Z resistant to up and down vibration from the pneumatic hammer/800-1200 hits per minute/. I mean how to move the Z? Obviously there has to be no clunky backslash , it had to be firm. I am also not worried about precision, eventual belt stretch for example can be compensated via pass depth and material springiness.

So i thought of 2 synchronously driven ballscrews with 2 nuts each to eliminate backslash and make it sturdy. Belt driven, where the belt absorbs a bit the shock, but how to power it, i will need a big extra wheel geared to the motor to transmit enough force to hold it in its place. What about roller chain with a similar construction?

Any help and ideas?

To understand it better here is how the machine will look and what it should do, though with a smaller hammer and smaller head, but you get the idea. Dont misjudge it from the drawing, i am making a small tank, all steel parts you see are 10mm thick at least:

[awerby]

While there are sturdy CNC routers that can handle a lot of machining stresses, that doesn't mean that they'll substitute for hammers. Forgive my saying so, but trying to combine the two functions doesn't sound like a very good idea. You're using a lot of expensive and rather delicate components like ball-bearing rail trucks to do something that's best done with much cheaper but more durable parts. The engineering requirements for a power hammer are much different from those of a precision cutting tool. Backlash is not likely to be an issue. If you want to make woks or whatever, by all means use a CNC machine to make the forms, but take it to another machine, like a forming press or power hammer, to push the metal into them.

Andrew Werby
www.computersculpture.com

[silyavski]

...You're using a lot of expensive and rather delicate components like ball-bearing rail trucks to do something that's best done with much cheaper but more durable parts. The engineering requirements for a power hammer are much different from those of a precision cutting tool. Backlash is not likely to be an issue. ...

Andrew Werby
ComputerSculpture.com ? Home Page for Discount Hardware & Software

Hi Andrew,

What would be that " more cheaper and more durable" ? I was contemplating using open plain supported bearings, but the bearing blocks are not cheaper than the roller supported square i intend to use. And what about the heat they will generate?
There will be no balls anywhere on the machine except may be at the eventual double balls crew at Z. The long roller blocks will support the stress. I also am contemplating spring mounting the hammer. Anyways, 1 bearing block supports around 40 K Newton , so the vibration spread onto 4 blocks that move the gantry and 4 blocks that move the Z assembly left right= ~ 320 K Newton , which is way enough, having in mind that the hammer can be handheld and the sheet is very soft.

The eventual backslash of Z will be a big issue if i use ballscrew because due to the constant vibration they will brake. A "non hard hit backslash " from belt stretching will be no problem.

So what kind of linear movement will be better than preloaded roller bearing blocks? I am open to hear all ideas.

[awerby]

I've never heard of using ball bearing slides and ball screws to run a power hammer. It seems like a big waste of money to build something that will self-destruct in a short time, but I suppose you can try it if you want. But before doing that, you might look on the web at various proven designs for power hammers. The Yoder is pretty typical: the ram slides in a dovetail, and reciprocates through being driven by an off-center pivot on a driving wheel, like an old-fashioned train wheel. Here's a diagram: http://www.ccookenterprises.com/pdf/yoder.pdf Another type of power hammer uses an air piston as a ram; that's also a lot simpler and more durable than trying to turn a CNC router into a hammer. Here's how those work: Air Hammer Plans, Air Hammer Construction Manual, Blacksmith power Hammer Plans

I have no idea what you mean by a "non hard hit backslash" but constantly subjecting delicate parts like roller bearings and ball screw (not balls crew) nuts to hammer-force impacts is not conducive to their continued longevity...

Andrew Werby
www.computersculpture.com