Will powerhammer crack slab?

[John N]

Dodge, sorry mate, I wasnt saying one hammer was better than another - it makes no odds to me, 99% of my works in industrial forging - I was just suggesting ways of minimising collateral damage from a hammer! I dont know what the biggest size of Phoenix hammer that has been made is, but suspect its a lot smaller than 1000lbs

The page just annoys me slightly because a) a heavy hammer frame does not make a good hammer, since it aint anvil mass. (a big flame cut is cheaper than a pattern and casting)
Cast Iron can be a superior material for a hammer frame as it deadens the vibration shock loading to the bearings etc in the machine, as we know, steel rings! - specifically calling my companies products 'past it' is beyond a joke, with over 140 years in production, and our machines making many of the parts for eurofighter, JSF airbus A380 etc

Steel makes a good anvil, a cast iron power hammer block works much like a cast 'blacksmiths' anvil with steel top, i.e very effectivly. rant over

Chris, I use James Walker Group - Machinery mounts (the TICO s pads)

this page has some good info

Fabreeka® - Products - Foundation Isolation - FABSORB

this is another company I use (occasionally) - the page has a couple of good isometrics of pit foundations

Isolated Foundations

the trick is tuning the frequency of the hammer to the foundation, so it cancels itself out, Im not smart enough to do this but... with a decent sized inertia block it has always been 30 / 50% of the base area of the pit covered in the pads!

I dont have any suppliers of the material non branded, but a read up on the above sites should give you enough knowledge to start looking, if that makes sense

[Dodge]

No offense taken John. BTW Phoenix does advertise a hammer rated at 3500# falling weight. That one I'm sure would need a footing! Total weight 54,000#. Watch yer toes!!!

[brucegodlesky]

Lotsa good posts here.
I dug a 4x4x3foot hole for the footer of my Fairbanks A(50#) and set 4 layers of bridge ties down. Topped them with an 8" layer of white ash. 15 feet aweay there is no vibration felt. i went heavy duty on the wood as the soil is a sandy clay .

[bigjohn]

When considering the specs supplied by Little Giant, bear in mind the concrete technology was not quite what it is today. A more shallow isolated footing can be used. And I have cracked 4" thick concrete with a 50 and 100lb LG the first ten minutes or so of operation. It kind of spiderwebs the concrete. It's kind of fun watching the dust jump around till the hammer starts to do it's little dance. Building a new shop now out of an old church. So down where the baptismal font was located is now a great spot for power hammers.

[Ice Czar]

Originally Posted by Candidquality

Can depend on the soil compaction in your area as well.

a point that may not have been stressed enough so far, the concrete is but an intermediary for the force of the hammer, what the soil (or dirt) does over time has a great deal to do with the mass the slab needs to be.

a range that stretches from bedrock requiring no slab to a swamp requiring a concrete boat

in the event you have (or someone reading this later) a very poor soil to work with
a very promising foundation technology that is rapidly growing is called rammed aggregate piers
(the main trade name being geopeir) the link explains the concept and its seeing rapid adoption in the construction trades, but its also something that many a smith might be able to replicate on a slightly smaller scale

[R Funk]

Ice Czar makes a very good point. The subgrade under the slab is almost as key as the slab or foundation itself.

Unfortunately there is no concrete answer to whether a slab will crack under a power hammer (no pun intended).

There are too many variables. These variables include:

*Type of soil (clay, sand, high organic matter (muck) etc
*Mositure content of soil both at concrete pour and current mositure level
*Compaction of soil prior to concrete pour.
*Strenght of concrete in psi (typically 3000 to 4000psi)
*Thickness of Concrete
*Reinforcement if any
*Hammer characteristics (Total weight, hammer weight, speed etc, wood subbase etc)
and many other variables.

You could go to an engineer and ask them to design a slab to withstand the hammer operation. However the first question they will ask is what is energy and characteristics of the hammer impacts. I would not know where to go for this information. Plus the cost of engineering a slab is not likely to be money well spent on engineering may be better spent on more concrete and reinforcement.

To be safe an independent foundation would be recommended. However as you can tell by the many comments that people have had sucess and failure placing a power hammer on a slab.

If you are pouring a new slab make certain that the subgrade is undisturbed low organic matter soil. If the soil has been disturbed it must be compacted in 4" to 6" lifts of soil. Place 4"-6" of soil compact, place another layer of soil, compact and repeat. Use a plate compactor or other vibaratory compactor. A bulldozer or similar equipment is a very poor compactor and not acceptable due low ground pressure of the equipment. A 4" or 5" slab would not be adequate in most applications

When pouring concrete get at least 4000 psi concrete. DO NOT ADD WATER to make the concrete easier to work as this will decrease the strength of concrete.

Do not allow concrete to set up in direct sun if possible. Wet the slab periodically with a light spray of water as it cures over the next several days.

Add reinforcement as reinforcement is relatively cheap in the overall project cost. Use "chairs" under the reinforcement to hold the reinforcement off the ground. It does not work to lift the reinforcement as you pour as it invariably ends up on the ground at bottom of the slab. I have demoed a lot of slabs and found the reinforcement on the ground at the bottom of the slab.

If slab is more than 15' to 20' in a linear dimension, joints should be cut to reduce slab size as soon as it cuts with an abrasive wheel without damage. (3 to 6 hours after the pour). One rule with concrete is if you pour it it will crack. As concrete sets up it shrinks. This shrinkage will cause cracks in larger slabs. It is better to cut expansion joints so the cracks will be uniform and straight and not random spider webs.

Clays and high organic matter soils move more due to the impact of hammer operation. Clays are bad for transitting vibration to your neighbors. A foundation will reduce this vibration transmission

Adding a wood subbase decreases the likehood of slab cracking as the wood cushions the impact from the hammer on the floor. Likewise rubber reduces the impact as well.

Good luck in what ever you decide.

[Valentin]

Originally Posted by Valentin

my power hammer sits on wood 25x25 mm thick and the floor has no crack ... and my normal anvil has cracked the floor from the sledge hammer

I fogot to mention the hammer is in use about 10 hour/day 2-3 days/week
cioc1 - Blacksmith Picture Gallery

[Peter HIrst]

At the shop where I have been helping out, we have a 25# Little Giant sitting idle because we are wary of crqacking the slab, and cant cut through it to build a pad. We are in a historic, town-owned building, and are very careful guests. Is there some mount we can use that has a reasonable expectation of working on a conventional 4" garage floor type slab?

[Mills]

Peter, the most reasonable expectation is some solid wood some thin rubber then the hammer. The rubber allows a little movement so that the lag screws don't come out as fast. I have done this with a 50 LG and it walks around so I have also lagged it into the slab. it is better.

No heavier than a 25 is, a friend has simply caulked the floor of his shop and set the hammer (same as yours) directly to the slab. It doesn't walk or bounce or crack. It is also well tuned and stays that way.

[R Funk]

This is a question with no definitive answer.

I guess I would go back and reexamine the premise that you can't put in a seperate foundation. Is it an issue of cost? Are there feelings that a separate foundation will jeopardize the future utility of the building?

As you can see many from the postings some smiths have good luck not having a slab crack. Others cracked almost imedeately.

Factors effecting why slabs crack or don't crack include:

What is the subgrade, the dirt under the floor (sandy, clay, high organic matter) Sand is best, clay and high organic matter worse

Is the subgrade compacted?, Is it tight against the floor. Subgrade can subside leaving the slab in poor contact with the subgrade.

What is the concrete specs and condition?

What reinforcement is present if any?

I doubt if you have any above information other than the general condition of the concrete floor.

Thus it is pretty much the luck of the draw....

Strategies to minimize the potential for cracking include:
1) A Larger base. Construct a base larger than the hammer to spread out the stress more.

2) Resiliant material. Wood, rubber, and similar items will absorb the vibration. Incorporate these into the base as they will reduce the shock transmission to the floor

3) I admit this one is way out in left field. Springs, air bags and similar items can be very effective at dampening out vibration and shock if properly selected. Some are 98% plus effective which is what you need. These present 2 problems: 1)Cost, you can spend hundreds of dollars and more on these. 2) Movement of the power hammer during operation. (it may go up and down as the isolators flex)

Google "Punch Press Vibration Isolators" or "Vibration Isolators"

Let us know how you procede.

Remember there are no garuanties (sp)