Monday, June 04, 2018


Original hammer / mounted in coal forge room
I have just taken delivery of a brand new build 'push / pull' style air hammer. Built by my long time friend David Robertson.

The concept behind these tools was introduced by ABANA's Ron Kinyon
An air cylinder with pressure on both top and bottom is controlled by a valving system. When air is released (via a foot switch) from the lower side, the block is dropped. At bottom of travel, air pressure is reversed, lifting the block. At the top of travel, the flow reverses again. If the bottom release is still open, the block drops again. This method cycles the head block up and down. Although the air cylinder does apply some downwards force, it is primarily the inertia of the head block that creates the impact effect between the dies. This style requires a stand alone (separate) large sized air compressor (needs 10 CFM at 90 psi).

David also built my original air hammer, a much earlier (and simpler) build based on the same principles. I had participated by funding the materials for TWO of the original pattern. David built the first prototype for himself. What he learned (with a few modifications I suggested) was used in the build of the second for my shop. This original hammer had :
• 50 lb head weight
• 1 1/2 x 4 inch die surfaces (set at 90 degrees)
• 3/4 inch cylinder shaft diameter
• 'rating' for up to 1 1/2 x 1 1/2 square stock (1)
• control via movable 'gas peddle'
• total weight of about 450 lbs
(a full description can be found on an earlier blog posting)
Now David has been tinkering, building (and selling) ever improved versions of that original light weight design for easily two decades now.  Safe to say the 'Mark 2018' is considerably improved !

New hammer / mounted on open shop floor
The new build specifications :
• 75 lb head weight
• 2 x 3 1/2 inch die surfaces (set at 45 degrees)
• 1 inch cylinder shaft diameter
• 'rating' for up to 2 x 2 square stock (2)
• control via fixed (front) lever
• total weight of about 1200 lbs (this build actually closer to 1400 lbs)

What is clear right from the specifications is that this is a much more robust machine. Frame weight alone is three times the old machine. The head weight is half again as much (with the corresponding increase in available force).

Some of the details (3) :

Close view of standard dies

One big functional improvement is the attachment of the dies at a 45 degree angle. 
This allows for long pieces of bar to be worked - able to extend the bar past the edge of the machine for both the spread and draw action. On the older machine, the dies were set at 90 degrees to the frame, which limited the spread action to only the last 12 inches of a bar. I have had David align the dies so the draw action will allow a bar to extend through the open door to the coal forge room. This effectively would allow me to extend the working end of a bar about 5 feet past the dies in that direction.
This alignment / attachment does result in the basic die blocks being a bit shorter ( reduction in length of 1/2 inch), but this is certainly balanced by the increase in width (plus 1/2 inch). I had always found attempting to use any accessory tools for punching difficult on the original hammer. A combination of the size (only 1 1/2 wide) and the action (you had to quickly insert the punch as the head moved on the upwards stroke).

Second of the other huge improvements to the new design is the construction of the lower die pillar - also clear in the image above. The original build used a pair of 2 x 2 heavy wall (1/4 inch) square tubes as the support for the lower die block plate. (I had filled those with lead shot to help increase machine weight and thus stability). You can clearly see the construction of the lower die pillar is a set of 1 x 6 inch *solid* flat bars, welded into a solid unit. This massive construction vastly improves stability / rigidity of the lower die pillar. The huge increase in overall weight is primarily here as well - which improves the overall stability of the machine.

Because of the overall construction and layout of the die mounting bolts, I am expecting to be able to construct an 'extension surface' that I can apply to both the top and bottom dies. This should allow me to increase the working surface to about 4 x 4 inches. The utility here would be for ease of texture punching and hopefully compaction of bloomery iron. (4)

Front - block guide
The third huge design improvement is the way the head block is supported.
On the original build, two flat plates extended off the sides of the head block. These plates ran down a channel formed by built up bars bolted together. The bearing surfaces were flush mounted brass plates. As these guides were open at both the top and down each hammer block side - there was a potential problem with fine particles accumulating along the moving surfaces. To avoid excessive wear and more importantly easy motion, considerable lubrication needed to be applied. This in turn certainly created a lot of oil mess - but increased accumulation itself.
The new build uses a 'block in a box' system, lined with replaceable nylon bearing surfaces. Although daily application of a light lube (like WD40) is indicated, this new construction is certainly both more stable and likely to prove more durable.

Upper right - showing adjustment levers
Fourth major improvement is the addition of a number adjustments to the working action.
On the older machine, there was not much you could adjust other than the relative striking height of the top block. (see also # 5 below)
There are three additional adjustments possible on the 2018 build, each easy and quick via levers:
a) Blue = Impact Force adjustment.
This allows you to quickly set for a maximum delivered force to each stroke. Although impact force can certainly be controlled by the speed (inertia) of the individual stroke on the foot control. This additional method of limiting input air (so maximum potential force) is likely to prove handy when working softer materials (copper based) or for detailed work (smaller stock sizes, decorative punching / stamping).
b) Red = Head Speed adjustment
This chokes off the total amount of air supplied into the hammer. The net effect is to slow down the cycle time between individual strokes. Although this does reduce inertia / impact force, this is not the prime intent. With the block moving slower, this allows for more setting time between individual strokes when using punches and stamps.
c) Yellow = Lock Up
This will make the hammer head lock upwards in the full open position. Essential for replacing modified dies or accessory tools. On the old build, you had to (attempt to) snap a suitable length bar into the die gap - as the hammer was cycling ! (5)

Lower 'air trip' valve
The fifth improvement is a better attachment for easy adjustment to the air trip valves. This improvement is a small one - but does correct something that was a major headache on the original. There is a lever type trip valve on either side of the head block. These control the switching of the high pressure air from top (drop) to bottom (lift) into the main cylinder. The air trip valves can be adjusted to set just where in the total up and down motion of the block the direction of travel is changed. The top setting is rarely modified (at least in my experience). The lower valve setting does control just where the hammer head will strike. This would normally be adjusted to conform for the 'resting' height of various accessory tools that might be in use.
The old hammer had a pair of small bars running down each side of the head block guides. The air trip valves were held in place by a pair of small bolts & nuts. As there is some sideways force (and a lot of vibration) resulting from every stroke, these often drifted out of alignment. (As well as up and down changes, shifting too far sideways kept the valve from operating correctly.)
You can see the new system uses the switch firmly bolted (4 x) to a heavy flat bar - which sets into a box attachment, keeping the valve from shifting out of alignment. A good sized 'wing nut' styled bar now is used to alter the position of the bottom height control.

Base, showing activation bar
The sixth improvement is the overall construction of the (exhaust) control lever. For this style of machine, bleeding air from the lower side of the cylinder activates the motion. The more air gets bled out, the faster the head motion cycles / the harder the impact stroke (and increase in strokes per minute as well).
On the original machine, the activation was via a separate 'gas peddle' styled control. I had it set up on a long hose - which sometimes proved valuable if I was working one end of a particularly long bar. (A feature that honestly was rarely necessary.) In the end the stability of the small foot peddle overpowered this possibility.
The new build uses a durable construction for a long bar extending along the whole front of the machine. The air exhaust is through the ball valve seen to the top right of the image. (6)

In this image you can also see the mounting for the hammer. It came supplied with a heavy rubber mat to cushion the base and reduce both vibration and possible floor damage. (Most shops have poured concrete floors.)
You can see that I have set the air hammer on to a raft made of four lengths of rail road tie - total is 36 wide by 48 inches long. These in turn rest on a dug out base of about 8 inches of sand pebble mix. I do expect some settling of the entire mount as the machine is used.

Overall First Assessment ? : 

A great improvement in construction detail, potential durability, ease of adjustment. 

As installed - image by David Robertson

(1) - I have seen up to 1 1/2 x 4 billets drawn out on that first air hammer. Slow - but it did manage it! 

(2) - This easily represents 'as big as I want to move around' !

(3) - At time of this writing, I freely admit that I have not actually * used * this new hammer yet for any forge work. (Expect a further commentary to come !)

(4) - I have built / altered a 30 ton hydraulic press specifically added for this task already.

(5) - Obviously a passive blocking bar should still be inserted between the dies before getting your hands any place near the die blocks!

(6) - I did find this a bit noisy in our settting up tests. Attaching a couple of feet of simple hose to the downstream side will allow the rushing air to vent further away. 

* With thanks to David Robertson for proofing and fact checking *

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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