Monday, December 03, 2018


I had gone into some detail about available angle grinders, and small hand power tools in general, some time back :
Makita Comes Through - January 15 - 2011

A bit of background to this post:
Right now I am attempting to get several past iron blooms cut up and distributed to the working teams involved.
I've certainly found over the years, that the ideal process for working with a raw bloom is to :
  •  compact as much as possible during the initial extraction heat, ideally from the 'half bowl' shape into a flattened disk / ' puck'
  •  while hot, cut into several 'quarters'
You can certainly imagine that specialised forge set ups, plus either lots of available (skilled) labour / specialised tools are required through all this.

Since the normal reason to undertake a bloomery iron smelt here is to investigate specifically historic process (rather than production itself), the blooms made tend to be smaller ( 5 kg range). The working teams are typically small, and in terms of forging ability, tend to be at best 'semi-skilled' (or most often complete neophytes).
And truthfully. I'm completely exhausted by the time I've set up and ran a smelt, extracted, and undertaken the initial 'clean and compact' heat.

So - this leaves me with a mass of bloomery iron, often at best a roughly flattened half bowl - now cold.
CAMELOT bloom - 5.26 kg, original top side down. Large score is from an attempt to hot cut after extraction.
I have found that the only effective way to cut a raw bloom is using a metal cutting disk. There are two main reasons here :
 The carbon content (so relative hardness) of the metal can vary considerably from top side to bottom, as well as from exterior to centre.
 As well as both solid metal and random voids, there are areas of glassy slag throughout the mass.
The glass especially presents a problem, as it will basically destroy most cutting blades (so using a band saw, for example, just is not effective.
Coupled with this is a second, major, problem :
How do you hold, and hold securely, something that shape? (1)

Taken altogether, I have found the best way, at least if working cold, is to use an angle grinder with a 'zip' cutting disk. (2)

Angle Grinders at the Wareham Forge
 Seen Left to Right :
  •  Aluminium / Size 7 inch / Unknown brand / Unknown power /  Weight 5.9 kg
  •  Blue / Size 5 inch / Mastercraft / 9 amp / Weight 2.5 kg
  •  Orange / Size 5 inch / Rigid / 7 amp / Weight 2.3 kg
  •  Grey / Size 4 1/2 inch / Maximum / 7 amp / Weight 1.9 kg
  •  Aluminium was purchased (heavily!) used at an auction. The name plate is so scratched up other information is not visible at this point. 
  •  Rigid Tools was purchased by Home Depot as their house brand. This tool was purchased in 2011, for about $150.*
  •  Mastercraft is the standard brand at Canadian Tire. This just purchased (not even used yet!), normally $90 (Currently on sale at half price). *
  •  Maximum is the 'better' brand at Canadian Tire. This purchase about two years ago, normally about $80 (also got on sale at half price). *
  •  * All these tools carry a three year warranty. 
As I had pointed out in the earlier posting on angle grinders, one of the selection limits on hand power tools for me is the relatively small size of my hands.  (3)
This is the reason why I especially like the orange Rigid tool. Although a bit heavier, the narrow shaft design allows me an excellent grip. Although heavier, the tool is nicely balanced, allowing for control even when used in one hand. In regular use in the shop, this tool has proved easy to use and certainly durable over time.
The 'Unknown' aluminium body is an absolute monster! This is one of those massive, almost indestructible tools, most likely from the 1960's (maybe even older?). Although the heavy weight does create a certain stability, the cost is a lack of fine control. There is incredible cutting power with this tool, but using it is extremely tiring. (I kept flipping the 15 amp breaker on the electrical panel while using this!)

Note that I have specifically chosen NOT to purchase the DeWalt angle grinder. In this price range ($100 - $150) the construction seems flimsy, especially the power switches. I also find the body size too large for my hands.
I had a chance at an industrial trade show a couple of years back to try out a Chicago brand small angle grinder. This tool was absolutely amazing. Virtually vibration free, quiet operation, with an 'instant stop' feature. Also $400 +, a bit steep for the operation scale at the Wareham Forge.
Getting a good quality hand power tool in recent years has proved a major problem. Certainly all the 'home workshop' and almost every one of the 'contractor' grade tools, reguardless of brand, are in fact 'made in China'. With the resulting downgrade in overall performance and durability. This is has become such a great problem (cost vs quality), that most other workshops I asked for advise on this simply wait for the cheapest knock-off brands to go on sale. Then purchase a pile of these - and simple throw them out when they fail after a month's shop use!

The task here does require the ability to make very deep cuts - and extremely wide cuts at the same time. Any of you you have used angle grinders with zip disks will instantly see the problem here. If there is the slightest twist off perfectly straight position, the thin disks can bind - and explosively shatter.

Cutting distances (with new wheel) :

Aluminium / 7 inch disk / 1 3/4 inch depth / no guard (!!)
Mastercraft / 5 inch disk / 1 1/8 inch depth / guard removable (spring clamp)
Rigid / 5 inch disk / 1 inch depth / guard shifts, but fixed in place
Maximum / 4 1/2 inch disk / 1 1/4 inch depth / guard removable (screw clamp)

I freely admit that using the Aluminium Monster is just plain scary. Note that it does not have any guard on it. (My normal here is to wear a leather welder's chest and arms over my full leather apron, gloves, plastic full face shield over normal safety glasses.) I have had a disk catch and explosively shatter in the past! Despite the too heavy weight, this tool does effectively make deep cuts. One advantage is that the significantly larger 7 inch disk does not wear away as quickly, meaning more consistent cutting depths.

You can see the 'looser' here is the Rigid, with by far the shallowest cutting depth. This is coupled with the fixed guard, which means it is basically not possible to 'oversize' the disk on this tool. Absolutely great for grinding - not so flexible for cutting. (4)

The new Mastercraft came with two separate disk guards. What I may do here is heavily alter one of these to allow for mounting a larger 7 inch cutting disk. This should potentially give me at least a two or even a two and a quarter inch cutting depth. The slightly heavier motor (at 9 amps) hopefully will prove powerful enough.
One of the additional features to this tool is the ability to rotate the end handle portion, changing the alignment of grip to cutting angle.
Any evaluation of performance or durability will need to be forthcoming.

1) I am working up a separate commentary on the process involved in cutting up this same bloom.

2) Early attempts to use a cut off saw (with the larger diameter metal cutting disks available) proved basically a disaster. Clamping the bloom securely proved almost impossible. If the bloom shifted even the smallest amount, the disk would either bind (see below) or shatter.
In the end, the way the disk attacked the mass (along with binding) resulted in actually overheating the motor. As the unit was both purchased used, and not the best quality, the result was melting the windings and destroying the tool.

3) My outstretched thumb to little finger measurement is 8 1/2 inches. The width of my palm is 4 1/4 inches. In the past this had lead me to purchase almost exclusively Makita hand power tools. Most 'American' brands are just too large and bulky for me to hold easily, thus control effectively.

4) The normal set up in the workshop is to keep the Rigid and the Maximum set near the forge workbench. The Rigid has a general metal grinding disk, the Maximum with a cutting disk (both with guards in place btw).
I also have an older Black & Decker 4 1/2 inch x 5 amp (again purchased used / cheap). This is set up with a cup wire brush for rust removal.

*** ADDITION ***

As many readers know, I flag new blog postings via my two Facebook feeds. Sometimes valuable comments come in through those portals :
Vargus Ulfr ... Please keep in mind that altering the grinders is not always a great approach. Some of the larger wheels do not have the same rpm rating as the smaller ones, and thus have a tendency to break more easily at the high rpm range.

1 comment:

David Robertson said...

I have had reasonably good luck with Bosch, Milwaukee,and Makita in that order. 4.5 inch or 5 inch.


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

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