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Chalk and cheese comparison between DMM and ISC

Richard Tregoweth - Friday, January 21, 2011

Any comparison between the new Treemagineers/DMM Impact Blocks and the existing ISC Arborist Blocks would be like comparing chalk with cheese!

Both these blocks are designed for arborist use and die-hard ISC fans will struggle to justify the need for anything new. Others find it hard to believe the Treemagineers could totally re-invent the ubiquitous arborist block into an improved new form.

The rounded edges and superbly designed, strengthening ribs on the Impact Blocks give the DMM option a very distinctive appearance but there are plenty of other additional features to differentiate these two competitors (contrary to what the ISC die-hards think).

With a 40kN WLL the small DMM Impact Block is equivalent in load strength to the very large, yellow ISC arb block. But the ISC weighs in at 3.7 kg with only 1.7kg for the DMM.

In terms of size, the small DMM should be compared with the small ISC RP051 or the stainless steel ISC RP056 .

The anchor thimble attachment, joining the two cheeks is similar to the threaded option on the ISC RP056 but somehow it seems very different in application. The knurled anchor knob is quite a bit larger than the RP056 making it easier to manipulate and the pulley sheave itself sports a larger diameter for an improved rope bend ratio.

There is a convenient pictogram on the anchor knob cap which rotates to top-center when the anchor pin is correctly seated.

The anchor thimble remains in a fixed (or locked) position when the anchor assembly is correctly seated unlike the ISC models where there is small amount of play in the anchor thimble. On the ISC models the thimble rotates slightly under load.

Both the large (60kN) and small DMM Impact Block models have an accessory cord tether hole for attachment to the climbers harness or for hauling into the tree. When combined with a DMM Revolver on a Hitch Climber system you have a simple 3:1 hauling system operated by your groundie so you don't have to carry the Block and/or associated bull rope into the tree.

The DMM Impact Block packaging includes a comprehensive instruction manual with plenty of pictures and easily digested written descriptions. The user manual is a welcome addition - DMM has taken some flak for their presentation of the Treemagineers Rigging Hubs released during 2010.

Price is likely to be the major difference between ISC and DMM. Currently, the ISC product totally dominates the NZ tree care market even though there are other arb block options available.

To date, pulley load capacity, the weight of the unit and rope diameter capacity of the sheave have featured over price.

The above set of criteria may change with the arrival of the DMM Impact Blocks. If you want the latest and greatest expect to pay a premium - Treetools will confirm pricing next week.

The ISC RP057 and the small DMM Impact Block pictured above. Both blocks are rated at 40kN.

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