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Techniques for CollectorsTrimming specimens

27th Aug 2018 15:53 UTCGreg Simmons

I did a search and didn't find a thread on this topic. I keep seeing references to trimming in threads relating to all aspects of cleaning, prepping, displaying, high cost, etc. but I've not found anything that tells me HOW to trim pieces. Can someone give a list of needed tools, what techinques are used, when you should or should not trim, etc.?

As an example prompting the question, I have three Herkimer specimens in matrix... a LOT of matrix. I'd really like to trim them back quite a bit so they a) don't take up so much space in my cabinet, and b) don't weigh as much on the shelf.. it's only glass.

Pretty much what I have is a rock pick and a cold chisel. I do have a rotary tool too but question if any of the attachments would work on rock.

Thanks in advance everyone!

27th Aug 2018 16:06 UTCDon Saathoff Expert

Greg, specimen trimming is an art that requires practice - on pieces of similar matrix but not important to you. With each new matrix you must discover how it breaks - will it cleave cleanly? will it crumble into myriad fragments? is it too tough (not hard) to respond to hammer & chisel? How much matrix needs to be removed? Do you have access to a trim saw?

We use a homemade splitter, a trim saw, horse hoof trimmers (flea market), tile trimmers, hammer & chisel, etc. Practice will teach what works on the matrix at hand....

Don

27th Aug 2018 16:19 UTCDavid Von Bargen Manager

Herkimers are going to be a real problem because the rock matrix is very tough. The Smithsonian had a display of Herkimer matrix with all the bent/broken tools that were used in it's reduction.

I wouldn't use a hammer and chisel on any specimen that would be rated as fair. You stand a pretty high chance of the rock not breaking the way you want it to and also popping off of any good crystals on the specimen. That method gives you almost no control on how the rock would break.

For small specimens (<1" or so), you can use tile nippers to reduce the matrix. Up to maybe 3" or so, you can use one of the screw type trimmers. For serious breaking, you step up to a hydraulic trimmer. The "professional" trimmers allow you to accurately put stress on the rock where you want it to break (this doesn't always work though).

These types of trimmers allow you to place a strain on the rock where you want to break the rock. They also usually have guards to protect you from flying rock chips and also keep the broken pieces in a known area.

27th Aug 2018 18:26 UTCDoug Schonewald

I just ordered a new engraving tool. I burned up the last one finally (I am pretty hard on tools). They are cheap and allow me to 'dress up' the cut marks from sawing so that it is nearly unnoticeable. It takes time and patience, but you can saw around nearly anything and then use the engraving tool to chip away the saw marks, especially those used to guide your splitting tool. Using this method it appears a lot more natural. Not completely natural, but more so than a bunch of saw cuts. As Don said, practice on something other than your fine specimens.

27th Aug 2018 18:36 UTCAlfredo Petrov Manager

A lot depends on the characteristics of the rock matrix. If its fracture properties are the same in all directions, as is often the case in hard limestones, granites, basalt, etc, then the rock will generally break where you want it to. Softer rocks, like a poorly indurated sandstone, mudstone, or volcanic agglomerate, are less predictable. And the worst are rocks with very directional fracture, like shale and mica schist, which tend to never break where you want them to - They will break right through the middle of the biggest crystal in the center of the vug you are trying to save. Tears of frustration guaranteed ;(( ...in such cases, you're pretty much obligated to make some saw cuts, as others have described above. Experiment with several pieces of waste rock from the locality, to get a feel for how it breaks, before starting to work on the good pieces.

27th Aug 2018 18:49 UTCSusan Robinson

My husband purchased a Zuber trimmer, German-made, many years ago, and it has been one of the best trimming tools he has ever used. Most specimens trim up very well and with ease. The trimmer is pricey, but not when you know that the specimens you trim will look so much better and not be ruined by using other methods like hammers and chisels.

27th Aug 2018 19:16 UTCHorst Schabereiter

Since 35 years I'm using a selfmade trimmer (see the foto). For larger specimens I have a Zuber trimmer. Both are good to handle and fulfill their purpose.

Horst

27th Aug 2018 19:35 UTCEd Clopton 🌟 Expert

A valuable trimming strategy is to study the rock itself for existing fractures and zones of weakness. Whether you want it to or not, it is most likely to separate in those places. A vug is almost always a weak spot, so the rock can be expected to break across the vug unless you can somehow make it easier for the fracture to follow some other path. Exploit the weaknesses if they are aligned to work in your favor, and don't press your luck if they aren't.

For a vug of crystals that can be easily washed out, filling the vug with thin mud helps absorb the shock of trimming the matrix by keeping free-standing crystals from "waving" and snapping off as shock waves reach them.

I don't know whether it's my imagination or whether it really works, but the effects of striking and breaking hard limestone and dolostone sometimes seem less (as in knocking crystals off the matrix some distance away from the trim) when the rock is wet. Maybe the water filling in the pores of the rock helps to absorb some of the shock.

For very small pieces (thumbnails and micromounts) I use a pair of cheap wire cutters. I bought them to use up on rocks, but they are still sharp enough to cut wire after 20+ years of off-and-on (ab)use.

To Alfredo's list of challenging rocks to trim I will add granite pegmatite. Fine-grained granite may be fairly homogeneous and inclined to break in a predictable direction, but the large crystal boundaries and cleavage planes that come with the coarser texture make trimming something on pegmatite matrix a real challenge and gamble.

After 30+ years of active collecting, I have evolved a keen sense of when I have just gone one whack too far and ruined something! (Still working on sensing when I'm about to take that last whack . . .)

27th Aug 2018 22:31 UTCGreg Simmons

Zuber? I will look it up. Thanks for all the comments, I welcome more still. I didn't think about it before but is anyone aware of any videos on youtube that are about rock trimming? I'll look when I have time.

28th Aug 2018 08:56 UTCUwe Kolitsch Manager

I heard that Zuber has stopped their small (family?) business a few years ago and since then only sell their remaining stock.

28th Aug 2018 13:11 UTCKeith Compton 🌟 Manager

Uwe

Don't know if they have stopped but the following supplier - Mikon Mineralienkontor - (advertises on Mindat) and has the Zuber trimmers and spare chisels listed as being available

https://www.mikon-online.com/

Cheers

28th Aug 2018 14:28 UTCHarold Moritz 🌟 Expert

Trimmers are the best way to reduce matrix. Here is a supplier of trimmers that work via a threaded rod. I have this one and it works great for hand sized specimens. Not cheap, but very durable, precise and easy to use. Bolt it down to a work bench or large metal plate to counteract the torque.

https://absoluteclarity.com/collectors/precision-splitters/

But for very large/tough matrix a hydraulic trimmer is needed. You may need one for the tough Little Falls dolostone found in the Herkimer area (I feel your pain). These are large and expensive, but you may be able to rent one instead. One advantage of these is that there is not torque, you pump the chisel tips together with a lever. They are marketed for splitting granite pavers, etc.

When doing any splitting, always start as far away from the area you want to keep as possible and work incrementally toward it. Splits have a tendency to "short-circuit" to the closest surface or open space in the rock rather than propagate through across, so start conservatively. Then after removing some matrix, the remaining piece becomes progressively easier to split and your control over where the split goes gets better.

One thing to remember when doing this is that the chisel tips need to be set against two matrix surfaces that are more or less parallel. Little natural notches or bumps in the surface will help hold them. If not, then as pressure is applied the chisel tips will either slide along a face rather than cut into it, or the piece will slip out. When a piece is rather tetrahedral in shape it can be difficult to split. So try cutting some small flat surfaces into the matrix where the chisels can be "set".

As mentioned above, practice. Take some dolostone with empty vugs and pretend there is a good crystal in there you want to save and have at it.

28th Aug 2018 14:53 UTCBob Harman

Field collecting for many years, I invested in 2 trimmers. These are my 2 trimmers. The larger one I had made for me in a machine shop. If you want a large hydraulic trimmer, it might be worth your while to check having one custom made vs buying a similar used or new one. For initially cutting away large portions of rock, prior to the actual specimen trimming, a stone saw (concrete saw) might be used. CHEERS.......BOB

28th Aug 2018 16:22 UTCHolger Hartmaier 🌟

Hi Greg,

Speaking from personal experience, be extremely cautious when considering trimming Herkimer crystal matrix specimens. The crystals are usually attached by a thin film of hydrocarbon material only and will not tolerate too much shock. Lots of good advice in the previous posts.

Also, it is worth noting that rocks are very weak in tension. The tensile strength is typically about 1/10 of the compressive strength. When loading a rock in compression in a vise or trimmer, the crack is propagated due to tensile forces acting at 90 degrees to the direction of loading. Naturally occurring planes of weakness, such as cleavage, bedding, foliation, fractures should be exploited first to remove excess material because there is some predictability where the rock is likely to break. Banging away on an otherwise solid-looking piece of matrix requires more energy to generate a fracture, with potential for unintended consequences.

As noted in previous posts, experiment with waste rocks of similar material. Don't load the trimmer to much or too rapidly. Gradual loading until you hear the first crack may be enough to allow removal of loosened material by hand, under controlled conditions. Building up a lot of strain will result in a more explosive, uncontrolled failure. Consider enclosing or wrapping the specimen in a bag to contain all the pieces and to prevent further damage to fragments when they fly around.

Good luck!

Holger

28th Aug 2018 17:53 UTCGreg Simmons

Thanks everyone! Great insights. looks like I have some practicing to do before I attempt on anything I want to keep. The process and tools are a bit "cruder" and less precise than I was imagining. Not what I was picturing at all. I guess I was imagining a set of specialized power tools like a dremel or assorted sized angle grinders for rocks. I learn something new every day. :-)

28th Aug 2018 18:10 UTCBeth Heesacker

My understanding that the Zuber rights and parts inventory has been purchased by Shannon. https://www.shannonsminerals.com/shop/

Last I heard he was waiting for everything to arrive and then tool up to build them.

My go-to trimmer for the large or hard material is a hydraulic bearing pusher from Harbor Freight equipped with knives. My hubby and my son are handy at wire welding.

I do not find it on Harbor Freight anymore but it looks somewhat like the one Bob pictured.

28th Aug 2018 22:51 UTCJohn Oostenryk

Ward's Scientific of New York built the unit in Bob's second picture*.

It has been discontinued for a couple years now. At half the price of a Zuber-I'd say it was a good deal! I got mine NIB for $600 about 5 years ago. Would re-buy same in a heartbeat!!

*He is mistaken-he did not have that made in a machine shop. IN a prior post- he said he borrowed it from a friend, ...https://www.mindat.org/mesg-19-291726.html

Must have changed the springs to a thicker coil - hence it will not close far enough to touch cutters together. (coils take up too much space.)

Mine is stock and definitely will close fully!

I have the exact same model- it is a wonderful workhorse! purchased in 2013

This is their 'newer model' with the springs captured around the lower connecting rod.

Note also the bolts that hold the brass sleeved guides for upper plate(slide bearing surface).

I have made thousands of trims so far... majority sedimentary strata. All good.

Occasionally needs a lil tightening of connectors, the jack is starting to bypass some pressure but no bigge

The earlier units did not have the removable guides(not easily-anyway-welded on) AND the springs were external, hanging from hooks. I use a model as such in the prep lab at my college. Works fine- but do run a piece of steel cable through the (external)springs to capture them, in case a hook should fail. not as bad as the old school garage door springs but same problem-flying off... ;)-

I commented on this prior: https://www.mindat.org/mesg-19-292033.html

ALSO:

https://www.swarfsystems.com/products Got some nice stuff- I have been meaning to purchase a new set of cutters from them!

Check out the Harbor Freight kit he offers.

https://www.midcornwallminerals.co.uk/cornish-mineral-sales/cornish-rock-trimmers/ I have spoke with him about his small trimmer units. Good Stuff!

Further threads on Mindat:

https://www.mindat.org/forum.php?read,19,49028,424680 More trimmer details

https://www.mindat.org/mesg-19-356256.html Lots about using grinder+diamond blade for trimming.

There are a few others too...

Overall--

YMMV?!

Good luck and have fun!

28th Aug 2018 23:58 UTCBob Harman

Just to bring anyone interested up to date, the pictured large trimmer was taken prior to my 2013 posting. It might be similar to other trimmers, but was machine shop constructed. As noted in that post, the chisel points did not come close together. More recently, new longer chisel points have been added, bringing the points closer together, thus able to split thinner sections of rock. I also returned the whole apparatus to my friend as I no longer have use for it. Hope that explains John's concern in his posting. CHEERS......BOB

29th Aug 2018 00:46 UTCBrian Gray

New tile saws (<$100 new) can be purchased from Harbor Freight Tools or as I did, I found a used 4 inch blade tile saw at a yard sale with the diamond blade for $10. Works great.

29th Aug 2018 03:40 UTCRobert Rothenberg

Regarding the last comment, be aware that some collectors object to saw cuts on their specimens.

Bob

29th Aug 2018 10:09 UTCPeter Nancarrow 🌟 Expert

Here is my trimmer:

- and in response to Bob's comment above, one of the things I have used it for is obliterating unsightly saw cut surfaces!

Pete N.

29th Aug 2018 20:24 UTCGreg Simmons

Thanks everyone! I've learned a lot... Not sure when I'll get to put it in practice but very informative. I love this site!

You guys ROCK!

:-)

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