Caught between a Rockstop and a Hard Place!
If you’re like me, chances are you’ve used many different rockstop styles over the years. From the myriad of options, ranging from hand carved wood with rubber bases to the ubiquitous metal squares with nylon straps featured in every Suzuki cellist’s toolkit, it can be hard to choose.
Here is a quick overview of the primary types with pros and cons:
Round strapless “rockstops” are broadly available and are widely used. Their common problem is slippage as they age and the rubber dries out, or perhaps doesn’t grip well in the first place. Another shortcoming of the traditional “rockstop” is its tendency to slip on dusty floors or carpet and its need to be cleaned frequently. Of this type, arguably the most widely used by professionals is the Dycem “Black Hole” brand pictured on the far right in the photograph above. These rubber discs grip well when new and can be rejuvenated by cleaning with water and non-greasy soap or alcohol. Dycem has been my go-to brand for more than 15 years and represents good value despite being more expensive than budget rockstops. One drawback I’ve encountered is that, over time, the plastic endpin holder in the center of the disc can deform and make a bump on the bottom of the rockstop which reduces its gripping ability. It will still function, especially after cleaning, but I find myself buying new ones every year or two to get the best grip. Another problem with the Dycems is their lack of a strap. Although they work well in many situations, it’s not uncommon to encounter environments where they just don’t hold and would benefit from an anchoring strap or string to fasten around a chair leg. Because of the EPDM rubber of which they are made, it’s not practical to attach a string - the rubber would rip, glue wouldn’t hold, etc.
So, what about the strapped versions of endpin anchors? As a tall cellist, the first issue that comes up for me is that the straps frequently aren’t long enough. Also, the width of the strap can sometimes interfere with foot positioning depending on how a cellist sits and which chair leg the strap is attached to. Some players will put their foot directly on top of the strap, but others find this uncomfortable. Strapped models almost always have either a metal ring or wooden plate with holes to attach to chair legs. This is great, as long as the chair has legs, but presents difficulty in the case of certain piano benches.
Another consideration is moveability. In the case of rubber disc rockstops, sliding them can pick up dust and make them slippery, requiring cleaning of both the floor and the disc before setting a new position. Because they have only one hole, I’ll often find myself moving my chair rather than dealing with repositioning the rockstop! A nice benefit of the strapped models with multiple holes is that a player can re-position somewhat from side to side or forward and back without losing stability.
In addition to the rockstops pictured above, there are less portable options like T-shaped strips of wood or plywood platforms on which players position their chairs. While these can be great in a permanent studio location, they aren’t practical “on the road.” One well-known maker of fine cellos even has a specially designed large stone tile which he advocates carrying around as an acoustical anchor! There are multiple “patented” rockstops with varying types of resonating chambers, but I find their benefits range from minimal to non-existent. In my experience, the best sounding rockstop is usually none at all! It’s hard to beat the stability or sound of sticking a sharp metal spike tip directly into a wooden floor or stage! But this is also impractical unless you have a very understanding spouse or landlord. A concert presenter, on the other hand, generally expects to find cello holes on stage!
This week, after burning through yet another Dycem rockstop, I decided to try a DIY approach. I found these EPDM rubber gasket strips with adhesive backing at McMaster Carr:
EPDM is the same rubber that gives Dycem rockstops their excellent grip. Buying it is gasket form allows DIYers to achieve Dycem’s “Black Hole” trademark holding power. (Be sure to use the softest “Durometer 40A” version from McMaster Carr for the best grip.) The adhesive backing is excellent and 1/8 inch thickness holds well without deforming under load. The two-inch by 1/8th inch strip is what I use here.
For my open-source design, I’ve attempted to address some of the weaknesses of the commercial options discussed above.
1. The excellent grip of EPDM rubber is only available in a few commercial rockstops — we use it here via the McMaster gasket sheets linked above. Unlike commercial designs, ours works well with our without the anchoring string. We offer it for additional security at the player’s discretion.
2. Generally, EPDM rockstop options don’t have multiple holes. We include them here.
3. Using Kevlar kite string instead of a strap interferes less with foot position and offers easier adjustments using a simple overhand loop through the 3-holed clasp (see photo below). Although many kinds of cord will work with this design, we recommend Kevlar kite string because in doesn’t stretch under load.
4. The optional chair leg ring can be removed for piano benches or to make the rockstop more pocket friendly. (Despite being included with most commercial strap rockstops, rings generally aren’t necessary. A string loop around the chair leg can work just as well.)
5. The two hole “dog tag” design makes the Saddle Rider rockstop reversible if the holes start to get worn after years of use.
6. 3-D printable open-source files are available here along with Saddle Rider’s other Creative Commons files. 3D printing using bio-friendly PLA filament is recommended. It’s durable, acoustically excellent, and is made from corn!
7. The EPDM rubber adhesive strip holds securely yet can still be removed and replaced if it dries out or become damaged over time. A $22 3-foot long strip can make between 10 and 18 rockstops depending on the shape and design.
These photos show the parts and basic assembly of Saddle Rider’s open-source rockstop. If you would like to make one, download the parts here and purchase the EPDM rubber and Kevlar kite string (Emma’s Kites brand from Amazon works well!) 500-800 pound test is a good choice for diameter even though the strength is overkill.
Next, follow the instructions below! (Photos notated from left to right)
Use Kevlar kite string because it doesn’t flex. A little superglue spread at the point where you cut it prevents unraveling. Cutting with a razor blade is best, but a sharp scissors also works.
Here are the four 3D printed parts in the assembly. The circular chair leg ring, the small bead is to keep track of the end of the adjustment string, the figure 8 clasp adjusts the string length, and the underside of the rockstop is shown with adhesive EPDM rubber already attached. (Note the rounded edges of the rubber to keep it from from catching carpet edges, etc.)
This photo shows a close up of how to tie the string when adjusting the length.
+ 5. These photos are bird’s eye images of entire assembly. Note that the the chair ring is optional. The cord can loop directly around the chair leg to form an effective anchor.
As always, we welcome your feedback and suggestions for improvements to our design. Please stay in touch!
