Replacement tripod clamp for Thomann "Orchestra Stand Premium"

prusaprinters

Replacement clamping block for the Thomann “Orchestra Stand Premium” (Art. 264338). The piece sits behind the lowermost thumbscrew that tightens the tripod section, and is what makes contact with the main body of the stand when the screw is tightened.This model comes in two versions, with additional subversions for different tolerances:M6 hex nut version: This version closely matches the original and can be used with either standard M6 hex nuts or with the low profile DIN 439 / ISO 4035 ones that the original uses.Note: This model is prone to deforming and rounding out with repeated use. This is the same issue that tends to break the original clamps. I do not recommend using this version of the model. It might work better if printing in engineering materials (e.g. nylon), but I have not tried it.Shown in the first picture above (right), next to an original clamp (left). M6 square nut version: While sourcing the hardware is more difficult, this version should be much stronger and not prone to rounding out. It should hold up to plenty of abuse even using common printing materials like PLA or PETG. Recommended.Shown in the second picture above.HardwareYou can pick a version to print to match the nuts you want to use. For hex nuts, either:1 x M6 nut: Use the model with the deeper profile (notestand-clamping-block-hex-cutout-deeper).1 x M6 low profile nut: Use the model with the original profile (notestand-clamping-block-hex-cutout-original). This profile is called DIN 439 / ISO 4035, with a nominal thickness of 3.2mm. It is the same kind of nut used in the original notestand, so you can reuse the nut if you still have it.For square nuts:1 x M6 square nut: The dimensions of these style of nuts seem to have a bit more variance. I provide one model (notestand-clamping-block-square) intended for the nominal dimensions I found online (maximum 5.6mm). For the nuts I ordered, I had to tweak the dimensions a bit (notestand-clamping-block-square-cutout-custom). You can tweak the dimensions to fit your particular nuts by downloading the original FreeCAD model too.All versions additionally require 1 x Thumbscrew of size M6. This is the same screw size as in the original, so you can reuse the ones you already have. Note that the original thumbscrew uses really poor materials and you easily wear out the threads easil or even stretch the whole screw, so I recommend replacing it anyway. Here is a suitable model that you can print yourself. Printing considerationsMaterial: PLA or PETG. (See above for the caveat about the hex profile.)I opted to print mine lying down with the cupped end facing upwards. This way, the layer lines are oriented in the same directions as the thrust load when tightening the notestand. You will need to add supports in the recess which holds the nut.I also tested printing it standing upright, which gives you a completely smooth arc for the cupped end, with no stair-stepping, which worked just as fine. In theory this will clamp the tripod more tightly, but do keep in mind that the layer lines will be running orthogonal to the pressure exerted by the screw as it tightens down. This might be more prone to shearing them apart than the other printing orientation.Some caveatsAfter using these in my orchestra for a year and a half, here are some observations and caveats:The original piece has a slight taper for it going in the vertical direction. This does not appear to have any impact on the clearance of the clamp, and I suspect they merely act as drafting angles in the manufacturing of the orignal. The original also incorporates a metal piece to prevent the thumbscrew from gouging into the piece when you tighten it. To prevent this, you could add an oversized washer for a much smaller thread size underneath the nut, to act as a thrust pad. I think these are also sometimes called “fender washers”. Aim for an outer diameter of at most 10mm. A cursory search through Amazon found me some M3 washers with an OD of exactly 10mm. Alternatively, McMaster-Carr also sells “washer blanks” without any hole punched in them, which ought to distribute the clamping load even more evenly. I could not find any metric sized ones as small as 10mm, however. The closest I could find was 3/8" imperial (around 9.5mm), but that should work fine.This applies to the hex profile version only: After repeated wear over about a year, I noticed that some of these parts ended up rounding out. This makes it successively more difficult to tighten the nut down, leading users to apply more force, thus accelerating the problem even more. Eventually it even became hard to remove the thumbscrew, since you couldn't even use the rounded out hex intent to untighten the nut, and I ended up having to break the part to get it out. Of course, this is not a huge problem since it's easy reprint it. Future improvementsDeepen the indent even more to fit a washer to act as a bearing surface and to distribute the pressure more evenly.Design considerations and abandoned ideas for improvementI have considered adding material that bridges the gap over the indentation for the nut, to help make it more rigid and thus strengthen it a bit against rounding out. One big problem both with the original and the replacement part is that the indent effectively only has four sides: Due to the narrow width of the slot where the clamp has to fit, there simply is not enough room to fit the final two vertical sides. This might be allowing the clamp to flex more than it should in response to the nut rubbing against it, and thus gives more leeway for the nut to (eventually, or with enough applied force) jump to a different rotation. Bridging the indentation with more material would at least prevent this sort of flexing.Unfortunately I believe this would actually interfere with the way the clamp works. The nut has to be mobile and move away from the clamp as you tighten it down, tightening itself against the side of the slot in the tripod that holds the clamp. The only contact between the clamp and the bolt is from the profile of the hex-indent, to rotate it relative to the thumbscrew.One could envision a two-part design: One part holding a captive nut, moving outward to the side of the tripod's clamping slot; and the other part being a simplified version of this current clamp design, with a cupped surface moving inward to clamp the tripod tube. However, thinner parts could be detrimental to the function of the clamp. The upper part would also be (even more) prone to tensile creep, since it would sandwich the plastic in between the nut and the side of the clamping slot. See alsoThis model for repairing the legs of this same brand of note stand.Compatible thumbscrews.A similar repair for the upper clamp.Changelog2024-04-25: I have added a version 2, which improves tolerances to hug the nut more tightly, and hopefully alleviate some of the rounding out problem. I also added an alternative model with a recess suitable for a square M6 nut, which should all but eliminate the problem entirely.