Thumper project

6 May 08:

Paul Bruesch has publicized this site on the ptg examprep list, and stated, "... there are instructions online to make your
own thumper."

Well, sorta ...

The purpose of this site was to document the development of the first prototype of a new thumper design. In the intervening two years since I first put up this site, I have made some revisions and built four 2nd-generation prototypes which were subsequently checked out at our recent convention. Based on feedback from examiners, I have made some more changes which will be introduced to the examiners at the Anaheim (2008) National Convention.

I will be updating the website in the next few months to reflect the most recent design.

That said, the description below can be used as a guide to building a thumper. The critical blow-determining parameters are correct; the changes I have made have been focused on ease-of-use, and durability.

If you do make a copy, please drop me an e-mail (with a photograph if you can!). I'd love to get the feedback.

If you would like to purchase a completed thumper of the latest design, please contact me:

jrhodes@pacifier.com

John Rhodes, RPT.
Vancouver, WA

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Updated 25 May 06:

Proof-of-concept prototype with stop block and roll pin. -- JDR

Click here to see velocity-measurement setup and data.

Here's a sketch of the thumper and wooden guide cage. The thumper design is based on the following nominal specifications: 51 mm test blow 10 mm dip 13 mm sharp height 4 mm dia roll pin 6.5 mm guide block thickness When the yellow brass rod is in its down position (roll pin resting on lower guide), about 28 mm of rod protrudes above the upper guide. The roll pin (black dot) limits rod travel when the rod is drawn up for a test blow. The red rectangle is a stop block which stops the roll pin when the rod is drawn up for naturals. For sharps, the rod is rotated so that the roll pin misses the block -- and stops against the upper guide. The cage is constructed from 1/4" birch plywood or clear fir molding. Dimensions of the cage: 40 x 40 x 190mm. Guide block holes will be bushed with cloth. right picture: 100 dpi scanned image of prototype
Double pad: 3/4" dia, medium-firm leather with Steinway punchings. The double-pad delivers a dead blow (no rebound). Brass rod: .750 dia, 187.5 mm long, weight = 454 grams.
Notice the roll-pin (arrow) is under the stop block in the left picture, while in the right picture the rod has been rotated so that the roll pin misses the stop block. The two rotation positions of the rod determine whether the test-blow will be for a natural, or for a sharp. [Ignore the scribed rings in the rod -- this is a prototype which was used to try many ideas!]
THUMPER POSITIONED FOR A NATURAL left picture: The cage centers the rod by straddling the key. Pressing down on the cage establishes the reference height for the test blow on the natural. Note that the roll pin (arrow) is rotated so that it stops underneath the stop block; this sets the correct test-blow distance for the natural. right picture: A 2-inch drop delivers a substantial blow.
THUMPER POSITIONED FOR A SHARP left picture: The 40 mm width of the cage fits nicely as shown, and when the naturals are depressed, establishes the reference height for the test blow on the sharp. The pin is rotated so that it passes the stop block and stops underneath the guide; this sets the correct test-blow distance for the sharp. right picture: Sharp test blow completed.