PCNC 770 Owner Chris Moller is work­ing on repro­duc­tion of a 18th cen­tury clock move­ment. He’s using the Tor­mach CNC Scan­ner to image the old pawls, ratch­ets, gears, etc. to get the cor­rect part pro­files of each move­ment before he cuts them on the mill. This is a per­fect job for CNC Scan­ner, and the scanned image really turned out nicely. Take a look:

More From Chris about the project:

Attached is a pic­ture of the orig­i­nal 18th cen­tury chime pawl and a copy I made on the Tor­mach based on the scanned image. I believe I had sent you the scan. I pho­tographed the part I made upside down, but it does look the same on the other side except the splines are going the oppo­site direc­tion! The process of going from CCD scan to CAD model to machined part really works. I intend to repli­cate the entire clock mech­a­nism mostly for fun, but also for learn­ing.

[Show as slideshow]

I milled a pro­file around the exte­rior splines with a 1/32 end­mill tak­ing .020 depth of cut until I went .020 beyond the actual thick­ness of the part (.108). This was easy because the stock is a piece of brass 3/8s thick and could be held in the step jaws. My strat­egy was to then turn the part over and face mill it to the cor­rect thick­ness. By going an extra .020 in depth dur­ing pro­fil­ing you get a cleaner edge, because the out­side mate­r­ial falls away well before you stop face milling the back side. To hold the part to face the back side, I drilled and tapped an M3 hole which is smaller than the hole needed to fit the axle. You can see the M3 hole which required a 2.5 mm drill in the pic­ture. I then milled flat two par­al­lel edges of a large thick washer and attached it to the front of the pawl via an M3 screw and a small lock washer. This enabled me to hold the reverse side flat but only on the edges of the flat­tened washer! This method works but only with very light cuts (less than .025). A heavy cut (> .050) will send the part fly­ing! Gog­gles are required!! This method only works if the part design has a cen­ter hole or if hav­ing a hole does not mat­ter. The final diam­e­ter of the hole in this case is .125 inches, so tap­ping a smaller hole has no impact on the fin­ished part. Lastly I engraved the inte­rior disk detail with the engrav­ing tool Eric rec­om­mended. It worked like a charm. Next time I think I will mill a .25 inch thick square boss within the area of the disk. This will allow a firmer hold so I take heaver cuts on the back side. Then I will toe clamp the part to the table and mill off the boss. If you know of a bet­ter way PLEASE let me know.

BTW, these are the engravers from Har­vey Tool that we’ve been get­ting really good results with lately here at the shop.

Thanks again for shar­ing, Chris!

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About Andrew Grevs­tad

With over ten years of pro­fes­sional expe­ri­ence in advanced man­u­fac­tur­ing sys­tems, dig­i­tal design tools, and applied soft­ware, Andy Grevs­tad has worked in prod­uct devel­op­ment and tech­ni­cal sup­port for Tor­mach since 2008. Grevs­tad has received engi­neer­ing degrees from Michi­gan Tech­no­log­i­cal Uni­ver­sity and a M.S. and Uni­ver­sity of Wisconsin-Madison. He is a reg­u­lar con­trib­u­tor to Dig­i­tal Machin­ist mag­a­zine and also blogs weekly about CNC milling and related top­ics on the Tor­mach blog, Milling Around.