A Wood Gear Clock

[jteneyck]

I just finished building this clock.







It's made from maple and walnut plywood from 2 to 8 mm thick, that I made by gluing up panels from shop sawn veneer with 3 to 5 layers depending upon the thickness.  Once the panels were made I cut out the parts on my CNC.  This is one group of some of the 8 mm parts.  



The people who developed the plans and files should be, well, I don't have anything kind to say about them.  There were so many errors in the parts list, files, and assembly instructions that I'd bet money I'm the only person to actually put one together that actually works.  When I contacted them with some of the problems, they told me they hadn't gotten enough customer feedback yet to fix the problems.  Huh?  At least one part had no drawing and they told me to substitute a larger one for which there was a drawing.  Well, no, that won't fit.  Never mind, I'll design my own.  There must have been at least 10 back and forths, all private.  I have not yet written a review.  I'm letting a little time lapse before I do that so I'm objective about it.  I just hate when people put out stuff that's incomplete and just plain wrong but are happy to take your money.  OK, done with the rant.  

Other than having to solve those problems it was a fun project, and I learned a lot about holding and milling really small parts on the CNC.  Double stick tape is your friend and small downcut spiral end mills can do some amazing work.  

John

[atgcpaul]

That looks so good.  I am really impressed with the sharp details that your CNC can cut.  There are some "perpetual" motion CNC artworks that I've seen, too, that look very nice.  I think it was a PBS special on "Longtitude" that talked about the different wood qualities clock makers explored to find ones that stayed lubricated and did not expand/contract too much.

My HS computer science teacher was trying to create a gadget that would cut wood gears but on the vertical instead on the flat using stepper motors.  This was in 1993, though

[Dumb_Polack]

I dunno....it looks nice and all....but if the computer did all the cutting, can you honestly call it hand made then???

[jteneyck]

I dunno....it looks nice and all....but if the computer did all the cutting, can you honestly call it hand made then???

I didn't say it was handmade but assembling all those machine cut parts required a lot of handwork, no different than with traditional woodworking (however you define that).  

Is a part you push across a tablesaw handmade?  What about your jointer and planer? Where do you draw the line?  As I see it, a CNC is just another machine that makes things easier and potentially more precise, but doesn't replace the design process or the process of tuning parts during assembly.  

John

[KC]

I dunno....it looks nice and all....but if the computer did all the cutting, can you honestly call it hand made then???

I've wondered this myself over the past severl years, but I think John's response is spot on.

[Rob Young]

Other than having to solve those problems it was a fun project, and I learned a lot about holding and milling really small parts on the CNC.  Double stick tape is your friend and small downcut spiral end mills can do some amazing work.  

John

Pretty cool. And good idea to make your own plywood. I've seen a few clocks people have made on the scroll saw or bandsaw and they used solid wood for gears instead of plywood. Teeth always seemed a weak spot to me.

re: workholding --

At work I get to interface with the Physics dept machine shop on a regular basis and one technique I learned from them was to drill whatever holes your part needs first and then peck drill a smaller size into the backer. Tap that and use a bold & nut to help hold smaller pieces in place as you cut them. Doesn't work in all cases of course.

I've done it a few times on my Shapeoko and also with the Shaper Origin where I had internal cut-out areas where maybe a little bit of a tab wouldn't show. So I could drive the screw through that, leave tabs to hold the main part and then cut the outer perimeter 100% free. A gear with internal "spokes" might be a good candidate for this method.

[jteneyck]

Pretty cool. And good idea to make your own plywood. I've seen a few clocks people have made on the scroll saw or bandsaw and they used solid wood for gears instead of plywood. Teeth always seemed a weak spot to me.

re: workholding --

At work I get to interface with the Physics dept machine shop on a regular basis and one technique I learned from them was to drill whatever holes your part needs first and then peck drill a smaller size into the backer. Tap that and use a bold & nut to help hold smaller pieces in place as you cut them. Doesn't work in all cases of course.

I've done it a few times on my Shapeoko and also with the Shaper Origin where I had internal cut-out areas where maybe a little bit of a tab wouldn't show. So I could drive the screw through that, leave tabs to hold the main part and then cut the outer perimeter 100% free. A gear with internal "spokes" might be a good candidate for this method.

As lousy as the plans were they advised to use plywood.  Solid wood would yield weak parts, as you said, and they would expand/contract with the seasons which might lead to binding or skipping.  Plywood avoids those problems and yields parts with uniform wear behavior, too.  Fortunately, I have lots of experience with slicing veneer and vacuum bagging so it was an easy process.   

I've used that hold down process on some projects, and would have done so again had the double stick tape not worked so well.  But it really does, so well in fact that I had no need to use tabs.  Intertape 591; good stuff.  

John

[Rob Young]

Intertape 591; good stuff.  

John

Indeed it is! I have 1" wide and 2" wide on hand.

[®smpr_fi_mac®]

That's a beautiful piece, especially considering the design flaws you had to deal with!

Yes, a CNC can be part of "hand made".  Just like a router table, table saw, or any other tool.  Only dinosaurs with tiny dinosaur brains think otherwise.

[jteneyck]

Just an update.  I've spent more time on getting this thing to run right than I can total up.  Turns out, none of the arbor centers were correct which caused the gears to not mesh properly with their respective pinion.  I figured out some of it by simple observation of what was causing it to stop.  But it was only after I bought Clayton Boyer's book on clock design that I fully comprehended the root of the problem.  The best solution now would be to machine new frames to put the arbors at the correct centers, but I haven't done that. I filed the holes in the direction needed for one axle and slide in some toothpicks to pin the arbor where it needed to be.  Amazing the difference 1 mm can make.  I sanded the sides of the teeth on some other gear sets so they would mesh better, even though the center distances were still incorrect, to get them to rotate w/o binding. As I was testing it I found that the front frame would sag down as the weight was hung.  I solved that by installing a brace between the front and back frames, on both sides, just like you would when building a barn door.  If I ever make new frames, they will need to be beefier or incorporate some kind of bracing.  Anyway, when all was done I found I could reduce the weight needed to keep the clock running by about 40%.  

I never liked the original hands so I designed and made some new ones from a set I saw on one of Boyer's clocks.  As it now sits it's still not a finished project.  In order to keep the frame from warping on the uneven wall I had to put a flat panel behind it.  My wife and I sort of like the concept, so I'm going to design a longer panel and probably paint it some color that hopefully helps the clock stand out and compliments the room. 



As much trouble as I've had with this, I have to thank the designers.  They forced me to learn a lot about wooden clock design, both by observation and from Boyer's book.  I'm developing a spreadsheet now that allows me to calculate all the gear ratios, tooth size, centerline distances, etc to build clocks.  I may build one of Boyer's clocks from his plans to make sure my spreadsheet syncs with it.  At that point, I'll be ready to design my own.  It should be an interesting Winter.  

I bought the CNC as a way to keep my brain active.  I had no way of knowing it would lead to such an interesting tangent, with equal brain teasers.    

John